HIGHWAY RESEARCH BOARD Special Report 80 A Critical Review...

H I G H W A Y R E S E A R C H B O A R D Special Report 80

A Critical Review of Literature Treating Methods of Identifying

Aggregates Subject to Destructive Volume Change When Frozen in Concrete and a Proposed

Program of Research

NCHRP Project 4-3 Intermediate Report

a t i o n a l A c a d e m y o f S c i e n c e s -

N a t i o n a l R e s e a r c h C o u n c i l

p u b l i c a t i o n 1164

HIGHWAY R E S E A R C H BOARD Of&coAs and Metnbc«» of the Executive Gnumittee

1964 OFFICERS

W M U R S. 8mm, Chaimm I>ONAU> S. BBBRT, FM Vice Cimrmm J. B. MoMoBS&N, Bmind Tiee Ctu^mm

D . GBANT MICKUES W. N . OABBT, JR., Deputy Eieeeutim Direetor jEssectrfwe ZWreefew-

]ôiative €k»miiiik«e RBX M . WHIXWHI, FOera Bif^mag AMnkkntlor, Butem xf iWo Jtoah <eK offiflio) A . E. JOHNSON, SxeaOive Seaetafp, Ameriem -Ameia^ tf icote Bifiwau Qfieiak (esc oOxm) LOUIS Joasus, Biseetdive Setr^^ DMsim 4 Ett^maing md Indiustnal Eem/rek, NtgAontA

Research Cmmeil (ex < cio) R. R. BASimaatrtEfli, Vice PreatdmO, tt. W. U^hmar & Co^ Chkago (ex ofibao. Fast Oiainnan

1962) C. D . Cvssms, SpeeuH Am^taA to AIM msaMêe Vim) PmMaa, Amarie^n Boad BuHderx'

Assoek^ (ex ciMa, Vek Chttir^ WSS} E. W. BAI;MAS, Mmagiag Direaorj, NaUeaeA Sk^ 4<IB<M >> DoNAU> S. VmoBX, Obaiman, Departtmit «f CMl S^^kêering, NnHumlwn Vniamity W . A . Boem, Parsom Brmikaltc^Tviet-Bfs^ M f^jUiaiSm MASON A . B i m m B , Coun<9 M i m a j 0 « r , j ^ ^

J. DouSLAS CimoLL, JR., DeipOy mrmUm, T k ^ ^ TrOfUj^KtaHon CmmHtee, York City HisasBR E . DAVIS, DMer, ImtMvte ^''Tmm»*l^^ *i«>^ ' 7 r < # c ESngitmring, Vnwmity

jyvtsW,J>mmetiAmmey<l&i&ai^Ciiaet^ JOHN T . BOWAS^, BetO, Dâftmm 4^ <M SUîima, PhmOuff, Mtasaehimtts InOUvte «/

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OscAB T. MABSEI^ Vi» PreaHml, Ptrndamenkd JfoBfajreb, U. 8. Corponriwn J. B . McMcNBttAN, S^tpervtOendea ^ Pme W»hs, if«a T«i* Siege DepaOiaent ef PtibUc Works VLVmmt F . RAsewBiUBR, ViCB PraÔM fur Besaartk, Defdiipnmt and Engfneering, /efens-

MmmOU CarporaUm M . L . SBjamviBS, State B^h^ ffagimrt 'Ckfif^^ BktM Bi^t^m Departmmt T . E . SraiunBNB, DweOer (4 RemrO^ Virt^Btfmttmia ^ Bi^mmgs Wiimwt8,Smi!B,WiBMr&m4ffiandAsmki^,'êm JOHN H . SÂsama, Bngimet^Mimeaa^ tiefmUmeat Bighm^ EDWAm> G. WasjOBL, The Pert ^ New Fm* ^ti«oi%, Ben Terk OHy E . B^Wâ^J^^&M tf Ova Eiif^mef^ ^mi Pk&sler, J « j » t Bigkwag BeBearek Prâi,

Satavial Staff D. GB&NT MICKLB Hiotîter P. Om.&Hi» E A B L B W. JACKSON 2101 Constittttiou Avûe Wadiiogton, D . C. 20418

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MKC H I G H W A Y R E S E A R C H B O A R D

S p e c i a l Report 80

A Critical Review of Literature Treating Methods of Identifying

Aggregates Subject to Destructive Volume Change When Frozen in Concrete and a Proposed

Program of Research

NCHRP Project 4-3 Intermediate Report

by T. LARSON, P. CADY, M. FRANZEN, andJ. REED

Department of Civil Engineerii^ The Pennsylvania State University

University Park, Pennsylvania

fflGHWAY RESEARCH BOARD of the

Division of Engineering and Industrial Research National Academy of Sciences-

National Research Council Washington, D. C.

1964

V10.S5

National Cooperative Highway Research Program ADVISORY COMMITTEE*

T. E. Shelburne, Chairman, Virginia Department of Highways A. E. Jolmson, American Association of State Highway Officials D. Grant Mickle, Bureau of Public Roads Bruce E. Foster, National Bureau of Standards J. A l Head, Oregon State Highway Department Alger F. Malo, City of Detroit R. L. Peyton, State Highway Commission of Kansas Thomas J. Sebum, Yale University E. A. Whitehurst, University of Tennessee

AREA 4 ADVBORY PANEL ON BENEFICIATION OF AGGREGATES*

E. A. Whitehurst, Chairman, University of Tennessee D. L. Bloem, National Ready Mixed Concrete Association L. F. Erickson, Idaho Department of Highways J. E. Gray, National Crushed Stone Association **A. R. Healy, Rhode Island Department of Public Works F. E. Legg, Jr. , University of Michigan Bryant Mather, Waterways Experiment Station W, T. Spencer, Indiana State Highway Commission D. O. WooU, Bureau of Public Roads

EX OFFICIO J. H. Swanberg, Minnesota Department of Highways Miles S. Kersten, University of Minnesota tR. E. Bollen, Highway Research Board t A. W. Johnson, Highway Research Board

HIGHWAY RESEARCH BOARD PROGRAM STAFF M. Earl Campbell, Program Engineer

W. A. Goodwin and E. A. Mueller, Assistant Program Engineers

»As of May 1, 1963 *»Liaison with AASHO Monitoring Conunittee tWithout vote

National Cooperative Highway Research Program

Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research.

In recognition of these needs the highway administrators of the American Association of State Highway Off icials initiated in 1962, an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by Highway Planning and Research funds from participating member states of the Association and it receives the fu l l cooperation and support of the Bureau of Public Roads, United States Department of Commerce.

The Highway Research Board of the National Academy of Sciences—National Research Council was requested by the Association to administer the research program because of the Board's recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as: i t maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; i t possesses avenues of communications and cooperation with federal, state, and local governmental agencies, universities, and industry; its relationship to its parent organization, the National Academy of Sciences, a private, non-profit institution, is an insurance of objectivity; i t maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them.

The program is developed on the basis of research needs identified by chief administrators of the highway departments and by committees of AASHO. Each year, specific areas of research needs to be included in the program are proposed to the Academy and the Board by the American Association of State Highway Officials. Research projects to f u l f i l l these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are responsibilities of the Academy and its Highway Research Board.

The needs for h^hway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs.

Foreword

by Highway Research Board Staff This report constitutes a critical review and annotated bibl i

ography of literature pertinent to National Cooperative Highway Research Prc^ram Project 4-3(2) on "Development of Methods to Identify Aggregate Particles Which Undergo Destructive Vol-imie Changes When Frozen in Concrete." Because of the depth and value of this interim report as a by-product of the research and in order that i t may readily serve other researchers and testing engineers in this subject area, the Advisory Panel requested its publication in the Special Report Series in advance of the final report due in December 1964.

The research, begun in March 1963, is under the direction of T. D. Larson, Department of Civil Engineerii^, The Pennsylvania State University, University Park, Pennsylvania. The project has as its general objectives the development of a rapid testto distinguish deleterious particles in aggregates and thereby predict their behavior under various degrees of exposure in concrete subjected to freezing and thawing.

Sponsorship of the research is provided for in a three-way agreement by and between the American Association of State Highway Officials, the U.S. Bureau of Public Roads, and the National Academy of Sciences—National Research Council. The program is administered by the Highway Research Board of the Academy—Research Council through a special unit designated as the National Cooperative Highway Research Program. This is the f i rs t publication issuing from this Cooperative Program.

Contents

INTRODUCTION 1

FREEZING-AND-THAWING EFFECTS, HISTORY, AND CURRENT THEORY 3

Building Stones and Brick 3 Concrete and Mortar 4 Aggregates 5

RESEARCH ON METHODS FOR IDENTIFYING FROST-SUSCEPTIBLE AGGREGATES 7

Soundness Tests 7 Petrographic Analysis 9 Pore System Studies 11 Physio-Chemical Properties Studies 16 Unconfined Freezing-and-Thawing Tests 21 Freezing-and-Thawing Tests 22 Test Method Proposed by T.C. Powers 26 Miscellaneous Possible Approaches 32

SUMMARY AND RECOMMENDED AREAS FOR RESEARCH 36

ANNOTATED BIBLIOGRAPHY 39 Soundness Tests 39 Petrographic Analysis 42 Pore System Studies 44 Physio-Chemical Properties Studies 54 Unconfined Freezing-and-Thawing Tests 64 Freezing-and-Thawing Tests 65 Test Method Proposed by T. C. Powers 72 Miscellaneous Possible Approaches 77

APPENDIX—List of Reference Sources 80 Bibliographies 80 Periodicals 80 Books 80 Theses 81 Symposia Proceedings 81 Miscellaneous Reports, Papers, and Bulletins 81

Introduction From extensive laboratory research and careful observation of field performance

has come a realization that the aggregate phase of portland cement concrete is neither dependably inert nor inherently innocuous, as was once commonly supposed. Rather, i t may exhibit either long- or short-term physio-chemical activity, in various mixtures and service environments, and be the source of stresses which act to destroy otherwise perfectly sound concretes.

A need exists, therefore, for methods of identifying unsound aggregates or unsound particles within an aggregate mass. From a practical viewpoint, the ideal solution to the problem would be the "black box" approach where the "box" would contain one input and two outputs. Aggregate would be funneled in, some sort of splitting would occur, and out of the other end would flow streams of "good" and "bad" aggregate. A more attainable goal, and the object of this research program, is the development of a test or series of tests of performance, or for the determination of basic properties, which would permit the identification of aggregates subject to destructive volume change during the freezing and thawing of concrete.

One purpose of this review is to locate and examine the literature treating this facet of the problem of deleterious aggregates. There is a very considerable body of literature dealing with the general problem of concrete durability and even with the specific matter of aggregate performance in concrete. A careful study of the more pertinent references was considered desirable even though several factors were recognized as serving to reduce the value of much of the research reported. These nullifying factors include (a) a lack of knowledge concerning the more basic variables to freeze-thaw durability when much of the work was performed, (b) the inherent inseparability of many variables even when recognized, (c) a natural disposition of practical researchers to utilize observations of simulated service and/or exposure conditions as a basic methodology with some consequent neglect of fundamental property studies, and (d) the absence of long-range research goals, resulting from the f i rs t three items and also from needs chaises in the total concrete industry. With these limitations in mind, a large number of articles was reviewed and many were found to contain data germane to the problem under investigation.

A logical second purpose of this review is to identify areas of uncertainty and gaps in knowledge where additional research appears to be most needed.

A survey of the problem under investigation was made using annotated bibliographies and survey articles. From this survey several categories were selected for use in classifying and evaluating all available references. Articles were evaluated by considering their applicability to the specific problem at hand, and their relevance in the light of the best current theory. A list of sources of references appears in the appendix. From these sources some 250 references were located and reviewed. Copies of the most significant ones were obtained for detailed study and many from this select list have been cited in support of the more notable advances in knowledge. A complete annotated bibliography of all references used is included as a possible aid to other researchers in this field.

References in the bibliography have been classified within the categories of reported research by attempting to assign articles to the following letter system:

A. Original Research and Development; articles reporting results of original research and development in which data are given to substantiate all conclusions.

B. Reviews or Compilations of Data; articles reviewing previously published research studies.

C. Descriptive Articles; miscellaneous articles of a general or descriptive nature covering aggregates subject to destructive

1

volume change when frozen in concrete, and closely related matters.

D. Books having a significant coverage of concrete aggregates. E. Unpublished Theses.

This division was difficult in many cases; therefore, many arbitrary assignments were made.

A section on the "history of thought" in this field and covering the current relevant theories has also been included. The history provides some perspective for understanding past research, whereas the current theories were used for evaluating the available references.

An attempt has been made to use sound original research reports and the best current theory in making al l judgments and interpretations. No complete objectivity is claimed, however, and some statements are the obvious result of cumulative reactions by the writers.

Freezing-and-Thawing Effects, History, and

Current Theory During the past 20 years many investigations have been carried out to study the dura

bility of concrete under freezing-and-thawing exposure. Much of this research was undertaken to determine the comparative behavior of concrete specimens made from various cements and aggregates with various mix proportions, water-cement ratios, and air contents; cured under controlled conditions and for various periods of time; and subjected to various freeze-thaw conditions. Some research has also been of a basic nature in order that the mechanisms of and contributory properties to deterioration be observed and understood. Although many of the significant developments are outgrowths of this more contemporary research, the seeds of ideas were planted much earlier. Therefore, this historical review, although principally concerned with studies of aggregate and concrete, also considers work on related materials, inasmuch as early studies of these led to the development of concepts since adopted in concrete technology.

BUILDING STONES AND BRICK Attempts to evaluate the durability of building stone by studies of absorption and

density date back to at least 1847. Freezing tests were used to evaluate durability of marble being utilized in the extension of the U. S. Capitol in 1856. Weight loss determinations were also used in 1876 to evaluate the decay of building stones exposed to freeze-thaw cycles. Investigators in this period appear to have based durability on the loss of weight and the loss in strength which occurred during various numbers of exposure cycles.

In 1907 studies on brick indicated that pores could be only partially filled, and that a portion of the water was forced out of the material as soon as freezing pressures were created. Results also indicated that no large pressures could form in a pore unless i t was more than 0. 91 fu l l . It was concluded that most of the damage done by freezing water was due to the moisture in the smallest pores because the water in these freezes last. A rate-of-absorption test was si^gested as a measure of pore size. Differences in thermal coefficients suggested that ice could only damage brick at the time of its formation.

Further work in the early 1900's utilized total porosity measurements and calculations of the degree of saturation. It was noted in 1910 that the type of porosity was of greater significance than the total pore volume. Also, the degree to which the pores became filled with water under natural conditions determined the freeze-thaw durability of building stone. Theoretical studies again indicated that the degree of saturation of building stone should be less than about 0. 91 to obtain good durability. Insufficient space for expansion of freezing water would occur at higher degrees of saturation. Later work (1923) indicated that critical degrees of saturation on the order of 0. 85 would result in extensive freeze-thaw damage. Such findings were due apparently to nonuniform distribution of water in the pore system. Some of the pores could be almost completely saturated while others remained relatively empty.

other investigators continued the study of relations between porosity, absorption, composition, compressive strength, and durability of building stone materials and brick. In 1927 the usual tests for strength, absorption, density, etc., were supplemented with studies of elasticity, permeability, shearing strength, discoloration, and weathering qualities of limestone, hi addition, a study was made of the thermal expansion of limestone. In studies made in Great Britain i t was found that the "coefficient of saturation" was a fair but not wholly reliable measure of frost resistance. It was suggested that strength, modulus of elasticity, and expansion during freezing were factors affecting

3

the liability to damage. A year later, further work on porosity, pore structure, and capillary properties of stone indicated that the expansions during freezing might be related to frost resistance.

Test results utilizing pore size determinations in the evaluation of the weathering of natural building stone were reported in 1932. The volume of pores having diameters less than 5 microns was correlated with the resistance of the stone to freezing and thawing. An apparatus employing the capillary rise principle was used to determine the pore size of the buildii^ stone. Another early method which yielded a value of pore size required the determination of the permeability of a specimen to gas or liquid flow. This method, and the application of Poiseuille's equation was used on brick to calculate the average size of pores.

CONCRETE AND MORTAR The earliest evaluation of the mechanism of frost action in mortar and concrete

appears to have been confined to the use in 1837 of sodium sulfate as a substitute for freezing water. Alternate soaking in the solution and washing with pure water resulted in specimens which were not long in showing signs of deterioration.

Many investigators in a 20-year period following 1885 studied the effects of frost on mortars and concrete. Atmospheric freeze-thaw tests were used. In the early 1900's a controlled-temperature room was used to observe the action of frost on mortars made with fresh water and brine. Strength tests were used as indicators of durability. Different methods of curing were used and it was observed that some specimens absorbed more water than others, but no real attempts were made to measure porosity. In 1913 one investigator made attempts to correlate permeability of mortar with deterioration of mortar based on mechanisms of frost action simulated through the use of sulfate tests.

Li the following 20 years some work was done on freeze-thaw testing methods, including studies of low-temperature testing versus the use of sodium sulfate. Field concreting methods were concurrently improving, for there seemed to be indications that carelessness and poor construction practices were more to blame for frost damage than were the cement or aggregates used. The idea that w/c ratio had a significant bearing on the problem was beginning to evolve.

In 1934, work at the Portland Cement Association's laboratory indicated that with a w/c ratio of 1.20, mortar deterioration was greater than with a w/c ratio of 0. 80. Sulfate tests were used to simulate frost effects. Subsequently, through 1940, theories and investigations were concerned with the effects on durability and permeability of curing time, w/c ratio, thermal coefficients, bleeding, and freezable water in concrete pores. Blends of cements, including natural cements, and rates of freezing were studied. Measurement of concrete deterioration by changes in the modulus of elasticity was reported.

In the period from 1941 to 1946 further refinements were made to the work done earlier, but the major milestone in this era was the advent of air entrainment and its acceptance as a factor affecting the durability of concrete.

At the end of a 10-year period which followed, laboratory and field experience had reasonably established that entrained air was effective in increasing concrete durability { as much as tenfold. Other technological advances included the following: concrete below some critical degree of saturation is highly durable to large temperature changes { regardless of thermal stresses; internal pressures resulting from freezing water within probably causes damage in water-soaked concrete in the hardened paste or aggregate,] or both. These pressures might be (a) due to the additional solid volume of freezing water; (b) hydraulic, due to the resistance of fine-grained paste capillaries to water moving before an advancing ice front; or (c) due to capillary ice body growth from gel water extraction. Air voids spacing is fundamental to the problem; current freeze-thaw test methods need re-examination (rapid freezing is thought to be misleading); lower w/c ratios improved durability and impermeability; fines composition of cement, although important in some concrete matters, seems not a factor in durability.

By 1962 these basic ideas had not changed significantly. Some support for hydraulic

pressure as the principal damaging force was evident. Specifications covering air entrainment and concreting techniques were well established. Further improvement in durability seemed most likely to result from aggregate research, inasmuch as hardened paste had the proven benefit of air-entrainment protection.

AGGREGATES Research on the durability of aggregates as a discrete material seems to be more

recent than studies of building stones, concrete, or mortar, although in 1913 test data on aggregates showed correlations with tests on concrete containii^ those aggregates. During the 1920's much thought was given to the influence of aggregates on concrete durability. Soundness tests, the relation between unsound aggregates and high absorption, the usefulness of petrography in the selection of aggregates, studies of elasticity and permeability, and sampling and testing standards were all developed during this period.

In the 1930's the problem of aggregate soundness in terms of confined versus uncon-fined discrete particles was considered. Accelerated soundness tests were based on the use of sodium and magnesium sulfate and low-temperature freezing and thawing, thermal volume changes, and petrographic properties. Service record data were also studied.

Between 1940 and 1945 much work was done on the detection of unsound particles, particularly chert, in aggregates. Freeze-thaw tests were made with mortar cubes containing evacuated and saturated chert, classified by specific gravity, absorption, degree of saturation, dye penetration, chemical analyses, and examination by microscope. One investigation suggested a lack of correlation between soundness tests and concrete durability and recommended field service tests over laboratory tests. Another study pondered the rate of absorbed moisture gain or loss relative to freeze-thaw tests and considered the resistance of varying sizes of aggregate particles. Studies were also made on linear thermal expansion related to crystal orientation, texture, and composition, and a case of concrete failure attributable to a low thermal coefficient was reported. Still another investigation suggested low specific gravity as the criterion of unsoundness, and later the same investigators suggested mechanical segregation of unsound particles by a flotation process.

In the following decade interest in aggregate research diminished somewhat because of the concentration on air-entrainment investigations. However, some efforts were made to link air entrainment with a^regate durability; aggregate acceptance tests were questioned; more work was done on thermal expansion; porosity studies were made; petrographic supplements to the standard acceptance tests were recommended; and a classification of deleterious characteristics of aggregare was proposed, based on recognition of harmful properties rather than types of materials. At the end of this period it appeared that the most acceptable frost damage mechanism for aggregate was explainable by the "degree of saturation" theory. It also appeared that entrained air in the cement paste could not be expected to subdue the effects of bad aggregate.

By 1962 the thinking had changed somewhat. For unconfined aggregates, the " c r i t i cal size" concept was advanced for saturated aggregates of a given pore system and rate of freezing. Even though aggregate pores are larger than those in hardened paste, hydraulic pressure from freezing water expansion behaves similarly in both. For low-porosity high-strength aggregate, an accommodating elastic deformation may occur, but for those having h^h porosity and low permeability, relief points such as microscopic voids or permeability to the outside boundary appear necessary. For example, chert-type aggregate of moderate absorption and low permeability has an estimated critical size of 72 i n . , whereas the critical size for dolomite, having greater absorption and higher permeability, is over 30 in. for the same exposure condition. For confined aggregates (in concrete), the critical size concept does not account for the surrounding paste. Outside pressure relief is dependent on the permeability and entrained voids of the paste.

Because the moisture content of aggregates within concrete is a factor, the problem appeared to be one of determining how rapidly relatively dry aggregate in cured

concrete can gain moisture. This, in turn depends on paste permeability, a function of w/c ratio and curing history. Pop-outs occur when a small amount of vulnerable aggregate exists in concrete; general deterioration wil l occur with a critical percentage of bad aggregates.

Research on Methods for Identifying Frost-Susceptible Aggregates

As noted in an earlier section, the existing literature on this subject was classified into several categories as a convenience for collection and study. These categories are used as the framework for this critical review and for defining subjects on which more research appears necessary. An annotated bibliography is appended in which the annotations are related to these categories by a numbering system.

Each section is presented with historical background, significant theoretical and experimental contributions, and recommendations concerning additional research. The problem of determining reliable methods for identifying a^regates which may undergo volume change when frozen in concrete was the primary objective of this study. It also was realized that a complex interrelationship of variables affecting the performance of aggregates in concrete exists. The diversity of the subjects treated in the various categories is evidence of this realization.

SOUNDNESS TESTS Historical Backgroimd

Laboratory tests have long been used to predict field performance and durability of materials. The economic advantages are evident. Early tests of concrete constituents were of the accelerated nature, usi i^ salts which crystallize readily (such as sodium or magnesium sulfate) in an attempt to duplicate the force of freezing water.

The sodium sulfate test was apparently f i rs t proposed by Brard in 1828 and is described in Annales de Chemie et de Physique. This early test consisted of f i r s t boiling specimens in a saturated solution of sodium sulfate for 30 min, cooling them in a fresh solution for several hours, and then suspendii^ them in air by threads for 12 hr in a dark room. The latter step was used to permit crystallization of the sodium sulfate within the test specimens. This test was used for a number of years to indicate the frost resistance of sedimentary rock.

The f i rs t reference to the accelerated soundness test for coarse aggregate by the American Society for Testing and Materials appears in Proceedings, Vol. 28, Part I , 1928. The proposed method required 10 small pieces with a total weight of about 1,000 gm to be immersed in a saturated solution of sodium sulfate at 70 F for 20 hr and then dried at 100 C for 4 hr.

la 1931 an improved tentative method was published under designation C89-31T, which specified the size groupings to be tested.

In the 1941 revision of the sulfate soundness test, the same sizes of corase aggregate as in the the 1931 revision were used, but each of three size groupings between the %-in. and 2/^2-in. sieves was separated into a coarse and a fine fraction. These fractions were then recombined in a fixed ratio.

The procedure was again revised in 1946 in an attempt to overcome some of the trouble inherent in the grading of the test fractions. A second grading scheme was presented, designated alternate A, which gave laboratories opportunity to select the grading scheme most suitable for their needs.

A number of changes have taken place over the years until today the accelerated soundness test most used is ASTM designation C88-61T. This procedure consists of immersing several size fractions of the aggregate in a solution of either sodium sulfate or magnesium sulfate for not less than 16 hr nor more than 18 hr at a temperature of 70 F± 2 F, followed by drying to constant weight at 221 to 230 F. This cycle is repeated as l o i ^ as desired. After the last cycle, the size fractions are shaken on the same sieves upon which they were retained at the beginning of the test. The material

7

passing the sieves is an indicator of the deterioration of each size fraction.

Significant Theoretical and Experimental Contributions Garrity and Kriege in 1935 (B105) and Wuerpel in 1938 (BUT) proposed essentially

identical theories regarding the action of sodium or magnesium sulfates on aggregates. They suggested that, during the 18-hr immersion of the dried specimen in the saturated sulfate solution, the aggregate pores become essentially filled with the liquid. During the subsequent drying period, the moisture evaporates, leaving a deposit of anhydrous salt within the pores. A second immersion of the specimen bri i^s fresh saturated solution into contact with the previously deposited anhydrous salt, producing recrystal-lization in the form of a hydrated salt. Hydration of the salt results in a volume increase of salt deposits and expansive forces within the pores. The resultant disruptive action on the aggregate is supposedly a measure of freeze-thaw durability.

This explanation of the action of either magnesium or sodium sulfate on aggregates persists to this day.

It has been suggested at various times that the use of magnesium sulfate solutions (MgSO* • 7HaO plus water) be substituted for the sodium solutions. It is argued that the solubility of the former is more nearly constant at the testii^ temperatures, varying from approximately 26 percent at 68 F to approximately 29 percent at 86 F. This is in contrast to the solubility of sodium sulfate, which varies from approximately 19 percent to approximately 41 percent within the same temperature range. Moreover, the magnesium sulfate has only one crystalline form at these temperatures, whereas sodium sulfate has three (B117, B i l l ) .

The sodium or magnesium sulfate tests have found favor over other test methods largely because they are rapid and involve little equipment. However, these sulfate tests do not represent the mechanisms of natural weathering. In the theory given, the mechanism of either sodium or magnesium sulfate action is expansive force produced by crystal growth in the pores of the aggregate due to hydration of crystal deposits during soaking cycles. As this expansive force increases, stress is developed which may cause the disintegration of the aggregate particles.

In natural weathering the disintegrating mechanism is cyclic freezing and thawii^ of water. Internal stresses are developed because freezing free water expands in volume by { approximately 9 percent. Expanding ice, however, is not the ma]or agent of disintegration. The major agent of disintegration is hydraulic pressure produced by water attempting to leave the frozen zones (C707). Consequently, the actions within particles in the sulfate tests do not parallel those of freezing-and-thawing tests.

Moreover, the disruptive action of the sulfate tests on unconfined aggregates is not representative of aggregates that are confined (B108). The confining nature of the mor-1 tar in concrete, for example, is important in determining the rate and amount of moisture movement into and out of the aggregates. It is not surprising, therefore, that the durability of concrete aggregates cannot always be correlated with the durability of the concrete in which these aggregates are embedded.

It has been shown by some investigators that i t is possible to correlate the results of sulfate tests with actual field performance of certain aggregates but not with others (Clio, B116, B501). In some cases durable concrete has been produced from ^ g r e -gates showing high losses in the sulfate test. For example, Vollick and Skillman reported results in which "durable concrete was obtained with aggregates that showed as much as 32 percent loss in the sodium sulfate soundness test with concretes containii^ 4 percent entrained air and with a water-cement ratio of 0.51 by weight" (B113). Goldbeck also reported an aggregate that failed in the sodium sulfate soundness test but performed satisfactorily in service. The sodium sulfate soundness test referred to here is that recommended by the Committee of the Sanitary Engineering Division of the American Society of Civil Ei^ineers on Filtering Materials for Water and Sewage Works which differs only in detail from the current ASTM procedure. The aggregate reported by Goldbeck was a limestone which was exposed to cyclic freezing and thawing during 25 years in a t r i ck l i i ^ filter (C106).

Due to the h^hly sensitive nature of the sulfate soundness tests, many instances

9

have been reported of difficulty in reproducing the same results in the same laboratory, or in different laboratories, for the same material and test procedure (B114). Blanks, in 1950, listed the foUowii^ major sources of variation: "(1) differences in the types of containers used; (2) differences in technique of drainage following the immersion period; (3) inadequate temperature control; (4) variations in length of the drying period; (5) differences in techniques of screening the samples; and (6) differences in grades of salt and concentrations of the solutions used in the test" (B302). Bloem, in 1956, lists similar variations (C102). Various recommendations have been made to remove these variations by further standardization, but so far these recommendations have not been adopted. Recommendations Concerning Additional Research

Sodium or magnesium sulfate tests on unconfined aggregates do not duplicate the mechanisms of natural weathering or the confining nature of mortar on the aggregates when they are embedded in concrete. Also, there is difficulty in reproducing sulfate test results and a lack of general correlation with field performance of concrete in which the aggregates under examination are incorporated.

For these reasons, i t is believed that sulfate tests are not sufficiently reliable for predicting in-place concrete durability, and no further efforts should be directed toward refinement of this method for testii^ questionable aggregate.

PETROGRAPHIC ANALYSIS Historical Background

Petrography is defined as the science of the description and classification of rocks. Concrete aggregates of particular types and particular characteristics have long been known to be better suited than others for making concrete. Therefore, the application of petrography to concrete technology to provide identification of rock aggregates is almost as old as that technolc^ itself.

Rhoades and Mielenz (C207) have provided an excellent bibliography covering the period from 1923 to 1944, during which there were many specific applications of petrography to field and laboratory investigations. The paper to which this bibliography is appended lists numerous "petrc^raphic properties" of aggregate and thereby defines a very broad sphere for the science of petrography.

The methodology for applyii^ the knowledge and techniques of the geologic sciences to concrete aggregates appears to have been f irs t described by Mather and Mather (C203) in 1950. A Recommended Practice for Petrographic Examination of Aggregates for Concrete (C295-54) was adopted by the American Society for Testing and Materials in 1954, based on this paper. Mielenz (C206) has presented a comprehensive description of petrography as used in the study of portland cement concrete and has, thereby, made the most general application of geologic science to concrete technology.

Significant Theoretical and Experimental Contributions The application of petrography as a method for identifying frost-susceptible aggre

gate is apparent when i t is considered to include the determination of basic properties of aggregate particles which originate in their mineralogic compositions, textures, and structures, and subsequently an evaluation of their concrete making properties. If experience has shown a particular mineral constituent as being consistently deleterious in behavior, petrographic identification serves as the agent whereby field service records may replace laboratory evaluation in preventing the use of inferior aggregate.

Many early investigators noted that certain mineral constituents can be deleterious in particular applications and environments. Kriege (B202) lists chert, shale, ocher, limonite, the clay minerals (kaolinite, beidellite, montmorillonite, nontronite), mica, pyrite, coal, lignite, weathered sandstones and granites, argillaceous limestones, alkaline salts, and others, and says: "These objectionable materials may reveal their presence in destructive tendencies through excessive volume change with changes in temperature or moisture content, with or without freezing, or by volume changes due to variation in the state of oxidation."

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Rhoades and Mie l enz l i s t the m o s t i m p o r t a n t pe t rograph ic p r o p e r t i e s as c h e m i c a l r e a c t i v i t y ; p o r o s i t y , p e r m e a b i l i t y , and absorp t ion ; bond and su r face t ex tu re ; i n t e r n a l f r a c t u r e ; p a r t i c l e shape; t h e r m a l expans iv i ty ; s u r f a c e coa t ing ; p r o p e r t i e s a f f e c t i n g d r y i n g shr inkage ; s t r eng th and e l a s t i c i t y ; spec i f i c g r a v i t y ; and spec i f i c heat and t h e r m a l conduc t iv i ty . Po re c h a r a c t e r i s t i c s , i n p a r t i c u l a r , a r e noted as a f f e c t i i ^ the f r e e z i n g -and- thawing d u r a b i l i t y of aggregates . A number of r e f e rences to inves t iga t ions where abso rp t ion has been used to p r e d i c t f r e e z i n g - a n d - t h a w i n g d u r a b i l i t y a re c i t e d . The best r e l a t ionsh ips of th i s type appear to have been found i n expe r imen t s on s i m i l a r r o c k types , but bas ic l i m i t a t i o n s a re noted as p r ec lud ing the use of abso rp t ion as a gene ra l index of soundness.

P e r m e a b i l i t y , pore s i ze , and su r face t ex tu re a r e cons idered by Rhoades and Mie l enz as having i n t e r r e l a t e d e f f ec t s on f r e e z i n g - a n d - t h a w i n g d u r a b i l i t y . Aggrega te p a r t i c l e s w h i c h a t t a in and m a i n t a i n h igh degrees of s a tu ra t i on undergo s t r a i n s caused by expansion d u r i n g the w a t e r - i c e phase t r a n s f o r m a t i o n . The degree of s a tu ra t i on i s a f u n c t i o n of p e r m e a b i l i t y , w h i c h a f f ec t s abso rp t ion r a t e , and of pore s i ze , w h i c h a f f ec t s the c a p i l l a r ; movemen t and r e t e n t i o n o f wa t e r . Sur face t ex tu re a f f e c t s the bond that i s developed between aggregate and paste. C o a r s e - t e x t u r e d absorp t ive aggregates tend to develop a good bond, w h i c h helps to r e s i s t the r e l a t i v e l y g rea t e r f r e e z i i ^ s t r e s s caused by th i s same high absorp t ion . Such i n t e r r e l a t i o n s h i p s reduce the l i k e l i h o o d of there ex i s t i ng any s ing le measureable p r o p e r t y hav ing a u n i f o r m l y h igh degree of c o r r e l a t i o n w i t h f r e e z i n g r e s i s t ance . The need f o r be t t e r tes ts to evaluate pore c h a r a c t e r i s t i c s i s , never the less , emphasized.

A l a t e r paper by Rhoades and Mie lenz (B208) again s t resses the need f o r m o r e knowl - | edge of the i n t r i n s i c p r o p e r t i e s o f aggregates and sv^gests tha t pe t rog raphe r s f a m i l i a r w i t h engineer ing p r o b l e m s can bes t p r o v i d e such i n f o r m a t i o n . They note that each m i n e r a l p a r t i c l e i s c h a r a c t e r i z e d by an i n t e r n a l t ex tu re , s t r u c t u r e , and compos i t i on w h i c h g ive r i s e to i t s p h y s i c a l and c h e m i c a l p r o p e r t i e s . A g a i n , the p h y s i c a l p r o p e r t i e s of p o r o s i t y , p e r m e a b i l i t y , and abso rp t ion a re noted as c o n t r o l l i n g f r e e z i n g - a n d - t h a w i n g d u r a b i l i t y . On the sub jec t o f petTogra.pby o f aggregates c o n t r i b u t i n g to f r e e z i n g - a n d -thawing breakdown of concre te , the authors note that aggregates can con t r ibu te to such b reakdown by v o l u m e change w i t h change i n m o i s t u r e a v a i l a b i l i t y , t h e r m a l expansion and con t r ac t i on , and c h e m i c a l r e a c t i v i t y , as w e l l as phenomena d i r e c t l y r e l a t ed to the f r e e z i n g and thawing of wa te r w i t h i n the concre te . They make no a t t empt to disentangle the e f fec t s of these f a c t o r s . M a t e r i a l s h a v i i ^ h igh p o r o s i t y and low p e r m e a b i l i t y , cha r a c t e r i z e d by voids less than 0 .004 m m i n d i a m e t e r , a re cons idered to be m o s t sub jec t to f r e e z i n g damage.

Wool f (C211) has desc r ibed a sy s t em f o r the i d e n t i f i c a t i o n of r o c k types w h i c h does not depend on p r i o r t r a i n i n g i n pe t rography . Such a s y s t e m , used i n con junc t ion w i t h f i e l d s e r v i c e r e c o r d s o r o ther pe t rog raph ic s tudies , i s a valuable t o o l f o r highway engineers to use i n evaluat ing concre te aggregates .

Mathe r and Ma the r (C203) set f o r t h the de ta i l s f o r m a k i n g pe t rograph ic examinat ions | of concre te aggregates . A s has a l r e a d y been noted, an A S T M Recommended P r a c t i c e evolved f r o m th i s paper . Specia l ized t r a i n i n g and equipment a re c l e a r l y r e q u i r e d i n the desc r ibed method and even w i t h these, the examina t ions a r e l i k e l y to be t i m e c o n -s u m i i ^ and cos t l y .

Swenson and Chaly (C210) desc r ibe an a r r angemen t f o r c l a s s i f y i i ^ de le te r ious aggre-j gate m a t e r i a l s based on a r e c o g n i t i o n of t h e i r h a r m f u l p r o p e r t i e s r a t h e r than on types of m a t e r i a l s . They cons ider that such a s y s t e m , r e q u i r i n g pe t rog raph ic ana lys i s , p r o vides a r e l a t i v e l y s i m p l e f r a m e w o r k w i t h i n w h i c h a l l i n f o r m a t i o n i s o f o p t i m u m value f o r m a k i n g aggregate evaluat ions . W i t h i n t h e i r proposed c l a s s i f i c a t i o n the i n t e r n a l phys i ca l c h a r a c t e r i s t i c s of undes i rab le pore sys tems , h igh vo lume change w i t h we t t ing and d r y i n g , and unfavorab le t h e r m a l expansion m i g h t con t r ibu te to excessive vo lume change d u r i n g f r e e z i n g .

I n h i s d i scuss ion of pe t rography as appl ied to concre te , Mie l enz states that f r e e z i n g of hardened concre te causes the development o f h y d r o s t a t i c p r e s su re s i n the paste and/or aggregate as a r e s u l t of the c r y s t a l l i z a t i o n of ice and tha t a i r en t r a inmen t o f f e r s only m i n o r r e l i e f to b reakdown due to unsound aggregate. T h i s paper s t resses the need f o r o v e r a l l evaluat ions o f a s t r u c t u r e and i t s env i ronmen t as an i n t e g r a l p a r t of the p r o - | cess of d e t e r m i n i n g causes of concre te d e t e r i o r a t i o n .

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Recommendat ions Concern ing Needed Research

The causes of de s t ruc t ive vo lume cha i se i n aggregate p a r t i c l e s a re c e r t a i n l y roo ted i n some p h y s i c a l o r c h e m i c a l p r o p e r t y o r g roup ing of p r o p e r t i e s . K pe t rography i s cons idered as inc lud ing the d e t e r m i n a t i o n and eva lua t ion of a l l f undamen ta l aggregate p r o p e r t i e s , i t m u s t encompass a l l r a t i o n a l methods f o r i d e n t i f y i n g unsound p a r t i c l e s . A s noted by Rhoades and M i e l e n z , however , r e s e a r c h to date has not succeeded i n d i s entangl ing any g rea t number of the m y r i a d f a c t o r s , even apar t f r o m basic m a t e r i a l c h a r a c t e r i s t i c s , that in f luence aggregate p e r f o r m a n c e , and so any p resen t ly known tes t ing o r c h a r a c t e r i z a t i o n w h i c h i s d i v o r c e d f r o m the use of engineer ing judgment i s u n l i k e l y to p rov ide s a t i s f a c t o r y evaluat ions .

The m o s t s i g n i f i c a n t p r o p e r t i e s w i t h r e g a r d to f r e e z i n g vo lume s t a b i l i t y have been i d e n t i f i e d as pore vo lume , pore s ize , and con t inu i ty of vo ids . S imple methods f o r evaluat ing these, i n d i v i d u a l l y o r c o l l e c t i v e l y , a re badly needed. The inf luence of o ther m a t e r i a l c h a r a c t e r i s t i c s on vo lume change d u r i i ^ f r e e z i n g should be s tudied as p a r t of a g e n e r a l p r c ^ r a m of i s o l a t i n g these v a r i a b l e s p r e p a r a t o r y to developing r e m e d i a l t r e a tmen t s .

The sys t ema t i c pe t rog raph ic examina t ion of concre te , f o l l o w i n g pe t rograph ic a n a l y s i s of the aggregates , should help to develop a f u n d of knowledge r e l a t i i ^ basic p r o p e r t i e s to v a r i o u s s e r v i c e env i ronmen t s . Such knowledge could u l t i m a t e l y se rve to f u r t h e r reduce the use of unsui table aggregates and p e r m i t the se lec t ive use of some now cons idered unacceptable .

PORE SYSTEM STUDIES

H i s t o r i c a l B a c l ^ r o u n d

E a r l y inves t iga t ions of the pore s t r u c t u r e of b u i l d i n g m a t e r i a l s we re conducted on b r i c k and b u i l d i n g stone, and these techniques w e r e appl ied l a t e r to concrete aggregates . The m o s t i m p o r t a n t accompl i shments i n s tudying pore sys tems of both hardened paste and concrete aggregates have been produced i n the l a s t 20 y e a r s .

I t has been recogn ized f o r some t i m e that the pore s t r u c t u r e of b u i l d i n g m a t e r i a l s in f luenced t h e i r d u r a b i l i t y . Numerous tests have been employed to measure p r o p e r t i e s of the b u i l d i n g m a t e r i a l s as in f luenced by t h e i r po re s t r u c t u r e . Seipp, i n 1909, c a l c u la ted that , t h e o r e t i c a l l y , the degree of s a tu ra t ion of b u i l d i n g stone should be less than about 0. 91 to ob ta in good d u r a b i l i t y . K r e u g e r , i n 1923, found c r i t i c a l degrees of s a tu r a t i o n on the o r d e r of 0. 85, due apparent ly to a n o n u n i f o r m d i s t r i b u t i o n of w a t e r i n the pore sys t ems .

Jones, i n 1907, conducted f r e e z e - t h a w d u r a b i l i t y tes ts on b r i c k s and suggested th ree tests as i n d i c a t o r s of f r o s t res i s tance : t o t a l po re space, p e r m e a b i l i t y , and c r u s h i n g s t r eng th .

The P o r t l a n d Cement A s s o c i a t i o n l abo ra to r i e s began s t u d y i i ^ the s t r u c t u r e and p r o p e r t i e s of hardened paste about 1936. In 1940 they used the B r u n a u e r - E m m e t t -T e l l e r method to measure the i n t e r n a l su r face a r ea and the o r d e r - o f - m a g n i t u d e s ize of the s o l i d p a r t i c l e s compos ing the hardened paste. These l a b o r a t o r i e s have a lso conducted p e r m e a b i l i t y s tudies and have made an extensive study o f vo lume changes produced by f r e e z i n g of w a t e r i n the hardened paste. A grea t dea l of l i t e r a t u r e has been produced since 1945 by P o w e r s , of P C A , dea l ing w i t h the s t r u c t u r e and p r o p e r t i e s of hardened paste. (See sec t ion on the Powers me thod . )

Today X - r a y , e l e c t r o n - o p t i c , and e l e c t r o n d i f f r a c t i o n techniques a re being used i n many l a b o r a t o r i e s to study the s t r u c t u r e of hardened paste.

S ign i f i can t T h e o r e t i c a l and E x p e r i m e n t a l Con t r ibu t ions

A s the r e s u l t of extensive inves t iga t ions . Powers and o thers have con t r ibu ted to the f o l l o w i n g d e s c r i p t i o n of hardened paste: The hardened paste i s composed of the h y d r a t i o n p roduc ts of cement and wa te r—namely , c a l c i u m hydrox ide and a m a t e r i a l c a l l e d cement g e l ; res idues of the o r i g i n a l cement ; res idues of the o r i g i n a l w a t e r - f i l l e d spaces of the f r e s h paste, c a l l e d c a p i l l a r y cav i t i e s ; a i r vo id s , w h i c h may be inc luded i n t e n t i o n a l l y ; and o ther m i n o r components . The cement g e l i s composed of g e l p a r t i c l e s

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i n t e r s p e r s e d w i t h g e l pores . The g e l pores a re minu te when compared to the c a p i l l a r y cav i t i e s , and the a i r voids a re l a r g e r than e i the r the g e l pores o r the c a p i l l a r y c a v i t i e s .

The s o l i d p a r t of the g e l i s thought to contain a p p r o x i m a t e l y 3CaO • 2Si02 • 3 H 2 O . I t s h igh ly d i so rgan ized s t r u c t u r e approx imates that of t o b e r m o r i t e ( C 3 3 3 ) , w h i c h i s a s e r i e s of c a l c i u m - s i l i c a t e hydra tes of va r i ous compos i t ions . The gene ra l s t r u c t u r e of t obe r m o r i t e i s a sheet two o r th ree m o l e c u l a r l aye r s t h i c k , ex i s t i ng as e i the r a c r u m p l e d sheet o r r o l l e d up to g ive the appearance of a f i b e r (A306) . A s seen w i t h the e l ec t ron m i c r o s c o p e , g e l cons is t s of f i b r o u s p a r t i c l e s w i t h s t r a i g h t edges. Bundles of these f i b e r s appear to f o r m a c r o s s - l i n k e d n e t w o r k cons t i tu t ing the s t r u c t u r e of the g e l and thus the s t r u c t u r e of hardened paste ( C 3 3 3 ) .

Aggregate p a r t i c l e s a re composed of hardened m i n e r a l o g i c a l m a t e r i a l i n t e r s p e r s e d w i t h vo ids v a r y i n g w i d e l y i n s i ze . Because of the analogous nature of the hardened paste and aggregate p a r t i c l e s ( so l id m a t e r i a l and voids) i t can be assumed that the same m e c h an i sms of wea the r ing w o r k on both , i n v a r y i n g degrees of course . The thought should be i n j e c t e d here tha t concrete m u s t be examined i n i t s e n t i r e t y and not by pa r t s ; namely , hardened paste and aggregate p a r t i c l e s .

Two complemen ta ry theor ies have been set f o r t h by Powers to exp la in the d i s r u p t i o n of hardened paste by f r e e z i n g - a n d - t h a w m g cyc les (C707, A713) . The f i r s t involves h y d r a u l i c p r e s su re genera ted by wa te r escaping f r o m a f r o z e n zone to a nonf rozen zone. The w a t e r m i g r a t e s i f the degree of s a tu ra t i on i s s u f f i c i e n t l y h igh to p revent the a c c o m moda t ion by the paste of the a p p r o x i m a t e l y 9 percent increase i n vo lume of f r e e z i i ^ wa t e r . The second theory invo lves the g r o w t h of ice lenses i n the l a r g e r c a p i l l a r y voids by c a p i l l a r y a t t r a c t i o n o f ava i lab le wa t e r . P resumab ly , the g e l pores a re too s m a l l to p e r m i t ice f o r m a t i o n (A713). The same theor ies can a l so be appl ied to aggregate p a r t i c l e s .

Powers states: " I f the aggregate p a r t i c l e s i n a spec imen of concre te a re less p e r meable than the paste, then they should increase the in t ens i ty of h y d r a u l i c p re s su re i n the r e g i o n where the paste i s sa tura ted , s ince , f o r a p a r t of the f r eezab l e wa te r , they b l o c k the m o s t d i r e c t paths to the unsatura ted r e g i o n .

" K the concre te contains unsa tura ted aggregate p a r t i c l e s that a r e m o r e permeable than the hardened paste, those p a r t i c l e s should modera te the h y d r a u l i c p r e s su re some- ' what as cav i t i e s do, u n t i l the p a r t i c l e s become sa tura ted . When the p a r t i c l e s a re sa tu ra t ed , w a t e r mus t escape in to the su r round ing paste d u r i n g f r e e z i n g o r p res su res w i l l develop that a r e h igh enough to d i s r u p t the aggregate p a r t i c l e s and the su r round ing m a t e r i a l . The in t ens i ty of the p r e s s u r e i n sa tura ted p a r t i c l e s thus depends on the p e r m e a b i l i t y of the paste that l i e s between the p a r t i c l e s and the unsa tura ted r e g i o n . "

A number of c h a r a c t e r i s t i c s of hardened paste o r of aggregate p a r t i c l e s a f f ec t ed by the pore s t r u c t u r e have been measured . These c h a r a c t e r i s t i c s a re p o r o s i t y , ab so rp t i o n , s a tu ra t ion , p e r m e a b i l i t y , and c a p i l l a r i t y .

P o r o s i t y . —Poros i ty i s expressed e i the r as a r a t i o of the v o i d vo lume to the bu lk vo lume of the m a t e r i a l o r as a r a t i o of the v o i d vo lume to the s o l i d v o l u m e . The f i r s t r a t i o i s f r e q u e n t l y ca l l ed the percentage p o r o s i t y and the second, the voids r a t i o (B326). | Somet imes p o r o s i t y i s de f ined i n t e r m s of e f f e c t i v e p o r o s i t y , w h i c h i s that p a r t , expressed i n pe rcen t of the b u l k vo lume , of a m a t e r i a l that i s composed of in te rconnec ted voids . ]

A b s o r p t i o n . —The abso rp t ion of a m a t e r i a l i s usua l ly based on the amount of wa te r i t can take up when i m m e r s e d f o r 24 h r . A b s o r p t i o n can a l so be based on vacuum t r e a t men t o r p re s su re t r ea tmen t . Powers and B r o w n y a r d in t roduced " a b s o r p t i v i t y " , K ^ , de f ined by (V/A)^ = K^^t, i n wh ich V i s the vo lume of c a p i l l a r y pe rmean t taken up i n t i m e t , and A i s the approach a r ea of the m a t e r i a l . They contended that the r a t i o of the a b s o r p t i v i t y to the p e r m e a b i l i t y c o e f f i c i e n t should be a measure of the s u s c e p t i b i l i t y of a m a t e r i a l to f r o s t ac t ion . Powers and B r o w n y a r d state: " A h igh a b s o r p t i v i t y means a c o m p a r a t i v e l y h igh r a t e of absorp t ion , w h i l e a l ow p e r m e a b i l i t y means a compara t ive re luc tance of the m a t e r i a l to p e r m i t the passage of w a t e r . Bo th e f f ec t s should tend t o w a r d an inc reased f r o s t s u s c e p t i b i l i t y and so the h ighe r the r a t i o the w o r s e . " (B312).

Sa tura t ion . —Wray and L i c h t e f e l d p e r f o r m e d f r e e z i n g - a n d - t h a w i n g tests on g rave l s of v a r y i n g degrees of sa tu ra t ion . The m o r e wa te r the aggregate contained, the p o o r e r was the d u r a b i l i t y (B340). Sweet l a t e r r e p o r t e d w o r k i n w h i c h he c o r r e l a t e d the degree of s a tu ra t i on of the aggregate w i t h both the l a b o r a t o r y and f i e l d f r e e z e - t h a w d u r a b i l i t y of the concre te conta in ing the aggregate (B340).

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Powers s tates: " A p r i n c i p a l d i f f e r e n c e among d i f f e r e n t k inds of r o c k p a r t i c l e s is the r a t e at w h i c h they become sa tura ted when g iven f r e e access to w a t e r . " The t i m e ra t e of change of the sa tu ra t ion can be expressed as d&^dt=Kg/2E' ( l / S ^ ) , i n w h i c h

i s the degree of s a tu ra t ion , i s the a b s o r b t i v i t y , and E i s the p o r o s i t y . D o l c h used values of K^/2E^ as a pa rame te r and produced a good separa t ion between good and bad aggregate (B312).

The degree of s a tu ra t i on i s the apparent p o r o s i t y o f a m a t e r i a l compared to i t s ac tua l p o r o s i t y . The ac tua l p o r o s i t y can be based on the amount of wa te r a spec imen can abso rb d u r i n g a 2 4 - h r i m m e r s i o n p e r i o d , w i t h e i the r the vacuum t r ea tmen t o r the p r e s sure t r ea tmen t . The re i s a g r ea t dea l of d i sagreement over the idea of us ing the degree of s a tu ra t ion as an index of a concre te ' s f r e e z e - t h a w r e s i s t a n c e . F o r concre tes of d i f f e r e n t pore s t r u c t u r e , the c r i t i c a l degree of s a tu ra t ion wou ld be d i f f e r e n t . Schulze and A l t n e r t h e r e f o r e conclude: " I t i s imposs ib l e to g ive any l i m i t values (of degree of s a tu ra t ion) . Thus i t appears imposs ib l e to r ep resen t f r o s t res i s tance by means of the sa tu ra t ion d e g r e e . " (B339). Th i s conc lus ion appears to be a l i t t l e ha r sh . I t i s c o n ceivable that degree of s a tu ra t ion , coupled w i t h o ther p a r a m e t e r s , m i g h t produce a good c o r r e l a t i o n w i t h f r e e z e - t h a w re s i s t ance .

P e r m e a b i l i t y . —Permeab i l i t y may be de fmed as the r a t e of d i f f u s i o n of a f l u i d th rough a porous m e d i u m . Dunagan p e r f o r m e d extensive p e r m e a b i l i t y tests on concre te . He concluded: " L a w s developed r e l a t i v e to m o i s t u r e movement f o r i n e r t m a t e r i a l s such as so i l s o r sands cannot be appl ied d i r e c t l y to p o r t l a n t cement concre tes . P o r t l a n d cement concre te has as i t s fundamenta l ingred ien t a m a t e r i a l w h i c h changes i n pore c h a r a c t e r i s t i c s w i t h each i n c r e m e n t of combined m o i s t u r e , and changes i n vo lume w i t h each i n c r e m e n t of loss o r ga in of m o i s t u r e . " Because a sui table subst i tu te has no tbeen found , D ' A r c y ' s l aw f o r v i scous f l o w th rough a porous m e d i u m i s s t i l l used to measure p e r m e a b i l i t y of hardened paste, aggregate, and concre te .

D ' A r c y ' s law i s O/A = K ' H / L , i n w h i c h Q i s the r a t e of f l o w , A i s the a rea of c r o s s -sec t ion under p r e s s u r e , H / L i s the r a t i o of p re s su re head to the length of f l o w , and K * i s the p e r m e a b i l i t y c o e f f i c i e n t . The measure of p e r m e a b i l i t y , the p e r m e a b i l i t y c o e f f i c ien t , i s g r e a t l y a f f e c t e d by the method of movement of the wa te r th rough the m a t e r i a l . F o r l i q u i d p e r c o l a t i o n , D ' A r c y ' s law as p r e v i o u s l y g iven holds . F o r c a p i l l a r y ac t ion th i s equat ion becomes Q = K* A V 0 , i n w h i c h V 0 i s the t o t a l w a t e r - m o v i n g f i e l d o r the t o t a l f i e l d tending to produce m o t i o n of the wa te r ; f o r example , the p re s su re g rad ien t f o r c e s and g r a v i t y . F o r vapor d i f f u s i o n , Q = K * A d p / d L , i n w h i c h dp i s the vapor p re s su re d i f f e r e n t i a l causing vapor movement (B313) .

There has been some con jec tu re that under c e r t a i n condi t ions vapor d i f f u s i o n m a y b e a combina t ion o f vapor movement and c a p i l l a r y ac t ion . Depending on the p o r o s i t y of the concre te and the t e m p e r a t u r e s , r e l a t i v e h u m i d i t i e s , and vapor p res su res on the opposite s ides of the m a t e r i a l , vapor may enter , condense, and be w i t h d r a w n by capi l l a r i t y and evapora t ion (B349). I t has been concluded that i n average concre te under average evapora t ion condi t ions c a p i l l a r y movement of wa te r f a r exceeds the amount of wa te r caused to move by other means, i n p a r t i c u l a r s ta t ic head (B313).

Dunagan a lso concluded tha t i n p e r f o r m i n g p e r m e a b i l i t y tes ts one mus t keep i n m i n d that "the f l o w of l i q u i d w a t e r th rough concre te w i l l be at a r educ ing ra te as w a t e r reaches the g r a m s of cement and hydra tes t h e m . Constants f o r f l o w of l i q u i d wa te r th rough c o n cre te can be developed only f o r a cond i t ion i n w h i c h a l l of the cement has been hydra ted , w h i c h means tha t wa te r has pe rco la ted e n t i r e l y th rough the concrete f o r a s u f f i c i e n t p e r i o d of t i m e . . . " (B313). M o s t i nves t iga to r s of p e r m e a b i l i t y f a i l to r e a l i z e these e f f ec t s of m o i s t u r e movement th rough hardened paste.

V a r y i n g the cement content a lso a f f ec t s the p e r m e a b i l i t y of the hardened paste—the h igher the cement content, the l o w e r the p e r m e a b i l i t y (A33 5).

D r y i n g of the paste has the e f f e c t of i n c r e a s i i ^ the p e r m e a b i l i t y . Powers , et a l . , be l ieve that shr inkage produced by d r y i n g may r u p t u r e some of the webs of g e l between c a p i l l a r y c a v i t i e s , thereby i n c r e a s i i ^ the p e r m e a b i l i t y (A335).

Using d i f f e r e n t aggregate s izes a l so a f f ec t s the p e r m e a b i l i t y , w i t h l a r g e r aggregate s izes p roduc ing h ighe r p e r m e a b i l i t i e s . Rue t tgers , et a l . , be l ieve that se t t l ement b e tween and beneath aggregate p a r t i c l e s produces r e l a t i v e l y l a r g e v o i d spaces, c o n t r i b u t ing to a h igh p e r m e a b i l i t y (A338) . The l a r g e r the aggregate s i ze , the g rea t e r the b r i d g i n g ac t ion and thus the l a r g e r the v o i d .

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F o r c o m m o n types of concrete made w i t h good aggregates and n o r m a l po r t l and c e ment , low p e r m e a b i l i t y i s usua l ly associa ted w i t h h igh s t r e i ^ t h and h igh res i s tance to wea the r ing (B354). H i g h - s t r e n g t h cements u sua l ly inc rease wate rUghtness to a l l f o r m s of m o i s t u r e movement i n p r o p o r t i o n to the amount i n w h i c h they inc rease the c o m p r e s s ive s t r eng th of the concre te (B313).

C a p i l l a r i t y . —A d i r e c t measure of the s ize and con t inu i ty of pores i s the f o r c e asso-c ia ted w i t h c a p i l l a r y movement of a l i q u i d t h rough hardened paste o r aggregate p a r t i c l e s . A device developed by Blanks to measure c a p i l l a r y f o r c e s cons is t s of a spec imen ho lde r cons t ruc ted so that the l o w e r face of the spec imen ( 1 . 5 i n . i n d i ame te r by 1 i n . th ick) i s exposed to the a tmosphere and the upper face to a sealed wa te r r e s e r v o i r . The w a t e r r e s e r v o i r i s i n t u r n connected to a manome te r . The ra t e of evapora t ion of wa te r a t the exposed face of the spec imen i s c o n t r o l l e d by the r e l a t i v e a rea of continuous c a p i l l a r i e s exposed. Wa te r tha t evaporates f r o m the su r f ace of the spec imen w i l l be r ep laced by wa te r f r o m the r e s e r v o i r because of c a p i l l a r y a t t r a c t i o n . The p r e s su re i n the r e s e r v o i r w i l l continue to decrease u n t i l i t equals the vapor p r e s s u r e of wa te r a t the t e m p e r a tu re o f ope ra t i on o r u n t i l i t equals the c a p i l l a r y f o r c e . M a t e r i a l s con ta in ing many c o n tinuous pores of s m a l l s ize w i l l ind ica te a r a p i d inc rease and u l t i m a t e l y h igh negative p r e s su re . M a t e r i a l s conta in ing a f e w l a rge voids w i l l ind ica te a s low increase and a c o m p a r a t i v e l y s m a l l u l t i m a t e negative p re s su re (B302).

Fundamenta l c h a r a c t e r i s t i c s of the pore s t r u c t u r e of hardened paste of o r aggregate p a r t i c l e s have a lso been measured . These c h a r a c t e r i s t i c s a re t o r t u o s i t y , su r f ace a rea , pore s i ze , and po re s i z e d i s t r i b u t i o n .

T o r t u o s i t y . —The path of f l o w th rough a porous m a t e r i a l w i l l be longer than the d i s -tance between i n l e t and out le t faces o f the m a t e r i a l . The square of the r a i o of th i s t o r tuous length of f l o w , L j . , to the g ros s length , L , i s c a l l ed the t o r t u o s i t y , k^, of the pore sys t em (B312). The t o r t u o s i t y se rves as an i n d i r e c t measure of the con t inu i ty o r d i s -con t inu i ty of the pore sy s t em of a m a t e r i a l . However , t o r t u o s i t y i s r a t h e r d i f f i c u l t to measure .

Surface A r e a . —As ment ioned under " H i s t o r i c a l B a c l ^ r o u n d , " the P o r t l a n d Cement A s s o c i a t i o n l abo ra to r i e s made measurements of the su r f ace a r ea of hardened paste. F r o m these measurements they deduced the theory of the s t r u c t u r e of the hardened paste g iven p r e v i o u s l y . In some cases, su r face a rea measurements have c o r r e l a t e d w e l l w i t h f r e e z e - t h a w d u r a b i l i t y ; the m a t e r i a l s w i t h h igh s u r f a c e a reas , w h i c h c o r r e spond to a f i n e pore s t r u c t u r e , have shown h igh d e t e r i o r a t i o n .

P o r e Size. —Schaffer r e p o r t e d tes t r e s u l t s of pore s ize de t e rmina t i ons on b u i l d i n g stone and found tha t the vo lume of pores having d i ame te r s less than 5 m i c r o n s cou ld be c o r r e l a t e d w i t h the f r e e z e - t h a w res i s tance of the stone (B326). C o r r e l a t i o n of the vo lume of pores less than 5 m i c r o n s i n d i ame te r w i t h the f r e e z e - t h a w d u r a b i l i t y of c e r t a i n b id iana l imes tones has a l so been r e p o r t e d by Sweet and Fea r s (B326) .

Pore Size D i s t r i b u t i o n . —The data of some inves t iga to r s indicate a r e l a t i o n s h i p be tween pore s ize d i s t r i b u t i o n coupled w i t h e f f e c t i v e p o r o s i t y , and f r e e z e - t h a w d u r a b i l i t y (B325).

The p r i n c i p l e i nvo lved i n d e t e r m i n i n g the pore s ize d i s t r i b u t i o n of a m a t e r i a l i s that , due to i t s su r f ace energy, a l i q u i d w h i c h does not we t a s o l i d i s denied entrance to a pore of tha t s o l i d by a p ressu re w h i c h v a r i e s i n v e r s e l y w i t h the s ize of the pore (B326). Exp re s sed m a t h e m a t i c a l l y , r = (2(T cos e)/P, i n w h i c h r i s the r ad ius o f the pores , i n c m ; <T i s the s u r f a c e tens ion o f the l i q u i d , i n dynes; 9 i s the contact angle o f the l i q u i d ; and P i s the appl ied p r e s su re , i n dynes pe r sq c m . The d i s t r i b u t i o n f u n c t i o n i s de t e r m i n e d f r o m D(R) = ^ ^^^gp^ ' ^" ""^^^^ ^ ® d i s t r i b u t i o n f u n c t i o n , Vo i s the i s the t o t a l e f f e c t i v e pore v o l u m e , and V i s the vo lume of pores having a r ad ius less than r . T h e r e f o r e , ( V Q - V ) i s the v o l u m e of l i q u i d i n j e c t e d in to the pores between z e r o

d(V - V) and p r e s s u r e P and P - i s the s lope o f the (Vg-V) ve r sus p r e s su re c u r v e (A308, A319 , B325) . ° ^

A c c o r d i n g to H i l l , th ree assumptions a re i nvo lved i n m a k i n g a p o r e - s i z e d i s t r i b u t i o n d e t e r m i n a t i o n : (1) Values mus t be assumed f o r the su r face tens ion and the contact angle of the m a t e r i a l en te r ing the po re s . R i t t e r and Drake used m e r c u r y and assumed

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a su r f ace tens ion of 480 dynes per c m and a contact angle of 1 4 0 ° ; (2) The pores a re assumed to be subs tan t i a l ly of u n i f o r m c i r c u l a r c r o s s - s e c t i o n ; and (3) A l l pores a re assumed to be u l t i m a t e l y access ib le to pene t ra t ion by the m e r c u r y at the su r f ace of the spec imen (A317) .

Pore c h a r a c t e r i s t i c s of m a t e r i a l a r e an i m p o r t a n t i t e m i n a sce r t a in ing t h e i r gene ra l d u r a b i l i t y . T h i s i m p o r t a n c e i s due to the e f f e c t po re c h a r a c t e r i s t i c s have on l i q u i d movement and r e t e n t i o n . Po re c h a r a c t e r i s t i c s a f f e c t f r e e z e - t h a w d u r a b i l i t y and a l a r g e t o t a l pore vo lume of s m a l l pores can mean a h ^ h r a t e of c h e m i c a l a t tack .

Pore c h a r a c t e r i s t i c s a l so have an e f f e c t on the p h y s i c a l p r o p e r t i e s of a m a t e r i a l . L a r g e r v o i d vo lumes mean a reduced spec i f i c g r a v i t y and h igher p o r o s i t y r e s u l t s i n l o w e r s t r e i ^ t h . B o t h roughness and the pore c h a r a c t e r i s t i c s of the su r f ace zone a f f e c t the su r f ace t ex tu re and the qua l i ty of bond between an a ^ r e g a t e p a r t i c l e and the h a r d ened cement paste. Po re c h a r a c t e r i s t i c s that p e r m i t no pene t r a t ion of the su r face of the aggregate p a r t i c l e a re not conducive to a good bond. The t h e r m a l p r o p e r t i e s of m a t e r i a l s a r e in f luenced by the pore c h a r a c t e r i s t i c s . S ign i f i can t changes occur i n the c o e f f i c i e n t of expansion, d i f f u s i v i t y , and conduc t iv i ty w i t h changes i n the m o i s t u r e content of the m a t e r i a l (B326).

I n the d e t e r m i n a t i o n of aggregate abso rp t ion , the pe r iods of i m m e r s i o n i n w a t e r g e n e r a l l y employed a re too s h o r t to p e r m i t some aggregates to r eabsorb a l l the m o i s t u r e they once contained (A720) . Even vacuum t r e a t m e n t w i l l not p e r m i t some aggregates to r e a t t a i n t h e i r n a t u r a l m o i s t u r e cond i t ion . F o r these reasons , a l i m i t a t i o n on abso rp t i on as a p a r a m e t e r of f r e e z e - t h a w d u r a b i l i t y p robably ex i s t s .

The concepts of h y d r a u l i c p r e s s u r e and i ce g r o w t h i n c a p i l l a r y pores of paste a re a lso appl icable to aggregates . B y analogy w i t h paste, the magnitude of the h y d r a u l i c p r e s su re developed i n aggregates depends on t h e i r degree of s a tu ra t ion , t h e i r p e r m e a b i l i t y , and s ize o f the aggregate p a r t i c l e . B lanks states that the m a j o r f a c t o r s i n f l u encing d u r a b i l i t y of a m a t e r i a l a re the s i ze , con t inu i ty , and abundance of pores (B302). A l s o , i f the degree of s a tu ra t i on of the aggregate i s s u f f i c i e n t l y h i g h to p reven t the ac -commoda t ion of the a p p r o x i m a t e l y 9 percent expansion of ice upon f r e e z i n g , w a t e r w i l l be expel led in to the paste su r round ing the aggregate . Thus , w a t e r o r i g i n a t i n g i n the aggregate may produce po ten t i a l ly d i s r u p t i v e h y d r a u l i c p res su res i n the paste. The p rope r t i e s of paste, i t s p e r m e a b i l i t y , a i r content, and p o r o s i t y , a re invo lved w i t h gen era ted h y d r a u l i c p r e s su re s ; i t s p e r m e a b i l i t y and th ickness a re invo lved i n the degree of s a tu ra t ion of the aggregate .

The m a j o r p h y s i c a l c h a r a c t e r i s t i c s of the aggregate and the paste i n f l u e n c i i ^ f r e e z ing -and- thawing res i s tance as g iven by V e r b e c k and L a n ^ r e n (C718) a re :

1 . "The t i m e r e q u i r e d f o r an aggregate to become c r i t i c a l l y sa tura ted when i n c o n c re t e exposed to w a t e r as in f luenced by:

(a) Po re s ize and p o r o s i t y of aggregate. (b) Thickness and p e r m e a b i l i t y of p r o t e c t i v e m o r t a r cover .

2. "The v a r i o u s phenomena i n the f r e e z i n g of f u l l y sa tura ted aggregate d e m o n s t r a t ing :

(a) E l a s t i c accommoda t ion by aggregate. (b) " C r i t i c a l " s ize of aggregate ( i n t e r n a l hyd rau l i c p r e s su re s ) . (c) In f luence of c o n f i n i n g m o r t a r ( ex te rna l expuls ion dis tance and e x t e r n a l

h y d r a u l i c p r e s su re s ) . (d) The inf luence of va r i ous f a c t o r s m o d i f y i i ^ these e f f ec t s of f r e e z i i ^ , that

i s , so luble m a t e r i a l s , degree of s a tu ra t i on and f r e e z i n g poin t depress ion i n f i n e aggregate p o r e s . "

V e r b e c k and Landgren be l ieve that an aggregate w i t h a f i n e pore s t r u c t u r e w i l l r each a h igh degree of s a t u r a t i o n m u c h m o r e r a p i d l y than an aggregate w i t h a coarse pore s t r u c t u r e , even i f the aggregates have the same p o r o s i t y . A l s o , f o r aggregates w i t h s i m i l a r pore s ize d i s t r i b u t i o n s , the one w i t h h igh p o r o s i t y should r e q u i r e m o r e t i m e to a t t a in any p a r t i c u l a r degree of s a tu ra t i on than the one o f l ow p o r o s i t y (C718).

B l o e m and s e v e r a l o ther i nves t iga to r s have r e p o r t e d tes t r e s u l t s that indicate that

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c e r t a i n aggregates contained i n concrete upon being d r i e d r eabsorb w a t e r r e l u c t a n t l y . Tn the resoaked concrete a g r e a t e r p r o p o r t i o n of the t o t a l absorbed w a t e r i s i n the ce ment paste where i t can be prevented by the use of en t ra ined a i r f r o m causing damage d u r i n g c y c l i c f r e e z i i ^ and thawing (A604).

B lanks r e p o r t e d tes t r e s u l t s tha t indica ted c a p i l l a r y w a t e r r e t e n t i o n of aggregates i n concre te (B302). Rhoades and Mie lenz s ta ted i n th i s connect ion: " W a t e r m o v i n g by c a p i l l a r i t y w i l l not enter aggregate conta in ing only l a rge vo id s , even i f these vo ids a re in te rconnec ted and penet rable . On the o ther hand, s m a l l voids w i l l be penetra ted; and t f these openings a r e s m a l l e r than those o f the cement paste , the w a t e r w i l l be p r e f e r en t i a l l y d r a w n in to t hem f r o m the paste . " (C207).

V e r b e c k and Landgren state: "These cons idera t ions o f the t i m e r e q u i r e d f o r c r i t i c a l s a tu ra t i on have qua l i t a t ive p r a c t i c a l s i g n i f i c a n c e . A comple te quant i ta t ive evaluat ion r e q u i r e s add i t iona l i n f o r m a t i o n about u n i f o r m i t y of d i s t r i b u t i o n of absorbed w a t e r i n aggregates , the process of d r y i n g of aggregates i n concre te , and the in f luence of the m o r t a r o ther than that of t r a n s m i t t i n g wa te r d i r e c t l y to the aggregates on the r a t e of s a tu ra t i on of the aggregate . " (C718).

Recommendat ions Concern ing A d d i t i o n a l Research

The m a j o r p o r t i o n of the data co l l ec ted to date involves c h a r a c t e r i s t i c s a f f e c t e d by the pore s t r u c t u r e and not c h a r a c t e r i s t i c s of the pore s t r u c t u r e . The re i s a c o r r e l a t i o n between the f r e e z e - t h a w d u r a b i l i t y of some m a t e r i a l s and t h e i r c h a r a c t e r i s t i c s a f f ec t ed by pore s t r u c t u r e , but there a r e many m o r e cases where no c o r r e l a t i o n ex i s t s . The re may be some value i n a t t empt ing a c o r r e l a t i o n between those c h a r a c t e r i s t i c s a f f ec t ed by the pore s t r u c t u r e o f the aggregate coupled w i t h the hardened paste, and f r e e z e - t h a w d u r a b i l i t y of the r e su l t an t concre te .

Of the many c h a r a c t e r i s t i c s a f f ec t ed by the pore s t r u c t u r e that can be measu red , the m o s t p r o m i s i n g i n r e g a r d to p r e d i c t i n g f r e e z e - t h a w res i s tance appear to be the p o r o s i t y , p e r m e a b i l i t y , and c a p i l l a r i t y . I t w o u l d be des i rab le to develop s i m p l e , r e l i a b l e , and r e p r o d u c i b l e tes ts of these f a c t o r s .

Of the c h a r a c t e r i s t i c s that d i r e c t l y r ep resen t a m a t e r i a l s pore s t r u c t u r e , the pore s ize o r pore s ize d i s t r i b u t i o n appear to be the m o s t i m p o r t a n t . The d i f f i c u l t y i n us ing these f a c t o r s as ind ices o f f r e e z e - t h a w res i s tance l i e s i n the d i f f i c u l t and t i m e c o n s u m i n g methods of measurement , b i add i t ion to these d i f f i c u l t i e s , d e t e r m i n a t i o n o f the pore s ize d i s t r i b u t i o n invo lves expensive equipment . I t wou ld be des i r ab l e to develop qu ick , s i m p l e , and inexpensive tests of these f a c t o r s .

I t m u s t be pointed out that s e v e r a l of the c h a r a c t e r i s t i c s , both those a f f ec t ed by the pore s t r u c t u r e and those that d i r e c t l y r e l a t e to pore s t r u c t u r e , a r e i n t e r r e l a t e d . F o r example , p e r m e a b i l i t y and c a p i l l a r i t y cannot be t o t a l l y separated to p e r m i t accura te measurement of e i t he r of these p a r a m e t e r s . A l s o , a b s o r p t i o n a n d s a t u r a t i o n a r e a f f e c t e d b y p e r m e a b i l i t y and c a p i l l a r i t y . T o r t u o s i t y and pore s ize , i n t u r n , a f f e c t p e r m e a b i l i t y and c a p i l l a r i t y . Thus] a c l e a r c u t d i s t i n c t i o n between the d i f f e r e n t c h a r a c t e r i s t i c s does not e x i s t .

I t seems u n l i k e l y tha t d e t e r m i n i n g the p r e v i o u s l y ment ioned f a c t o r s of aggregate alone w i l l produce a tes t that w i l l adequately p r e d i c t the a ^ r e g a t e ' s f r e e z e - t h a w r e s is tance . Perhaps d e t e r m i n i i ^ a l l o r j u s t s e v e r a l of these f a c t o r s of both hardened paste and aggregate p a r t i c l e s w i l l produce a tes t that w i l l p r e d i c t a concre te ' s f r e e z e -thaw res i s t ance . Only add i t i ona l extensive r e s e a r c h w i l l t e l l .

Cons iderab le data on the p e r m e a b i l i t i e s of hardened pastes of d i f f e r e n t w a t e r - c e m e n t r a t i o s ex i s t . However , d i f f e r e n t i nves t iga to r s have employed d i f f e r e n t p rocedures and d i f f e r e n t apparatus , thus not obta in ing comparab le r e s u l t s . Because of the nature of hardened paste, r e p r o d u c i b l e r e s u l t s of p e r m e a b i l i t y a r e d i f f i c u l t to ob ta in i n the same l a b o r a t o r y . F o r these reasons , i t i s f e l t that add i t i ona l r e s e a r c h in to the p e r m e a b i l i t y of hardened pastes i n connect ion w i t h the f r e e z e - t h a w res i s tance of aggregates i s needed.

P H Y S I O - C H E M I C A L PROPERTIES STUDIES

H i s t o r i c a l Background

P h y s i o - c h e m i c a l p r o p e r t i e s r e l a t e d to e n v i r o n m e n t a l d u r a b i l i t y of concrete f a l l i n to

17

two m a i n categories—those tha t tend to produce vo lume changes w i t h cha i se s i n e n v i r o n m e n t a l condi t ions , and those that gove rn the s t r e s s - v o l u m e change c h a r a c t e r i s t i c s of the aggregate-paste s y s t e m .

I t has long been r ecogn ized tha t condi t ions o ther than f r e e z i n g o f w a t e r i n pore spaces can produce d i s r u p t i v e vo lume changes i n concre te . I n any study of f r e e z e - t h a w d u r a b i l i t y , t h e r e f o r e , i t i s i m p e r a t i v e that these o ther condi t ions be thoroughly unders tood and evaluated, at leas t q u a l i t a t i v e l y . The condi t ions other than f r e e z i n g of wa te r i n concrete that can produce d i s r u p t i v e vo lume changes include a lka l i - aggrega te r eac t i on , w e t t i n g - a n d - d r y i n g cyc le s , t h e r m a l cyc le s , t empe ra tu r e g rad ien t s , and t empe ra tu r e cha i s e s . These condi t ions , coupled w i t h appropr ia t e values of phys i ca l p r o p e r t i e s of aggregate and paste, can be des t ruc t ive to concre te . The p h y s i c a l p r o p e r t i e s of p r i n c i p a l i n t e r e s t i n t h i s r e s p e c t a r e (a) c o e f f i c i e n t s of t h e r m a l expansion; (b) t h e r m a l c o n d u c t i v i t y (o r d i f f u s i v i t y ) ; (c) absorp t ion ; (d) presence of planes of weakness o r c r y s t a l o r i e n t a t i o n conducive to amso t rop i c behavior w i t h respec t to t h e r m a l expansion; (e) e l a s t i c c o e f f i c i e n t s , e spec ia l ly m o d u l i o f e l a s t i c i t y and r e s i l i e n c e ; (f) su r face t ex tu re ; (g) s t reng th ; and (h) c reep c o e f f i c i e n t . The f i r s t f o u r a r e "causa t ive" f a c t o r s that a r e capable of p roduc ing d i s r u p t i v e s t resses and the l a t t e r f o u r a re " a f f e c t i v e " f a c t o r s that i n f luence the degree of d i s t r e s s by the amount of t h e i r r e s t r a i n i n g ac t ions .

I t should be recogn ized i n i t i a l l y that f a i l u r e of concrete due to wea ther ing processes cannot gene ra l l y be a t t r i b u t e d e n t i r e l y to a s ing le cause. A concre te f a i l u r e a t t r i b u t e d to hydros ta t i c p r e s su re of f r e e z i n g w a t e r , f o r example , a l m o s t c e r t a i n l y has s u f f e r e d to some degree f r o m the e f f ec t s of d i f f e r e n t i a l t h e r m a l expansion between ingred ien t s i n the mass and/or va r i ous reg ions w i t h i n the mass . Thus , i t i s quite evident that u l t i mate f a i l u r e i n gene ra l i s the r e s u l t of a combina t ion of i n t e r n a l s t resses induced by a v a r i e t y of e x t e r n a l s t i m u l i . One f a c t o r usua l ly predomina tes i n such f a i l u r e s and th i s i s , t h e r e f o r e , l abe led as the cause of f a i l u r e . Unfo r tuna te ly , i t i s v i r t u a l l y imposs ib l e to separate the u l t i m a t e s t r e s s in to i t s causat ive components even i n c o n t r o l l e d l a b o r a t o r y tests o r by ana lys i s o f m a t h e m a t i c a l analogs. I t i s easy to see, then, why f a i l u r e s of concre te due to t e m p e r a t u r e changes r e p o r t e d i n the l i t e r a t u r e over the past 35 yea r s have been a t t r i b u t e d to such v a r i e d causes as the ac t ion of f r e e z i n g wa te r , d i f f e r e n t i a l expansion of ing red ien t s , d i f f e r e n t i a l vo lume change of mass , and f a i l u r e of aggregate bond.

The re has been no sys temat ic study of a l l o f the p r o p e r t i e s of aggregate and concrete as r e l a t ed to the p r o b l e m of vo lume change due to w e a t h e r i i ^ p rocesses . B e f o r e about 1930 i t was gene ra l l y assumed that a l l concre te de s t ruc t i on due to low t empera tu re s was produced by f r e e z i n g o f w a t e r w i t h i n the concre te . The body of i n f o r m a t i o n ga thered i n the 30 to 35 years s ince has been l a r g e l y the r e s u l t of numerous analyses of concre te f a i l u r e s i n s e r v i c e o r t e s t r e s u l t s i n w h i c h i t has been found that va r i ous p h y s i o - c h e m i c a l p r o p e r t i e s of the sy s t em play s i g n i f i c a n t r o l e s i n concre te d u r a b i l i t y . Instances of sha rp ly c o n f l i c t i n g conclus ions r e g a r d i n g the e f f ec t s of c e r t a i n p r o p e r t i e s a re evident i n the l i t e r a t u r e , c l e a r l y po in t ing up the c o m p l e x i t y of the p r o b l e m .


D e s t r u c t i v e v o l u m e change of concre te r e s u l t s f r o m changes i n m o i s t u r e content and t empe ra tu r e (above as w e l l as w i t h i n the f r e e z i n g range) , and c h e m i c a l r eac t ions . The l a t t e r phenomenon, m o s t common ly associa ted w i t h c h e m i c a l r eac t ions between c e r t a i n s i l i ceous aggregates and a l k a l i s i n cement , was f i r s t r e p o r t e d by T . E . Stanton i n 1940.

Al though a l l s i l i ceous aggregates r eac t w i t h a l k a l i i n cement , on ly opal , p h y l l i t e , and c e r t a i n i n t e rmed ia t e and ac id ic vo lcan ic r o c k s r eac t s u f f i c i e n t l y to be o f i m p o r t a n c e . The a lka l i - agg rega t e r e a c t i o n is man i f e s t ed as expansion and c r a c k i n g f a l l i n g in to e i the r of two i d e n t i f i a b l e f r a c t u r e sys tems; tha t i s , (a) those associa ted w i t h i r r e g u l a r and v a r i a b l e expansion, and (b) those r e p r e s e n t i n g s t r u c t u r a l f a i l u r e due t o d i f f e r e n t i a l vo lume change i n m e m b e r s .

The c r acks f o r m e d a re apt to be v e r y wide at the su r f ace , bu t not extending deeply in to the concre te . Whi t e amorphous deposi ts and gelat inous ex t rus ions ( sodium and po tass ium s i l i c a gels) appear at a f f ec t ed a reas . The gelat inous m a t e r i a l f i l l s the v o i d space between the r e a c t i v e aggregate and the su r round ing cement paste. The outside

18 EFFECT OF VARIOUS

Effect of Temperature Change Effect of Moisture Change

I Cement A Type

B Composition and Fineness

C Degree of hydration

Thermal coefficient varies somewhat with brand (B4Q6)

Thermal coefficient varies with degree of hydration (A429)

Varies with brand {B406)

1 The finer the cement the greater the volume change (B406)

2 Chemical composition, especially presence of CaS04 may influence volume changes (B406)

n Aggregate A Type

C Moisture content

D Surfece texture

Thermal coefficient is small for limestone and large for quartz (B406) No good correlation founa"betwecn thermal coefficients and freeze-thaw durability (A418) (A444) DiHerenT^thermal coefficients should not exceed 3 milbonths (A403)

Sandstone traprock and gravel concretei may show volume change 50-100% greater than limestone or quartz (B406)

Relation between thermal coefficient and relative humidity depends on a^regate type, but maximum coefficient occurs at about same % relative humidity (A429)

Effects are less than f rom aggregate type, influenced mainly by character of materia passing No 200 sieve—volume change gre: for clayey material (B406)

in Mix A Richness

B W/c ratio

C Admixtures

D Consistency

E Proportions

Thermal coefficient greater for richer mixes (B406) No apparent effect on thermal coefficient (B406)

Volume change greater for r i ch mix (B40e

L ime-no effect, integral waterproofing compounds-no effect, clay increases volume change (B406) Volume change varies with quanbty of mixing water (B406)

Small variations apparently make no appreciable difference (B406)

A Size and shape B Temperature Amount of permanent set and destruction

increases with mcreasing rate of temperature change (A4441 Resistance ofconcrete is more nearly related to the thermal coefficient of the concrete than to difference between coefficients of constituents» a trend exists for concretes of high coefficient to f a i l more rapidly (A444) Destruction is caused by temperature differences withm mass rather than difference in coefficients of ingredients (A444) Thermal coefficient of concrete is approximately the weighted average of the coefficients of the ingredients (A444)

Effects greater for thinner sections (B406 Magnitude of volume change somewhat related to thermal coefficient of expansiot (A429)

C Moisture content

D Age

E Mixing and placing (absorptiveness of mold)

F Reinforcing steel

G Curing

Thermal coefficient slightly higher for wet concrete (B406) Thermal coefficient is minimum at 0 and 100%. relative humidity and maximum at 60-70% relative humidity (A429) Apparent thermal coefficient dependent on capillary pore pressure which is dependent on relative humidity (A429)

1 Thermal coefficient may increase slightly with age (B406)

2 Apparent thermal coefficient decreases with age at optimum relative humidity (rel hum giving max thermal coeff ) True kineUc thermal coefficient (at 0 or 100% r e l hum may increase s ight ly with age (A429)

Environment (alternaUons of high and low temperature)

1 A small change m atmospheric humidi can make a measurable volume c h a i ^ concrete that has reached moisture equilibrium with its environment (B40

2 Volume change is zero at 95% relative humidity, negative at less than 95% ai positive at values above 95% (A429)

3 Weight chaise is zero at 85% reSl ive humidity, negative at less than 85% at positive at values above 85% (A429)

Expansion in water apparently stops at about 10 years, contraction in air continues beyond 20 years (B406)

Temperature alternations tend to decrease thermal coefficient (B406)

Shrinkage reduced when concrete cast in | absorptive mold ( B 4 0 6 ) Reinforcement inhibits volume c h a i ^ ( B 4 0 6 ) m e a t cement bars contract when cured

in a i r , expand when cured in water (BJ 2 Contraction m air aliout 3 times ex

pansion in water but varies markedly I with aggregate ( B 4 0 6 )

3 Length of imbal'waEer curing has no apparent effect on ultimate air shrinkJ { B 4 0 6 )

OF VOLUME CHANGE

ect of Strength Relations Summary

Thermal coefficient of concrete and volume change with change in moisture content varies with brand of cement Volume change with change in moisture content is also dependent on fueness of cement and amount of gypsum (CaSOi) present The thermal coefficient varies with the degree of hydration of the cement

19

ical reactivity not necessarily lated with increased bond ;th (A401)

Volume changes produced by temperature changes are strongly influenced by aggregate type and moisture content Thermal coefficients for aggr^ates vary f r o m small nesative values (about one mill ionth per * ^ m the direction o l certain crystallographic axes o l highly anisotropic crystalline materials (e g , calcite) to about plus 10 miUionths Although some mvestigators failed to find a correlation between thermal coefficients and freeze-thaw durability, i t seems reasonable that high differential thermal coefficients between aggregate and paste w i l l produce stresses lending to concrete destruction It has been recommended that differential thermal coefficients not exceed 3 miUionths The thermal coefficient of the aggregate is found to be dependent on its moisture content The maximum apparent thermal coefficient occurs at about 70% relative humidity Volume changes associated with changes in moisture content are pr imar i ly influenced by aggregate type and gradation Aggregate surface texture mfluences bond strength

strength increases with isir^ roughness (A4011

strength decreases with Lsmg water content of mix J corresponding to linear mship between proportion lent in paste and log bond ;th (A401)

The thermal coefficient and volume change with change in moisture content both increase with increasing richness of mix The only other mix parameter that apparently plays a part in volume change is the quantity of mixing water used This factor affects the volume change characteristics of the concrete with respect to moisture changes and affects the bond strength in an inverse manner

igential stress at surface of lerical mclusion is tensile 1 = (Youngs Modulus) (temp ! ) X (1 + Poisson's Ratio) m) ny physical interrelations ibine to fo rm large r e -Eiined deformations to give ures due to incompatibility 40) npressive and splitting engths increase with de-asing temperatures, ab-ite values dependent on lent content, w/c ratio, regate type, age, and sture condition Also ngs modulus increases with reasing temperature, but ison's ratio remam& es-:ially constant (A431) nkage strains inaiiced in

|crete by high temperatures be evaluated qualitatively

Analysis of lattice analogy |lO)

•B-3 above

Volume change as governed by temperature changes is affected by thermal, moisture and age characteristics of mass concrete The resistance of concrete was found to be more nearly related to the thermal coefficient of the concrete than to the difference between coefficients of ingredients, and the amount of permanent set and destruction increases with increasing rate of temperature change This suggests that destruction is caused by temperature differences within mass rather than differences between thermal coefficients However, the difference in thermal coefficients in this work was not really great enough to display any effects High rates of temperature change easily clouded any effects due to delta temperature coefficients The moisture content has a decided effect on the thermal coefficient in much the same manner as i t does on aggregate, that is , the thermal coefficient IS minimum at zero and 100% relative humidity and maximum at about 60-70% relative humidity The apparent thermal coefficient is dependent on capillary pore pressure which is dependent on relative humidity The thermal coefficient decreases with age at relative humidity giving maximum thermal coefficient (60-70%) but may increase slightly with ^ e for true kinetic thermal coefficient (at zero or 100% relative humidity)

Volume change as governed by moisture changes is affected by the following characteristics and conditions of concrete mass thermal, moisture, age, character of molds reinforcing and curing The magnitude of volume change with chaise in moisture content is somewhat related to the thermal coefficient of expansion A small chaise in atmospheric humidity can make measurable volume change in concrete that has reached moisture equilibrium with i ts surroundings With regard to age, i t has been stated that expansion in water stops at about 10 years, but contraction in air continues beyond 20 years Use of absorptive molds has been found to reduce shrinkage Reinforcement in concrete inhibits volume change Water curmg retards ini t ia l shrinkage, but apparently has no effect on ultimate air shrinkage

Strei^th relationships that bear indirectly on volume change due to the mechamsm of restraint also deserve mention Compressive and splitting strengths increase with decreasing temperature, absolute values depending on cement content, w/c ratio, a^regate type, age, and moisture condition Also Young's Modulus increases with decreasing temperature, but Poisson's Ratio remains relabvely constant

Temperature alternations tend to decrease coefficient of thermal expansion

20

of the r e a c t i n g aggregate i s darkened to a depth i nd i ca t i ng the extent of r e a c t i o n . The f a c t o r s found to inf luence a lka l i - aggrega te r e a c t i o n inc lude a l k a l i content of

cement , t e m p e r a t u r e o f c u r i n g and s to rage , m o i s t u r e a v a i l a b i l i t y , cement content o f m i x , and amount , s i ze , and r e a c t i v i t y o f aggregate. R e a c t i v i t y increases w i t h i n c r e a s es i n each of the f o r e g o i i ^ f a c t o r s w i t h the except ion of aggregate s ize . I t has been found tha t f o r v e r y r eac t i ve substances, such as opal , the m a x i m u m expansion tends to increase w i t h decreas ing p a r t i c l e s i ze , whereas the opposite i s t r u e f o r less r eac t ive aggregates .

E x p e r i m e n t s have revea led that the source of the d i s r u p t i v e f o r c e i n a lka l i - aggrega te r e a c t i o n i s o smot i c p r e s s u r e , w i t h the concre te ac t ing as a s emipe rmeab le membrane between a m o i s t u r e source and the hyd rophy l i c s i l i c a g e l f o r m e d at the r e a c t i o n l o c a t i ons .

A lkaU-aggrega te r e a c t i o n can be qui te r e a d i l y c o n t r o l l e d . The best means f o r ac c o m p l i s h i n g th i s i s to se lec t non - r eac t i ve aggregates and l o w - a l k a l i cements . Con c re t e a d m i x t u r e s , such as pozzolans w h i c h r e a c t the f r e e a l k a l i , can a l so be used to i n h i b i t a lka l i - agg rega t e r e a c t i o n . C o n t r o l of the v o i d spacing i n the paste and p r e v e n t i o n of w a t e r i ng res s in to the concre te can a l so a i d i n a l l e v i a t i n g the r e a c t i o n .

Vo lume cha i se s induced by changes i n t empera tu re and m o i s t u r e condi t ions a re i n t e r r e l a t e d and quite c o m p l i c a t e d . F o r example , Dav i s (B406) and M e y e r s (A429) ind ica ted the presence of a r e l a t i o n s h i p between the m o i s t u r e condi t ions e x i s t i n g w i t h i n the concre te and the c o e f f i c i e n t of t h e r m a l expansion of concre te . I t becomes i n c r e a s i n g l y evident , as the many va r i ab l e s i nvo lved a r e examined , tiiat the i n t e r p l a y between the v a r i o u s f a c t o r s i s so complex tha t i t i s d i f f i c u l t to separate t h e m . T h i s poin t i s i l l u s t r a t e d i n Table 1, w h i c h s u m m a r i z e s s i g n i f i c a n t i n f o r m a t i o n f r o m ava i l ab le l i t e r a t u r e on t h i s sub jec t .

The p h y s i o - c h e m i c a l p r o p e r t i e s o f aggregates that in f luence des t ruc t ive vo lume change and the manner i n w h i c h they act may be b r i e f l y s u m m a r i z e d as f o l l o w s : T h e r m a l c o e f f i c i e n t s ac t i n two d i f f e r e n t ways . F i r s t , l a rge c o e f f i c i e n t s , pos i t i ve o r negat i v e , produce l a rge s t resses i n the presence of t empe ra tu r e g rad ien t s . The amovmt of s t r e s s i s p r o p o r t i o n a l to the slope of the t empe ra tu r e g rad ien t and c o e f f i c i e n t o f t h e r m a l expansion. Second, d i f f e r e n c e s i n t h e r m a l coe f f i c i en t s of the paste and aggregate , o r d i f f e r e n t t h e r m a l c o e f f i c i e n t s a lo i% the c r y s t a l l o g r a p h i c axes of aggregate p a r t i c l e s , w i l l a l so produce s t r e sses . These f a c t o r s w i l l be ac t ive above as w e l l as w i t h i n the f r e e z i n g range. T h e r e f o r e , c y c l i c t e m p e r a t u r e v a r i a t i o n s above f r e e z i n g , a l though incapable o f developing the s t resses found i n sa tu ra ted concre te be low f r e e z i n g , w i l l add to d e s t r u c t i o n of concre te by the m e c h a n i s m of f a t i gue . T o compl i ca t e m a t t e r s f u r t h e r , apparent o r e f f e c t i v e t h e r m a l c o e f f i c i e n t s a re not constant—they v a r y app re c i ab ly w i t h h y g r o m e t r i c condi t ions . T h e r e f o r e , changes i n m o i s t u r e can a l t e r t h e r m a l s t r e s s condi t ions . M o i s t u r e v a r i a t i o n s a l so induce vo lume changes i n the paste phase, i r r e s p e c t i v e of t h e r m a l condi t ions . A d d to these compl i ca t ed i n t e r r e l a t i o n s the p o s s i b i l i t y o f an a ^ r e g a t e tha t r eac t s w i t h cons t i tuents o f the paste t o produce v o l u m e changes and i t becomes qui te evident that s u c c e s s f u l t h e o r e t i c a l approaches to the p r o b l e m a r e quite u n l i k e l y .

The ac tua l vo lume changes and degree of d i s t r e s s that r e s u l t f r o m the f a c t o r s g iven w i l l be f u r t h e r dependent on the s ize and shape of the concre te mass , the e l a s t i c and fa t igue p r o p e r t i e s of the paste and aggregate, and the paste aggregate bond. Note that these p r o p e r t i e s , w h i c h de t e rmine the r e l a t i o n between e x i s t i n g s t r e s s condi t ions and resu l t an t s t r a i n , a r e not independent of the e n v i r o n m e n t a l f a c t o r s tha t produce the s t ress condi t ions ; f o r example , the modulus of e l a s t i c i t y of the paste i s s t rong ly in f luenced by the m o i s t u r e condi t ions ex i s t i ng i n the concre te .

The basic p r o b l e m i n the path of quant i ta t ive ana lys i s of the many f o r c e s ac t ing to produce vo lume change i n concre te w i t h change i n e n v i r o n m e n t a l condi t ions i s r e a d i l y recognized as the heterogeneous cha rac t e r of the m a t e r i a l . However , a qua l i t a t ive i n d i c a t i o n o f the e f f ec t s of the many f a c t o r s i nvo lved can be d r a w n f r o m Table 1 .

Recommendat ions Concern ing A d d i t i o n a l Resea rch

The inves t iga t ion of p h y s i o - c h e m i c a l p r o p e r t i e s of a g g r ^ a t e s and t h e i r r e l a t i o n to

21

p r o p e r t i e s of concrete i s a f e r t i l e f i e l d f o r f u t u r e r e s e a r c h . I t i s envis ioned that such r e s e a r c h wou ld include (a) quant i ta t ive eva lua t ion of the in f luence o f p h y s i o - c h e m i c a l p r o p e r t i e s on the p e r f o r m a n c e of aggregate i n concre te , and (b) s t r e s s m o d e l s tudies us ing , f o r example , photoelas t ic techniques as desc r ibed i n "Misce l l aneous Poss ib le A p p r o a c h e s , " w i t h m a t e r i a l s of known phys io -e l a s t i c p r o p e r t i e s to analyze s t r e s s d i s t r i b u t i o n s ve r sus e n v i r o n m e n t a l changes.

F r o m the s tandpoint of basic r e s e a r c h , the w o r k suggested w o u l d f i l l c u r r e n t gaps i n the state of knowlec^e of concre te aggregates . F r o m the appl ied r e s e a r c h v i e w , assembly and c o r r e l a t i o n of such data cou ld help to p rov ide an index o r c r i t e r i o n f o r aggregate p r o p e r t i e s as r e l a t e d to t h e i r a b i l i t y to produce durab le concre te imde r speci f i e d e n v i r o n m e n t a l condi t ions (see "Misce l l aneous Poss ib le Approaches" ) . However , r e a l i z a t i o n of these b r o a d goals i s beyond the scope of the c u r r e n t s tudy.

U N C O N F I N E D F R E E Z I N G - A N D - T H A W I N G TESTS


The development of a f r e e z i n g - a n d - t h a w i n g tes t of unconf ined aggregates to detect unsound aggregates be fo re they a re used i n concre te cons t ruc t i on i s an ou tg rowth of the su l fa te tests and the evo lu t ion o f su i table l a b o r a t o r y f r e e z e r s . E x p l o r a t o r y w o r k began on th i s method d u r i n g the 1920's and publ ished data and proposed tes t methods began to appear i n 1930. The unconf ined f r e e z i n g - a n d - t h a w i n g tes t of concre te aggregates has, however , not a t ta ined the popu l a r i t y of the su l fa te tests and the re a re f o r t h i s reason f ew data on th i s me thod . The g rea t e r cos t of l a b o r a t o r y equipment and the i n c reased t i m e needed to conduct the unconf ined f r e e z i n g - a n d - t h a w i n g tes t has l e d to th is unpopu la r i t y .


Because of the many v a r i a b l e s present , a number of f r e e z i n g - a n d - t h a w i n g tes ts of unconf ined aggregates have been developed. These va r i ab l e s inc lude , a m o r ^ o the r s , method of p r e p a r a t i o n of samples , r a t e of coo l ing and f i n a l t e m p e r a t u r e reached, r a t e of thawing and f i n a l t e m p e r a t u r e reached, length of t i m e l e f t f r o z e n o r thawed, m o i s t u r e cond i t i on o f samples p r i o r to f r e e z i n g , and type of f r e e z i n g - a n d - t h a w i n g m e d i u m used (water , a i r , w a t e r - a l c o h o l , b r i n e , e t c . ) .

In 1931 Lang and Hughes r e p o r t e d the development and r e s u l t s of a tes t w h i c h c o n s i s t ed of i m m e r s i n g the specimens i n hot w a t e r a t 200 to 212 F f o r 5 m i n , i n ice w a t e r a t 35 to 40 F f o r 5 m i n , and f i n a l l y i n c a l c i u m c h l o r i d e b r i n e at 0 ± 10 F f o r 30 m i n (B503).

&ri938 W u e r p e l r e p o r t e d on a p rocedure w h i c h consis ted of the f o l l o w i n g . The specimens w e r e separ ted in to 200-g samples of the p a r t i c l e s izes s p e c i f i e d i n the then c u r r e n t A S T M su l fa te tes t . The samples were p e r m i t t e d to soak i n w a t e r ma in ta ined at 70 ± 2 F f o r 24 h r . They w e r e then placed i n the f r e e z i i ^ chamber , ma in ta ined at a t empe ra tu r e between 0 F and -5 F , f o r 6 h r . A f t e r the f r e e z i n g p e r i o d the samples w e r e p laced i n a thawing va t conta in ing w a t e r a t a t empera tu re between 55 F and 65 F f o r 18 h r . F o r f i n e aggregate, the cyc les w e r e cont inued u n t i l the loss i n w e ^ h t of the samples exceeded 10 percen t o r the number of cyc les reached 70. F o r coarse agg re gate, the cyc les w e r e cont inued u n t i l the loss i n we igh t exceeded 10 percen t o r the number of cyc les reached 15 (B117).

I n 1932, as the appendix to " R e p o r t of C o m m i t t e e C-9 on Concre te and Concre te A g g r e g a t e s , " a proposed f r e e z i n g - a n d - t h a w i n g tes t of unconf ined aggregates appeared en t i t l ed "Proposed Method of Tes t i ng Concre te and Concre te Aggregates by F r e e z i n g and T h a w i n g " (B504). I n 1938 an A S T M tenta t ive tes t en t i t l ed "Ten ta t i ve Method of Tes t f o r Soundness of Aggregates by F r e e z i n g and T h a w i n g " (C137-38T) was publ i shed . The tes t cons is ted essen t i a l ly of soaking the aggregate samples i n w a t e r a t r o o m t e m p e r a t u r e f o r 24 h r , f r e e z i i ^ the samples i m m e r s e d i n w a t e r a t -20 F f o r 30 m i n thawing the samples i n w a t e r a t 80 F , and m e a s u r i n g the d i s i n t e g r a t i o n as i n the sod ium and magnes i u m su l fa te soundness t es t method (C505, A621) . The tentat ive unconf ined f r e e z i i ^ -and- thawing tes t o f concre te aggregates was d iscont inued by A S T M i n 1944.

22

fii 1941 Gibson proposed a method based on cumula t ive percentages r e t a ined on a s e r i e s of s ieves ins tead of on separa t ion in to a number of s izes by the passed and r e ta ined s y s t e m . T h i s p roposa l was intended to evaluate those pieces of c rushed a g g r e gates w h i c h a re c r a c k e d d u r i n g the c r u s h i n g process and w h i c h subsequently separate i n one cyc le of f r e e z i n g and thawing (B502).

B r i n k , i n 1958, compared t h r ee t e s t methods that we re a l i ke i n a l l respects except f o r the f r e e z i n g - a n d - t h a w i n g m e d i u m . I n method A the aggregate samples w e r e f r o z e n , i n a sa tu ra ted cond i t ion , i n w a t e r and a l so w e r e thawed i n w a t e r . Tn method B the sa tu r a t e d samples w e r e f r o z e n and thawed i n an a l c o h o l - w a t e r m i x t u r e . Jn method C the sa tura ted samples w e r e f r o z e n i n a i r and thawed i n wa t e r . The r e s u l t s of th i s c o m p a r i s o n showed tha t 16 cyc le s of method B w e r e equal ly as e f f e c t i v e as 5 cyc les of the sod ium su l fa te tes t , bu t w e r e m o r e de s t ruc t i ve than 50 cyc les of e i the r method A o r method C. The r e s u l t s of method B w e r e i n reasonable agreement w i t h the s e r v i c e r e c o r d s of the m a t e r i a l s f o r w h i c h such i n f o r m a t i o n was ava i lab le (B501). T h i s i s e ssen t i a l ly the p rocedure c u r r e n t l y used b y the Iowa State Highway C o m m i s s i o n f o r de t e r m i n a t i o n of f r e e z e - t h a w d u r a b i l i t y of aggregates (B318).

The f r e e z i i ^ - a n d - t h a w i n g tes t of unconf ined aggregate i s not an adequate tes t f o r p r e d i c t i n g concre te d u r a b i l i t y . T h i s tes t , l i k e the su l fa te tes t s , does not dupl ica te the conf ined state of the aggregates as they e x i s t i n concre te . I t has been concluded by many inves t i ga to r s that the unconf ined f r e e z i n g - a n d - t h a w i n g tes t i s no m o r e ind ica t ive of f i e l d p e r f o r m a n c e than the su l f a t e soundness tes ts (B117, C102, £ 5 0 5 ) . A s w i t h the su l fa te t e s t s , unconf ined f r e e z i n g - a n d - t h a w i n g tes ts do c o r r e l a t e w i t h the f i e l d p e r f o r m a n c e o f some aggregates , bu t not w i t h o thers (B501). Resul ts a re r e p o r t e d where aggregates h a v i i ^ poor f i e l d p e r f o r m a n c e have passed the unconf ined f r e e z i n g - a n d -thawing tes t and o thers w i t h good f i e l d p e r f o r m a n c e have not (B318).

Recommendat ions Concern ing A d d i t i o n a l Resea rch

The f r e e z i n g - a n d - t h a w i n g t e s t o f unconf ined aggregate does not dupl ica te the n a t u r a l f r e e z i n g and thawing of concre te i n s e r v i c e . The re i s , t h e r e f o r e , a l a c k of gene ra l c o r r e l a t i o n between f r e e z i n g - a n d - t h a w i n g tes ts of unconf ined aggregate and f i e l d p e r f o r m a n c e of the concre te i n w h i c h the aggregate i s i n c o r p o r a t e d . I t appears that a m o r e i nd i ca t i ve and su i tab le t e s t f o r de tec t ing unsound concre te aggregates m u s t be developed.

F R E E Z I N G - A N D - T H A W I N G TESTS


The res i s t ance of aggregates i n concre te to f r e e z i n g - a n d - t h a w i i ^ cyc les has been inves t iga ted i n a wide v a r i e t y of a r t i f i c a l exposure condi t ions . M o s t of these tes t p r o cedures i nvo lve some a c c e l e r a t i o n of the processes of d e t e r i o r a t i o n e i t he r by ra t e of t e m p e r a t u r e change o r r a t e of r e p e t i t i o n , and a r e c l a s s i f i e d as " s l o w " o r " r a p i d " de pending on the degree of a c c e l e r a t i o n .

Scholer (A626) appears to have desc r ibed the f i r s t l a b o r a t o r y f r e e z i n g - a n d - t h a w i n g t es t i n 1928. I ^ e l a b o r a t o r i e s o f the B u r e a u of Standards, B u r e a u of Rec lama t ion , B u r e a u of Pub l ic Roads, N a t i o n a l Sand and G r a v e l A s s o c i a t i o n , Na t i ona l Crushed Stone A s s o c i a t i o n , Corps o f Eng inee r s , and s e v e r a l highway depar tments and i m i v e r s i t i e s developed equipment and w o r k e d out de t a i l s o f t e s t methods i n the p e r i o d f o l l o w i n g t h i s f i r s t p r o p o s a l . B y 1944 two coopera t ive i n t e r l a b o r a t o r y r e s e a r c h p r o g r a m s on f r e e z ing -and- thawing tes ts f o r cement and concre te had been conducted by the Highway R e sea rch B o a r d C o m m i t t e e on D u r a b i l i t y of Concre te—Phys ica l Aspec t s . The A m e r i c a n Society f o r Tes t i ng and M a t e r i a l s p r epa red f o u r tenta t ive methods of tes t f o r Resis tance | of Concre te Specimens to F reez ing and T h a w i i ^ , A S T M Des ignat ions , C290-52T, C 2 9 1 -52T, C292-52T, and C310-53T, c u l m i n a t i n g a p e r i o d o f b r o a d expe r imen ta t i on and de ve lopment .

In 1959 the Highway Research B o a r d C o m m i t t e e on D u r a b i l i t y of Concre te—Phys ica l Aspec t s conducted another i n t e r l a b o r a t o r y p r o g r a m on f r e e z i n g - a n d - t h a w i n g tes ts u t i l i z i n g A S T M procedures as the t e s t methods . Cons ide r ing th i s l a s t p r o g r a m and i t s

23

predecessors , a g r e a t a m o u n t of e f f o r t h a s b e e n expended i n these coopera t ive p r c ^ r a m s . When the many r e p o r t e d p r i v a t e inves t iga t ions a re a l so examined , the t o t a l e f f o r t i s found to be t remendous by any measure .

The body of knowlec^e concern ing tes ts and tes t i n t e r p r e t a t i o n f o r the f r e e z i n g - a n d -thawing res i s tance of concre tes , and p a r t i c u l a r l y f o r concrete aggregates , i s r a t h e r f r a g m e n t a r y and vague i n the l i g h t of th i s vas t r e s e a r c h e f f o r t . T h i s cond i t ion can be expla ined, a t leas t i n p a r t , by cons ide r ing some phases of the p r o b l e m .

E a r l y tests w e r e intended to measure concre te d u r a b i l i t y by f r e e z i n g and thawing , but as v iewed today they w e r e made wi thou t due r e g a r d f o r , o r unders tanding of , the many v a r i a b l e s i n v o l v e d . F o r example , f a i l u r e s due to bad pastes w e r e not r e a d i l y d is t inguishable f r o m those caused by bad aggregates . The d i s cove ry of a i r e n t r a i n -m e n t and i t s adopt ion f o r use i n t e s t concre tes , however , g r adua l l y caused many f r e e z ing -and- thawing tes ts to be compara t ive tes ts of aggregate d u r a b i l i t y when o ther v a r iab les w e r e c o n t r o l l e d at one l e v e l , e i the r by accident o r by d e s ^ n . F r e e z i n g - a n d -thawing tes ts a re usua l ly conducted on specimens p repa red i n the l a b o r a t o r y so that c o n t r o l of known v a r i a b l e s i s o f t e n a t ta inable . T h i s g radua l s h i f t i n t e s t emphasis and s ign i f i c ance , evident when v iewed i n r e t r o spec t , has delayed a c l e a r s ta tement of r e sea rch ob jec t ives and de t rac ted f r o m the l a s t ing value of some e a r l y w o r k . The i n h e r ent complex na ture of concrete as a cons t ruc t i on m a t e r i a l m u s t a l so be cons idered as an unrespons ive sub jec t f o r any quant i ty and qua l i ty of r e s e a r c h .

Rap id f r e e z i n g - a n d - t h a w i n g tes ts may now be used f o r eva lua t ing the f r o s t r e s i s t ance and, by d i r e c t i n f e r e n c e , the vo lume s t a b i l i t y of aggregates cast i n concre te . Even under A S T M s tandard iza t ion , however , m a j o r tes t p rocedure d i f f e r e n c e s e x i s t and make s p e c i f i c evaluat ions f o r po ten t i a l f i e l d use d i f f i c u l t . Table 2 s u m m a r i z e s p e r f o r m a n c e data on equipment used by l abo ra to r i e s i n the 1959 coopera t ive study and g ives c u r r e n t s p e c i f i c a t i o n values f o r s i g n i f i c a n t aspects of the t es t methods.

Jones and L e a (C612) publ ished the r e s u l t s of a quest ionnaire c i r c u l a t e d to 30 l abo r a t o r i e s i n 13 coun t r i e s . The r e s u l t s ind ica ted that m o s t l abo ra to r i e s use t h e i r Own methods and es tab l i sh t h e i r own c r i t e r i a f o r evaluat ing r e s u l t s .

T h e i r appears to be l i t t l e reason to expect that va r ious methods would c l a s s i f y c o n c re tes o r aggregates i n the same r e l a t i v e o r d e r of f r o s t res i s tance when spec imen m o i s t u r e c o n d i t i o n i i ^ , f r e e z i n g - a n d - t h a w i n g r a t e s , specimen s ize and exposure , and other tes t de ta i l s a r e as w i d e l y d i f f e r e n t as th i s su rvey shows t hem to be. The e x p e r i ence of i n d i v i d u a l l abo ra to r i e s and advancements i n concrete technology have, however .

TABLE 2

TYPICAL PERFORMANCE DATA, ASTM FREEZING-AND-THAWING METHODS

Freezing Phase Thawing Phase

Method Value Total Time (mm)

Time from 37F to 3F

(min) Rate (°/hr)

Total Time (mm)

Time from 3F to 37F

(min) Rate (°/hr)

c2go Lab., range^ 60-170 29-118 17-70 60-70 42-54 42-49 avg.^ 100 63 43 64 48 44

Spec. 2-to 4-hr total cycle, a minimum of 25/0 thawing time, be

C291 tween 3F and37FtDusehalf of avail, tune for that phase''

C291 Lab., rangec 80-180 39-130 16-51 30-180 13-32 65-157 Lab., avg."^ 135 93 26 58 22 98 Spec. 180 max. 90 mm. - 60 max. 30 mm. _b

C292 Lab., ranged- 1440 852-1158 3.5-4.7 1440 960-1350 3.0-4.1 Lab., avg.^ 1440 940 4.4 1440 1216 3.3 Spec. 1080-1440 1080-1440«* - 1080-1440 1080-1440 _b

C310 Lab., range^ 1026-1080 288-324 6.3-7.2 360-414 21-108 19-97 Lab., avg. 6 1069 304 6.8 370 68 40 Spec. 960-1200 300-420 — 300-420 90-120 _b

^our laboratories. ^Temp. difference, surface to center of specimen, must not exceed 50 F . °Eight laboratories. C292 specifies range of 70F to 3F. ^Five laboratories.

24

made f r e e z i n g - a n d - t h a w i n g tests a w ide ly used method f o r evaluat ing the f r o s t res i s tance of aggregates .


The p o s s i b i l i t y of us ing f r e e z i n g - a n d - t h a w i i ^ tes ts on concrete as a means of s tudyi n g the f r o s t res i s tance of aggregates was recognized e a r l y , but Jackson (A611) i n 1932 r e p o r t e d tha t d i f f e r e n c e s i n m o r t a r qua l i ty w e r e so g rea t that v a r i a t i o n due to type and cha rac t e r of coarse aggregate w e r e obscured . Lang (A617) i n 1938 cas t concrete s p e c i mens i n w h i c h the coarse aggregate was composed e n t i r e l y of suspic ious p a r t i c l e s . He found tha t i f concre te s t r eng th and f r e e z i n g - a n d - t h a w i n g d e t e r i o r a t i o n o f aggregate were cons idered together they were be t t e r ind ices o f bad m a t e r i a l than f r e e z i n g and thawing of the aggregates alone. I n 1939 C a n t r i l l and C a m p b e l l (B605) presented compar i sons of f r e e z i n g - a n d - t h a w i n g tes ts and f i e l d p e r f o r m a n c e of v a r i o u s concre te aggregate. They used these compar i sons to es tab l i sh l a b o r a t o r y t es t p e r f o r m a n c e c r i t e r i a f o r a g gregates , and so made f r e e z i n g - a n d - t h a w i n g tes ts a bas is f o r f i e l d acceptance of agg re gates , i ^ e c i m e n s made w i t h the aggregate i n quest ion w e r e cons idered to be acceptable i f they d i d not show a r educ t ion o f f l e x u r a l s t r eng th g r ea t e r than 30 percen t when subj ec t ed to 40 cyc les of f r e e z i n g and t h a w i i ^ . Aggregate absorp t ions above 3 percent w e r e cons ide red as evidence o f unaccep tab i l i ty .

Reagel (B624) presented a study o f f r e e z i n g and thawing i n nature and i n the l a b o r a t o r y . He a t tempted to answer such questions as: (a) How s h a l l d e t e r i o r a t i o n be m e a s u red? (b) What a re the e f fec t s of spec imen c u r i n g and c o n d i t i o n i i ^ ? (c) What f r e e z i n g -and- thawing cyc l e should be used? and (d) Can the e f f ec t s of aggregates on concrete d u r a b i l i t y be p r e d i c t e d f r o m f r e e z i i ^ - a n d - t h a w i i ^ tes ts? I t i s w o r t h no t ing that no pos i t i v e answers have ye t been found t o these quest ions .

A s i g n i f i c a n t coopera t ive t e s t p r c ^ r a m was r e p o r t e d i n 1944 (A606) . A m o n g the o b se rva t ions made w e r e the f o l l o w i n g : (a) a r educ t i on i n dynamic E of 30 percent c o r r e s ponds to an average decrease i n modulus of r u p t u r e of 45 percent , bu t on ly a 9 pe rcen t loss i n compres s ive s t r eng th ; (b) v e r y r a p i d coo l ing ra tes h inde red d i s c r i m i n a t i o n between known good and poor a b r o g a t e s ; and (c) vacuum-p re s su re s a t u r a t i o n appeared app rop r i a t e f o r cond i t ion ing aggregates (28 i n . H g vacuum and 125 to 150 ps i ) .

The A m e r i c a n Society f o r Tes t i ng and M a t e r i a l s publ ished a s y m p o s i u m (A632) on f r e e z i n g - a n d - t h a w i n g tes ts of concre te i n 1946. P rocedures and p rac t i ce s i n the m a j o r U . S. l a b o r a t o r i e s w e r e presented i n d e t a i l , w i t h many opinions r e g a r d i n g the i n t e r p r e t a t i o n o f such tes t s . T h i s s e r i e s of papers i s r i c h i n u s e f u l i n f o r m a t i o n even today, but some i t e m s a re p a r t i c u l a r l y pe r t i nen t to a study of aggregate tes t methods . F o r e x a m p le , a de t a i l ed p rocedure i s g iven f o r t e s t ing concre te conta in ing aggregate of i m c e r t a i n q u a l i t y . Some observa t ions w e r e : (a) h igh a lkaU cements should be avoided; (b) agg re gates should be b rough t to f i e l d m o i s t u r e condi t ions and c a r e f u l l y con t roUed ; (c) the m a x i m u m p a r t i c l e s ize should not exceed o n e - t h i r d the m i n i m u m spec imen d imens ion ; (d) a i r content should be c a r e f u l l y c o n t r o l l e d ; (e) concre te expansion can be used as an i n d i c a t i o n of spec imen d e t e r i o r a t i o n ; and (f) a l though f r e e z i n g - a n d - t h a w i n g tes ts a r e u s e f u l f o r eva lua t ing aggregate, m u c h m o r e m u s t be known about t h e i r conduct and i n t e r p r e t a t i o n .

Severa l l a b o r a t o r y s tudies d u r i n g the p e r i o d 1948 to 1957 made p a r t i c u l a r l y s i g n i f i cant con t r ibu t ions to the p r o b l e m of eva lua t ing aggregates by f r e e z i n g - a n d - t h a w i n g t e s t s . B o t h Sweet (B340) and B l a c k b u r n (A603) publ i shed r e s u l t s o f extensive tes ts on concre te aggregates i n 1948. Some i m p o r t a n t points made by Sweet w e r e : (a) spec imen we igh t ga in d u r i n g soaking seemed a p p r o x i m a t e l y equal when vacuum sa tura ted and 24 -h r soaked aggregates w e r e used, so w a t e r ga in was assumed to have o c c u r r e d i n the paste; (b) geologic data on the r o c k s s tudied seemed to be of l i t t l e value i n p r e d i c t i n g p e r f o r m a n c e ; (c) a l though no r e l a t i o n s h i p appeared to e x i s t between t o t a l vo ids , degree of s a tu r a t i on , spec i f i c g r a v i t y , abso rp t ion , and d u r a b i l i t y , the vo lume of aggregate voids s m a l l e r than 5 m i c r o n s d i d seem s i g n i f i c a n t ; (d) f r e e z i n g - a n d - t h a w i n g tests should be evaluated i n t e r m s of the m o i s t u r e condi t ions of the spec imen; and (e) t empe ra tu r e cyc les above f r e e z i n g can cause concre te d e t e r i o r a t i o n . B l a c k b u r n used a s a tu ra t i on c o e f f i c i e n t and noted tha t en t r a ined a i r reduced spec imen sa tu ra t i on i n a l l cases and

25

i m p r o v e d d u r a b i l i t i e s . The l i m i t i n g value f o r degree o f s a tu ra t i on appeared to be i l l de f ined , probably because of n o n u n i f o r m w a t e r d i s t r i b u t i o n . Whi t e s ide and Sweet (A631) pursued inves t iga t ions of m o r t a r s a tu ra t i on and found that a degree of s a tu ra t i on o f l e ss than 0. 88 ind ica ted a h ^ h l y durab le spec imen and tha t low sa tura t ions cou ld convenient ly be obtained by a i r en t r a inmen t .

About 1950, the concept of u s ing a i r en t ra inment as a means of m a k i i ^ the paste m a t r i x r e s i s t an t to f r o s t damage appears to have been f i r m l y es tabl i shed, aggregate c o n d i t i o n i n g techniques w e r e ava i l ab le , and p r o c e d u r a l de ta i l s had been c a r e f u l l y ou t l i ned . Jn add i t ion , a basic theory of f r o s t ac t ion had been presented by Power s . T h e r e f o r e , m o r e m e a n i n g f u l s tudies of the f r o s t res i s tance of aggregates by f r e e z i n g - a n d - t h a w i n g tests could be reasonably expected. However , i n 1953 Kennedy and M a t h e r (A613) a t t empted to compare the r e s u l t s of advanced l a b o r a t o r y f r e e z i n g - a n d - t h a w i n g tes ts w i t h f i e l d exposure . Th i s e f f o r t c l e a r l y showed tes t i n t e r p r e t a t i o n was d i f f i c u l t , because d i f f e r e n t i n t e rp r e t a t i ons m i g h t be expected f o r each set of m a t e r i a l s . Sophis t ica t ion i n tes t methodology alone was shown to be inadequate f o r m a k i n g aggregate eva lua t ions . F o l l o w i n g th i s r e p o r t m o r e e f f o r t m i g h t w e l l have been devoted to f i e l d - l a b o r a t o r y c o r r e l a t i o n s .

In 1954 L e w i s and Ven te r s (A619) noted that d u r a b i l i t y of concre tes made w i t h Indiana g r a v e l appeared r e l a t e d to spec i f i c g r a v i t y . In 1956 W a l k e r and M c L a u g h l i n (A630) r e po r t ed that the l a r g e s t p a r t i c l e s w e r e m o s t sub jec t to d e t e r i o r a t i o n , that a d i l u t i o n o f bad aggregates w i t h sound stone i m p r o v e d d u r a b i l i t y , and that r a p i d f r e e z i i ^ - a n d - t h a w -ing tes ts w e r e su i table f o r aggregate evaluat ions when used by exper ienced engineers . Legg ' s (A618) f i n d i n g s on s tudies of M i c h i g a n g rave l s w e r e s i m i l a r and a l so gave r a t h e r extensive c o r r e l a t i o n s between l a b o r a t o r y tes t r e s u l t s and f i e l d s e r v i c e r e c o r d s . Some s i g n i f i c a n t points made w e r e : (a) Th ree types of de le te r ious p a r t i c l e s w e r e i d e n t i f i e d as be ing s o f t p ieces , c h e r t s , and h a r d absorbent types; (b) Speci f ic g r a v i t y separa t ion at 2. 55 r emoved m o s t bad c h e r t p a r t i c l e s ; and (c) Specimen f a i l u r e s o c c u r r e d f r o m breakdown due to a concen t ra t ion of bad p a r t i c l e s and f r o m g e n e r a l d i s i n t e g r a t i o n .

A r n i , Fos t e r , and Clevenger (A602) r e p o r t e d i n 1956 on studies made w i t h a l l A S T M methods on good and bad concre tes . A l l tes ts r anked the aggregates i n the same o r d e r , but the t i m e r e q u i r e d f o r d i s c r i m i n a t i o n v a r i e d w i d e l y . I n 1957 F l a c k (A610) r e p o r t e d a s i m i l a r study made by the B u r e a u of Rec lama t ion . A g a i n , a l l tes ts r anked aggregates i n the same o r d e r and showed that spec imen shape had l i t t l e apparent in f luence on tes t r e s u l t s . The s low f r e e z e cycle i n w a t e r seemed to g ive the leas t v a r i a b l e r e s u l t s .

These las t two papers showed tha t w i t h i n one l a b o r a t o r y any of the A S T M methods cou ld g ive m e a n i n g f u l r e s u l t s . Another cooperat ive tes t (A625) r e p o r t e d i n 1959, however , showed a d i scourag ing l ack of agreement i n r e s u l t s between l a b o r a t o r i e s . Some valuable lessons w e r e l ea rned , but the l i m i t a t i o n s of l a b o r a t o r y tes ts wi thou t extensive f i e l d c o r r e l a t i o n s w e r e again h i g h l ^ h t e d . No spec i f i c tes t me thod was r ecommended , and good p e r f o r m a n c e by a concrete i n l a b o r a t o r y tes ts was cons idered only as evidence of a h igh degree of d u r a b i l i t y .

Some recen t inves t iga t ions have added to the f u n d of methodology. L ' H o p i t a l l i e r (A620) has r e p o r t e d a s i m p l i f i e d f r e e z i i ^ - a n d - t h a w i n g tes t w h i c h s t a r t s by thawing a f r o z e n spec imen and has the spec imen under a constant s t r e s s cond i t ion . Cook (C607) and Cordon (C608) have desc r ibed au tomat ic f r e e z i i ^ - a n d - t h a w i n g equipment to mee t one o r s e v e r a l A S T M methods .

Other recen t s tudies have made s i g n i f i c a n t con t r ibu t ions o r helped s u m m a r i z e e x i s t ing knowledge. Schuster and M c L a u g h l i n (A627) s tudied c h e r t and shale g r a v e l s i n c o n c re te and r e l a t e d aggregate c h a r a c t e r i s t i c s to f r e e z i n g - a n d - t h a w i n g re s i s t ance . They found reason to quest ion the s ign i f i cance of the s m a l l (less than 5 m i c r o n s ) aggregate po res . B l o e m (A604) noted a l so the s ign i f i cance of p a r t i c l e s ize to d u r a b i l i t y and that d r y i n g between c u r i n g and tes t ing g r e a t l y i m p r o v e d d u r a b i l i t y . The i m p r o v e d res i s t ance appeared to be r e l a t e d to the locus of f r eezab le wa t e r . D r y i n g apparent ly r e m o v e d wa te r f r o m the aggregates and subsequent s o a k i i ^ r e t u r n e d m o i s t u r e to the paste phase, whe re a i r voids p rov ide a measure of f r o s t r e s i s t ance .

C o m m i t t e e 201 of the A m e r i c a n Concre te Ins t i tu t e publ i shed an extensive s u m m a r y on concrete d u r a b i l i t y (B601). The m o s t recen t theor ies of P o w e r s , V e r b e c k and Landgren , and o the r s w e r e used to evaluate c u r r e n t tes t methods . I n s u m m a r y , they

26

state that "freezing-and-thawing tests on aggregates in concrete probably provide the best measure of aggregate soundness," but that "current tests are unable to measure aggregate durability with the certainty needed."

The ACI statements are appropriate for describing the current state of the art. Methods of evaluating aggregates by freezing and thawing are available, but they are usable only in local situations where sound engineering judgment is available to complement the test findings.

Recommendations Concerning Additional Research There appears to be little reason for large-scale "developmental" research on the

rapid freeze-thaw test methods for evaluating a^regates. When used in their present form for within-laboratory evaluations, and where experienced engineerii^ judgment is available to supplement raw test findings, they serve as one means for separating aggregates on the basis of predicted freezii^-and-thawing resistance. As contrasted with those available, new test methods appear to be needed to minimize the judgment factor, to establish the degree of equipment complexity really needed, and to provide criteria for reliable differentiation of materials with differing degrees of frost resistance so that acceptance limits may be established.

TEST METHOD PROPOSED BY T. C. POWERS Historical Background

A new method for testing the freezing-and-thawing resistance of concrete or aggregates was suggested by T. C. Powers of the Portland Cement Association in 1955. This method was based primarily on theoretical considerations relating to frost resistance of concrete developed over the period 1935-1950. The author made rather detailed comments on procedural aspects of the test but did not publish any data confirming its applicability.

The California Division of Highways was f i rs t to report, in 1961, a practical application of the Powers method. They developed specimen preparation and conditioning methods, testing and measuring techniques, and performance criteria. The method was used to evaluate several aggregates for a major highway construction project. This highway appears to have performed well since the time of construction.

An unpublished thesis prepared at the University of Maryland in 1962 reported some further developments and described laboratory applications of the Powers method. Conditioning and measuring techniques were changed and somewhat simplified. Test results were compared with findings from conventional freezing-and-thawii^ tests.

Significant Theoretical and Experimental Contributions Powers prefaced his presentation of a new test rationale by a critical review of the

existii^ procedures for freezing-and-thawing tests on concretes and noted several inconsistencies or weaknesses in them. For example, in the light of hydraulic pressure theory he felt that high and widely variable freezing rates tended to give a distorted picture of relative frost resistance rather than the hoped for simple acceleration of natural processes. That is, the mechanisms by which frost damage m^ht occur at natural cooling rates, approximately 5 F per hour maximum, could not be correlated with those at rates of 10 to 100 F per hour, the high rates causing unrealistically high stress conditions. Considering the growth-of-capillary-ice theory, and perhaps the osmotic pressure theory, this rapid freezing could lead to an underestimate of natural freezing conditions where relatively loi^periodsatlow temperatures are commonplace.

The significance of moisture conditioning of aggregates and concretes in test methods was noted and related to several categories of field conditions. Many concrete structures are in environments where some seasonal drying is possible and for this reason laboratory tests on only saturated concretes appeared too severe.

A proposal for a modified test procedure was then made to overcome the limitations just noted and other less vital ones. Because concrete has no intrinsic, measurable property of frost resistance, and because the contributory properties are numerous and

27

difficult to evaluate quantitatively, he proposed to use volume change characteristics of concretes under controlled conditions as the basic test methodology. Specimens would be prepared and conditioned so as to simulate field conditions and then be subjected to continual soaking with intermittent slow-rate freezing and periods at low temperature. Concretes subject to frost damage should reach some critical saturation level, after which they would expand on freezing. Periodic measurements of dilation and temperature would permit identification of this critical point and the time required to reach i t . Because of its theoretical background and its partial simulation of field conditions, i t was hoped that the proposed procedure would yield data that could be interpreted in a meaningful fashion. It also would require only relatively simple and inexpensive equipment to handle sizeable test programs.

Some conditional questions were raised by Powers and some procedural points needed examination. He did, however, lay a theoretical foundation, drawing from extensive literature search, and only then proceeded to outline a laboratory test procedure for evaluating the frost resistance of concrete or aggregate.

Powers' step by step description of significant aspects of the new test suggested that a tabular arrangement (see Table 3) might be appropriate for presenting the original proposal, significant experimental and theoretical background and developments, and a summary of major gaps st i l l hampering a thorough understanding of the freezing-and-thawing resistance of concrete and concrete aggregate. Recommendations Concerning Additional Research

The concept of testing a^regates in specimens of concrete using slow freezing-and-thawing cycles has considerable theoretical support and some experience has beengained in its application. The summary In Table 3 permits a review of theory, practice, and remaining questions and leads to (a) an evaluation of practice in the light of current theoretical and experimental knowlec^e, and (b) proposals for research to f i l l the identified gaps in imderstanding. A step by step evaluation with proposals for future work is given in following paragraphs.

Materials. —The ordinal proposal of using materials from the project under investigation appears acceptable with the reservation that differences in laboratory and field performance must be considered. For example, field exposure might cause alkali-aggregate reactions to be additive to frost deterioration. Short-term laboratory tests might not produce this effect, whereas long-term soaking at room temperatures might cause such a reaction. No consideration has been given to this matter in the work to date. As another example, an aggregate particle deeply imbedded in a massive concrete section would not cause failure as i t might in a thin section or near the surface, regardless of its size. Procedures I and I I used aggregates with the least dimension equal to one-third the minimum test specimen dimension and having a gradation similar to the source gradation. Whether or not the proposed 3 to 1 ratio of specimen to particle size is satisfactory is not known.

The degree of saturation of the aggregate particles at the time of freezing is a c r i t i cal factor in determining their performance. The original proposal hoes not specify initial aggregate moisture; procedure I uses aggregate in a stream-wet or vacuum-saturated condition, procedure n uses vacuum-saturated coarse aggregate. It has not been found possible to duplicate stream-wet conditions in a reasonable length of time by any process and maintaining aggregates in this condition after quarrying poses a difficult handling problem. Therefore, i t seems desirable to use some artificial reproducible degree of saturation for all test aggregates.

Proposal for Needed Research. —The use of a blend of several Type I low alkali content cements (less than 0.670 expressed as soda equivalent) should reduce the possibility of alkali-aggregate reaction in freezing-and-thawing tests. Fine aggregate should be from a single uniform source having proven good performance. Coarse aggregates should be separated into four or five size fractions (No. 4 - ysin.; %in . - y 2 i n . ; 72 in. - y4 i n . ; in. - 1 i n . ; and 1 in. - \% i n . , i f needed). For most investigations the material passing the V z - i n . sieve should be replaced by a known durable aggregate. This step wi l l reduce test variability and the expense of handling and testing fractions that have been shown to play a minor role in freezing-and-thawing test results.

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Aggregates of questionable quality should be studied by reducing the size of the biggest through crushing and also by entirely removii^ i t . In general, all test aggregates should be saturated to some uniform degree by the vacuum method. If aggregates are used on the job in some drier state, this should then be the reference for moisture con-ditionii^.

Concrete Mixture. —The paste matrix of a concrete made with a water-cement ratio of 0. 5 by weight, with a slump of 2 to 3 i n . , and with air voids having a spacing factor

THE POWERS METHOD FOR TESTING THE F R E E ZING-AND-THAWING DURABILITY OF

Item Powers' Proposal Californid, Procedure I University of Maryland, Proct

Materials Cement AE agent Aggregate

2 Concrete Mixture w/c ratio % OA-FA Slump Air content

3 Specimens

Gagmg system Curing

Conditioning

Use those in question

Job size aggregate - no lab crushing (Powers anticipated usingsemi-dry aggregate)

0 49 w/c by weight (5% gal/sack)

Provide a known spacmg factor of 0 01 in or less

Large enough to permit joba^re-gate use

2 wks moist curmg

2 v/ks in laboratory air (should be based on specimen size and related to field conditions)-2 wks in water prior to first slow cycle

Those used on ]obs under consideration Neutralized Vinsol resm iVs-in max. size, with job moisture (2 California gravels, 1 Iowa limestone used)

Use the ]ob cement factor and slump (5 3 sacks and 2 in slump used in lab )

4 5 ± 0 5 percent air, spacing factor not measured

4V2 - by 9-m cylinders

End studs cast in specimens 24 hrs in molds, 14.day total moist cure 7 days at 73 4 + 3 F over sodium acetate (70-75 R H ) 14 days m water at room temperature (5 drymg schedules proposed R.H values at 100, 97, 87, 70-75, and a 50-75 combination)

Blend of 5 brands of Type I cemen Neutralized Vinsol resin Cumberland river chert and Glory limestone, 1-in max size

SVa sacks per c y (w/c approx 0 Apparent volume of C A = 0 67 ( 3- to 4-in slump 4.5 1 0 5 percent air. Spacing fai measured

3- by 4- by 16- m beams

End studs and brass plugs (two su 24 hrs in molds, 14 days total mi

Immediate slow freeze for some s 7 days drying at 40-60 percent R others

4 F - T Cycle Cool at 5F per hr from bath temperature (laboratory tern ) to 0 F , with a "rest" period just above freezing and hold overni^t, thaw in water. Repeat cycle every two weeks

Cool in kerosene bath at 5 i 1 F per hour from above 45 F 0 i 5 F Thaw to room temperature (No delay) Five mtermediate cycles per week, a measured cycle every two weeks

Cooling in polyethylene bags at ap] 5 F per hr (Cooled in steps, to IC 0F.)Cycle every two weeks, thaw and store at 40 F

5 Experimental Measures Weight

Relative E Dilation Temperature Length change

Freezing point depression Tensile strength

6 bistrumentation For weight Relative E Dilation

Temperature

Length change Freezing pomt depression Tensile strength

7. Test Results

Limits

Evaluation and application

Throughout test period

No During F cycle (after 42 days) During F cycle Throughout test period

No No

Use scale

Use automatic recordmg stram meter

Use recording thermometer

Not specified

Time of soaking to first dilation Rate of dilation (D = A") First dilation (transitory or permanent not specified)

Relate time of soaking to climate conditions to determme acceptable performance

At 14, 21, 35 days, before and after F - T cycles No At 35 days, during F cycle During F cycle At 14, 21, 35 days, before and after F - T cycle

No No

Use scale (+ 1 gm)

Strain frame with Imear variable differential transformer Thermocouple (both strain and temp automatically recording) Length comparator (ASTM C157)

Passmg or failing of specimens

Pass if (1) no dilation exceed 50 millionths, (2) final length does not exceed 14-day cure length by more than 0 006 percent The passing of 65 percent of the specimens representing any aggregate is required

At 14 days, before and after F - T c

At 14 days, before and after F - T c At 14 days or 21 days, during F c; Durmg F cycle At 7 days, before and after F - T cy

No No

Use scale ( 1 1 gm) Sonic apparatus (ASTM C21S) Stram frame with dial gage

Thermocouple (automatically reco Whittemore strain gage

Cycles to specified condition level (based on E) Transfer to rapid cycle at dilation 0-100, 100-200, 200-400, 400-80C Failure assumed at 50 percent loss i

29

of 0.005 ± 0.0025 i n . , should be immune to frost damage. Powers proposal specified that such conditions be met in this test method. Procedures I and I I followed the original proposal except that they did not measure characteristics of the air voids in the hardened concrete.

Proposal for Needed Research. —Initial mix water content and the water-cement ratio vary widely on different jobs and to some extent on a sii^le job. An investigation should be conducted to determine how sensitive this test method for aggregates is to these

iREGATES BASIC PROCEDURES, RELEVANT THEORY, AND REMAINING QUESTIONS

Theoretical and Experimental Substantiation Significant Unanswered Questions in Current

Theoretical or Applied Understanding

The possibility of having alkali-aggregate reaction in freezing and thawing tests exists, particularly in long time tests with water storage The use of low alkali cement (less than 0 6 percent) should mmimize this possibility (D703) Particle size is critical to F - T durability (A1Q2, B708. e718.A7!!2,A6a4)

Well-cured cement paste with a w/c ratio of 0 3-0 4 has no freezable water at ordinary freezing temperatures. (C713. B704. 0711) In general, rich well-cured concretes have higher durability fB7Q9. A U J , B7Q4. A7151 Paste can be given very long term immunity to high saturation conditions by maintaining a spacing factor of less than 0.01 m. Total air content is only a general indicator of this factor (A710. C712. D705, B3301 Stress strain relationships between paste and aggregate depend m part on the section (A420) Natural stone deterioration is affected by specimen size (A714) Continued curing increases the strength ot paste and concurrently more freezable space is filled with cement gel (B709. A3Q9. C707) Concrete undergoes some irreversible shrinkage when dried after curing (C7011 This shrinkage plus continuing hydration limits water absorption to less than the amount lost (A702. A713. A604) Drying removes water from saturated aggregate and impermeable paste slows its re-entry (C7071 Paste permeability is increased by drying (C7181 Micro-crackmg of paste may speed aggregate saturation (A421. C405. A7191 Concrete reaches the relative humidity of its enviroment (A329. A715)

Natural coolmg in temperate zone seldom exceed 5 F per hour (A715. A714.C707) More rapid cooling increases hydraulic pressures as water is compressed by the advancing zone of freezing (A714. A716. A707. A713) Additional water freezes as temperature is lowered (A717,A706) Thawing rate can affect air void saturation (QTQT) Prolonged low temperatures can cause expansion by capillary ice growth (B7Q81

How should aggregates be conditioned before testing"" Can a bad aggregate be processed to have smaller maximum size and theretiy become an acceptable one? Do several cement-paste-aggregate reaction phenomena confound the analysis of test results?

How much are test results influenced by the amount of freezable water as it varies with w/c ratio and curmg' How sensitive are test results, particularly on nearly saturated concretes, to spacing factor How, and for how long, do air voids remain unsaturated and continue to protect the paste phase' What model-prototype relationships must exist for test results to be applicable to job conditions What curing period provides the time stability needed for testing' Does casting position (beams vs cylinders) affect test results, 1 e , dilation and set' Assuming that all laboratory specimen soakmg and drying is artificial, should specimens be conditioned to some job related R H ' Does forced drying and saturation, per se, affect test results' Can paste, aggregate, concrete reactions to conditioning, 1 e , rate of saturation or drying, be used to predict durability' Do minor cracks developed in curing, conditioning, or testing affect aggregate saturation'

How much are test results influenced by coolmg and thawing rates and enviroments' Based on the artificiality of laboratory exposure, can a "forced" soaking procedure be developed to reduce test time' Under what conditions of saturation and to what extent do temperature cycles alone affect the nature and rate of concrete dismtegration'

Tests must detect 'time of critical saturation, when the concrete will fail with additional water and additional F - T cycles Deterioration can occur as a surface phenomenon, as deep seated failure or both (A627. C718) Measures of deterioration are weight change (Slfll), dynamic E (A633), tensile strength (C707), dilation (A716. A715. A719).length change (C7Q7. A715. A719^and freezmg point depression (A416) No single best measure of deterioration and rate of deterioration is known Dilation should be more sensitive than E , since E is partially restored by curing (A633. A719)

Which measure, or set of measures, gives the most reliable indication of mferior performance' Are there unknown measures superior to those known'

If changes in each specimen characteristic occur as functions of the several variables, then graphs of these functions originate at the origin of the axis system and may be asymptotic there Arbitrary limits on refinement of measurements must, therefore, be established New findings and interpretations are probable as greater instrument sensitivity is developed (B708,A719)

What refinement is necessary for acceptable test results' Will extreme accuracy and precision change apparent results or aid m finding laboratory-field correlations '

A saturation of 91 7 is the theoretical maximum which will permit 9 percent expansion at freezing (D409) The nature of the specimen, the distribution of moisture, and the type of exposure all suoport the existence of a range of saturations over which deterioration is progressive at some exponential rate. This rate should be critical measure (B708, A719), (both in field and laboratory) Until all the theoretical considerations are understood, a test designed to have true similitude with field exposure conditions seems improbable. (A613) Test limits must be established through correlations with field performance (B708. A715, A625, A613, C718) Complex interrelationships between material characteristics make some understanding of them mandatory for sound evaluation (C718)

Can laboratory-field performance correlations be established between particular field structures and environments and properly designed tests' What limits applied to the several measures are significant to field conditions' How much information on test materials, chemical and physical nature, can be used in evaluating test results' Does a basic rate-of-decay function for freezing and thawing damage exist' What I S I t ' How can intended job application and environment be shown m this function'

*The Powers procedure for making volume change characteristics determmations is referred to in all cases although questions may apply to other freezing-and-thawing test methods

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factors when a proper air void system is maintained. In a companion investigation the test response to minor variations in air content should be studied.

Specimens. —Powers proposed that specimens be large enov^h to accommodate job aggregates. There are few known data which support any given specimen-to-particle size ratio. The position in which specimens are cast (horizontal versus vertical) may also be significant because of pressure and sedimentation considerations and because air entrapped under aggregates wil l have different orientation with respect to the dimension used for length or dilation measurements. Procedures I and I I used cylinders and beams, respectively, with the choice probably based on facilities for handling such specimens and experience in evaluating the results. Without further test data such practical bases for choosing specimen size and configuration must be used.

Gage points for length change measurements were cast into the specimens in procedures I and n. Procedure I used the distance between the imbedded ends of the gage studs as the gage distance, whereas the total specimen length was used in procedure I I . ASTM CI57 specifies the method followed in procedure I and this should be adopted when imbedded studs are used.

Powers proposed two weeks of moist curing for test specimens and both procedures follow this recommendation. The adequacy of this curing time depends on the specimen conditioning to follow. The original proposal called for two weeks in laboratory air (R. H. unspecified) and two more weeks under water before the f i r s t freeze-thaw cycle. Procedure I followed the proposal except that 7 days of d ry i i ^ in air at the controlled R. H. was specified. Procedure I I permitted testing some specimens after 14 days moist curing, and others after curing plus 7 days drying at a controlled R. H. Strength and freezable water content, both vital factors in freezing-and-thawing tests, are affected by curing time. Test specimens should, therefore, be given a period of 28 days of moist or water cur i i^ . Some drying period is then desirable to simulate natural drying of field concrete. Research has shown that concrete attains the R. H. of the ambient atmosphere and so drying should continue to equilibrium with the highest R. H. that is typical of the intended exposure.

Proposal for Needed Research. —Studies should be made to determme specimen size versus conditioning effects; presently standardized specimens should be f i rs t investigated. The possible effects of casting position versus length change or dilation measurement position should be investigated. Cylinders cast in horizontal and vertical molds could be used for developing this information. Additional studies should be made in an attempt to relate degree of saturation for paste and/or aggregate and/or concrete to freezing-and-thawing durability and also to determine if forced or rapid wettii^ or d ry i i^ , per se, affects test performance.

The mechanism of moisture migration in the paste and the aggregate phases during wetting and drying is not well understood. The relatively finer pore structure of the paste indicates a higher paste-than-aggregate moisture content at other than dry or saturated conditions if the paste envelope is unbroken. Experimental evidence supports the existence of curing-stress micro-cracks around aggregates that might be channels through which aggregates become more readily saturated. The migration of moisture in the system should be studied by tracer techniques and specimens should be examined methodically by microscope or X-ray to determine the extent and probable impact of this cracking.

Freezing and Thawing Cycle. —The unnatural overload conditions imposed by accel-erated freezing-and-thawii^ tests led Powers to specify a coolii^ rate of 5 F per hour from room temperature to 0 F. Hydraulic pressures should then be developed that would be of the same magnitude as those occurring in field concrete. Specimens should be maintained at a temperature just above freezing until equilibrium is established within the specimen. The thermal coefficient line, from which subsequent expansions or contractions should be measured, can be established by using this point and one established at room temperature. Specimens were to be held at 0 F overnight, or for some period of time which would permit the growth of capillary ice when conditions were conducive to the occurrence of this phenomenon. This cycle was to be repeated every two weeks. Procedure I partially met these specifications, but did not provide for the "rest" period at freezing or for an extended period at low temperature. Procedure n specified

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cooling at approximately these rates but maintained test specimens at 40 F during the test program. Also, the "rest" period and an extended period at low temperature were not provided for.

Supercooling, rate of cooling, rate of cooling versus temperature, and duration of temperature depression have been shown to be significant and should all be carefully controlled in the test cycle. Neither of the procedures has met all of these requirements.

Storage at room temperature may permit additional hydration but this simplification appears justified if adequate curing and conditioning time are provided.

Procedure I called for specimens to be stored in a room temperature water bath for the two weeks between tests and required that they be given five intermediate slow cycles per week inasmuch as this procedure was found to be more severe than water storage with no intermediate cycles. Procedure I I specified storage at 40 F and cycles at two-week intervals only. Powers anticipated that intermediate cycles at less than a critical degree of saturation ( i .e . , before there was any measurable dilation) would not increase the rate of absorption and so would not affect the severity of the test. The data now available appear to support the assumption that absorption rates are not affected, but that intermediate cycles do hasten disintegration. Factors included in this phenomenon may include micro-cracking of the paste providing channels to aggregates, increase in freezable water through internal strain adjustments, and fatigue failure of some elements of the system.

Proposal for Needed Research. —A carefully standardized cycle meeting the applicable theoretical limitations should be established; one that can be produced without elaborate equipment and that requires a minimum of hand labor. After this base cycle has been developed, studies could be made to simplify i t without losing significant effects.

Intermediate freezing-and-thawing cycles at a rate approximating field exposure conditions may be necessary to give a realistic appraisal of durability. Research on this aspect of the test method should include (a) investigations of freezing-and-thawing effects on concretes maintained at some degree of saturation below that causing the f i rs t measurable dilation, (b) how to produce intermediate slow cycles in the most e f f i cient manner, and (c) how many such cycles are needed to simulate field exposure.

The possibility of forced saturation, by vacuum, pressure, or by immersion in water treated to reduce surface tension, should be considered as one means of reducing the testily time requirement. Because the specifying of continuous water storage between cycles constitutes an artifical exposure condition for most concretes to start with, means of accelerating absorption may have negligible added detrimental effect on the authenticity of test conditions.

Experimental Measures. —Powers proposed that weight, length change, and dilation duri i^ freezii^ be the principal experimental measures. Procedure I specified just these measures; procedure I I also used relative E for purposes of comparison. Experimental evidence indicates that relative E is less sensitive than dilation to internal deterioration and so its use should be discontinued except in special research studies.

The question of whether permanent length change or dilation during freezii^ would best indicate inferior test performance was raised by the author of this method. He felt that transitory dilation, instead of shrinkage, during freezing was the more attractive possibility inasmuch as no reference measure would thus be needed. The authors of procedure I found dilation to be the most consistent measure of aggregate performance. Experiments conducted following procedure H indicated that residual length change was more sensitive and more reliable for measuring the same thing. Obviously, this very important matter needs further investigation.

Freezing point depression has also been used as a measure of internal disintegration of concrete. The sensitivity of this measure has not been compared with those already discussed.

Tensile strength is a relatively sensitive indicator of damage to the concrete matrix. Past objections to using this measure have been that (a) it is a destructive test, and (b) concrete tensile strength was not easily determined. The relatively new tensile splitting test method may offer a solution to the second of these objections.

Proposal for Needed Research. —Various aggregates, of good, bad, and intermediate

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quality, should be included in studies using residual length change and dilation in an attempt to find the simplest, most reliable indicator of specimen damage. Companion tests could be made using freezing point depression and possibly tensile splitting strength so as to evaluate their relative worth m this regard.

Instrumentation. —The nonuniform distribution of moisture in concrete and the expo-nential form of the functions that have been obtained from plottii^ the various measures of deterioration indicate that an abrupt length change or dilation is improbable. Rather, it would appear that these phenomena wil l be observed when they have reached such proportions that they fal l within the capabilities of the instrumentation. Hence, no positive specification for sensitivity can be drawn.

Procedure I involved the use of an induction-type strain gage and a strip recorder which permitted strain measurements of approximately 3 millionths. Dial gages and a Whittemore strain gage were used in procedure H. The dial gages permitted reading dilation strains of approximately 6 millionths, while the Whittemore gage permitted the measurement of permanent length changes of approximately 10 millionths. The discussion given imder "Experimental Measures" suggests that the difference in instrumentation may have affected the findings in these two experiments.

Freezing point depression has been measured with thermopiles and a sensitive potentiometer. It would appear desirable to have precise temperature data for al l future research and developmental studies.

Proposal for Needed Research. —Again, no best system of instrumentation is apparent from the work to date. The system selected should be efficient and easily set up and used. An investigation of permanent length chaise and dilation phenomena should be made using the most sensitive instrumentation available. The degree of refinement should be reduced in increments and an evaluation made to determine a consistent level of accuracy and precision.

Test Results. —Powers suggested that the end point of the proposed test be either the f i rs t occurrence of permanent dilation after thawing or the occurrence of dilation during the freezing process. The time required for concrete to absorb enough moisture to exhibit one or both of these characteristics would be a measure of its period of immunity. This time would be the principal measure of frost resistance and the rate of dilation once it had begun would be a secondary measure.

The investigators in both experiments recognized their instrumentation limitations and set values to define the test end point. These limits should reflect system capabilities, because there is no other apparent basis for selecting this point. Where more sensitive measurements are made, the rate of dilation might become a primary measure of frost resistance.

Concretes made of different materials must perform in different environments. It seems unlikely that any single set of criteria would serve all purposes adequately. The materials used and the intended environment for the concrete must somehow be reflected in the evaluation of the test results.

Proposal for Needed Research. —Field studies of temperature and moisture conditions in concrete structures in various environments are needed to aid in judging the results of test performance. Field and laboratory studies which would attempt to relate test findings with natural exposure should constitute the final developmental stage of such a test method.

MISCELLANEOUS POSSIBLE APPROACHES S^nificant Contributions

Tests to identify coarse aggregates that tend to produce destructive volume changes when used in concrete subject to frost action may be divided into two general classes: (a) weathering tests, actual field and simulated; and (b) measurement of some physical property which has previously been correlated with durability. In weathering tests the intent is to duplicate actual field conditions; thus, tests in this class tend to be complicated and time consuming, though probably of fe r i i^ the h^hest degree of accuracy in results. The Powers method would fal l into this class.

The second class comprises the empirical tests wherein physical properties of

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aggregates (specific gravity, porosity, absorption, pore distribution, etc.) are used as measures of durability. Although offering the advantage of speed, the tests in this class have not been too reliable. However, the need for a test of greater simplicity and of shorter duration than the freeze-thaw test st i l l exists.

It has long been recc^nized that aggregates from sources considered to be unacceptable often contain a relatively small percentage of particles which may produce destructive volume change. This factor suggested the possibility of aggregate bene-ficiation by removal of the "bad" particles. The beneficiation is accomplished by taking advantage of differences in physical properties between good and bad materials. Thus, aggregate beneficiation is a direct outgrowth of tests falling into the second class previously listed.

Major contributions have been made toward beneficiation of aggregates by means of specific gravity fractionation. Certain cherts and mixed river gravels have been improved significantly. This process has been in use commercially for about 15 years. The process involves passii^ the aggregate through a fluid bath of the desired specific gravity. The material that floats is discarded; that which sinks is the beneficiated aggregate. The separating medium generally used in commercial plants is a suspension of finely divided magnetite or ferrosilicon in water. It has been shown (B807, A619), that removal of lightweight particles can significantly increase freezing-and-thawing resistance of many aggregates.

Other commercial beneficiation techniques that may improve frost resistance of aggregates include jigging, hydraulic classification, and elastic fractionation (B807). Jigging is the name for a process that separates heavy grains from light by utilizmg a difference in the abilities of the grains to penetrate a semi-stationary bed formed by pulsating water currents. Although performing essentially the same function as heavy-media separation at a lower investment cost and approximately equal operating cost, jigging does not have the operating flexibility nor does i t make as definite a separation as heavy-media methods (B807).

In hydraulic classification, the aggregate is dropped into a vessel where r i s i i ^ water currents carry light material upward and out of the "good" aggregate. This process, which has been used extensively in the coal industry, is cheap to operate and maintain, but does not make a definite specific gravity separation.

Elastic fractionation removes softer particles (usually of lighter materials) from an aggregate. This is accomplished by dropping the aggregate on an inclined steel plate. Bins are arranged to catch the rebounding aggregate, thus affording classification in relation to elastic rebound. This method is generally applicable only to natural (gravel) aggregates.

Aside from the aggregate beneficiation techniques, the only major contributions in the miscellaneous category are the various attempts to correlate specific aggregates with field performance of actual pavements. Essentially all of the published work in this field has been done in the midwestern states and encompasses mainly chert gravels and crushed limestones. As early as 1939 Cantrill and Campbell reported on the condition of some 1,100 miles of concrete pavement in Kentucky (B605). This was followed in the early 1940's by similar investigations of 1,170 miles of concrete pavement in Kansas by White and Peyton, 450 miles of Missouri pavement by Reagel and Gotham, and 3,300 miles of Indiana pavement by Woods, Sweet, and Shelburne (B810). The last study mentioned was by far the most comprehensive and covered about 78 percent of all the rigid pavements constructed in Indiana between 1921 and 1943 (A811). This represented 725 projects and included cements from 17 sources, sands from 138 sources, and coarse aggregates from 155 sources. As a result of this survey highly significant correlations were obtained between certain sources of coarse aggregate and good or bad field performance as measured by "blow-ups" or "pop-outs." Sources of fine aggregate and cement had no significant effect on the correlations.

The major disadvantage of the service record approach to durability rating of aggregates is the time required to produce significant data. Woods, Sweet and Shelburne (A811) state that a pavement must be in service 10 years before an evaluation can be made. This method is obviously useless for rating new aggregate sources.

Summary and Recommended Areas for Research From this critical review, it can be concluded that the probability of finding one

simple, reliable, low-cost test method with a capability for identifying good, bad, and all intermediate qualities of aggregate with regard to their potential volume stability in freezing environments is small. If the test method can be made responsive to such factors as aggregate type, condition and size, the class of concrete to be used, the structural elements involved, and the service environment, the possibility exists for making the desired identifications. Development of such a fully responsive test certainly wi l l require a massive research effort. Current research should, however, lead to the development of tests which wi l l permit sounder judgment to be exercised regarding the selection of aggregates for specific applications. It should also emphasize, for both aggregate producers and consumers, the fact that the consistent production of quality concrete requires a more thorough understanding of the role of aggregate than has been demanded in the past.

Soundness Tests Experience has shown that sodium or magnesium sulfate tests for soundness of ag

gregate do not provide reliable indications of frost resistance. The mechanism of destruction involved, crystallization within aggregate pores, is not comparable with the hydrostatic pressure generated by advancing ice fronts in the pores under actual conditions. Also, the test is too sensitive to test variables. In view of these difficulties, no further research effort should be devoted to sodium or magnesium sulfate soundness tests and these should be deleted from specifications as soon as suitable replacements are available.

Petrographic Analysis It may be stated axiomatically that volume stability, or lack of i t , stems from cer

tain fundamental aggregate properties. If petrography may be considered to include the evaluation of these fundamental properties, i t must be a part of all rational methods for identification of unsound particles. Thus, i t seems quite likely that petrographic procedures wi l l constitute an integral part of tests for frost resistance, either directly or under some empirical parameter.

The most important characteristic of aggregates which affects frost resistance apparently is the pore structure. Research aimed at developing simple methods for evaluating this is badly needed.

Pore System Studies The nature of the entire pore system is a most important consideration to under

standing the frost resistance of aggregate and paste. It is, for example, through its effect on the pore system that air entrainment imparts frost resistance to concrete.

The most widely accepted theory regarding frost damage of concrete—that proposed by T. C. Powers—recognizes the importance of pore structure of paste and aggregate. The susceptibility to frost damage is dependent on the quantity of moisture present, the distribution of the moisture, the rate, degree, and duration of temperature changes, and the pore structure of the paste and aggregate, separately and in relation to each other. Because the quantity and distribution of moisture in the paste and aggregate depend on pore characteristics, they and thermal exposures essentially determine the effects of frost action.

The characteristics that describe the size, shape, and quantity of voids making up the pore system are pore size, pore size distribution, tortuosity, and surface area. Unfortunately, these and the properties that are affected by the pore characteristics

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(porosity, absorption, saturation, permeability, and capillarity) are interrelated and difficult to evaluate separately. However, inasmuch as destruction by frost action is predominantly a manifestation of these characteristics and properties, development of simple, reliable tests for them should provide good indicators of frost resistance. Pore size or pore size distribution is the most important pore characteristic in this regard. Whereas porosity, permeability and capillarity are the properties affected by pore structure that are most sensitive to frost resistance. Therefore, the first and basic step toward development of new procedures for detection of frost-susceptible aggregates ancVbr concretes is the development of simple, reliable tests for pore size or pore size distribution, and porosity, permeability, and capillarity. It is strongly suspected that, although the foregoing items may not give highly significant correlations with frost resistance per se, they wi l l contribute toward an index rating of aggregates for frost resistance. In addition to pore characteristics, this index would incorporate petrographic, physio-chemical, and environmental conditions into a rating system for aggregates. Physio-Chemical Properties Studies

There are factors other than the stress from freezing water in paste and/or aggregate pores that are capable of influencing the over-all distress of concrete under changing environmental conditions. These include differential thermal expansion (within a mass and between aggregate and paste phases); differential hygrometric expansion; chemical reactivity between paste constituents and aggregate; bond strength; and the strei^th, elastic, creep, and fat^ue properties of paste and aggregate. Many of these factors are interrelated in a manner which makes individual scrutiny impossible. However, the physio-chemical properties are of sufficient importance because of their influence on frost resistance, and because they affect all stress-strain relationships, that further investigation is warranted. It is important to use a systematic approach to permit resolution of the interactions that are known to exist between physical properties and environmental conditions; as, for instance, between thermal coefficient or modulus of elasticity and hygrometric conditions. A lack of regard for these interactions has severely hampered the general utilization of much published data on the effects of physio-chemical properties on frost resistance of aggregates and concrete. Additionally, stress model studies employing photoelastic techniques to analyze stress distributions versus environmental changes may prove highly profitable. This application of photo-elasticity, while relatively untried, appears feasible and should aid in analyzing basic stress-strain phenomena.

Unconfined Freezing-and-Thawing Tests Unconfined freezir^-and-thawii^ tests, like sodium sulfate tests, fai l to duplicate

natural conditions. Thus, they too display a general lack of correlation with field performance of aggregates in concrete. It appears, therefore, that unconfined freezing-and-thawing tests should be discontinued as soon as other suitable tests for detecting unsound aggregates can be developed.

Freezing-and-Thawing Tests Freezing-and-thawing tests of concrete currently comprise the most reliable labo

ratory means of evaluating frost resistance of aggregates. However, the tests are incapable of supplying the degree of discrimination needed and require a high degree of judgment for interpretation of test results. Also, the lack of a single uniform test procedure and the cost and complexity of equipment required have discouraged universal recognition of freeze-thaw tests as a prime acceptance criterion for concrete aggregates.

Bi view of the obvious deficiencies in the freeze-thaw tests and their lack of s imilitude to natural exposure environments, i t is recommended that no further research work be considered along these lines. However, it is suggested that freeze-thaw companion tests might be run in conjunction with the development of new test methods, when appropriate, in order that use may be made of the large fund of freeze-thaw data.

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Test Method Proposed by T. C. Powers The theories and test for frost resistance of aggregate proposed by T. C. Powers

constitute what is believed to be the most rational test for aggregate frost resistance. Aspects of this method requiring additional research include development of better means for determining the test end point, development of an efficient cooling cycle, specimen and aggregate conditioning procedures for retaining compatibility with natural conditions, development of accelerating processes to reduce test time without impairing relation to natural weatherii^ conditions, and development of equipment and instrumentation to simplify and improve the reliability of the test. Fullest utilization wil l likely result from careful correlation of the Powers test method with actual field results.

Miscellaneous Possible Approaches A few avenues of investigation into means of identifying frost-susceptible aggregates

were not covered in previous sections. The most promising of these, and perhaps the ultimate goal in the search for methods of evaluatii^ frost resistance is the "index" approach which has already been mentioned briefly. This involves the formulation of an index which takes into account physio-chemical properties of the paste and aggregate phases and environmental conditions. It is evident that the index ra t i i ^ could reject an aggregate under one set of conditions and accept i t under another, thus providing the ultimate in flexibility and economy. Formulation of such an index wil l involve extensive test programs to provide the required correlations among the many variables. Field performances under monitored conditions must also be obtained to provide a tie between the field and the laboratory.

Other possible approaches warranting careful study include (a) expansion or expansive pressure of a freezii^ aggregate particle as a means of predicting its volume stability, and (b) study of moisture movement in concrete with dyes or radioactive tracers.

Annotated Bibliography

SOUNDNESS TESTS DlOl. ASTM Standards 1961, Part 4:599, 1961.

Contains sodium and magnesium sulfate testing procedure, ASTM designation C88-61T.

C102. BLOEM, D. L . , "Soundness and Deleterious Substances." Significance of Tests and Properties of Concrete and Concrete Aggregates, ASTM, Special Publication No. 169:346-352, 1956.

Presents a discussion of the tests for detecting the soundness of aggregates. The conclusions reached are: (a) at present the sulfate test is the best available method; (b) freezing-and-thawing tests of unconfined aggregates are no more dependable than the sulfate method; (c) i t appears that freezing and thawing tests of concrete are extremely valuable for comparing potential performance of different concrete materials; and (d) none of the tests for aggregate soundness is sufficiently quantitative to permit its arbitrary use as a basis for accepting or rejecting aggregates exclusive of other considerations.

A103. BRARD, M . , Annales de Chemie et de Physique, 38:160, 1828. Contains description of early sodium sulfate test which was used to test the frost resistance of rocks (CI04).

C104. EMMONS, W. J . , "The Present Status of the Sulfate Crystallization Test for Soundness of Aggregates." HRB Proc., 16:167-173, 1936.

This report discusses the factors which influence the magnitude and uniformity of sulfate test results and shows that the test method is not adequately defined or explored. One of the conclusions arrived at is: "Even if refined to a greater degree than at present, i t is doubtful if the test under consideration wi l l constitute an entirely satisfactory measure of soundness. The search for a better soundness test should be continued.'

B105. GARRITY, L. V . , and KRIEGE, H. F . , "Studies of the Accelerated Soundness Tests." HRB Proc., 15:237-260, 1935.

A critical study of the sulfate test technique is made and several changes are recommended. The constancy of check determinations with materials from several sources is shown.

C106. GOLDBECK, A. T. , "Another Instance of Unreliability of the Sodium Sulfate Soundness Test." Crushed Stone Journal, 16-18, July-August, 1939.

Gives the sodium sulfate soundness test procedure recommended by the Committee of the Sanitary Engineering Division of the American Society of Civil Engineers on Filtering Materials for Water and Sewage Works. Cites an example of a limestone which has performed satisfactorily during 25 years of exposure in a trickling fi l ter but fails the sodium sulfate soundness test. Recommends that the sodium sulfate test be discarded.

C107. GOLDBECK, A. T . , "Durability Investigations." HRB Proc., 19:279-280, 1939.

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Mention is made of certain factors regardii^ aggregates and conditions of exposure that are being overlooked in connection with laboratory investigations of soundness. Attention is called to some of these phenomena with the purpose of stimulating discussion which may lead to a clarification of the needs in connection with soundness testing.

B108. GONNERMAN, H. F . , and WARD, G. W., "Studies on the Soundness and Durability of Aggregates and Concrete." (Abstracted version) Pit and Quarry, No. 12, 22:33-43, 46, September 9, 1931.

Report of sodium sulfate soundness tests on both fine and coarse aggregate, and freezing and thawing tests on mortar cubes in which both the fine and coarse aggregate are incorporated. The most outstanding feature of the tests is the very marked influence of the quality of the protectii^ cement-water paste on the resistance of the aggregates to f reezii^ and thawing in mortar and concrete.

C109. KRIEGE, H. F . , "An Accelerated Soundness Test." Civil Engineering, Pa r t i , No. 2, 1:120-122, November 1930.

Discusses sodium sulfate test in use at that time and suggests several changes. One such change would be to cause a definite temperature variation to occur during each cycle. This would add crystals to the growth already begun within the pores of an immersed sample and increase the destructive action of the soundness test.

Clio. LITEHISER, R.R., "Effects of Deleterious Materials in Concrete." Rock Products, 41, No. 9:39-40, September 1938.

Report of freezing and thawii^ tests and sodium sulphate soundness tests on concrete containing known deleterious coarse aggregates.

B i l l . PAUL, I . , "Magnesium Sulphate Accelerated Soundness Test on Concrete Aggregates." HRB Proc., 12:319-328, 1932.

The use of magnesium sulphate solution is proposed as a substitute for the commonly used sodium sulphate, because the solubility of the former only varies from 26.2 percent to 29 percent for temperatures from 68 to 86 F, whereas the solubility of sodium sulphate varies from 19.4 percent to 40. 8 percent within the same temperature range. Moreover the magnesium sulphate has only one crystalline form at these temperatures while sodium sulphate has three.

B112. TEMIN, M . , PIGMAN, W., and TUCKER, J. , "The Selection of Durable Aggregate for Concrete." Rock Products, No. 16, 34:37-42, August 1, 1931.

Three general types of materials, crushed rock, gravels, and slags, were tested. The crushed rocks may st i l l be further subdivided into granites, traps, limestones, and sandstones. Four disintegration treatments were used on the unconfined aggregate: (a) sodium sulfate solution; (b) sodium chloride solution; (c) boiling and drying; (d) freezing and thawing. Used a disintegration number, D, as an index.

i - » inn Y ft final fineness modulus \ "^ -^^^ [ } - initial fineness modulus ) Conclusions: 1. Clay inclusions in an aggregate appear to increase its disintegration. 2. The absorption and the porosity values are useless as criteria of

ability to withstand disintegration. 3. The four disintegration treatments when intercompared do not give

concordant results. 4. The pore space and disintegration are unrelated.

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B113. VOLLICK, C.A., and SKILLMAN, E . I . , "Correlation of Sodium Sulfate Soundness of Coarse ^gregate with Durability and Compressive Strength of A i r -Entrained Concrete." ASTM, P roc , 52:1159-1168, 1952.

Coarse aggr^ates from 70 dlfferentsources were subjected to five cycles in the sodium sulfate soundness test. The same aggregates were also used to fabricate 3- by 6-in. cylinders of air-entrained concrete having uniform grading and water-cement ratio. One half of the cylinders were tested for 28-day compressive strength and one half were subjected to alternate cycles of freezing and thawing until 25 percent of the original weight was lost from deterioration of the specimens. The test results were studied from the standpoint of relationships between the principal variables: sodium sulfate soundness, freezing and thawing durability, compressive strength, and cement content.

B114. WALKER, S., and PROUDLEY, C.E., "Studies of Sodium and Magnesium Sulfate Soundness Tests." ASTM, Proc , 36, Par t i , 327-335, 1936.

This report describes some of the experiences of the National Sand and Gravel Association in the conduct of tests for soundness of aggregates using sodium and magnesium sulfate. The tests were made to furnish information on the effect of variations in procedure.

C115. WOOLF, D. O., "Improvement in the Uniformity of the Accelerated Soundness Test of Coarse Aggregate." ASTM, Bull. 187, 42-46, January 1953.

The development of the present standard gradings used in the accelerated soundness test for coarse aggregates is described with an explanation of a reason for the lack of agreement among different laboratories in check tests of the same aggregate. To correct this difficulty the testing of aggregates in single sizes and the use of the "half-size" sieve for the determination of the loss are recommended.

B116. WOOLF, D. O., "Relation Between Sodium Sulphate Soundness Tests and Absorption of Sedimentary Rock." Public Roads, 8:225-227, December 1927.

Results of tests are shown which, although they do not establish a definite relation between percentage of absorption and unsoundness as determined by the sodium sulphate test, do indicate that rocks having high percentage of absorption wil l in the greater number of cases prove to be unsoimd.

B117. WUERPEL, C.E., "Factors Affecting the Testing of Concrete i^gregate Durability." ASTM, P roc , 38, Par t i , 327-351, 1938.

Presented are the results of a series of tests of the characteristics of three methods of testing concrete aggregate durability; the magnesium sulfate and the freezii^-and-thawing methods of testing unconfined aggregate, and the freezing and thawing of aggregate confined in concrete. It is stated that in the final analysis the tests are simply relative and bear no fixed relation to the natural attack upon a concrete mass.

C118. WUERPEL, C.E., "Modified Procedure for Testing Aggregate Soundness by Use of Magnesium Sulfate." ASTM, P roc , 39:882-891, 1939.

Recommends changes in ASTM tentative test C88-37T to remove some of the testing variables. Recommends that magnesium sulfate be used in place of sodium sulfate, and this, and the other recommendations appear in a proposed test method in the appendix of the article.

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PETRCXJRAPHIC ANALYSIS A201. DOLAR-MANTUANI, L . , "Concrete Aggregate Examination by Prolonged

Copper Nitrate Staining Method." Ontario Hydro Research News (Toronto), No. 2, Second Quarter, Vol. 14, 1962.

Describes early background in the examination of structural mineral with a copper nitrate method. To make certain impurities more easily visible, i t was found advantageous to increase the immersion period proposed by earlier workers. The effect of the immersion period is discussed and the copper nitrate stainii^ method is compared with the sulfate test.

The experience of the Hydro Electric Power Commission of Ontario over the past years using the copper nitrate staining method is described and some of the advantages and disadvantages of the tests are enumerated.

B202. KRIEGE, H. F . , "Mineral Composition of Aggregates." Report on Significance of Tests of Concrete and Concrete Aggregates, ASTM, Second Edition, 152-162, 1943.

Gives the description of a number of principal rock types and their chief mineral constituents. Also lists the deleterious mineral constituents. Presents a brief discussion of mineral properties such as soimdness, toughness, abrasion, etc., and their effect on concrete characteristics.

C203. MATHER, K . , and MATHER, B . , "Method of Petrographic Examination of Aggregates for Concrete." ASTM, Proc., 50:1288-1313, 1950.

A detailed description of the method for petrographic examination of aggregates for concrete as i t has been developed for use by the Concrete Laboratories of the Corps of Engineers is presented. The differences in procedure which depend upon the nature of the sample submitted and the purposes of the examination are described. Suggestions are made concerning the features to be delineated, the amount of material to be examined, and the organization and presentation of the results of the examination.

C204. MIELENZ, R.C., "Petrographic Examination of Concrete Aggregates." Geological Soc. of America, Bulletin, 57:309-318, April 1946.

Methods employed and the point of view adopted in performance of the petrographic examination are discussed in this paper. Physical and chemical properties of aggregates which significantly affect concrete are outlined.

C205. MIELENZ, R . C , "Petrographic Examination." Significance of Tests and Properties of Concrete and Concrete Aggregates, ASTM, Special Technical Publication, 169:253-273, 1956.

Purposes of petrographic examination: (a) to reveal the composition and physical and chemical characteristics of the constituents, and (b) establishes the fundamental nature of aggregates so that aggregates from unfamiliar sources can be compared with aggregates upon which information is available.

A petrographic examination should supply the following: mineralogic and lithologic composition, particle shape, surface texture, fracturation, coatings, porosity, permeability, and absorption, volume change, softening, and disintegration with wetting and d ry i i ^ , thermal properties, strength and elasticity, density, hardness, chemical activity.

Deleterious substances: sulfides, soluble salts, and alkali reactive substances; free lime (CaO) and magnesia (MgO) because of their increase m solid volume resulting from hydration or carbonation; metallic iron, iron carbide, coke and incompletely fused fluxstone.

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C206. MIELENZ, R. C., "Petrography Applied to Portland Cement Concrete." Reviews in Engineering, Geological Society of America, 1-38, 1962.

Sets forth the purpose of the petrographic examination of concrete. The possible causes of concrete deterioration are: (a) freezing of plastic concrete, (b) freezing of hardened concrete, (c) alkali-a^regate reaction, (d) sulfate attack, (e) failure under stress, (f) d ry i i ^ shrinkage, (g) attack by acidic waters, (h) carbonation of surface of plastic concrete, (i) sand-gravel reactions, (j) differential thermal volume change, and (k) oxidation, hydration, or carbonation of aggregate. The linear-traverse method and the point-count method for determining void volume in cement paste are described. Petrographic methods, such as thin-sections, polished-sections, etc., are also described.

C207. RHOADES, R., and MIELENZ, R. C,, "Petrography of Concrete Aggregate." Journal, American Concrete Institute, No. 6, 42:581-600, June 1946.

The need for tests on aggregates which would permit an interpretation of their concrete making properties is emphasized. Properties of the aggregate assemblage such as gradation, moisture content, and bulk weight are easily determined. Properties of individual particles originate in their mineralogic compositions, textures, and are called petrographic properties. Among these are: (a) chemical reactivity, (b) porosity, permeability, and absorption, (c) bond and surface texture, (d) internal fractures, (e) particle shape, (f) thermal expansivity, (g) surface coatings, (h) properties affecting drying shrinkage, (i) strength and elasticity, (j) specific gravity, and (k) specific heat and thermal conductivity. Each of these petrographic properties is discussed in terms of aggregate performance in concrete. The methods used by the Bureau of Reclamation in making petrographic studies of concrete aggregates are presented.

B208. RHOADES, R., and MIELENZ, R. C , "Petrographic and Mineralogic Characteristics of Aggregates." Symposium on Mineral Aggregates, ASTM, Special Technical Publication No. 83 , 20-48, 1948.

Petrographic and mineralogic composition and internal texture and structure of the particles control the physical and chemical properties of the aggregate. The physical properties of particles important to the quality of aggregate are: porosity, permeability, and absorption; surface texture; volume change with wetting and drying; thermal characteristics; strength and elasticity; density; hardness; shape; and coatings. The important chemical properties are: solubility; susceptibility to oxidation, hydration, and carbonation; and reactivity with constituents of portland cement. The interrelation of petrographic character and serviceability of concrete aggregate is demonstrated by several case histories. There is also a discussion of the petrography of aggregates contributing to freezii^ and thawing breakdown of concrete.

A209. ROY, THOMAS, WEISSMANN, SCHEIDER. "Geologic Factors Related to Quality of Limestone Aggregates." HRB Proc., 34:400-412, 1955.

Gives detailed petrographic analyses of several good and poor Iowa limestones. It was concluded that the presence of swelling type clay material and absorption capacities in excess of 2% favored reactions which produce stresses capable of seriously affecting the durability of the concrete. Fresh limestones of certain types displayed absorption capacities less than 2%, but after weathering, absorption increased to values in excess of 2%. The aggregates, which were originally satisfactory aggregates, became unusuable after weathering.

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C210. SWENSON, E . G . , and CHALY, V . , "Basis fo r Classifying Deleterious Characterist ics of Concrete Aggregate Mater ia l s . " Journal, American Concrete Institute, 52:987-1002, May 1956.

Deleterious characteristics of concrete aggregate materials are reviewed, and a simplif ied arrangement for their classification is proposed. This arrangement is based on a recognition of harmful properties rather than on types of materials, thus providing the testing engineer with a more systematic basis fo r laboratory evaluation of aggregates. These properties are discussed in relation to the limitations of conventional methods of test and the need for supplementary testing based on petrographic and chemical techniques. The suggested classification is as follows:

Deleterious Characteristics of Concrete Aggregate Materials

hemical

Independent of Cement

Oxidation Hydration Carbonation A i r - e n t r a i n i i ^ Impurities Solubility

External

Encrustations Weathered surfaces Polished surfaces Undesirable shape Extreme fineness

Physical

Reaction with Internal

Undesirable pores High volume change

with wetting and drying

Laminations and cleavage

Soft and weak particles

Unfavorable thermal expansion

Cement Alka l i reactivity Orgamc impurities Salt impurities Base exchange

C211. Public Roads, No. 2, WOOLF, D. O. , "The Identification of Rock Types. Vol . 26, June 1950.

A method for identifying rock types which is suitable fo r use by highway engineers is presented. It describes identification procedures that do not require an extensive knowledge of petrography.

PORE SYSTEM STUDIES

A301. BLAINE, R. L . , HUNT, C M . , and TOMES, L . A . , "Use of Internal-Surface-Area Measurements on Freezing and Thawing of Mater ia l s . " HRB Proc. , 32:298-306, 1953.

Exploratory experiments on the application of Brunauer-Emmett-Teller surface-area measurements to freezing-and-thawing research have been carr ied out. Results to date have indicated that surface areas calculated f r o m low-temperature nitrogen-sorption measurements were larger on the average for certain stones, bricks, and hydrated cement which failed in a few cycles of very rapid freezing-and-thawing than f o r materials which failed only after a large number of cycles of freezing-and-thawing. Surface-area measurements by water-vapor sorption on a few of the same materials did not show as consistent a relationship to durability as the nitrogen surface areas. It would seem pointless to attempt to relate the durability of concrete to the surface area of the aggregate, because the surface area of cement paste is higher than the surface area of any aggregate tested in this program.

B302. BLANKS, R. F . , "Modern Concepts Applied to Concrete Aggregate." Transactions of The American Society of C iv i l Engineers, 115:403-431, 1950.

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Aggregates influence the durability of concrete through numerous physical and chemical properties, most important of which are the size, continuity, and abundance of internal voids; the bonding characteristics; and the alkali reactivity. An apparatus to measure the capillary movement of water in concrete is shown and described. Studies of capillary phenomena in rocks and concrete have revealed a diagnostic relation between pore characteristics and freezing-and-thawing durabili ty.

A303. BROWN, L . S., and PIERSON, C . V . , "Linear Traverse Technique for Measurement of A i r in Hardened Concrete." Journal, American Concrete Institute, No. 2, 47:117-123, October 1950.

Describes equipment for measurement of air content of hardened concrete by linear t r a v e r s i i ^ and calculation of various parameters.

B304. BROWNMILLER, L . T . , "The Microscopic Structure of Hydrated Portland Cement." Journal, American Concrete Institute, No. 3, 39:193-210, January 1943.

Presents a study of neat hydrated portland cements using microphoto-graphs.

D305. BRUNAUER, S., "The Absorption of Gases and Vapors." Princeton, Princeton University Press, 1:3-497, 1943.

Contains information on experimental methods, absorption isotherms, heat of absorption, the surface and pore structure of the absorbent, and the kinetics of physical absorption.

A306. BRUNAUER, S., "Tobermorite Gel -The Heart of Concrete." American Scientist, No. 1, 50:210-229, March 1962.

Contends that tobermorite gel is the most important constitutent of hardened Portland cement paste. Tobermorite gel is a series of calcium silicate hydrates two or three molecular layers thick existing as crumpled sheets or rol led up to give the appearance of f ibers . Explains three mechanisms of expansion of tobermorite gel.

A307. BRUNAUER, S., and GREENBERG, S.A., "The Hydration of Tricalcium Silicate and j3-Dicalcium Silicate at Room Temperature." Papar n i - 1 . Chemistry of Cement, Proceedings of the Fourth International Symposium, Washington 1960. National Bureau of Standards, Monograph 43, Vol . I , August 1962.

The hydration of t r icalcium silicate and 6-dicalcium silicate produces the hydration products of calcium silicate hydrate and calcium hydroxide. The chemical and physical properties of the calcium silicate hydrate, which is a member of a series of hydrates called tobermorites, are d is cussed in considerable detail.

A308. BUTTERWORTH, B . , "Pore Sizes, Their Measurement and Significance." Claycraft , 30:2-9, October 1956.

Presents some merits and limitations of the mercury pressure method fo r determining pore size distributions. The relationship between pore sizes and f ros t resistance is explored.

A309. COPELAND, L . E . , "Specific Volume of Evaporable Water m Hardened Portland Cement Pastes." Journal, American Concrete Institute, No. 8, 52:863-874, A p r i l 1956.

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The mean specific volume of chemically f ree water i n saturated hardened Portland cement pastes was found to be 0.99, independent of the extent of hydration of the cement or the water-cement ratio of the paste. This i m plies that there is no difference between the specific volumes of gel water and capillary water in saturated pastes. The total pore volume of a hardened paste is thus 99% of the weight of evaporable water in the hardened paste.

A310. COPELAND, L . E . , and HAYES, J. C , "Determination of Non-Evaporable Water in Hardened Portland-Cement Paste." ASTM, Bu l l . 194, 70-74, December 1953.

A revised method for de termini i^ the non-evaporable water of hardened Portland cement pastes is described. This method consists in drying samples in an evacuated space which is connected to a moisture trap held at -79C. The new method is simpler to use than the old method.

A311. COPELAND, L . E . , and HAYES, J .C . , "Porosity of Hardened Portland Cement Pastes." Journal, American Concrete Institute, No. 6, 52:633-640, February 1956.

Continued study of the properties of hardened Portland cement pastes has provided information which makes i t possible to estimate porosity of pastes more precisely than is possible by using the original equations of Powers and Brownyard. The total pore volume of hardened pastes is 99% of the weight of evaporated water in the hardened paste. Capillary pore volume is the difference between total pore volume and pore volume characteristic of the gel in hardened pastes. The pore volume of the gel is assumed to be the lowest pore volume that has been observed in hardened pastes. The paste with the lowest pore volume was made with W Q / C = 0.235 and cured f o r 11 years. The gel porosity calculated f o r this paste is 0.26.

B312. DOLCH, W. L . , "Studies of Umestone i^gregates by Fluid-Flow Methods." ASTM, P r o c , 59:1204-1215, 1959.

Fluid-f low measurements were made in an attempt to learn more about the pore characteristics of coarse aggregates and their influence on the freezing-and-thawing durability of concrete. Determinations of density, porosity, absorption, degree of saturation, specific surface area, capi l lary absorptivity permeability, and tortuosity factor were made on four Indiana limestones with both good and poor f i e ld and laboratory durability

.records. Absorption was found to be better than permeability as an index of surface area. The poor stones had consistently larger values of porosi ty, absorption, specific surface, permeability, absorptivity, ratio of absorptivity to permeability, and coefficient of rate of saturation increase than those fo r the more durable materials.

B313. DUNAGAN, W. M . , "Methods of Measuring the Passage of Water Through Concrete." ASTM, P r o c , 39:866-881, 1939.

Permeability implies f lu id passage in liquid f o r m , as capillary-evaporation moisture, and by water vapor movement. This paper presents the beginnii^s of a correlation of data concerning these methods. In i t are presented: (a) a discussion of permeability; (b) some tests of the same concrete tested f o r water passage under a l l three conditions; (c) tests of identical specimens at low heads alone and f o r capil lari ty; and (d) a proposed method to compare high-head liquid flow of water to capi l la r i ty .

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B314. FEARS, F . K . , "Correlation Between Concrete Durabili ty and A i r - V o i d Character is t ics ." A i r Voids in Concrete and Characteristics of Aggregates, H R B B u l l . 196, 17-28, 1958.

Five characteristics of the air voids in portland cement paste were investigated and statistical methods were applied to the results. The corre lation studies of the relationship between each of the a i r -void characteristics and durability show the spacing factor to be most highly correlated with durabil i ty. The specific surface is almost as highly correlated wi th durab i l i ty as the spacing factor. The other a i r -vo id characteristics studied were the number of voids per inch, the hypothetical number of voids per cubic inch, and the total a i r content.

E315. FEARS, F. K . , "Determination of Pore Size of Four Indiana Limestones." M . S. Thesis, Purdue Umversity, January 1950.

The purpose of the study was to establish a standard procedure fo r making pore volume determinations. The methods investigated were (a) the use of drawings of pore areas made f r o m polished sections of stone with the camera lucida attachment to the microscope, and (b) the use of drawings of pore areas made f r o m photomicrographs of thin sections of the stone.

A316. HANSEN, W. C. , "Porosity of Hardened Portland Cement Paste." Journal, American Concrete Institute, No. 1, 60:141-155, January 1963.

Discusses the structure of hardened portland cement paste f r o m the standpoint of solid state reactions as opposed to through solution reactions and coagulation of a sol to produce a gel. This is followed by calculations designed to determine the nature of the reaction products f r o m data fo r the evaporable and nonevaporable water contents of the hardened paste.

A317. H I L L , R. D . , " A Study of Pore-Size Distribution of Fired Clay Bodies." Transaction of the Br i t i sh Ceramic Society, No. 6, 59:189-212, June 1960.

Part I—Test-pieces of kaolinite, i l l i t e , mont-moril lonite and two industrial clays were f i r e d at temperatures ranging f r o m 600° C to 1,150° C, and their pore-size distributions were determined by the method of mercury penetration.

Part n—Sources of e r ro r in the conventional interpretation of pore-size distributions are discussed and i t is shown that these er rors may be sufficient to invalidate the interpretation. I t is shown that mercury in a f i l l ed cyl indrical pore is in unstable equilibrium when the pressure is reduced below half that at which penetration occurred. The use of this phenomenon in improving the interpretation obtained f r o m the mercury penetration data is discussed.

B318. HILTROP, C . L . , and LEMISH, J . , "Relationship of Pore-Size Distribution and Other Rock Properties to Serviceability of Some Carbonate Aggregates." Physical and Chemical Properties of Cement and Aggregates in Concrete, HRB B u l l . 239, 1-23, 1960.

The pore-size distribution of some carbonate rocks was determined as part of an investigation concerned with the properties of aggregate which affect the durability of portland cement concrete. Pore-size distribution is considered c r i t i ca l in controlling f low and retention of water in aggregate. Those properties, i n turn, might be related to an aggregate's effect on the resistance of concrete to freezing and thawing.

A319. INGLES, O . G . , "Design and Operation of a High Pressure Mercury Porosimeter ." Australian Journal of Applied Science, No. 2, 9:120-126, June 1958.

48

Structural and operational problems of a mercury penetration porosimeter designed fo r pressures up to 50,000 psi are described. The total volume of pores with rad i i of the order of tens of Angstroms or greater may be accurately determined. The instrument is fu l ly hydraulic in operation.

C320. JOHNSON, N . C . , "The Microstructure of Concrete." ASTM, Proc . , Part H, 15:171-213, 1915.

The wr i t e r of this paper estimated that not over 20% of total cement added to concrete is hydrated. The cement matr ix w i l l exhibit shear planes or rel ief planes f r o m tremendous confined crystalline pressures. The amount of material producing the crystals w i l l grow by capillary attraction i f a source is available. He also notes the oxide composition of cement and comments on the effects of surface tension of mix water.

C321. JONES, J . C . , "The Relation of Hardness of Br ick to Their Resistance to F ros t . " Transaction, American Ceramic Society, 9:528-576, 1907.

Discusses the disintegrating forces due to change in temperature; the physical properties of water; the disintegrating effects of freezing water; and freezing tests. Suggests that three tests—total pore space, rate of flow through the pores, and c rush i i^ strength—should give a correct ind i cation of the power of a b r ick to withstand f ros t .

A322. KROONE, B . , and CROOK, D . N . , "Further Studies of Pore Size Distribution in Mor t a r s . " Magazine of Concrete Research, No. 40, Vol . 14, March 1962.

The method of mercury penetration was used to study the influence of variations in sand/cement and water/cement ratios on pore size dis t r ibutions of mortars , down to pore sizes of 0.01 microns diam. The total volume of pores with diameters greater than 5 microns increased as sand/cement ratio increased, but decreased as water/cement ratio i n creased; cross-section of pores became more i rregular as sand content increased.

A323. KROONE, B . , and CROOK, D . N . , "Studies of Pore Size Distribution in Mor t a r s . " Magazine of Concrete Research, No. 39, 13:127-132, November 1961.

Pore size distributions of mortars cured by hydration, carbonation, and under atmospheric conditions were measured down to a pore size of 0.01 microns diameter by the method of mercury penetration. Hydration decreased the volume of the larger pores and carbonation decreased the volume of the intermediate size pores but increased the volume of pores exceeding 5 microns in diameter.

B324. LANG, F. C . , "Absorption of Concrete in Water as Affected by Aggregates—Its Ultimate Effect in Expansion of Road Slabs." HRB Proc. , 4:129-130, 1924.

A summary of the data obtained to 1924 on the absorption of concrete as affected by aggregates and the expansion of aggregates as affected by absorption.

B325. LEMISH, J . , RUSH, F . E . , and HILTROP, C. L . , "Relationship of Physical Properties of Some Iowa Carbonate Aggregates to Durabili ty of Concrete. A i r Voids in Concrete and Characteristics of Aggregates, HRB Bul l . 196, 1-16, 1958.

Pore size distribution data and effective porosity were determined fo r several Iowa carbonate aggregates. Aggregates showing poor freeze-thaw resistance have pores that are imiformly small and average 0.1

49

microns in radius. These aggregates have high capillary pressures and more pore area available f o r reaction. The data collected fo r this i n vestigation point out the subtle relationship of pore size distribution, effective porosity, and freeze-thaw results.

B326. LEWIS, D . W . , DOLCH, W. L . , and WOODS, K . B . , "Porosity Determinations and the Significance of Pore Characteristics of Aggregates." ASTM, Proc. , 53:949-962, 1953.

This paper has been developed f r o m material obtained f r o m a review of the l i terature covering research data collected f r o m the laboratory and the f i e ld . Attention is directed toward various methods of test which have been employed fo r determining the characteristics of pores, and emphasis is given to the relationship of these characteristics to absorption and degree of saturation of aggregate and to the durability of concrete. I t is concluded that the abundance, shape, size, and continuity of pores influence the physical properties and the chemical stability of aggregates and control certain durability characteristics of portland cement concrete. I t is concluded fur ther that there is a definite need fo r research in connection with the development of methods of test f o r the determination of pore characterist ics.

A327. LINDSAY, J, D . , " I l l inois Develops High Pressure A i r Meter for Determining Air-Content of Hardened Concrete." H R B P r o c , 35:424-435, 1956.

This paper describes the development of an apparatus and test procedure fo r determining a i r content of hardened concrete, ut i l izing pressure and the principles of Boyle's Law. The method has been found to be a valuable addition to the procedure for control of the production of concrete. Good reproducibility of a i r contents is obtained in independent tests of the same specimens at different ages, and the method provides excellent differentiation between concretes of different air contents. A reasonably satisfactory agreement was fo'ind between a i r contents of cyl indrical specimens determined with the apparatus and air contents subsequently by microscopic means. A i r contents of plastic concrete can be determined with good accuracy in the high pressure apparatus, which is taken as a general indication of the soundness of the method.

A328. LORD, G. W . , and WILLIS, T. F . , "Calculation of A i r Bubble Size Distribution f r o m Results of a Rosiwal Traverse of Aerated Concrete." ASTM, B u l l . 177, 56-61, October 1951.

Gives graphical and mathematical derivation of methods of calculation of various parameters associated with a i r dispersed in hardened cement paste.

A329. MENZEL, CARL A . , "A Method fo r Deteriming the Moisture Condition of Hardened Concrete i n Terms of Relative Humidity." ASTM, Proc. , 1085-1108, 1955.

A method fo r determining relative humidity i n concrete is outlined. Pieces of hardened concrete are b ro i^h t to equilibrium with the surrounding a i r in a closed container and the R. H. measured by a sensitive mechanical indicator. Equipment details are given along with procedures for ca l i bration and test performance. Mention is also made of electrical resistance and colorimetric methods fo r measuring R. H. in hardened concrete.

B330. MIELENZ, R . C . , et aL , "Origin, Evaluation, and Effects of the A i r Void System i n Concrete." Journal, American Concrete Institute, 55:507-517, July and August 1958.

50

Data are presented on air void parameters in hardened concrete f r o m structures and control cylinders f r o m various projects. Data on both plain concrete and air-entrained concrete are given. Correlation of these results with those given in the preceding papers seems to show that the requirements for recommended practice f o r selecting proportions fo r concrete usually assure development of a void system adequate to protect cement paste f r o m freezing and thawing. An appendix describes and d i s cusses the methods for optical measurements of a i r voids in hardened concrete.

B331. MYERS, B . , "Free Moisture and Absorption of Aggregates." Report on Significance of Tests of Concrete and Concrete Aggregates, ASTM, Second Edition, 129:137, 1943.

Presents several methods and equations for determining the f ree moisture and/or absorption of aggregates.

A332. NORTON, P. F . , and PLETTA, D . H . , "The Permeability of Gravel Concrete." Journal, American Concrete Institute, Abstracts, 27:1093-1132, 1931.

Tests were made for the purpose of determining the relationship between permeability and water-cement rat io, and between permeability and such other properties as strength, consistency, absorption, cement-voids rat io and grading of aggregate. An apparatus is presented f o r measuring the permeability of concrete. When measuring the permeability i t must be remembered that the results are qualitative rather than quantitative. The results of these tests are:

1. Permeability increases as the water-cement rat io increases. 2. Permeability decreases as strength increases. 3. Permeability decreases as the cement voids rat io increases. 4. There is no relationship between permeability and absorption. 5. Tests at higher pressure indicate that more water w i l l f low through

the specimen, but the increased flow is not directly proportional to the added pressure.

C333. POWERS, T . C . , "Structure and Physical Properties of Hardened Portland Cement Paste." Journal, American Ceramic Society, No. 1, 41:1-6, 1958.

Methods of studying the submicroscopic structure of portland cement paste are described, and deductions about structure are presented. The main component, cement gel, is deposited in water - f i l led space within the visible boundaries of a body of paste. Space f i l l e d with gel contains gel pores; space not f i l l ed by gel or other solid material is capillary space. Hygroscopicity of cement gel and capillary pores accounts for various aspects of the properties and behavior of concrete. Data on gel and paste structure are used in discussing strength, permeability, volume stability, and action of f ros t .

A334. POWERS, T . C , COPELAND, L . E . , and MANN, H . M . , "Capillary Continuity or Discontinuity in Cement Pastes." Journal, Research and Development Laboratories, Portland Cement Association, No. 2, 1:38-48, May 1959.

This is a study of the capillary structure of cement paste in terms of data on permeability to water. Some practical consequences of capil lary continuity or lack of i t are discussed.

A335. POWERS, T . C , COPELAND, L . E . , HAYES, J. C . , and MANN, H . M . , "Permeability of Portland Cement Paste." Journal, American Concrete Institute, No. 3, 26:285-298, November 1954.

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Apparatus and methods fo r measuring the permeability of portland cement pastes are described. Test results are given showing the effects of curing, cement content, cement composition, and cement fineness. Also, data on some rocks are compared with data on hardened pastes.

E336. REILLY, R. J . , "The Effect of Moisture Content and Distribution on the Durabil i ty of Concretes Containing Various Coarse Aggregates." M . S. Thesis, University of Maryland, 1962.

Determination of freeze-thaw durability and absorption of hardened concrete specimens were made. In addition the following properties were determined f r o m unconfined aggregates in an attempt to discover something about the basic void properties: (a) absorption; (b) specific gravity; (c) rate of absorption; (d) specific gravity distribution; and (e) moisture retention at a constant relative humidity. The moisture content of the aggregate particles in the concrete is a most important factor affecting the durabili ty. The deterioration of aggregates is most l ikely caused by a combination of total porosity, pore size, pore shape, and continuity.

A337. RICHARDS, L . A . , "Capillary Conduction of Liquids Through Porous Mediums." Physics No. 5, 1:318-333, 1931.

The flow of liquids in unsaturated porous mediums follows the ordinary laws of hydrodynamics, the motion being produced by gravity and the pressure gradient force acting in the l iquid. By making use of D'Arcy 's law, that f low is proportional to the forces producing flow, the equation Kv' <J) + V k • v0+gdk/dz= -PgAaift/at may be derived f o r the capillary conduction of liquids in porous medium. Data are presented and application of the equation is made for the capillary conduction of water through soil and clay but the mathematical formulations may be used for other liquids and mediums.

A338. RUETTGERS, A . , VIDAL, E. N . , and WING, S. P . , "An Investigation of the Permeability of Mass Concrete with Particular Reference to Boulder Dam." Journal, American Concrete Institute, 31:382-416, March-Apr i l 1935.

This paper consists of four parts; f i r s t , a br ief description of the laboratory experimental apparatus and technique; second, the test results; th i rd , some practical applications of the data; and fourth, an appendix containing a theoretical discussion of the factors controlling the f low of water through concrete and the resultant corrosion.

B339. SCHULZE, W . , and ALTNER, W . , "The Significance of Saturation Degree fo r Estimating the Frost Resistance of Concrete." International Symposium on Durabili ty of Concrete, Final Report, Prague, 93-108, 1962.

The authors review the concept of "saturation degree" and indicate how i t may be measured in concrete. The freezing process is then examined aloc^ with the possible variables. Among these are cement content, w/c rat io, u l t ra- f ine grain size, and a r t i f i c i a l a i r pores. I t is concluded that degree of saturation can be of value only when a l l other conditions are very carefully controlled. The requirements fo r f ro s t resistant concrete are given as: lowest w/c ratio and lowest cement factor, controlled air pore volume, aggregates graded to give minimum density.

B340. SWEET, HAROLD S., "Research on Concrete Durability as Affected by Coarse Aggregate." ASTM, Proc . , 48:988-1016, 1948.

A pr imary object of this investigation was the determination of methods by which aggregates giving good f ie ld performance could be differentiated

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f r o m those with unsatisfactory f ie ld performance in concrete pavements. I t is concluded, on the basis of the comparison of f i e ld performance, aggregate characteristics, and resistance of laboratory concrete to freezing and thawing, that freezing-and-thawing tests on concrete beams containing the aggregate can be used to differentiate materials with good f ie ld performance f r o m those with poor performance. The other aggregate properties which were investigated showed no consistent relationship with f i e ld performance with the exception of the factor of pore volume and size; the volume of voids smaller i n diameter than 0.005 mm, expressed as a rat io to the volume of solids, was less than 0.06 fo r the aggregates with good f ie ld performance and greater than 0.10 for the aggregates with bad service records.

A341. TERZAGHI, K . , "Stress Conditions fo r the Failure of Saturated Concrete and Rock." ASTM, P r o c , 45:777-792, 1945.

The mechanisms are investigated fo r : (a) fa i lure of concrete and rock with empty voids; (b) effect of a confining pressure on the strength of specimens with empty voids; (c) effect of a confining pressure exerted by a liquid which permeates the voids of the specimens; and (d) effect of a confining pressure on the strength of a specimen in which the voids are f i l l ed with a liquid under pressure less than the confining pressure.

D342. TROXELL, G. E . , and DAVIS, H . E . , "Composition and Properties of Concrete." McGraw-Hil l , 434 pp., 1956.

A detailed discussion of most of the important aspects of concrete technology is presented and documented with numerous l i terature references. Aggregates are treated in a chapter and then in the context of other d is cussions. Permeability and durability are covered and closely associated in another chapter. Factors affecting permeability are outlined in chart f o r m . The essential variables in freeze-thaw testing are discussed and limitations are noted fo r any accelerated method. The effect of specimen size is given some emphasis. Volume change f r o m a l l causes is given good coverage.

B343. TYLER, I . L . , and ERLIN, B . , "A Proposed Simple Test Method fo r Determining the Permeability of Concrete." Journal of the Research and Development Laboratories, Portland Cement Association, No. 3, 3:2-7, September 1961.

A method f o r measuring the permeability of concrete to water under pressure is proposed. Other methods for measuring the permeability are slow, since they require the measuring of the rate of water flow under the pressure through the concrete after steady rates of flow have been attained. With the thought of providing a more rapid method of test for permeability, a somewhat different approach to the problem is offered using the ordinary 6- by 12-in. concrete specimen normally made f o r compressive strength tests. The method depends on measurement of the rate at which water under pressure is forced into the concrete cylinder and the total amount of water that can be forced i n . I t is not offered as a f u l l y developed test method but rather to interest others in its possibilities.

C344. VERBECK, G . , "Pore Structure." Significance of Tests and Properties of Concrete and Concrete Aggregates, ASTM, Special Publication, No. 169, 136-142, 1956.

Concrete may be visualized as consisting of a heterogeneous mixture of components, each component having its own characteristic pores. In terms of the other pores in the concrete, the a i r voids, normally the coarsest of a l l , may constitute f r o m less than 1 to more than 10% of the

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total volume of the concrete. Approximately 75% of the concrete is aggregate, frequently heterogeneous, with an internal pore volume varying f r o m almost 0 to 20%, the pores ranging f r o m relatively fine to coarse. The cement paste component usually contains both extremely fine gel pores and the coarser but submicroscoplc capillary pores. The gel pores constitute about 20 to 30% of the paste volume, the capillary pore volume varying f r o m 0 to perhaps 40% in well-cured pastes of the normal range of water-cement ra t io . For cement pastes not completely hydrated, the gel pore volume would be less and the capillary pore volume greater than the amounts indicated.

A345. V E R B E L S K n , G. P . , "Structure and Water Permeability of Concrete." Trudy Soveshchaniya po Tekhnol Betonov Akad. Nauk. Armyan . , S. S. R. , 251-68, 1953. (Pub. 1956)

A newly perfected and satisfactory method fo r permeability testing of concrete by the use of a vacuum technique is described. Repeated vibration increases the H2O impermeability of concrete. At the same time, the mechanical s t re i^ th of such concrete increases. Addition of sulfi te-alco-hol slops increases the self-packing of concretes. This addition is of exceptional importance in the case of dry-keeping concrete.

A346. V A I L , P . G . , "Use of Pressure Type A i r Entrainment Indicator f o r Aggregate Moisture Tests." Journal, American Concrete Institute, 46:221-222, November 1949.

Describes a method fo r f i e ld determination of f ree moisture in aggregate using a pressure type a i r entrainment indicator.

C347. WASHBURN, E . W . , "Porosity: I . Purpose of the Investigation. I I . Porosity and the Mechanism of Absorption." Journal of the American Ceramic Society, 4:916-922, 1921.

Outlines the purpose of the investigation to be reported in later art icles. Discusses the different pertinent factors affected with the porosity.

C348. WASHBURN, E . W . , and BUNTING, E . N . , "Porosity: VL Determination of Porosity by the Method of Gas Expansion." Journal of the American Ceramic Society, 5:112-129, 1922.

Presents the theory of determining the porosity by means of gas expansion and describes the necessary apparatus. Also, describes anew porosimeter.

C349. WASHBURN, E . W . , and BUNTING, E . N . , "Porosity: V . Recommended Procedures for Determining Porosity by Methods of Absorption." Journal of the American Ceramic Society, 5:48-56, 1922.

A detailed procedure is given fo r using vaseline as the absorption liquid and also a new pycnometer method is described.

C350. WASHBURN, E . W . , and BUNTING, E . N . , "Porosity: VE. The Determination of the Porosity of Highly V i t r i f i e d Bodies." Journal of the American Ceramic Society, 5:527-537, 1922.

Describes the McLeod-Gauge type porosimeter and an apparatus f o r measuring the porosity of f u l l size br icks . Also, points out that the simpliest and most accurate porosity determinations were made using the new apparatus described in "Porosity: V L , " Section 68.

A351. WASHBURN, E. W . , and BUNTING, E. N . , "Porosity: IV. The Use of Petroleum Products as Absorption Liquids ." Journal of the American Ceramic Society, 4:983-989, 1921.

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Discusses the use of paraffine or vaseline as absorption liquids with bodies containing large pores.

C352. WASHBURN, E . W . , and FOOTITT, F. F . , "Porosity: HI . Water as an Absorption L i q u i d . " Journal of the American Ceramic Society, 4:961-982, 1921.

Reviews the work of previous invest^ators. Discusses the different absorption methods, the effect of absorbed gases upon dry weights of test pieces, saturation by boiling at atmospheric pressure, method of cooling the test piece, the saturation procedure, and the necessity of a soaking period.

A353. WILEY, G . , and COULSON, D. C. , " A Simple Test fo r Water Permeability of Concrete." Journal, American Concrete Institute, 34:76-4, September-October 1937.

A cheap and simple apparatus fo r determining the permeability of concrete is described. Increasing the fineness of cement is to decrease the permeability of concrete and this effect is amplified under dry curing conditions. At ordinary water-cement ratios dry-cured concrete is two to three times as permeable as moist-cured concrete.

B354. WITHEY, M . O. , "Permeability and Absorption of Concrete." Report on Significance of Tests of Concrete and Concrete ^grega tes , ASTM, Second Edition, 79-83, 1943.

Describes and discusses absorption tests and permeability tests of concrete.

A355. ZAGAR, L . , "Determination of Pore Size Distribution in Refactory Mater ia l s . " Archiv f i i r das Eisenhiittenwesen (Henry Brutcher Translation No. 3924, Altadena, Cal i f . ) No. 9, 26:561-562, 1955.

A pore-size distribution procedure is described which is based on the consideration that when pores of different sizes are f i l l ed with water, a i r pressures of corresponding different magnitudes are required to drive the water out of the pores.

PHYSIO-CHEMICAL PROPERTIES STUDIES

A401. ALEXANDER, K . M . , "Strength of the Cement-Aggregate Bond." Journal, American Concrete Institute, No. 5, 56:377-390, November 1959.

Determinations were made of Portland cement-aggregate bond strengths and Portland cement paste strength. Cement-^gregate bond s t re i^ th decreases with increasing water-cement ra t io and alkali content, and increases with increas i i^ age. A l l cement-aggregate bond strengths observed were considerably lower than the strength of the adjacent Portland cement.

A402. BONNELL, D . G . R . , and HARPER, F . C . , "The Thermal Expansion of Concrete ." Journal, Institution of C i v i l Engineers, London, No. 4, 33:320-330, February 1950.

Measurements of the coefficient of thermal expansion of different aggregates, and of concretes prepared f r o m them with different cements, have been made over the temperature range 32 F to 104 F. Siliceous materials have the h^hest coefficients of expansion. The magnitude of the coefficient of expansion of concrete depends largely on the aggregate used. The coefficient of thermal expansion of neat hydrated cement is higher than that of any aggregate measured in the tests. Saturation of the aggregates has a lowering effect on the coefficient of expansion.

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A403. CALLAN, E. J . , "Thermal Expansion of Aggregates and Concrete Durabi l i ty . " Journal, American Concrete Listitute, 48:485-504, February 1952.

Differences in durability of concretes containing aggregates f r o m the same source and s imi lar concretes containing different fine and coarse aggregates are explained part ial ly by differences in thermal expansion of the coarse aggregate and the mortar . Concretes were tested in accelerated freezing and thawing, yielding durability factors, DFE, for each combination. The DFE's were statistically analyzed with the difference between the thermal coefficients of coarse aggregates and mortars , A C , and coarse aggregate absorption, A, as variables. For 78 concrete combinations a relation DFE = 109.65-8. 76 A C -15. 22A was developed with a correlation coefficient of 0. 719, which is highly significant. Thus, the durability of these concretes was reduced when the differential expansion of mortar and coarse aggregate increased. The methods developed for determining coefficients of thermal expansion of coarse aggregate and mortar are described.

C404. CARLSON, R . W . , "Remarks on Durabili ty of Concrete." Journal, American Concrete Institute, 35:359-364, A p r i l 1939.

The author makes a conservative statement of factors affecting the durabi l i ty of concrete: the fatigue action of volume chaises produced by changes in temperature and moisture; the freezing of water in the pores of concrete; the phenomenon of bleeding; the nature of the constituents of concrete and their interrelation.

C405. CORTON, H. T . , and PARK, F . R . , "Frac ture ." International Science and Technology, No. 15, 24-36, March 1963.

The general topic of fracture of materials is treated in some detail and wel l i l lustrated. The causes of fracture; stress concentrations and plastic deformations, crack propagation and velocity, effects of environments, and available theories fo r interpretations of these phenomena are among the items covered. Some information in this art icle applies directly to concrete but the major effor t is directed at presenting a unified fracture theory.

B406. DAVES, R. E . , "A Summary of Investigations of Volume Changes in Cements, Mortars and Concretes Produced by Causes Other Than Stress." ASTM, Proc. , Part I , 30:668-685, 1930.

This summary has been prepared with a view of bringing tc^ether the results of what are considered to be some of the more important investigations having to do with volume changes produced by causes other than stress. F i r s t , changes due to variations in temperature are summarized. Second, volume changes as affected by moisture conditions are reviewed. And th i rd , a bibliography is given.

A407. DAWLEY, E . R . , "Volume Changes of an Early-Strength Concrete." ASTM, Proc. , Part H, 32:642-658, 1932.

This investigation consisted of a study of the chaises in length accompanying changes in the temperature and moisture content of concrete specimens of various mixes and consistencies when made with ordinary portland cement and when made with a certain early-strength portland cement. The compressive strengths, the coefficients of thermal expansion, the coefficients of moisture expansion and the absorption were determined fo r the various kinds of concrete studied.

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A408. DAWLEY, E. R . , "Alternate Heating and Cooling of M o r t a r . " Journal, American Concrete Institute, No. 5, 32:609-620, May-June 1936.

Presents results of tests in which mortar specimens were subjected to alternate heating and cooling while submerged in water. The temperature range was f r o m 70 F to 166 F. The general results were: the compressive strength of the specimens was reduced, they permanently increased in length and in weight.

D409. DORSEY, N . E . , "Properties of Ordinary Water-Substance." National Bureau of Standards, New York, Reinhold, 1940.

Information is given regarding the properties of pure, ordinary water i n a l l its phases—water vapor, water, and the several ices—and regarding the phenomena and data pertaining to its synthesis and dissociation and to its transition f r o m phase to phase. Tables of properties are included.

A410. DOUGILL, J. W . , "The Effects of Thermal Incompatibility and Shrinkage on the Strength of Concrete." Magazine of Concrete Research, No. 39, 13:119-126, November 1961.

The effect of shrinkage of the mortar on the strength of a concrete specimen is demonstrated by means of a lattice analogy fo r concrete at high temperatures. The r i ch mix concrete and that containing an aggregate having a high coefficient of thermal expansion w i l l experience the greatest reduction in s t re i^ th . This approach can be used to study the effects of incompatibility on the strength of concrete at low temperatures or in any circumstance where internal stresses are set up by shrinkage, or expansion, of the cement paste with respect to the aggregate.

A411. FARRAN, J . , "Bondings Between Cement and Aggregate and Their Behavior in Fros t . " R I L E M B u U . 40, 23-27, 1958.

The bond between cement and aggregate is established by surface roughness of the aggregate and by epitaxic adhesion. The resistance of the bond to destruction by f ros t action is dependent p r imar i ly on the latter bonding mechanism. The mechanism of epitaxic adhesion varies greatly with aggregate and cement type, being s t r o i ^ for calcite and cements that deposit gelatinous coatings f r o m which f ine crystall ization subsequently occurs, and weak f o r quartz and cements depositing automorphous crystals upon contact with aggregate. Conclusions are supported by experimental data.

A412. FOX, R. G . , and DOLCH, W. L . , " A Techmque f o r the Determination of a Thermal Characteristic of Stone." HRB Proc. , 30:180-186, 1950.

A method has been developed for the direct determination of the thermal dlffusivi ty of rocks. The change in thermal dif fusivi ty of rocks with moisture content is very large—on the order of 20 to 80 percent fo r less than 5 percent saturation of the voids. Values of thermal di f fus ivi ty are given for two aggregates with good f ie ld performance and fo r two wit i i poor f i e ld performance when used in concrete pavements.

A413. GRIFFITH, J. H . , "Thermal Expansion of Typical American Rocks." Iowa Engineering Experiment Station, Bu l l . 128, October 1936.

The paper gives the results of an investigation to determine the coefficients of thermal expansion of approximately one hundred representative American rocks of varying chemical constitutions and diversif ied geographical locations. The expansions appear to be dependent upon the amounts of f ree s i l ica i n the rocks. The rocks having a maximum of f ree s i l ica expand the most and those with a maximum of combined s i l ica expand the least.

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A414. HANSEN, W. C. , "Influence of Sands, Cements, and Manupulation Upon the Resistance of Concrete to Freezing and Thawing." Journal, American Concrete Institute, No. 2, 39:105-123, November 1942.

Cements and sands affect freeze-thaw durability only to the degree by which they affect water/cement rat io. Excessive working of a slab surface, likewise, w i l l not effect F - T durability except fo r the affect on water/cement rat io of the top layer. Author found absorption of concrete related to F - T durabili ty.

A415. HATT, U . K . , "The Effect of Moisture on Concrete." Transactions, American Society of C i v i l Engineers, 89:270-315, 1926.

The pr imary purpose of this investigation was to measure the maximum warping and surface deformations produced in a concrete road slab as a result of a non-uniform distribution of moisture. Some of the conclusions of this investigation were: (a) Saturated concrete w i l l have 80 to 85% the s t re i^ th of dry concrete; (b) The thermal coefficient of expansion of concrete varies with the temperature; (c) Concrete expands when immersed in water and contracts on drying; and (d) Concrete road slabs warp upward at the corners and at the edges when the surface becomes dry, and also when the bottom absorbs moisture f r o m the sub-grade.

A416. HAVENS, J . H . , "Thermal Analysis of the Freeze-Thaw Mechanisms in Concrete." Ei^ineering Experiment Station Bu l l . 59, University of Kentucky, March 1961.

Time-temperature records were made f r o m cyclic freezing and thawing of several concrete specimens. Dense coarse aggregate, h^h ly absorptive coarse aggregate, a i r entraining, and non-air entraining were used to make the specimens. The time-temperature records in the cases where sufficient moisture was present in the specimens, showed freezing-point depressions which were manifestations of pressure. A description of the equipment and instrumentation used in the study is given.

A417. HELMUTH, R. A . , "Dimensional Chaises of Hardened Portland-Cement Pastes Caused by Temperature Changes." HRB Proc. , 40:315-336, 1961.

A theoretical basis fo r expecting the moisture distribution in water-soaked hardened portland-cement pastes to change with temperature is presented. The theory predicts shrinkage after warming and swelling after cooling. A method fo r measuring length changes of paste specimens during and after temperature changes is described. The results of dimensional change measurements are consistent with the theory presented as are also the weight chaises of specimens saturated with water at 25C and OC. The i n i t i a l dilations produced by freezing water-soaked pastes, l i ke wise, show the effect of moisture distribution changes.

A418. HIGGINSON, E . C . , and KRETSINGER, D . G . , "Prediction of Concrete Durabi l i ty f r o m Thermal Tests of Aggregate." ASTM, Proc . , 53:991-1001, 1953.

Data are presented on the effect of freezing-and-thawing, w e t t i i ^ and drying, and other simulated weathering tests on various concretes containing either natural aggregate or aggregate composed of individual rocks and minerals. The effect of thermal coefficient and diffusivi ty of these aggregates on the deterioration occurring d u r i i ^ these tests is discussed, but no correlation is found between the test results and the thermal properties of the materials. Evidence is presented showing that the expansion occurring in saturated concrete during the measurement of coefficient of expansion can be correlated with freezii^-and-thawing test results, thus providing a quick method of predicting durability of concretes.

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A419. HOCKMAN, A . , and KESSLER, D. W . , "Thermal and Moisture Expansion Studies of Some Domestic Granites." Journal of Research, National Bureau of Standards, 44:395-410, A p r i l 1950.

As a part of a study of the physical properties of building stone, thermal expansion determinations were made on 48 samples of domestic granites by the different ia l interferometer method (with an interferograph recording attachment) over the temperature range -20 to +60 C. Thermal coefficients computed between -20 and +60 C ranged f r o m 4. 8 to 8.3 x 10~" per deg C with an average of 6.2 x 10"' per deg C. Coefficients obtained on cooling (60 to 0 C) averaged 6. 7 x 10"' per deg C. Expansion curves drawn f o r a l l samples indicate slight i r regular i t ies i n the 0 to 20 degree range in the heating curves of at least 65% of the samples. These i r r e g ulari t ies are probably caused by moisture changes in the sample during the test. Moisture expansion determinations were made on the 48 samples by means of the Tuckerman optical s train gage over a 24-hour period at constant temperature. The expansions obtained ranged f r o m 0.0004 to 0.009% and averaged 0.0039%. Details of the apparatus used are given.

A420. HSU, T. T , C . , "Mathematical Analysis of Shrinkage Stresses in a Model of Hardened Concrete." Journal, American Concrete Institute, No. 3, 60:371-388, March 1963.

Jn an investigation i t was found that microcracks exist at the interface between coarse aggregate and mortar in concrete before loading. To explain this fact, a model of hardened concrete was constructed consisting of r i g i d c i rcular discs of aggregate, arranged in a square array and surrounded by mortar subjected to volume changes; these might be due to hydration, wetting, and drying, or temperature change, etc. A numerical elastic stress analysis of this model by a point matching method showed that large tensile stresses exist at the interface between aggregate and mortar , when the clear distance between aggregate is smal l . It is believed that these tensile stresses cause the microcracks to appear.

A421. HSU, T . T . C . , SLATE, F . O . , STURMAN, G . M . , and WINTER, G . , " M i c r o -cracking of Plain Concrete and the Shape of the Stress-Strain Curve ." Journal, American Concrete Institute, No. 2, 60:209-223, 1963.

Cylinders were axially loaded in compression to various strains f r o m 0 to 0.0030 inches and internal cracks were examined by means of thin slices. Cracks at the interface between coarse aggregate and mortar are widespread even in nonloaded concrete. These "bond" cracks are preponderate at a l l stages of straining, while mortar cracks begin to increase noticeably, and bridge between bond cracks to f o r m continuous crack patterns at loads of about 70 to 90 percent of ultimate. This condition leads to a descending stress-strain curve and eventual disruptive fa i lure .

A422. JOHNSON, W. H . , and PARSONS, W. H . , "Thermal Expansion of Concrete Aggregate Mater ia l s . " Journal of Research, National Bureau of Standards, 32:101-126, March 1944.

As a part of a study of the properties of concrete aggregate, thermal-expansion determinations were made on 123 specimens of aggregate mater ia ls by the optical interferometer method over the temperature range -20 to +60 C. Crystal orientation, rock texture, and composition are d is cussed with regard to their effects on the relation of the thermal expansion j of aggregates to the durability of concrete.

A423. KOENITZER, L . H . , "Elastic and Thermal Expansion Properties of Concrete as Affected by Similar Properties of the Aggregate." ASTM, Proc . , Part H, I 36:407-410, 1936.

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An apparatus to manually measure length changes in concrete specimens and stone cores is described. The elastic properties and thermal coefficient of expansion were determined on specimens cut f r o m the samples of stone and on concrete specimens containing the crushed stone as coarse aggregate. Tests were made on the stone and concrete specimens in a dry condition, frozen in a dry condition, heated to 190 F, in a moist condition, and frozen in a moist condition. The data presented indicate that engineers should not draw conclusions f r o m the results secured upon individual materials that enter into concrete mixtures since a combination of these materials may give an entirely different set of results i n the concrete, depending upon the condition of the specimens at the time of testing.

A424. LANG, F . C . , "Temperature and Moisture Variations i n Concrete Pavements." HRB Proc . , 21:261-271, 1941.

Presents data obtained f r o m 6 thermocouples placed at various depths in a 7-in. concrete slab, 5 elevations in subgrade and one in a i r fo r one year. Also presents moisture data by means of Bouyoucos moisture blocks in center of slab and three places in subgrade.

C425. LANG, F . C , "Deleterious Substances." Report on Significance of Tests of Concrete and Concrete Aggregates, ASTM, Second Edition, 138-144, 1943.

This paper presents a discussion of: (a) substances having volume change, (b) structurally weak substances, (c) aggregates having surface coatings, (d) particles that are excessively f l a t or elongated, and (e) substances affecting chemical activity.

A426. LA RUE, H. A . , "Modulus of Elasticity of Aggregates and Its Effect on Concrete." ASTM, P r o c , 46:1298-1309, 1946.

This paper gives a report of some studies made on the properties of Missouri aggregates and their effects on the concretes in which these aggregates were incorporated. Aggregates produce a decided effect on the elastic properties of concrete, stone having a high modulus of elasticity developing correspondii^ly higher moduli in the concretes than stone h a v i i ^ low moduli. The relation of the modulus of elasticity of aggregates to that of the concrete is not a linear function but may be expressed by an equation of exponential type. No correlation between the compressive strength of concrete and the modulus of elasticity is evident f r o m a study of the data.

A427. L 'HERMITE, R . C . , "Volume Changes of Concrete." Chemistry of Cement, Vol . n . National Bureau of Standards, Washington, D. C . , 1962.

An up-to-date account is given of volume change in concrete resulting f r o m hygrometric, thermal, chemical and dynamic phenomena. A mathematical treatment of the drying process of concrete is presented. T ime-volume change curves are given to i l lustrate different conditions and d i f ferent types of materials.

A428. MC M I L L A N , F. R. , and WARD, G. W . , "Influence of Coarse Aggregate on the Durability of Concrete." ASTM, P r o c , Part I I , 29:816-823, 1929.

A br ief review is presented of the l i terature bea r i i ^ on fai lure of aggregate of various types. In this review an e f for t has been made to present in compact f o r m the essential characteristics of the rock groups which are l ikely to be encountered in aggregate materials, and to point out to which of these characteristics fai lure can be attributed. Consideration is given to texture, structure and those impurities that may cause rock

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failure. Points to be guarded against in selection of aggregates are pointed out.

A429. MEYERS, S. L . , "Thermal Expansion Characteristics of Hardened Cement Paste and of Concrete." HRB Proc., 30:193-203, 1950.

The apparent thermal coefficient of expansion of hardened, neat Portland cement varies with its relative humidity, or state of moisture. With young pastes the apparent thermal coefficient reaches a maximum at a relative humidity of about 70 percent. Older pastes show the same thermal characteristics as young pastes, but to a lesser degree. The apparent thermal expansion of concrete also varies with its state of relative humidity. The range between maximum and minimum coefficients is smaller than with hardened, neat paste because of the restraining action of the aggregates, fii general there is a relation between the magnitude of the moisture volume changes of a paste and the magnitude of change, or range, of the apparent thermal coefficient.

A430. MITCHELL, L . J . , "Thermal Expansion Tests on Aggregates, Neat Cements, and Concretes." ASTM, Proc , 53:963-977, 1953.

The thermal coefficient of expansion of various aggregates, neat cements, and concretes were measured. An analysis of the collected data produced the following conclusions: 1. Similar rocks from different sources may have totally dissimilar

coefficients of expansion. 2. Anisotropy is likely to exist in rocks having crystalline structure. 3. The principal factor contributing to the thermal coefficient of neat

cement is moisture content. 4. The thermal coefficient of neat cement is minimum for a saturated

condition, slightly higher when oven dried, maximum at some intermediate moisture content.

5. A specimen above a criticaldegree of saturation wi l l expand excessively upon a single freezing and break apart in a very few cycles.

6. Durability and thermal coefficient of expansion are both affected by the ease with which concrete becomes saturated and the degree of actual saturation.

A431. MONFORE, G.E., and LENTZ, A . E . , "Physical Properties of Concrete at Very Low Temperatures." Journal of the Portland Cement Association Research and Development Laboratories, No. 2, 4:33-39, May 1962.

Results of an investigation of compressive strengths, splitting strengths. Young's moduli of elasticity, and thermal contractions of three sand and gravel concretes and one light-weight aggregate concrete at various temperatures from 75 to -250 F are reported in the present paper. Young's modulus of elasticity of a particular moist concrete increased from 5. 5 X 10' psi at 75 F to 8. 5 X 10* psi at -250 F, The compressive strength of this concrete increased from about 5,000 psi at 75 F to over 17,000 psi at -150 F. In the range from 0 to -75 F, the lightweight aggregate concrete exhibited an expansion. The other moist concretes tested, although not expanding did exhibit less contraction within this range than either above or below it .

A432. PARSON, W.H. , and JOHNSON, W. H . , "Factors Affecting the Thermal Expansion of Concrete Aggregate Materials." Journal, American Concrete fiisUtute, No. 5, 40:457-460, Apri l 1944.

Thermal expansion determinations were made on 137 specimens of aggregate

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materials and single crystals by the optical interferometer method over the temperature range -4 to + 140 F. The thermal expansivities of most aggregate materials are close to or within the range of expansivities of hardened portland cements. Crystal orientation, rock texture, and composition are discussed with regard to their effect on the thermal expansion of aggregate materials and their relation to the durability of concrete.

A433. PEARSON, J. C., "A Concrete Failure Attributed to Aggregate of Low Thermal Expansion," Journal, American Concrete Institute, No. 1, 38:29-34, September 1941.

This paper describes a failure of "cast stone" steps containing dolomitic limestone of low thermal coefficient. Laboratory tests pointed to low thermal coefficient as being the cause of the trouble.

A434. PEARSON, J. C., "Supplementary Data on the Effect of Concrete Aggregate Having Low Thermal Coefficient of Expansion." Journal, American Concrete Institute, No. 1, 40:33-37, September 1943,

A limited number of tests were made on 2 x 2 x 10-in, bars contalnli^ two types of low coefficient aggregates and one type of silica pebbles, which were submitted to cycles of temperature changes from -20 F to room temperature. After 100 cycles of temperature changes, the bars were soaked in water and submitted to freezing-and-thawing cycles of the same temperature range as before. The bars containing the low coefficient aggregates succumbed very rapidly to the frost action while the silica bars were only moderately affected by the same treatment. The results lend further support to the conclusion of the earlier paperby the author, namely, that low thermal coefficient aggregates can be a source of danger in concrete exposed in cold climates.

A435. PICKETT, G., "The Effect of Biot's Modulus on Transient Thermal Stresses in Concrete Cylinders." ASTM, Proc., 39:913-918, 1939.

This paper deals with thermal stresses due to temperature differences throughout the concrete. The magnitude of maximum stress during a cycle of temperature change depends on shape of the body, elastic constant^, and Blot's modulus. Biot's modulus is defined by the equation: B = o/kb' where k' = conductivity and b' = thickness of the insulating layer (air, water, membrane, covering, etc.) and k = conductivity (thermal) of concrete and b = radius of the concrete cylinder. Author proceeds to derive mathematical stress relations for any point in a concrete cylinder subjected to a sudden change in temperature.

A436. PICKETT, G., "Effect of Aggregate on Shrinkage of Concrete and a Hypothesis Concerning Shrinkage." Journal, American Concrete Institute, No. 5, 52:581-590, January 1956,

A theoretical formula is derived for effect of aggregate on shrinkage of concrete during drying. Experiments designed to test the validity of the formula are reported. In addition to indicating the validity of the formula the data give the following indications: (a) f i r s t shrinkage is greater than any subsequent expansion or shrinkage resulting from moisture change, (b) at a given aggregate content the shrinkage is approximately proportional to water-cement ratio, (c) after f i rs t shrinkage, subsequent volume changes are approximately independent of water-cement ratio, (d) when shrinkages of specimens of the higher water-cement ratio are plotted against the square root of period of drying, the shapes of the curves for second shrinkage are appreciably different from those for the f i rs t shrinkage in that they have considerable curvature near the origin. An explanation of these effects is given.

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A437. ROPER, H . , "Volume Changes of Concrete Affected by Aggregate Type." Journal of the Research and Development Laboratories, Portland Cement Assoc., Vol. 2, No. 3, September 1960.

Excessive dimensional chaise phenomena associated with the use of certain aggregates has led to rapid deterioration of concretes in Southern Africa, and this paper presents briefly some observations on the effects and probable causes of the distress. Some aggregates found in the U. S. have dimensional changes greater than 0.15 percent when dried and subsequently placed in water. The PCA is proceeding with an investigation of the compressibility and the internal structure of these aggregates. The National Buildii^ Research Institute of South Africa is conducting surface area studies of the aggregates found in their area.

A438. SCHOLER, C.H. , "Studying the Durability of Concrete." Journal, American Concrete Institute, 32:593-607, 1936.

A discussion of the factors affecting the durability of concrete is presented. These factors include cement, aggregate, time, temperature, water, and placing methods.

A439. SCHOLER, C.H. , "Durability of Concrete." Report on Significance of Tests of Concrete and Concrete Aggregates." ASTM, Second Edition, 29-37, 1943.

This paper discusses the major disintegrating forces of natural weathering action on concrete. They are: (a) freezing and thawir^, (b) temperature changes, (c) changes in moisture content, and (d) adverse chemical action of aggressive solutions or chemical instability of the paste or aggregate.

A440. SMITH, G. M . , "Physical Incompatibility of Matrix and Aggregates in Concrete.' Journal, American Concrete Institute, 52:791-798, March 1956.

A theoretical analysis is made of the stresses that might result in a matrix surroundii^ a spherical body due to the thermal incompatibility of the matrix and the spherical body. The analysis indicates that the magnitude of the stresses depends upon the thermal expansion, Poisson's ratio, modulus of elasticity, and size of the inclusion.

A441. SNOWDON, L. C., and EDWARDS, A. G., "The Moisture Movement of Natural Aggregate and Its Effect on Concrete." Magazine of Concrete Research, No. 41, 14:109-116, July 1962.

This paper summarizes the background and development of the work carried out at the Scottish Laboratory of the Building Research Station on the quality of concrete prepared from various aggregates. It established that many natural crushed rock and gravel aggregates undergo changes of volume, to a greater or lesser extent, as they take up or lose water, and shows how this characteristic influences the shrinkage and durability of concrete in which they are incorporated.

A442. THOMSON, U. T. , "Measuring Changes in Physical Properties of Concrete by the Dynamic Method." ASTM, Proc., 40:1113-1129, 1940.

The properties of the material most readily affected by deterioration are the modulus of elasticity and the decrement of vibration, both of which can be measured by the dynamic method. This paper presents tests performed on concrete composed of various aggregates with different water-cement ratios. It was concluded that: (a) The largest change in the modulusj of elasticity and the decrement of vibration takes place during the f i r s t few cycles of freezing and thawii^. (b) Between good and poor specimensl

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there is no apparent difference in the modulus of elasticity or the decrement of vibration at zero cycles of freezing and thawing, (c) Poor specimens can generally be detected within 20 cycles of freezing-and-thawing. (d) The decrement measurements obtained from the resonance curve are subject to a certain amount of variation.

A443. VERBECK, G.J., and HASS, U.E. , "DiMometer Method for Determination of Thermal Coefficient of Expansion of Fine and Coarse Aggregates." HRB Proc , 30:187-193, 1950.

The described dilatometer method is suitable for the determination of the thermal coefficient of expansion of sands and coarse aggregates and should be of value in conjunction with the study of the effect of this factor on the degree of physical compatibility of the various components within concrete when subjected to temperature chaises.

A444. WALKER, S., BLOEM, D. , and MULLEN, W.G., "Effects of Temperature Changes on Concrete as Influenced by Aggregates." Journal, American Concrete Institute, No. 8, 48:661-679, Apri l 1952.

This paper describes tests on concrete and mortar exposed to water and air at temperatures ranging from 0 to 140 F. Combinations of quartz sand and gravel, crushed traprock, calcareous sand (crushed), manufactured limestone sand, manufactured granite sand, chert and granite coarse aggregate were studied. The tests revealed: (a) A fast rate of temperature change is more destructive than slow rate; (b) Resistance of concrete to temperature change is more closely related to thermal coefficient of concrete itself than to delta thermal coefficients for ingredients (concretes of high thermal coefficients most susceptible); (c) Rates of temperature change required to produce destruction much greater than found in nature suggesting coefficient of expansion not an important consideration in evaluating field potential; (d) Thermal coefficients of concrete approximately equivalent to weighted coefficients of ingredients; and (e) Thermal coefficients are greatly affected by degree of saturation.

A445. WASHA, G. W., "Volume Changes and Creep." Significance of Tests and Properties of Concrete and Concrete Aggregate, ASTM, Special Publication, No. 169, 115-128, 1956.

An average value of the coefficient of thermal expansion for unrestrained concrete is 5. 5 millionths per degree F though it may vary between 2. 5 8.0 millionths. The coefficient of thermal expansion of neat cement varies between 5.0 and 12. 5 millionths per degree F and increases about 25% as the fineness is increased from 1,200 to 2,700 sq cm per gram. Chert, quartzite, sandstone, and some highly impure limestones have thermal coefficients of expansion between 4. 5 and 6. 5 millionths per degree F, while the coefficient for purer limestones, basalt, granite, and gneiss have values between 1.2 to 4. 5 millionths per degree F. Feldspar has values of 9. 7, 0. 5, and 1.1 millionths per degree F along three different axes.

A446. WEINER, A . , "A Study of the Influence of Thermal Properties on the Durability of Concrete." Journal, American Concrete fiistitute. No. 9, 43:997-1008, May 1947.

An attempt is made to rationalize the effect of air content and type of aggregate on the durability of concrete by a consideration of the thermal properties. The increased durability developed by addition of an air-entraining admixture does not appear to be a result of the sl^ht change in thermal properties accompanying air entrainment. When differences

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in thermal diffusivity exist between mortar and coarse aggregate, rapid freezing and thawing may cause failure by internal expansion. The conclusions set forth in this paper are tentative, subject to verification by further research.

B447. WHITE, A. H . , "The Fundamental Cause of the Disintegration of Concrete." Concrete, No. 5, 26:157-161, May 1925.

Presents a discussion of the factors producing disintegration of concrete. These factors are volume changes due to moisture, temperature, and corrosion of reinforcing steel.

A448. WILLIS, T. F . , and DeREUS, M. E . , "Thermal Volume Change and Elasticity of Aggregates and Their Effect on Concrete. " ASTM, Proc., 39:919-929, 1939.

This paper describes methods and results of tests to determine elastic and thermal properties of Missouri aggregates. Limestones exhibited lowest thermal coefficients and siliceous materials the highest. Thermal coefficients of mortars were almost identical with thermal coefficients of aggregate from which they were made. Modulus of elasticity of mortar found to be dependent on strength of paste and modulus of elasticity of aggregate.

UNCONFINED FREEZING-AND-THAWDSfG TESTS B501. BRINK, R. H . , "Rapid Freezing and Thawing Test for Aggregates." HRB

Bull. 201, 15-23, 1958. This report describes an unconfined freezing and thawing procedure which requires about the same test period as the sulfate soundness test. Sixteen cycles of this method, which involves freezing and thawing the aggregate specimens in a water and alcohol solution, are equal in severity to 5 cycles of the sulfate soundness tests and are much more severe than 50 cycles of freezing-and-thawing in water. Freezing and thawing in the water-alcohol solution, however, resulted in a different order of soundness beii^ indicated for the various materials than when water was used.

B502. GIBSON, W.E. , "Significance of Soundness Tests of Aggregates." HRB Proc., 21:283-287, 1941.

A method of test by freezing and thawing of unconfined aggregate and evaluation of results is proposed which differs from that of the American Society for Testing Materials principally in that the result is based upon cumulative percentages retained on a series of sieves instead of upon separation into a number of sizes by the passed and retained system. The result of the test is expressed as the ratio of the sum of the cumulative percentages retained on each of the sieves after freezing-and-thawing to the sum of the cumulative percentages before the test.

B503. LANG, F. C , and HUGHES, C.A., "Accelerated Freezing and Thawing as a Quality Test for Concrete Aggregates." ASTM, Proc , Part I I , 31:435-452.

Several cycles of freezing and thawing are presented. The purpose of this investigation was to develop a definite test for the quality of gravel pebbles for use in exposed concrete. The results of accelerated tests (10 cycles per day) are given for 10, 20, and 30 cycles of freezing-and-thawing on gravel pebbles from eighteen different sources, two sedimentary rocks, and nine deleterious materials.

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B504. SCHOLER, C.H. , and STODDARD, A . E . , "Proposed Method of Testing Concrete and Concrete Aggregates by Freezing and Thawing." ASTM, P roc , Par t i , 32:364-366, 1932.

A method is proposed for freeze-thaw testing of both concrete cylinders and concrete aggregates. The test consisted of saturating the specimens by immersing them in water at 70 F for 24 hours, freezing the specimens in water using a freezer capable of going below 24 F in less than 4 hours, and thawing the specimens in water at between 60 and 100 F. Disintegration of the concrete cylinders was determined visually and that of the aggregate by weighing.

C505. WALKER, S., "Soundness of Aggregates." Report on Significance of Tests of Concrete and Concrete Aggregates, ASTM, Second Edition, 112-122, 1943.

A discussion is presented of the salt tests and freezing-and-thawing tests of unconfined aggregate. These tests detect the unsoundness of some aggregates but not of others. Concludes that the accelerated freezing-and-thawing test of concrete made with the aggregate under examination appears to offer the greatest likelihood of affording a quantitative method for evaluating the quality of aggregate.

FREEZING-AND-THAWING TESTS B601. ACI COMMITTEE 201, "Durability of Concrete in Service, Chapter 1, Freezing-

and-Thawing." Journal, American Concrete lastitute. No. 12, 59:1774-1784, 1962.

Presents a summary of the mechanisms of frost action, considering the cement paste fraction and the aggregate fraction of the concrete. Current ASTM test methods have been criticized: (a) They use initially saturated concrete test specimens where as concrete in the field is normally not saturated at the beginning of the freezing season; (b) The two rapid methods require freezing rates greater than those encountered in the field; and (c) The test methods do not insure that the aggregate particles at the start of the test wi l l be as highly saturated as they might be in field concrete. Also, present laboratory tests, while useful, are unable to measure aggregate durability with the certainty needed.

A602. ARNI, H . F . , FOSTER, B .E . , and CLEVENGER, R.A. , "Automatic Equipment and Comparative Test Results for the Four ASTM Freezing-and-Thawing Methods for Concrete." ASTM, Proc , 56:1229-1256, 1956.

A description of automatic apparatus used to operate simultaneously all four of the ASTM tentative methods of test for resistance of concrete specimens to freezing and thawing is given. Time-temperature curves obtained with thermocouples embedded in specimens illustrate the operation of each of the four methods. Confidence intervals are plotted to show which methods best separate the different concretes as well as how many cycles of test are required to give a reliable separation between these concretes.

A603. BLACKBURN, J .B. , "Freeze and Thaw Durability of Air-Entrained Concrete Using Indiana Aggregates." Reprint No. 49, Engineering Experiment Station, Purdue University, October 1949.

This paper reports a study of the freeze-and-thaw durability of seven Indiana aggregates used in concrete with varying air contents. Results show: (a) Air entrainment increased the durability of the concrete; (b) The percentage strength lost per cycle of freezing and thawing is a fair indicator of pavement performance; (c) The lower the air content the

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higher the flexural strength; and (d) The least durable concrete was made with normal portland cement and saturated aggregates. A method for computing a saturation coefficient is presented.

A604. BLOEM, D. L . , "Factors Affecting the Freezing and Thawing Resistance of Concrete Made With Chert Gravel." HRB Highway Research Record Number 18, 48-60 (1963).

The author investigated aggregate source, particle size, curing and moisture content of concrete, and cement factor of concrete containing chert gravels. The test showed that: (a) Reduction in the size of the chert gravel improved the resistance of concrete to freezing and thawing; (b) Partial drying of the concrete before exposure greatly improved its performance; (c) Once partially dried, the concrete was not easily re-saturated to the point of vulnerability to freezing damage; and (d) Under some combinations of saturation and exposure, increasing cement content reduced the resistance of concrete to freezing-and-thawing.

B605. CANTRILL, C., and CAMPBELL, L . , "Selection of Aggregates for Concrete Pavement Based on Service Records." ASTM, P roc , 34:937-945, 1939.

Comparison of F-T durability and field performance for various concrete aggregate materials in the state of Kentucky led to the conclusion that concrete in which an aggregate is incorporated shall not show a reduction in flexural strength greater than 30% when subjected to 40 cycles of freezing and thawing (frozen in water for 16 hr at -5 to -10 F and thawed in water at 70 F for 8 hr). It was also concluded that aggregate absorptions greater than 3% could not be tolerated.

A606. COMMITTEE ON DURABILITY OF CONCRETE, "Progress Report." HRB Proc., 24:174-202, 1944.

A series of freeze-thaw tests were made by seven independent laboratories using aggregate from three sources and the results were evaluated to determine the effects of various factors on number of F-T cycles to produce 30% loss in dynamic E. Some of the more important observations and conclusions included: (a) An average reduction of 30% in dynamic E corresponds to an average decrease of 45% in modulus of rupture, but only 9% in loss of compressive strength; (b) Too rapid temperature drop in freezi i^ cycles fails to give results that discriminate between known good and poor aggregates; (c) Vacuum-pressure saturation (vacuum 28-in. Hg for 24 hr and water pressure of 125-150 psi for 24 hr) was used to saturate aggregate; (d) Neither absorption nor rate of absorption of concrete appeared to correlate with F-T durability; and (e) Specimens frozen in water were more severely affected in F-T tests than those frozen in air.

C607. COOK, H. K. , "Automatic Equipment for Rapid Freezing and Thawing of Concrete in Water." HRB BuU. 259, 7-27, 1960.

This paper describes the construction and operation of an automatic, twenty-five-specimen capacity, freezing-and-thawing device for the testing of concrete specimens.

C608. CORDON, W. A . , "Automatic Freezing-and-Thawing Equipment for a Small Laboratory." HRB Bull. 259, 1-6, 1960.

This paper discusses the details of construction of automatic freezing-and-thawing equipment and also presents typical test results obtained with the development model of this equipment.

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A609. "Factors Affecting Time-Temperature Relations in Automatic Freezing-and-Thawing Tests of Concrete." Misc. Paper No. 6-178, Waterways Experiment Station, May 1956.

Comparisons of time-temperature data between specimens of different size under the same conditions and between specimens of the same size under different conditions were made. Observed cooling rates were found to range 21 to 240 degrees F per hr between 30 and 15 F. Maximum temperature differences between center and surface ranged from 2 to 32 F.

A610. FLACK, H. L . , "Freezing-and-Thawing Resistance of Concrete as Affected by the Method of Test." ASTM, Proc., 57:1077-1095, 1957.

The data presented in this paper are a compilation of test results of several investigations performed by the Bureau of Reclamation to determine the factors which may influence results of laboratory freezing-and-thawing tests. Several combinations of freezing-and-thawing periods including four tentative ASTM methods were used to test the effect of initial cures, degree of saturation, and specimen size and shape. In addition, the time-temperature relationships were established for different locations in an 18-in. cylindrical specimen to simulate the relative effect on structural concrete for various patterns of freezing-and-thawing.

A611. JACKSON, F .H . , "The Resistance of Concrete to Frost Action." PubUc Roads, No. 2, 13:32-38, Apri l 1932.

Results are given of an investigation for the purpose of determining how the resistance of concrete to frost action is affected by the character of the coarse aggregates used in the mixture. Eighteen different coarse aggregates of widely varying characteristics were treated. It was concluded that within the range in variation of aggregate quality covered by these tests, variations in the quality of mortar caused by changes in the water-cement ratio of the cement paste w i l l have a greater effect upon the resistance of concrete to frost action than wil l variations in the type and character of the coarse aggregate,

C612, JONES, F. E , , and LEA, F. M . , "Methods of Carrying Out Freezing and Thawing Tests on Concrete." The International Sub-Committee on Concrete for Large Dams, Paper presented to Fifth International Congress on Large Dams, Question No. 19, Paper No. 1, R70, 260-280, 1955.

Summary of answers from a questionnaire sent to thirty concrete laboratories in the U. S., Canada, and Europe. The questionnaire asked the laboratories to give their methods of carrying out freezing-and-thawing tests on concrete. A list of the thirty laboratories is given.

A613. KENNEDY, T . B . , and MATHER, K . , "Correlation Between Laboratory Accelerated Freezing and Thawing and Weathering at Treat Island, Maine." Journal, American Concrete Institute, 50:141-172, October 1953.

Six coarse and eight fine aggregates were used in 48 combinations to make concrete specimens, all with the same water-cement ratio, air content, and slump, for comparative testing in accelerated freezing and thawing and exposure to natural weathering at mean-tide elevation at Treat Island, Maine.

Comparison of laboratory field results indicates that each aggregate combination behaves in an individual manner in each exposure, as influenced by differences in materials and exposure. Prediction of behavior in one type of exposure from behavior in another cannot be made unless all the differences between the two can fully be evaluated, which is not yet

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possible. The appendix contains hypotheses to explain the behavior of the fine and coarse aggregates used.

A614. KLIEGER, P., "Effect of Entrained Air on Strength and Durability of Concrete Made With Various Maximum Sizes of Aggregate." HRB Proc , 32:177-201, 1952.

This report includes information on the effect of entrained air on freeze-thaw resistance, strength, resistance to salt scaling, volume change, and absorption of concretes. In all cases, the entrainment of air increased the resistance to freezing and thawing and to surface scaling. Concretes continuously moist cured required more entrained air for adequate resistance to freezing and thawing than concretes whose curing included a period of air-drying. These latter concretes could be provided with adequate resistance to freezing and thawing by providing a constant air content of 9%. The reduction in strength with entrainment of air decreases as the maximum size of aggregate decreases and the cement content decreases. This is due to a reduction in water requirements. There was no s%nifleant effect of air content on volume changes during curing.

A615. KLIEGER, P., "Notes on the Effect of Maximum Size of Aggregates on Tests for Frost Resistance." The International Sub-Committee on Concrete for Large Dams, Paper presented to Fifth International Congress on Large Dams, Question No. 19, Paper No. 9, R70, 335-338, 1955.

Presents three criteria for conducting laboratory freeze-thaw tests on -concrete. First, the concrete that wi l l be used in the structure should be duplicated in the test specimen. Second, the same moisture and temperature changes that the concrete in the structure wi l l undergo should be duplicated in the test specimen. Third, the specimen should be under the same physical restraint as the concrete in the structure. Freezing-and-thawing tests of aggregate indicate that the resistance of the aggregate to the action of freezing and thawing decreases as the size of aggregate increases.

A616. LANDGREN, R., and SWEET, H. S., "Investigation of Durability of Wyoming Aggregates." HRB Proc , 31:202-217, 1952.

Laboratory results of freezing-and-thawing tests, wetting-and-drying tests, thermal-shock tests, slow heating-and-cooling tests, and mortar-bar alkali-reaction tests on a number of aggregates are given. A study of the effect of rate of temperature change on concrete deterioration indicated that too rapid a change in laboratory tests may introduce factors not present in natural weathering conditions. Some exploratory data on possible chemical factors entering into temperature-change tests are also 1 presented.

A617. LANG, F. C., "Testing for Deleterious Materials in Concrete Aggregates." HRB Proc., Part I , 18:250-254, 1938.

The harmful effects of deleterious substances in aggregates were tested by means of concrete beams in which the coarse aggregate was composed entirely of particles of the materials under suspicion. The beams were tested in flexure and subjected to freezing and thawing. Freezing and thawing damage and low structural strength indicated the materials which had bad effects. This appears to be a better method of testing than freez- | ing and thawing of the aggregates alone.

A618. LEGG, F. E . , Jr. , "Freeze-Thaw Durability of Michigan Concrete Coarse Abrogates." Freeze-Thaw Durability of Aggregate in Concrete, HRB BuU. 143, 1-13, 1956.

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This paper presents laboratory freeze-thaw results as well as field observations on the major Michigan aggregate sources and is considered a f i rs t step in formulation of a policy regarding acceptance of future aggregates of unknown service behavior. The complete method for testing aggregates is described, and classes of bad a^regates are identified. The use of rapid freezing-and-thawii^ tests for evaluating aggregates is found to be valuable.

A619. LEWIS, D. W., and VENTERS, E . , "Deleterious Constituents of Indiana Gravels." HRB Bull. 94, 1-10, 1954.

Several gravels are separated by liquid flotation into various specific gravity ranges. The gravel fractions thus obtained were tested to determine absorption, specific gravity, degree of saturation, lithologic composition and durability in air-entrained concrete subjected to freezing and thawing. The results show that the principal deleterious constituents of Lidiana gravels are lightweight sandstones and cherts.

A620. L'HOPTALLIER, P., "On a Number of Observations Made in the Course of Frost Tests by the Conventional Method and a New Test Method." RILEM, Bun. 41, 17-32, 1958.

A new method for making freeze-thaw tests is described in this paper. Concrete prisms are set in water containers for a portion of their length (long axis vertical), then this water is frozen and maintained in a -25C brine bath. A heating coil is applied to the exposed portion of the concrete and F-T cycles occur near the water line as heat is applied and withdrawn. A moment is applied to the specimen by eccentric loadir^ during the F-T testily. The test duration is reduced since specimens fa i l when flexural strength reaches some predetermined amount. There is a limited amount of test data presented which appears to indicate that this procedure gives the same type of durability evaluation as conventional tests, but, in a shorter time. The test apparatus is illustrated by a line diagram and a photograph.

A621. MUNGER, H. H . , "The Influence of the Durability of Aggregate Upon the DurabiUty of the Resulting Concrete." ASTM, Proc , 42:787-803, 1942.

Unconfined aggregate and 2- by 2- by 11.4-in. concrete beams in which the aggregate embedded was tested by cyclic freezing and thawing. The dynamic modulus of elasticity was used as an index of progressive deterioration of the concrete beams. Data are presented that indicate among other things: 1. There is no dependable correlation between results of the soundness

test upon aggregate, per se, and the durability of the resulting concrete.

2. Thermal shock may be a much more important factor in laboratory tests than is generally recognized.

A622. ORTH, M . , "Frost Resisting Concretes, Results Obtained by the Alps n HydrauUc Equipment Region." RILEM, Bull. 41, 33-65, 1958.

The author lists and describes the factors believed to influence concrete durability. Among the factors are (a) cement—composition, firing, fineness; (b) aggregate adhesion—paste aggregate bond bears directly on frost resistance; (c) rock flour—some types of below 100-micron dusts reduce durability; and (d) test specimen and aggregate size—some specimens appear more resistant and large aggregates seem to give better durability. Data and figures are presented to support the observations.

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B623. PRICE, W.H. , and KRETSINGER, D.G., "^gregates Tested by Accelerated Freezing and Thawing of Concrete." ASTM, Proc., 51:1108-1119, 1951.

The automatic freezing-and-thawing apparatus used for testing concrete in the laboratory of the Bureau of Reclamation at Denver is described and the results are compared with those obtained with the manually operated apparatus used prior to 1946, The procedure employed in determining the suitability of aggregates by testing them in concrete subjected to alternate cycles of freezing and thawing is outlined and the results obtained with aggregates from a number of projects are presented. The effect of variation in the test procedure is discussed.

B624. REAGEL, F. V . , "Freezing and Thawing Tests of Concrete." HRB Proc., 20:587-598, 1940.

Presents a discussion and some data on the freezing-and-thawing cycles occurring in Missouri between 1931 and 1936. Also, presents a discussion and data on laboratory freezing-and-thawing tests made on concrete specimens. Attempted to answer the following questions in relation to laboratory tests: (a) How shall deterioration be measured? (b) What are the effects of various curing treatments? (c) What cycle of freezing and thawing should be used? and (d) Can the effect of a^regates on the durability of concrete be predicted by a freezing-and-thawing test? Results of tests show general tendencies but don't answer the questions as above stated.

A625. "Report on Cooperative Freezing and Thawing Tests of Concrete." HRB Special Report 47, 1959.

A complete study of ASTM F-T methods using three concretes. Reviews history of F-T testing and sets rules for procedures in future work. Describes in detail the 4 cycles studied lab by lab. Notes on findings in- ' elude: (a) high air—good and high air—poor, concretes were readily differentiated; (b) six specimens seems minimum for this study; (c) microscopic air was lower than fresh air; (d) voids/in. correlated with spacii^ factor; (e) water freezing was most severe; (f) rapid and slow water test results were similar, cycle for cycle; (g) water methods distinguish very good from very bad concretes readily; and (h) more field studies are needed. I

A626. SCHOLER, C.H. , "Some Accelerated Freezing and Thawing Tests on Concrete.' ASTM, P roc , Part I I , 28:472-486, 1928.

Found that more uniform freezing could be obtained if the cylinders were placed in containers of water and then the containers immersed in alcohol. Found that at age 28 days results were very erratic, cylinders sometimes gaining strength until they fel l apart. Therefore, specimens were aged to 90 days.

A627. SCHUSTER, R, L , , and MC LAUGHUN, J, F , , "A Study of Chert and Shale Gravel in Concrete," Tests for Concrete and Durability of Concrete Aggregates, HRB Bull. 305, 51-72, 1961.

In this study, pore characteristics, mineralogy, texture, and structure were determined for chert and shales from nine Indiana glacial gravel deposits. Despite significant differences in their mineralogies, no difference was noted in the freeze-thaw durabilities of the various chert samples. Although the basic properties of the shales varied even more widely than those of the cherts, none of the shales caused deep-seated failure of the concrete. However, the most porous shales caused "popout" damage. The significance of the 5 micron pores was questioned.

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A628. SWEET, H. S., "Chert as a Deleterious Constituent in Indiana Aggregates." HRB Proc , 20:599-620, 1940.

A study has been made of Indiana limestone quarry cherts and their performance when subjected to alternate cycles of freezing and thawing. The most unsound cherts had a ratio of 0.85 or more between the absorption by one hour evacuation and 23 hours immersion and that calculated for one hundred percent saturation. They had an absorption of 3% or more, and a bulk specific gravity, saturated surface-dry, of less than 2. 50. The results indicated that freezing of water in the voids was the primary cause of disruption. The performance of the cherts was dependent on the degree of saturation.

A629. TRUDSON, E. , "Experiments on Concrete Bars: Freezii^ and Thawing Tests." Progress Report K2, Committee on Alkali Reactions in Concrete, Danish National Institute of Building Research and Academy of Technical Sciences, Copenhagen, 195C.

Describes freezing-and-thawing tests on 66 concrete bars of 31 different mixes. A detailed description is given of the test methods; the method of measurement is explained together with the procedure for calcaulation of the "mean durabili^ factor." Relationship of aggregates to durability is discussed and the aggregates tested are compared.

A630. WALKER, R. D. , and MC LAUGHLIN, J. F . , "Effectof Heavy Media Separation on Durability of Concrete Made With Indiana Gravels." HRB Bull. 143, 14-25, 1956.

The purpose of this study was to obtain laboratory freezing-and-thawing data that would indicate what effect, i f any, the addition of crushed stone and the use of heavy media separation have on the durability of concrete made with gravel coarse aggregate. It was found that:

1. Aggregate size influenced durability and specific gravity separations on the -Vs-in. fraction, but did not offer much benefit.

2. Adding various amounts of good aggregate improved concrete dura-biUty.

3. Concentrations of bad particles in specimen made test results difficult to evaluate.

4. Rapid freezing-and-thawing tests could be used for aggregate evaluations when the results were examined by an experienced engineer.

A631. WHITESIDE, F . M . , and SWEET, H.S., "Effect of Mortar Saturation in Concrete Freezing and Thawing Tests." HRB Proc., 30:204-216, 1950.

This paper presents the results of laboratory freezing-and-thawing tests on concrete in which certain variables were controlled as closely as possible so that variations in durability could be related to variations in the water content and available air space in the mortar or paste component. Changes in weight and in unit weight were determined at intervals through the course of curing and freezing and thawing. Methods were developed for using these data in calculating the degree of saturation of the mortar phase of the concrete, in connection with a semi-empirical calculation of the change in volume of the cement-plus-combined-water component, and an estimate of freezable water based on relationship with the "non-evap-orable water content" of the cement. It is concluded, on the basis of these tests, that concrete subjected to freezing and thawing when the mortor component has a degree of saturation of 0.91 or greater wi l l deteriorate rapidly. A l l specimens with degree of saturation below 0.88 were highly durable. The lower degree of saturation is conveniently obtained by air entrainment.

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A632. WITHEY, M. O., "Considerations Involved in the Making of Freezing-and Thawing Tests on Concrete." A Symposium, ASTM, P roc , 46:1198-1207, 1946.

Factors influential in developing freezing-and-thawing tests and the types of tests commonly used are considered. The more important details of procedure for testing concrete containing aggregate of uncertain quality, the principal indices of damage, and the selection of the end point are discussed. A brief consideration is also made of the s^nificance of freez-ing-and-thawii% tests and the further research which is needed to provide proper standards for procedure.

B633. WOODS, H . , "Observations on the Resistance of Concrete to Freezing and Thawing." Proceedings, American Concrete Institute, No. 4, 51:345-349, December 1954.

A survey and analysis of the more important invest^ations on freezing and thawii^ of concrete show that significant general conclusions can be drawn. Conclusions: (a) concrete of normal water-cement ratio, without entrained air, is vulnerable to freezing and thawing when water soaked; (b) the locus of damage may be the aggregate, or the hardened cement paste, or both; (c) no portland cement clinker composition has any significant advantage over any other; (d) the primary function of entrained air is to protect the hardened cement paste from destructive pressure arising from the freezing of water therein; (e) a possible alternative to entrained air may be the use of a low water-cement ratio, below about 0.4 by weight;, and (f) entrained air can produce resistance to surface scaling consequent to the application of salts for ice removal.

TEST METHOD PROPOSED BY T, C. POWERS D701. AKROYD, T.N.W., "Concrete, Properties and Manufacture." New York,

Pergamon Press, 1962. This text treats the properties, materials, mix design, manufacture, and control of portland cement concrete along with some special topics. The theoretical consideration of concrete durability is current and complete. Aggregates are discussed in several sections of the book and their influence on the properties of fresh and hardened concrete, particularly as related to volume stability in hardened concrete, is especially well covered.

A702. AXON, E.O., WILUS, T. F . , and RE AGE L, F .V . , "Effect of Air-Entrapping Portland Cement on the Resistance to Freezing and Thawing of Concrete Containing fiiferior Coarse Aggregates." ASTM, Proc , 43:981-994, 1943.

Observations are made on the performance of aggregates in air-entrained concretes. Two specimen conditioning procedures were used and it was noted that a period of air-drying not only lowered the moisture content but kept i t below that of water stored specimens even after a resoaking period.] Concrete made with stream-wet chert was notprotectedby air entrainment while vacuum saturated limestone aggregate concrete performed well. Beneficial effects of air entrainment appeared related to aggregate quality, aggregate moisture condition, and specimen conditioning.

D703. BLANKS, R. F . , and KENNEDY, H. L . , "The Technology of Cement and Concrete." New York, John Wiley and Sons, 1955.

This text has a section devoted to concrete aggregates, covering their exploration, processing and essential qualities. Petrographic studies are discussed in an adaptation from Rhoades and Mielenz. Essential qualities of aggregates are treated in detail and volume stability is treated under

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moisture and thermal properties headings. Clay minerals can cause significant expansion of aggregates during wetting and drying. Thermal expansion can cause distress if a^ r^a te and paste are not compatible. Alkali-aggregate reactions can cause significant volume expansion when siliclous aggregates, high-alkali cement and high moisture conditions occur simultaneously. A thorough description is given of a test for porosity of concrete and data are shown relating capillarity movement of water to durability.

B704, NERENST, PAUL, "Frost Action in Concrete." Chemistry of Cement, Vol. E, National Bureau of Standards, Washington, D. C., 1962.

The author describes 3 mechanisms for frost damage: (a) macroscopic ice segregation, (b) microscopic ice formation, and (c) hydraulic pressure, bnportant observations on freeze-thaw action include the following: 1. Macroscopic ice segregation wil l only take place in mature concrete

with w/c above 0. 9 and only under special conditions. 2. Water drawn from gel by microscopic ice lenses can cause shrinkage.

Time affects lens growth while hydraulic pressure depends on freezing rate.

3. Microscopic lenses can occur with w/c below 0. 55 but at w/c 0.3-0.4 concrete may be immune to frost damage.

4. Cement paste has high porosity and low permeability which leads to high hydraulic pressures. This pressure appears to be a function of permeability, strength, saturation, rate of ice growth. Powers originally used 250 n as a. maximum void spacing but now indicates 50 n as more suitable.

5. Rock pores are much larger than those of gel so water in them freezes faster. Permeability is high so water moves more freely. The paste may seal and change aggregate performance.

6. Evaluation of frost damage is done by strength tests, tests for variations in volume and length, and tests for changes in elastic properties. Tensile tests are suitable and sensitive.

7. Freeze-thaw resistance has been reported as a function of cement type and properties, maximum particle size, compacting method, curing method, admixtures and additions, w/c ratio, total water, consistency, and grading of aggregate.

8. Mature paste should be immune to frost with proper air entrainment so aggregate frost resistance can be investigated.

9. Studies of aggregate pore structure, along with specific gravity determinations seem most promising.

D705. ORCHARD, D. F . , "Concrete Technology." Vol. I and I I , 2nd Ed., New York, John Wiley and Sons, 1962.

This two-volume set gives a very complete coverage of materials and methods associated with concrete technology. Significant characteristics of aggregates and methods for identifying and classifying these are covered in portions of both volumes. The discussion of test methods is particularly good since i t serves as a recent compilation of studies in this area.

The frost resistance of concrete and aggregates and al l the related aspects of this matter are covered thoroughly and most of the significant research work in England, Australia, and the United States is cited.

These volumes provide a broad perspective of many problems in concrete technology, among them durability and frost resistance of aggregates, and give many excellent references that can be used for deeper studies on particular subjects.

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A706. PICKETT, G., "Flow of Moisture in Hardened Portland Cement During Freezing." HRB Proc., 32:276-284, 1953.

A mathematical analysis, based upon idealized assumptions, is made of the flow of moisture between the components of hydrated-cement paste during freezing or thawing. The components considered are the gel substance, the capillary pores, and the air-entrained spaces.

It is shown that a change in temperature for temperatures below 0 C gives rise to differences in thermodynamic potentials between gel water, capillary water or ice, and ice frozen in the air spaces. The potentials result in part from pressures produced by volume changes resulting from freezing and, in part, from differences in the vapor pressures of ice and water. Based on these potential differences the analyses show, for example, that during freezing, in which the temperature is being lowered continuously, flow may f i rs t be from capillary to gel, then from gel to capillary and finally again from capillary to gel. During the same time, flow may be continuously from gel to air space.

By taking into account the change in volume resulting from freezing or thawing of ice in the capillary spaces and the changes in shrinking or swelling tendency resulting from changes in amount of gel water, various volume-time-temperature relations are deduced. In particular, it is shown that water movements and volume chaises for a specimen depend not only on the present temperature changes but on the past temperature history of the specimen.

C707. POWERS, T. C., "A Working Hypothesis for Future Studies of Frost Resistance of Concrete." Journal, American Concrete Institute, No. 4, 41:245-272, February 1945.

Destruction of concrete by freezii^ is caused by hydraulic pressure generated by the expansion accompanying freezing of water rather than by direct crystal pressure developed through growth of bodies of ice crystals. There exists a critical degree of saturation above which suscep-| tibility to freeze-thaw damage is severe. Experimental evidence indicates that ice formed in the paste occurs only in the capillary system within the j gel substance and not within the gel substance itself. Distance between , air spaces rather than total volume of air space determines the degree of protection afforded to freeze-thaw. The smaller the distances (or the smaller the average air space size for a given air content) the greater the protection. No general correlation between rate of disintegration and porosity of the whole concrete should be expected.

B708. POWERS, T.C. , "Basic Considerations Pertaining to Freezing and Thawing Tests." ASTM, P roc , 55:1132-1155, 1955.

Knowledge about the mechanisms of frost action in hardened paste and in rock is summarized. Emphasis is placed on concepts of critical thickness and critical saturation, and the roles of air bubbles in paste and macropores in absorptive rock. Rapid freezing in the laboratory may destroy concrete that is immune to frost under natural conditions. In the laboratory, too, important effects of seasonal drying are not taken into account. A new procedure is proposed that takes category of field exposure into account and uses the period of immunity to frost attack as the primary measure of frost resistance.

B709. POWERS, T. C., "Some Physical Aspects of the Hydration of Portland Cement." Journal of the Research and Development Laboratories, Portland Cement Assoc., No. 1, 3:47-56, January 1961.

An explanation is given of the process of hydration and how it is controlled

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by physical conditions. The hydration of portland cement requires a doublii^ of the volume of solids in a specimen of paste. Half of the reaction products are deposited inside the boundaries of the cement grains, and half outside, simultaneously. The process requires an insoluble material to remain in solution for great lengths of time. Also, the process occurs without much dilation of the specimen.

A710. POWERS, T. C., "The Air Requirement of Frost-Resistant Concrete." HRB Proc , 29:184, 1949.

The theoretical maximum permissible void spacing is found analytically to be a function of paste properties, degree of saturation of the paste, and rate of cooling. A spacing factor for the voids in hardened concrete, as well as the total volume of air can be calculated from data obtainable by the linear-traverse method. The necessary mathematical relationships are given in this paper. The actual maximum spacing factor for certain frost-resistant concretes was estimated to be about 0,01 in. The air requirement for a given rate of coolii^ depends upon the paste content, the specific surface of the voids, and the maximum permissible spacing factor. When voids are too widely spaced to prevent failure of saturated paste, failure wi l l also occur at moisture contents below saturation; within limits, the denser the paste the lower the degree of saturation at failure,

C711, POWERS, T. C,, "The Nonevaporable Water Content of Hardened Portland Cement Paste—Its Significance for Concrete Research and Its Method of Determination," ASTM, Bull, No, 158, 68-76, May 1949,

The physical composition of hardened portland-cement paste can be computed from empirical relationships involving the original water content of the fresh paste, the nonevaporable water content of the hardened paste at the existing stage of hydration, and the nonevaporable water content when the cement is completely hydrated. The relationships between physical composition and strength, frost resistance, and other factors are discussed with reference to research procedures. Experimental methods for measuring the nonevaporable water content and other qualities of the paste are described.

C712. POWERS, T. C., "Void Spacing as a Basis for Producing Air-Enti:ained Concrete." Journal, American Concrete bstitute. Vol. 50, No, 9, May 1954.

A procedure is suggested for designing a fixed spacing factor where such procedure is economically feasible. The fimction of entrained air is to protect the paste and this effectiveness depends on the distance from void to void in the paste. Freezing-and-thawing tests show different mixes have nearly equal frost resistance when the spacing factor is about 0,01 inches. The amount of air required for a given spacing factor is directly proportional to the paste content and is greater the smaller the specific surface of the air voids.

A713. POWERS, T .C. , and HELMUTH, R, A , , "Theory of Volume Changes in Hardened Portland-Cement Paste During Freezing." HRB Proc., 32:285-297, 1953.

Experimental data are presented on the freezing of hardened portland-cement pastes with and without entrained air. They are explained in terms of two mechanisms: (a) the generation of hydraulic pressure as water freezes in capillary cavities, and (b) the growth of the bodies of ice in the capillary cavities or air voids by diffusion of water from the gel. Air

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voids limit the hydraulic pressure and shorten the period during which the ice in the cavities can increase. The closer the air voids are to each other the more effective they are in controlling either mechanism.

A714. THOMAS, W. N . , "Experiments on the Freezing of Certain Building Materials." Building Research Technical Paper No. 17, Dept. of Scientific and Industrial Research, 1938.

This paper contains an excellent discussion on the stresses and strains occurring in building stones as a result of water freezii^ in the pores of the stone. Extensive test work is described in detail. Some of the more important observations and conclusions included: (a) excessive strains during freezing resulted in permanent set after thawing; (b) stresses developed depend on rate of cooling; (c) influence exerted by rate of coolii^ is greatest during early period after crystallization has been induced; (d) artifical and natural coatings greatly influence damage caused by frost; (e) large specimens with low ratio of surface area to volume suffer more than small specimens; and (f) a gradual decrease in strain occurs with time for a given specimen at a constant low temperature.

A715. TREMPER, B . , and SPELLMAN, D. L . , "Tests for Freeze-Thaw Durability of Concrete Aggregates." HRB Bull. 305, 1961.

Tests of aggregate in air-entrained concrete were made by methods suggested by T. C. Powers for resistance to freezing and thawing. The procedure differs from that of currently used test methods in several important respects. Among these are: (a) maintenance of the original moisture in the aggregates, (b) testii^ of the largest particle sizes to be used in the work, (c) subsequent conditioning of the cured concrete by drying to a degree found appropriate to exposure conditions at the site of construction, and (d) freezing at a rate commensurate with natural conditions.

A716. VALORE, R.C., "Volume Changes Observed in Small Concrete Cylinders During Freezing and Thawing Using a Mercury Displacement Dilatometer." Journal of Research, National Bureau of Standards, 43:1-27, July 1949.

A mercury displacement dilatometer is described for continuously determining the changes in bulk volume of small concrete cylinders during freezing and thawing. Various types of freezing and thawing cycles were employed in which the 40 to -20 F range was covered at various rates. The results presented are representative volume-temperature relationships obtained for specimens tested in air-dry, partially saturated, and "vacuum saturated" moisture conditions. Relationships for air-dry speci-| mens yielded uniform thermal-expansion data, but those for partially saturated specimens showed departures from uniformity that are ascribed ] to the freezing and thawing of water in the pore structures of the specimens. Vacuum-saturated specimens showed much larger departures and failed as a result of a single cycle of freezing and thawing.

A717. VERBECK, G., and KLIEGER, P., "Calorimeter-Strain Apparatus for Study of Freezing and Thawing Concrete." Instrumentation for Measuring Characteristics of Concrete, HRB Bull. 176, 1958.

This paper describes the development and operation of an apparatus for determinii^ (a) the amount of water actually freezing within a concrete specimen as a function of temperature and time, and (b) the physical response of the specimen in terms of l e i ^ h change as this water is frozen. Examples of the type of information that can be obtained are presented and discussed.

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C718. VERBECK, G., and LANDGREN, R., "fafluence of Physical Characteristics of Aggregates on Frost Resistance of Concrete." ASTM, P roc , 60:1063-1079, 1960.

The durability of concretes made with different aggregates depends upon the rate at which the aggregates become critically saturated in the concrete and upon the different physical responses of the aggregates to freezing. The different responses of aggregates to freezing when saturated depend upon the pore characteristics of the aggregates and the cement paste. Saturated aggregates of low porosity may accommodate pore water freezing by simple elastic expansion. Saturated aggregates of moderate or high porosity may fai l internally because the particle dimension exceeds a certain critical size or may cause failure in the paste immediately adjacent to the aggregate particle because of aggregate pore water displacement. The magnitude of the hydraulic pressures developed is significantly influenced by the size of the aggregate particle and the permeability and air content of the surrounding paste.

E719. WILLS, M . H . , JR., "An Investigation of the Behavior of Two Frost Susceptible Concretes When Exposed to the Slow Freeze-Thaw Test Method." Unpublished Master's Thesis, University of Maryland, 1962.

This paper represents a further study of the Powers proposal for a freez-ing-and-thawlng test of concrete. Dial gages and a Whittemore strain gage were used to measure length changes and dilation during slow freezing cycles. Specimens were also tested in a rapid freeze-thaw device for comparison purposes. Permanent length changes appeared to be the most sensitive indicator of damage with dilation measurements and relative E somewhat less sensitive. A period of air-drying after curing proved to be beneficial in al l cases.

A720. WRAY, F. N . , and LICHTEFELD, H. J . , "The Influence of Test Methods on Moisture Absorption and Resistance of Coarse Aggregate to Freezing and Thawing." ASTM, P roc , 40:1007-1020, 1940.

The authors studied the following: (a) The effects of different treatments on the amount and rate of moisture loss of a thoroughly saturated aggregate; (b) The effects of different treatments on the amoimt and rate of moisture absorption, including vacuum treatment; (c) The relationship between deterioration from freezii^ and thawing and the degree of moisture saturation at the beginning and end of freezing tests; and (d) The absorptive properties and resistance to freezing and thawing of different sizes of aggregate particles.

Normal soaking would restore approximately 70% of stream moisture while vacuum saturation would restore approximately 90% for the material studied. Smaller particles regained moisture more rapidly than larger ones. Freezing resistance (unconfined method) was less for larger particles and high degrees of saturation.

MISCELLANEOUS POSSIBLE APPROACHES A801. COLLINS, A.R. , "The Destruction of Concrete by Frost." Journal, Institution

of Civil Engineers, Paper No. 5412, 23:29-41. This paper discusses frost resistance of concrete based on assumptions that failure from freezing is similar to frost heave in soils. Author postulates that freezing occurs to certain depth and then stops because ice crystals in this area have drawn up moisture from concrete immediately below. At this point a lamination occurs. As cooling proceeds downward, ice crystals form again at some lower depth in the slab and the process is repeated.

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B802. GILBERT, J. R., "The U. S. Corps of Engineers Approach to More Durable Concrete." The Crushed Stone Journal, No. 2, 24:3-30, June 1949.

The U. S. Corps of Engineers approach to securii^ durable concrete is discussed. Their specifications are constantly changed and improved. Their specifications place no quantitative limit on such tests as magnesium sulphate, absorption, abrasion, etc., but rather rate the possible aggregate sources qualitatively. Briefly describes the petrographic, weather-mg, and thermal properties determined and the tests employed by the Corps.

A803. JACKSON, F. H . , "Relation Between Durability of Concrete and Durability of Aggregates." HRB Proc., 10:101-131, 1930.

This paper contains suggested outlines of research to attempt the correlation of durability of concrete to durability of aggregates.

A804. JACKSON, F .H . , "Long Time Study of Cement Performance m Concrete-Chap. 9, Correlation of the Results of Laboratory Tests with Field Performance Under Natural Freezing and Thawing Conditions." Journal, American Concrete fiistitute, No. 2, 52:159-193, October 1955.

Summarizes and evaluates the results of laboratory tests spanning 14 years of the long time study of cements and concrete containing them.

Laboratory freezing-and-thawing tests of concrete correlate well with with field performance in showing the markedly improved durability of air-entrainedconcretes. An over-all appraisal of the results of the long time study tests to date indicates that, of the many physical tests made of the long time study of cements, only the test for air content is of any value in indicating relative resistance to freezing and thawing.

A805. MONFORE, G. E. , "A Small Probe-Type Gage for Measuring Relative Humidity." Journal of the Research and Development Laboratories, Portland Cement Association, No. 2, 5:41-47, May 1963.

This paper describes design, calibration, and use of a new probe-type relative humidity gage and its application to use in portland cement concrete.

B806. OPPEL, G. U . , "Photoelasticity Applied to the Determination of Properties of Concrete." Rock and Concrete Research, The Pennsylvania State University J 1960.

This paper describes the use of photoelasticity to examine strain conditions in concrete under stress.

B807. PRICE, W . L . , "Ten Years of Progress in Gravel Beneficiation." NSGA Circular No. 71, March 1958.

The various methods of gravel beneficiation such as heavy media separation, jigging, hydraulic rising current classification and elastic fractionation are described.

B808. SCHOLER, C.H. , "S^nificant Factors Affecting Concrete Durability." ASTM, Proc , 52:1145-1158, 1952.

This paper presents a discussion of some of the factors that may influence] concrete durability and attempts to point out the direction for further research. An outline of the various factors that may influence concrete durability as prepared by ASTM Committee C-9 is appended to this paper.

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B809. SWEET, H. S., and WOODS, K. B . , "Evaluation of Aggregate Performance in Pavement Concrete." Journal, American Concrete Institute, No. 10, 44:1033-1040, June 1948.

This paper is a review of published information on aggregate as a variable influencing the durability characteristics of portland cement concrete.

B810. WOODS, K. B . , MC LAUGHLIN, J. F . , and SCHUSTER, R. I . , "Quality Aggregates for Mdiana Highways." Civil Ei^ineering Reprint, No. 145, Purdue University, January 1959.

This paper is a summary of the many investigations that have been carried out on aggregates used in Indiana highways. Field performance of concretes containing the various aggregates and correlations between field performance and laboratory studies are presented. Effects on performance of ^gregate beneficiation are also given.

A811. WOODS, K . B . , SWEET, H. S., and SHELBURNE, T.C. , "Pavement Blowups Correlated With Source of Coarse Aggregate." HRB Proc., January 1946.

This paper reports, in part, the results of the performance of 3,300 miles of rigid pavements constructed in todiana from 1921 to 1943. An outstanding correlation existed between certain coarse aggregates used in the concrete mix and the blowup performance of the pavements.

B812. WOOLF, D.O., "Needed Research." Symposium on Mineral ^ r ega t e s , ASTM, Special Technical PubUcaUon No. 83 , 221-233, 1948.

A discussion of the need for research in the field of mineral aggregates is presented. Attention is directed to a number of characteristics of mineral aggregates which should be studied.

A813. WUERPEL, C.E., "Detecting Unsound Chert in Aggregate." Engineering News-Record, No. 19, 124:652-654, May 9, 1940.

A study of unsound concrete aggregates containing chert showed that pebbles of low specific gravity are the source of trouble. They can be separated by flotation in a heavy liquid. Apparatus for carrying out the separation is described.

A814. WUERPEL, C. E. , and REXFORD, E. P., "The Soundness of Chert as Measured by Bulk Specific Gravity and Absorption." ASTM, Proc , 40:1021-1043, 1940.

The test data and discussion of results areprecededby a symposium of data and comments on chert by other investigators. The object of the studies was to investigate the possibility of isolating the sound and unsound varieties of chert in concrete coarse aggregate by some means more precise than visual examination and more practical than microscopic analysis. The results of the investigation indicate a close relationship between the void structure (porosity), the bulk specific gravity, and the resistance of most chert particles to freezing and thawing. A procedure is described for mechanically segregating unsound particles of chert from gravel aggregate by flotation.

Appendix LIST OF REFERENCE SOURCES

Bibliographies 1. Battelle Technical Review 2. Current Reviews in the Journal of American Concrete Institute 3. Cement and Concrete Association Reviews 4. Chemical Abstracts 5. Engineering Index

6. Highway Research Board Abstracts and Bibliographies

Periodicals 1. American Ceramic Society, Journal and Transactions 2. American Concrete Institute, Journal 3. American Scientist 4. American Society of Civil Engineers, Transactions 5. American Society for Testing Materials, Bulletins, Proceedings, and Standards 6. Annales de Chemie et de Physique 7. Australia Journal of Applied Science 8. British Ceramic Society, Transactions 9. Bureau of Standards, Journal of Research

10. Ceramic Age 11. Civil Engineering 12. Claycrait 13. Concrete 14. Crushed Stone Journal 15. Engineering News-Record 16. Geological Society of America, Bulletin 17. Highway Research Board, Bulletins and Proceedings 18. Institution of Civil Engineers, Journal 19. International Science and Technology 20. Journal of Geology 21. Magazine of Concrete Research 22. National Sand and Gravel Association, Circulars and Bulletins 23. Ontario Hydro Research News 24. Pit and Quarry 25. Physics 26. Portland Cement Association, Journal of the Research and Development

Laboratories 27. Public Roads 28. RILEM Bulletin 29. Roads and Streets ' 30. Rock Products

Books 1. The Absorption of Gases and Vapors, Brunauer 2. Composition and Properties of Concrete, Troxell and Davis 3. Concrete, Properties and Manufacture, Akroyd 4. Concrete Technology, Orchard 5. Properties of Ordinary Water Substance, Dorsey 6. Technology of Cement and Concrete, Blanks and Kennedy

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81 Theses

1. F.K. Fears, M.S. Thesis, Purdue University 2. R.J. Reilly, M.S. Thesis, University of Maryland 3. M.H. Wills, Jr. , M.S. Thesis, University of Maryland

Symposia Proceedings

1. Chemistry of Cement, Proceedings of Fourth International Symposium 2. Fifth International Congress on Large Dams 3. International Symposium on Durability of Concrete, Final Report

Miscellaneous Reports, Papers, and Bulletins 1. Archiv f i i r das Eisenhiittenwesen 2. Corps of Engineers, Waterways Experiment Station 3. Danish National Institute of Building Research and Academy of

Technical Sciences 4. Department of Scientific and Industrial Research (U. K.) 5. Engineering Experiment Station, Purdue University 6. Engineering Experiment Station, University of Iowa 7. Engineering Experiment Station, Universily of Kentucky 8. Pennsylvania State University, Rock and Concrete Research 9. Trudy Soveshchaniya po Tekhnol Betonov Akad. Nauk. Armyan.

r r i H E NATIONAL A C A D E M Y OP S C I E N C E S — N A T I O N A L R E S E A R C H COUN-I CIL is a private, nonprofit organization of scientists, dedicated to the

furtherance of science and to its use for the general welfare. The A C A D E M Y itself was established in 1863 under a congressional charter signed by President Lincoln. Empowered to provide fo r all activities appropriate to academies of science, i t was also required by its charter to act as an adviser to the federal government in scientific matters. This provision accounts for the close ties that have always existed between the ACADEMY and the government, although the A C A D E M Y is not a governmental agency.

The NATIONAL R E S E A R C H COUNCIL was established by the A C A D E M Y in 1916, at the request of President Wilson, to enable scientists generally to associate their efforts wi th those of the limited membership of the ACADEMY in service to the nation, to society, and to science at home and abroad. Members of the NATIONAL R E S E A R C H COUNCIL receive their appointments f rom the president of the ACADEMY . They include representatives nominated by the major scientific and technical societies, representatives of the federal government, and a number of members at large. I n addition, several thousand scientists and engineers take part in the activities of the research council through membership on its various boards and committees.

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HIGHWAY RESEARCH BOARD Special Report 80 A Critical Review...

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