FRAMEWORK FOR DEVELOPMENTOF A CLASSIFICATION PROCEDURE FOR USE OF AGGREGATE FINES IN CONCRETE

RESEARCH REPORT ICAR – 101-2F

Sponsored by the Aggregates Foundation

for Technology, Research and Education

Technical Report Documentation Page

1. Report No.

ICAR 101-2F 2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

Framework for Development of a Classification Procedure for Use ofAggregate Fines in Concrete

5. Report Date

October 2001 6. Performing Organization Code

7. Author(s)

Dan G. Zollinger and Shondeep Sarkar 8. Performing Organization Rep ort No.

Research Report ICAR 101-2F 9. Performing Organization Name and Address

Texas Transportation InstituteTexas A&M University SystemCollege Station, Texas 77843-3135

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

Project No. ICAR 10112. Sponsoring Agency Name and Address

Texas Department of TransportationResearch and Technology Transfer OfficeP. O. Box 5080Austin, Texas 78763-5080

13. Type of Report and Period Covered

Research:

14. Sponsoring Agency Code

15. Supplementary Notes

Research performed in cooperation with the International Center for Aggregate ResearchResearch Study Title: Engineering Uses for Fines in Concrete

16. Abstract

Although data on use of aggregate fines in portland cement concrete are largely very encouraging,there is a lack of proper definition, and knowledge regarding nature, and characteristics of different aggregatefines, their properties, and effects on portland cement concrete. The focus of this project was to examine themethods and test procedures used in the past to characterize the properties of fines, and develop, on apreliminary basis, a framework to characterize and catalogue the properties of aggregate fines, propose newones that would eventually complement a set of guidelines for the use of aggregate fines in portland cementconcrete. A test run of this classification process is provided as a demonstration of its utility to distinguishaggregate fines possessing different properties and characteristics. Possible applications of aggregate fines,such as in high-performance concrete, controlled low strength materials, and insulated concrete forms arediscussed as future directions of research.

17. Key Words

Physical, Chemical, Durability and MechanicalCharacterization, Screening Tests, Petrography,Mixture Proportions, Compression Strength, HPC,CLSM, ICF

18. Distribution Statement

No restrictions. This document is available to thepublic through NTIS:National Technical Information Service5285 Port Royal RoadSpringfield, Virginia 22161

19. Security Classif.(of this report)

Unclassified20. Security Classif.(of this page)

Unclassified21. No. of Pages

12022. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

FRAMEWORK FOR DEVELOPMENTOF A CLASSIFICATION PROCEDURE

FOR USE OF AGGREGATE FINES IN CONCRETE

by

Dan ZollingerAssociate Research Engineer and Associate Professor

Texas Transportation InstituteTexas A&M University

and

Shondeep L. SarkarResearch Scientist

Texas Transportation InstituteTexas A&M University

Research Sponsored by International Center for Aggregate Research

Research Project No. ICAR 101

Research Report ICAR 101-2F

TEXAS TRANSPORTATION INSTITUTEThe Texas A&M University SystemCollege Station, Texas 77843-3135

October 2001

v

DISCLAIMER

The contents of this report reflect the views of the authors who are responsible forthe facts and the accuracy of the data presented herein. The contents do not necessarilyreflect the official view or policies of the International Center for Aggregate Research orAAB Building Systems. The report does not constitute a standard, specification, orregulation, nor is it intended for construction, bidding, or permit purposes. The engineer incharge of this project was Dan G. Zollinger, P.E. # 67129 and the Research Scientist wasShondeep L. Sarkar, P.E. # 85266.

xiii

IMPLEMENTATION RECOMMENDATIONS

Disposal of aggregate fines generated by quarries has become a major problem in the

aggregate industry. The Fines Expert Task Group in acknowledging this problem, has

identified the incorporation of fines in portland cement concrete (PCC) as a potentially

beneficial use; other possible engineering uses of fines in the construction sector have also

been defined. This report resulted from a project, entitled Engineering Uses for Fines,

focusing on the feasibility of the use of fines in several different applications and the

identification of potential markers for aggregate fines. This research report, in response to

the first objective, presents a tentative framework for the classification of aggregate fines

for use in concrete. The framework outlines factors that affect performance of high-fines

concrete and suggests different criteria to determine the type of concrete that can be

produced using a given source of aggregate fines. These criteria along with the suggested

percentages of fines for a given type of concrete should be considered as preliminary at this

stage in need of further research and verification. In response to the second objective,

potential uses of fines were researched and identified for consideration later.

Subsequent to an exhaustive literature review, the researchers recognized the need to

first develop a practical and systematic procedure for classification of fines. This became

apparent when conventional ASTM test procedures for fresh concrete materials failed to

uniquely characterize concrete mixtures containing the same amount of fines from different

sources. Thus, the focus of this research has been directed to an evaluation of the

applicability of different characterization techniques for developing guidelines for use of

fines in a specific type of concrete mixture. The classification procedure, however,

requires additional efforts before it can become universally implementable. There are clear

indications from the results obtained to date that fines from different sources are rarely very

similar, and therefore, it is necessary to classify them according to their physical, chemical,

and mineralogical properties in order to predict their behavior in concrete mixtures. Two

sets of fines were used to develop the classification framework, presented in this report.

xiv

The results demonstrate that the sand equivalent (SE) test may serve as an adequate

procedure by which to screen aggregate fines sources for different concrete applications.

Since the SE value may not change significantly even up to 20% blending of certain

aggregate fines with sand, it is being suggested that this test be applied on quarry fines

independent of sand. The additional characterization tests that have been proposed for

verifying the applications of fines in different types of concrete are described at some

length.

Our results show that at higher water-cement ratios (W/C), replacement of sand by

aggregate fines over a 10 to 30% range, leads to a decrease in compressive strength, and an

increase in paste porosity. This supports the need for further research on how to reduce the

w/c for sand replacement to be effective. The current replacement values indicate an

optimization trend at about 15 to 20% by mass of sand for at least one set of fines. Future

research efforts should concentrate on establishing the optimum replacement percentage of

fines from different sources. This will help in drafting the techno-economics of the concept

of partially replacing sand by fines. At present, three specific applications of fines are being

considered, namely in structural concrete, high-performance concrete, and controlled low-

strength concrete. The durability issue of high fines concrete must be addressed through

numerous ASTM and AASHTO specified durability related tests.

It may be of interest to the industry to investigate the possibility of replacing a portion

of cement with aggregate fines. This concept, which has already been accepted by a number

of countries, represents a more efficient use of cement. However, it is more likely that a

manufacturer of portland cement will use his own raw mix as a clinker extender rather than

purchasing aggregate fines from an aggregate producer.

vii

TABLE OF CONTENTS

PageLIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ixLIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiIMPLEMENTATION RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiiiCHAPTER 1 - INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1

Background Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2Report Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2

CHAPTER 2 -LITERATURE REVIEW ON USE OF FINES IN CEMENT AND CONCRETE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1

Definition of Fines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1Use of Fines in Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1Use of Limestone Fines in Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6Implications of the Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.15Summary of State of the Practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.17

CHAPTER 3 - DEVELOPMENT OF CLASSIFICATION FRAMEWORK METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1

Approach to Classification of Fines Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1Proposed Classification Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3Proposed Testing Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4Screening Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5

Physical Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7Level 1 Tests (Tests of Minus No. 200 Fines) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8

Physical Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8Chemical Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9Mineralogical Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9

Level 2 Tests (Tests of Fines Used in Concrete) . . . . . . . . . . . . . . . . . . . . . . . . . . 3.10Physical Characterization of Fresh and Hardened Concrete . . . . . . . . . . . . . . . 3.10Durability Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.13Mechanical Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.18Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.21

CHAPTER 4 - APPLICATION OF CLASSIFICATION FRAMEWORK . . . . . . . . . . . . 4.1Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1Screening Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1

Sand Equivalence Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1Level 1 Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3

Particle Size Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3Petrography of Fines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4

viii

TABLE OF CONTENTS (Continued)

Page

Mineralogical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5Chemical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5Inferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6

Level 2 Testing Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7Mixture Proportions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9Porosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10Inferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13CHAPTER 5 - POTENTIAL APPLICATIONS OF AGGREGATE FINES . . . . . . . . . . 5.1 Limestone-Filled Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1

High-Performance Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3Structural Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3Controlled Low Strength Material (CLSM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4

Current Status of ICF Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4Commercial Application of Aggregate Fines in ICF . . . . . . . . . . . . . . . . . . . . . 5.7

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8CHAPTER 6 - AREAS OF FUTURE RESEARCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1Research Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R.1APPENDIX A - MICROGRAPHS OF AGGREGATE FINES . . . . . . . . . . . . . . . . . . . A.1APPENDIX B - X-RAY DIFFRACTION PATTERNS OF AGGREGATE FINES . . . B.1APPENDIX C - APPLICATION OF HIGH-FINES CONCRETE . . . . . . . . . . . . . . . . . C.1

ix

LIST OF FIGURES

Figure Page

3.1 Schematic of Proposed Classification Framework. Note: HPC-High

Performance Concrete; SC-Structural Concrete; CLSM-Controlled Low

Strength Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.33.2 Details of the Different Levels of Proposed Testing . . . . . . . . . . . . . . . . . . . . . . 3.53.3 Sand Equivalent Results of Fines No. 1 and No. 2, and Sand with 10%

Fines No.1 and No.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.74.1 Water Demand of Reference Concrete and Concretes Containing 10

Percent Fines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.84.2 Compressive Strength at 7 and 28 Days, where LS = Limestone, N2 Siliceous . 4.94.3 Porosity of Reference Concrete, and Concretes Containing 10,

20, and 30 Percent Siliceous Fines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.114.4 Porosity of Reference Concrete, and Concretes Containing 10,

20, and 30 Percent Limestone Fines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.114.5 Shrinkage vs. Time for Concrete Samples Containing Limestone Fines . . . . . 4.125.1 Residential Concrete Building Systems. Left to Right: Hebel Block,

Rastra ICF, and Polystyrene ICFs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5A.1 Showing the Distribution of Fine and Coarse (A) Particles . . . . . . . . . . . . . . . A.3A.2 Subrounded and Subangular Morphology of Grains . . . . . . . . . . . . . . . . . . . . A.3A.3 An Elongated Particle (A) with a High Aspect Ratio of 8:1 . . . . . . . . . . . . . . . A.4A.4 Distribution of Dolomite Rhombs (A) and Subrounded Calcite

Crystals (B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.4A.5 Distribution of Elongated (A) and Coarse (B) Particles . . . . . . . . . . . . . . . . . . A.5A.6 Quartz (A) and Calcite (B) Grains in the Sample . . . . . . . . . . . . . . . . . . . . . . . A.5A.7 Overall Particle Size Distribution is Finer Than That of Sample

No. 1 Shown in Figure A.8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.6A.8 Particle Size Distribution of Sample No. 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.6B.1 X-ray Diffraction Pattern of Fines No. 1 (Limestone) . . . . . . . . . . . . . . . . . . . B.3B.2 X-ray Diffraction Pattern of Fines No. 2 (Siliceous) . . . . . . . . . . . . . . . . . . . . B.4C.1 Temperature Curves for Limestone Fines Concrete and High

Volume Fly Ash Concrete up to 120 Hours . . . . . . . . . . . . . . . . . . . . . . . . . . . C.4C.2 Compressive Strength of Limestone Fines Concrete and High

Volume Fly Ash Concrete at 3, 7 and 28 Days . . . . . . . . . . . . . . . . . . . . . . . . . C.5C.3 Porosity of Field Concrete at 28 Days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.6C.4 Small, Circular Air Voids Uniformly Distributed in the Paste . . . . . . . . . . . . . C.7C.5 Unhydrated Cement Particles (ö) in the Paste . . . . . . . . . . . . . . . . . . . . . . . . . C.7C.6 Paste-Aggregate Interface, where A = Aggregate, B = Paste . . . . . . . . . . . . . . C.8C.7 CH (ö) Around a Fine Aggregate Particle . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.8C.8 A Particle of Limestone Fine (A) in the Paste (B) . . . . . . . . . . . . . . . . . . . . . . C.9C.9 CH (A) in the Paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.10

x

LIST OF FIGURES (Continued)

Figure Page

C.10 Paste-Aggregate Interface. A = Aggregate, B = Ettringite, C = CH . . . . . . . . C.10C.11 Paste Microstructure, where A = Pore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.11C.12 Small, Circular Air Voids Uniformly Distributed in the Paste . . . . . . . . . . . . C.11C.13 Paste-Aggregate Interface, where A = Aggregate, B = Paste . . . . . . . . . . . . . C.12C.14 Fly Ash Particles in the Paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.12C.15 Paste Microstructure Showing an Abundance of Unreacted Fly Ash . . . . . . . C.13C.16 CH (A) in the Paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.13C.17 Reacted and Unreacted Fly Ash Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.14C.18 Porous Paste - Aggregate Interface, where A = Aggregate, B = Paste . . . . . . C.15

xi

LIST OF TABLES

Table Page

3.1 Influence of Material Properties of Minus No. 200 Aggregate Fineson Performance Factors of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2

3.2 Parameters to Classify Fines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.64.1 Sand Equivalent Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.14.2 Classification of Particles in Fines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.34.3 Elemental Composition (Percent by Mass) of Aggregate Fines . . . . . . . . . . 4.64.4 Mixture Design for Limestone Fines Concrete . . . . . . . . . . . . . . . . . . . . . . . 4.8C.1 Compositions of Concrete Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.3

1.1

CHAPTER 1

INTRODUCTION

Background Information

A research project focusing on by-product fines was initiated by the Fines Expert Task

Group (FETG) to focus on (a) engineering uses of fines, (b) development of a database on the

use, types and physical properties of fines, (c) marketing of fines, and (d) fines production. This

initiation has been fueled in recent years over concerns regarding the large amount of

accumulated or stockpiled fines being stockpiled in the aggregate mining operations around the

country. Many reports have been compiled indicating the potential for the use of fines in

concrete. There have been demonstrated advantages documented in the literature with regard to

improved workability (rheological properties) and overall quality afforded by high fines portland

cement concrete (PCC) mixtures. However, there have also been documented cases where fines

sands decrease workability of the fresh concrete with an increased water demand and lower

concrete quality as a result.

The initiation of the development of a data base on the use, type, characteristics and

production of fines was summarized in a session on the use of fines at the 5th Annual ICAR

Symposium at the University of Texas at Austin (Saeed et al. 1997). This study’s objectives

were:

• Study the extent and magnitude of fines stockpiling,

• Gain an understanding of the different types of fines and the processes leading to

their production,

• Study the various processes involved in the handling and disposal of fines,

• Explore the current uses of fines,

• Investigate the potential uses of fines, and

• Determine the factors hampering widespread use of these materials.

1.2

This study concluded that very few uses presently exist for the approximately 102 million

tons of minus 75 mm (No. 200) fines produced each year, and aggregate fines from several

different sources continue to accumulate with time. Large amounts of variation may also be

associated with the characteristics of these fines from different sources which may lead to wide

ranges in performance of concrete mixtures containing them. Thus, there appears to be a distinct

need to formulate a process or methodology to identify and characterize those properties of fines

that would be critical to the development of guidelines for incorporation of aggregate fines in

PCC.

Objectives

Although research data regarding the use of aggregate fines in PCC are largely very

encouraging, very few will argue with the fact that a lack of knowledge exists relative to the

definition, nature, and characteristics of different fines, their properties, and effects on PCC. The

focus of this project has been to:

• examine the methods and test procedures used in past research efforts to characterize

the properties of fines, and

• develop, on a preliminary basis, a framework to characterize and catalogue the

properties of fines or propose new ones that would eventually complement a set of

guidelines for the use of fines in PCC. A test-run of this classification process is

provided as a demonstration of its utility to distinguish fines possessing different

properties and characteristics.

Report Organization

The FETG identified two potential uses of fines in portland-cement concrete:

• fines in concrete, and

• fines in flowable fill.

1.3

Research in this project pertains to the use of fines in PCC. A substantial amount of

interesting, often incomplete, data are available on PCC containing fines; however, the use of

fines has been an area of great interest within the industry and has been the topic of several

presentations at recent ICAR Symposium (Fowler and Constantino, 1997; Jackson and Brown,

1996). Some of the current thinking relative to the characterization of fines for use in PCC is

discussed in Chapter 2 of this report in terms of the latest information on cements and concretes

containing aggregate fines. Chapter 3 evaluates the techniques available for characterization of

fines both individually and in concrete. The chapter also describes which ones are most

appropriate for classification purposes. A basis for the development of a fines classification

procedure and how the parameters of such a procedure should relate to the type of use are

discussed in this chapter. Following this discussion a tentative classification framework is

presented. Chapter 4 reports the application of the classification framework in terms of fines

from two different sources in which the feasibility of the proposed classification procedure is

assessed. Chapter 5 suggests potential uses of fines in cement and concrete relative to the

classification framework presented previously, and discusses the feasibility of each use. Chapter

6 focuses on future research areas where efforts must be directed to promote the applications

eventually developed in this project.

The study reported herein represents the initial phase of research in the development of

guidelines for the proportioning of high-fines PCC mixtures relative to high-performance

concrete, structural concrete, and controlled low-strength materials. Although some data from

the various tests that were identified in the classification framework in Chapter 3 are not

available at present, the work to date has succeeded in addressing the need to develop a practical,

reliable, and meaningful classification process for use of quarry fines in concrete.

2.1

CHAPTER 2

LITERATURE REVIEW ON USE OF FINES IN

CEMENT AND CONCRETE

Definition of Fines

Currently aggregate fines are arbitrarily defined as by-product particles generated in any

rock quarry and passing through a 75 :m (No. 200) sieve. Whether this is the most appropriate

definition or whether the term needs to be redefined remains to be established, because most sand

and gravel quarry fines normally retain up to 15% on the No. 200 sieve. This definition sets an

upper limit on particle size, but there are no such restrictions on fineness. Whether a sort of

fineness modulus value or a range of values should be adopted is not established. This is

discussed later in Chapter 4 (Sand Equivalent section). It also needs to be examined whether a

certain percentage of clay content would be an acceptable parameter in the definition of fines,

because some limestone deposits have many argillite seams.

Use of Fines in Concrete

While the use of aggregate fines in concrete represents a relatively new concept, several

research studies have been conducted on some of the effects of these fines on the properties of

concrete. In recent years the incorporation of particle size adjusted-reactive mineral powders to

obtain the closest packing for reactive powder concrete (RPC) has been gaining attention as an

ultra-high strength material.

Fowler and Constantino (1997) recently presented an up-to-date review of research on

different aspects of application of an increased percentage of fines in concrete that have either

been performed in the last couple of decades or are in progress in various locations across the

globe. Research on mineral fines in concrete, has shown that in general, up to 15 percent of fines

can be used in the fine aggregate without causing significant changes in the strength of the

concrete. It is of some significance that most of these research efforts have focused the use of

fines as a replacement for sand in concrete, rather than a replacement of cement.

2.2

One such study was performed in Canada by Malhotra and Carrette, (1985). In their

research, they examined the effects of incorporating limestone dust as a partial replacement of

sand. They used limestone fines at percentages varying from 0 to 20. The limestone dust was

collected from two separate dust collectors (to insure uniform blend) from a limestone quarry in

Montreal, Quebec, Canada. Careful attention was paid to the grading of coarse and fine

aggregate. Chemical analysis of the dust, which they presented in their report in 1985, indicates

that it contains a significant amount of silica (13.5 percent) and alumina (5.2 percent). The low

magnesium oxide ( 1.99% MgO) in their sample is indicative of low dolomite content. Thus, it

can be surmised that the limestone dust they used in their study was a siliceous limestone, which

incidentally, closely resembles the mineralogical composition of one of the fines samples

(Sample No 2) used in the present study. Although water absorption for coarse and fine

aggregates was measured by Malhotra and Carrette [1985], the absorption of the limestone dust

was not reported.

A total of 13 concrete mixtures were prepared. The slump and air content were held

constant using an air entraining admixture and a high-range water reducing admixture (HRWRA)

(so called “superplasticizer”). A normal Canadian Type 10 (equivalent of ASTM Type I)

portland cement was used. The aggregate/cement ratio ranged from 8.9 at W/C = 0.70 to 4.4 at

W/C = 0.40. Similarly, the cement content varied from 217 kg/m3 to 379 kg/m3 as the W/C

decreased. The amount of fine aggregate decreased from 870 kg/m3 to 560 kg/m3, while coarse

aggregate increased from 1070 to 1100 kg/m3 as the W/C decreased.

They found that the substitution of limestone fines affected the strength of the concretes

marginally to significantly. For example, at a W/C = 0.70, the strength at 28 days was

comparable to or higher than that of the non-substituted concrete. For 15 and 20 percent

limestone dust, the strength was 25 to 30 percent higher than that of the control at 7 days. No

significant effect on the strength was observed at W/C = 0.53, and at W/C = 0.40 the strength

was lower at all ages for 10 percent limestone dust. For concretes with 20 percent limestone

dust the strength was either comparable to the reference concrete without any limestone dust in it,

or was higher. The reason for this upsurge in strength at 20 percent replacement remains

unexplained. This is interesting, because it will be shown later that the results in a recent study

2.3

conducted at Texas Transportation Institute some of the compressive strength results follow a

similar trend. Malhotra and Carrette (1985) did, however, suggest that the filler effect of

limestone dust probably plays a role in increasing the strength, especially in concrete with W/C =

0.70. Additionally, the accelerated hydration of cement, and the formation of carboaluminate

may have been contributory factors. They, however, did not perform any experiments to confirm

these speculations.

Malhotra and Carrette (1985) also reported an increase in drying shrinkage due to the

addition of fines, which was attributed either to the formation of calcium carboaluminate or

accelerated early-age hydration of cement resulting in a volume increase of cement hydrate gel.

The drying shrinkage was tested over a period of 217 days according to ASTM C 157 method,

which consisted of exposing the test prisms to air-drying at 230 C and 50 percent RH at the end of

7 days of water curing.

The researchers considered that the increase in plastic shrinkage at 10 percent limestone

dust incorporation level was of little practical consequence. The use of limestone dust did impart

better cohesiveness to the mixture, which can be regarded a definite advantage in a concrete

containing HRWRA or when segregation in placement is a concern. The demand for air-

entraining admixtures to maintain a given air content also depended on the replacement

percentage. Contrary to field experience, the air content increased significantly when the cement

and dust contents increased. At limestone dust content greater than 20 percent, there was

considerable loss in air content as well as slump. The HRWRA demand was primarily a function

of the percentage of dust, and the w/c.

A study was performed in Spain by Ramirez et al. (1990), except that they only used two

different cement contents of 420 and 550 lb/cy, with fines content varying from 5 to 25 percent,

while holding the slump constant. Furthermore, they attempted to monitor the percentage of clay

present in the fines using the sand equivalent test to keep the clay within the range of 0 to 4

percent. As a result of this study, they found that the compressive strengths were not affected by

a replacement of sand with up to 25 percent fines, provided the fines contained 0 percent clay

particles. Texas fines study revealed a direct relationship between the increase in clay content of

the fines and decrease in compressive strength of concrete containing fines. It should be noted

2.4

that the sand equivalent only measures the relative amount of clay-sized (<0.02 mm) particles,

not the actual amount of clay present in the fines. Whereas it is more than likely that clay content

in a sample of fines increases with increasing clay-size particles, it is not universally true.

Ramirez et al. (1990) used methylene blue dye technique to identify and eventually quantify the

amount of clay holds greater potential for this type of investigation.

According to these researchers, the three most important parameters which influence the

mechanical properties of concrete containing fines, are as follows:

• fines content,

• clay content in fines, and

• cement content.

Researchers have demonstrated the possibility of using up to 15 or 20 percent sand as a

mineral filler powder but only limited work has been done to date to develop a sound and

practical procedure for determining the optimum percentage. The importance of minimizing the

clay content when using limestone powder as a constituent of concrete has been described by

others, such as Cochet and Sorrentino (1993). A low value of <1.5 of methylene blue for 100 g

of fine limestone powder has been proposed because the presence of clay leads to an increase in

water demand, and thus reduces the positive effect of limestone filler. The properties of cement,

such as its fineness, C3A and gypsum contents, rather than the cement content is considered more

important for developing a filler type of product.

Nehdi et al. (1996) recently completed another study on filler fines in concrete. They

used limestone fines and silica fume to develop a triple-blended cement. The concentrations of

fines and silica fume were varied while everything else was kept constant. The results show that

a triple-blend with 10 percent limestone fines and 10 percent silica fume was able to achieve

higher compressive strength than normal concrete at 12 hours. The 28-day strength obtained

using ordinary portland cement was outperformed when a total of 20 percent fine powder by

mass of cement compressing a combination of 10 percent limestone filler and 10 percent silica

fume was used, yet at the same time, the concrete was more cost effective. In tracing the strength

2.5

development pattern of these concretes, they noted that the highest strength was obtained in

concrete containing 6 to 10 percent limestone fines. At 3 days, the filler had limited effect on the

strength of concrete with silica fume content less than 5 percent. For higher silica fume contents,

the strength decreased as the limestone filler proportion increased. At 7 days, the silica fume

appeared to play a dominant role, and the strength increased with increasing silica fume,

regardless of limestone filler content. At this age, the limestone filler did not have any effect on

the strength. The 28 days compressive strength increased with increasing silica fume and

decreased with higher limestone filler content. This study is of some significance to the

development of high-performance concrete using aggregate fines to compensate for the deficit in

fine particles in the particle size distribution curve.

Since the silica fume particles were finer than either the cement or limestone filler, silica

fume was expected to influence the very early strength gain. The results, however, indicated that

the limestone filler has a greater effect, which the authors attributed to possible accelerated early

hydration of alite (C3S) in the presence of CaCO3 as the particles became finer and increased in

amount. It has also been suggested that in the presence of carbonates and sulfates, both

sulfoaluminate and carboaluminate form, the latter providing a better bonding. Whether the

higher strength limestone concrete is due to a nucleation mechanism, a chemical accelerating

effect, to the formation of carboaluminates, or due to other effects were not investigated. The

authors suggested that this aspect needs further investigation.

At this stage it is difficult to explain why concrete containing limestone filler at certain

percentages and a particular W/C achieves higher strength, a complete understanding of the

mechanism governing this strength enhancement process is desirable. It is in this light that in the

final chapter of this report (Chapter 6) we prioritized the mechanism of filler action as the

desirable course for further research.

Nehdi et al. (1996) also carried out a cost analysis as a function of compressive strength

of concrete. Their figures were based on the Canadian prices of cement, HRWRA, silica fume,

and limestone dust. They proposed the following equation to estimate the cost effectiveness.

CEFi = f’‘ci /C x100 (1)

2.6

where CEFi is the cost effectiveness factor at age i [MPa/$ x 100]

f’‘ci is the compressive strength of concrete at age i, and

C is the cost of 1 m3 of concrete

Their calculation showed that the cost effectiveness factor for a triple-blended binder, such as

limestone dust-silica fume-cement, may be higher than the traditional silica fume-cement blend,

both at the early and late ages. Although it remains to be ascertained whether this statistical

approach is a valid function, it does provide future researchers a basis for more accurate cost

analysis, perhaps taking transportation and power costs into consideration.

Use of Limestone Fines in Cement

Addition of limestone fines is currently being used in cements throughout the world. The

American cement industry is in the ASTM process of trying to obtain a revision of ASTM C 150

to permit incorporation of 5 percent interground limestone. This comes from a need to reduce

CO2 emissions to conserve energy, and a desire to use the more efficient air separators that have

been developed in the last decade. These permit making a more closely sized product without

over-grinding the clinker. The limestone would replace the finer cement particles.

Researchers have been studying the effects of interground and blended limestone on the

particle size distribution of cement and workability of mortar and concrete. Hydration behavior,

in addition to the engineering and durability-related properties, and interaction with mineral and

chemical admixtures of limestone-portland cement are being tested in various laboratories

around the world. Quality control aspects of limestone-portland cement and concrete have also

been emphasized by various researchers to meet the specification requirements.

It has been concluded that addition of up to 5 percent limestone does not affect the

performance of portland cement. The Canadian cement standard (CSA, 1993) has permitted the

use of up to 5 percent limestone in portland cement since early 1980's. The European

prestandard - ENV 197-1 (CEN, 1992) allows for some cements to contain up to 21-35 percent

ground limestone (CEM II/A-L and CEM II/B-L type of portland cements respectively). Already

more than 25 countries allow the use of between 1 to 5 percent limestone addition in the portland

2.7

cement (Cembureau, 1991). Many countries even allow up to 35 percent limestone filler in their

portland cement. The United Kingdom, Italy, Australia, and New Zealand have modified their

standards by permitting limestone addition in portland cement.

The loss in strength due to interground additives, which participate to a small extent in

the hydration, is due partly to dilution and partly to concentration of the clinker in the coarser

particle fraction, as stated by Schiller and Ellerbrock (1992). This loss in strength, however, can

be compensated by narrowing the particle size distribution of the clinker fraction (the result of

intergrinding with a more easily grindable material such as limestone), or by overall finer grading

of the cement. Moir (1995) pointed out that with high efficiency separators in modern milling

systems, the particle size distributions may be too steep to increase bleeding and may delay the

initial setting. Limestone inclusion up to 5 percent broadens the particle size grading, thus

offsets such disadvantages. Schiller and Ellerbrock (1992) noted that to produce cement having a

28-day strength of 7,500 psi (50 MPa), 10 percent and 20 percent limestone cement would reduce

the position parameter from 30 :m and 14 :m respectively. Schmidt (1992) reported that since

strength of concrete is not reduced by 5 to 10 percent addition of limestone, additional grinding

may not be necessary.

Whether limestone is incorporated by blending or by intergrinding, it is vital to arrive at

an appropriate level of fineness to achieve a minimum water demand. Intergrinding clinker and

dry blending produce somewhat different particle size distributions. According to Sprung and

Siebel (1991) separate grinding generally led to very wide particle size distribution. Menetrier-

Sorrentino (1988) showed that separate grinding of constituents of portland-limestone cement

offers greater opportunity for optimization of the particle size distribution of the individual

materials.

Sprung and Siebel (1991) pointed out that particle size distribution has a considerable

influence on the water demand of cement; a narrower particle size distribution results in higher

water demand, while wider particle size distribution leads to a reduced water demand. Since the

easily ground limestone usually has a wide particle size distribution that allows the limestone

particle to fill the gaps between the clinker particles, it reduces the water demand and densifies

the structure of the hardened cement paste. They demonstrated that the densifying effect can lead

2.8

to increased strength when the limestone content is less than 10 percent. The water demand was

related to the clay content of limestone (measured by methylene blue value); the higher the value,

the higher was the water demand.

Schiller and Ellerbrock (1992) reported that addition of limestone up to 10 percent, with

either a narrow or a broad particle size distribution, decreased water demand of the cement. They

also found that even when portland limestone cement had to be ground finer in order to achieve

the same strength as portland cement made from the same clinker, the water demand was lower

because of the improved particle size distribution. Schimdt (1992) suggested that the beneficial

effect of limestone addition on concrete rheology can be related to improvement in particle size

distribution. The fine particles displace some of the water from the voids between the coarser

particles, making it available as an additional internal lubricant. Thus, the concrete is less stiff

and water retention is improved. In other words, less water is needed to make a workable mix,

and reduced water content may increase the strength. Schmidt et al. (1993) noted that limestone-

portland cement containing 13-17 percent limestone required about 10 L/m3 less water, so as to

reduce the W/C from 0.60 to 0.57 and increase the strength by as much as 120 psi (8 MPa).

Tezuka et al. (1992) demonstrated that the workability of mortars of different cement

contents improved with the addition of limestone even at 5 percent level. Brookbanks (1993)

illustrated the advantages of optimizing the particle size grading of limestone. He stated that

replacing 5 percent of cement with limestone dust or dried silt from a gravel aggregate increased

the required W/C of concrete by an average of 0.01 and 0.22 respectively, over that required.

Finely ground limestone has long been used in masonry cements to improve the retention

of water in the mortar. Albeck and Sutej (1991) reported that by intergrinding 18 percent

limestone (CaCO3 content of 90.8 percent) with clinker they were able to produce portland

limestone cement which exhibited less bleeding, and the bleeding stopped sooner than that of the

parent cement. Moir (1995) reported that the effect of limestone at low concentrations is purely

physical related to cement surface area, particle packing, and surface forces.

Ingram et al. (1990) found that during the course of the reaction between gypsum (2

percent), limestone (6 percent), and clinker (92 percent), ettringite formation proceeds normally.

In a similar type of experiment, this time Type II cement being used, Klemm and Adam (1990)

2.9

found that crystalline carboaluminate hydrate is slower to form than ettringite and after 129 days

of hydration, 80-90 percent of the limestone or calcium carbonate remains unreacted. They

concluded that with Type II, limestone additions act primarily as an inert diluent. Barker and

Cory (1990) found monocarboaluminate forming in preference to monosulfate. They reported

that for cements with higher C3A contents the amount of monocarbonate increases at all ages

with increasing level of limestone addition.

Bensted (1980) examined the possibility of substituting limestone for some or all of the

gypsum used to control the early hydration of C3A. He concluded that because of differences in

their stereochemistry, sulfate ions enter more readily than carbonate ions into solid solution.

Kantro (1978) found that limestone at 5000 cm2/g Blaine has some effect on the setting of

cement, but is less effective than gypsum in controlling flash set. Campiteli and Florindo (1990)

found that optimum SO3 increases with increasing fineness and decreases with increasing

limestone content, but neither relationship is linear.

Sprung and Siebel (1991) stated that the calcite from limestone participates only to a

small extent, if at all, in the hydration reaction, mainly on the surface of the limestone particles.

Sometimes physical effects may play a significant role, such as the provision of nucleation sites

for the hydration products. Further, Livesey (1993) reported that the addition of 5 percent

limestone resulted in acceleration of the early hydraulic activity of the clinker. Soroka and Setter

(1977) and Ramachandran and Zhang (1988) also obtained similar results.

The effect of limestone additions will have on the calculated Bogue compositions

depends on the oxide composition of the limestone itself. Addition of 5 percent limestone on a

typical portland cement raises the apparent (Bogue calculated) amounts of C3S and C3A, which

reduces the apparent C2S content (Gebhardt, 1995).

Hooton (1990) determined the 7 days values for heat of hydration according to ASTM C

186 for ASTM and CSA from the same clinker and found that there was no consistent effect of

limestone on heat of hydration. Barker and Matthew (1993) examined the peak rate of heat

evolution for limestone cements prepared differently. Those prepared by blending showed either

no effect or some retardation, while those prepared by intergrinding showed an acceleration of

peak heat evolution. And the cement prepared with a limestone having high clay content

retarded the peak heat evolution. In general, the total heat evolved is reduced by the presence of

2.10

limestone. Livesey (1991a) reported that increasing limestone content reduced both the rate and

total amount of heat released. The introduction of limestone retarded the maximum heat

evolution where cements were of a similar fineness to that of parent cement, but they accelerated

heat evolution where the limestone cements had greater fineness.

Sellevold et al. (1982) who studied the effect of silica fume on the hydration and pore

structure of cement paste containing CaCO3 reported a finer structures and somewhat reduced

total pore volume in the latter. Barker and Cory (1991) observed 25 percent limestone addition

enhanced the formation of hydration rims of calcium silicate hydrate surrounding C3S particles as

they increased the rate of hydration of C3S. Increasing levels of limestone addition increased the

formation of ettringite at early ages.

Hooton (1990) observed no clear trend for the effect of limestone addition on setting

times. Similarly, in a series of tests conducted by Hawkins (1986), addition of limestone appears

to have little effect on the setting time for limestone where ground to more or less constant

Blaine fineness. Whereas, in the second series of experiments where limestone was ground to

<325 mesh value (and was kept more or less constant), limestone addition indicated a reduction

in setting time. Bobrowski et al. (1977) pointed out that the false set is reduced considerably

when limestone is used as a partial substitution for gypsum, but setting time is not markedly

affected.

Albeck and Sutej (1991) showed that strength development for commercial portland

cement and portland limestone cement, which are made from the same clinker to the same Blaine

fineness of about 400 m2/kg over the period of 5 months were quite similar. Hawkins’ (1986)

test results showed that with increasing fineness, limestone-cements give comparable strengths.

Bedard and Bergeron’s study (1990) on the effect of carbonate additions on the strength of heat

cured concrete also showed similar strength development for both concretes, that is, with and

without additional limestone. Sprung and Siebel (1991) and Schimdt (1992a) concluded that

dilution effect is seen at higher dosage of limestone and may lower the strength of cement and

concrete. However finer grinding, which reduce the water/cement ratio because of improved

particle packing, will compensate the dilution effect.

Adams and Race (1990) demonstrated a slight increase in drying shrinkage for Type I and

Type II limestone-blended cements. Detwiler (1996) observed that drying shrinkage is not

2.11

affected by the addition of limestone for the control concrete with or without addition of a Class

C fly ash. Similar mixed results were obtained for the rate of carbonation in portland limestone

cement; increase in some cases, decrease in others, and similar for the rest, compared to the

control portland cement mortar.

Permeability is the key to durability of a porous material. Deterioration mechanisms

involve the ingress of water and/or other harmful species (oxygen, carbon dioxide, chlorine,

sulfate ions, acids etc.). Pore size is less important than the connectivity of the pore system.

Moir and Kelham (1993) reported that permeability to oxygen for a series of concrete made with

cements with or without 5 percent or 25 percent limestone slightly reduced due to the presence of

limestone. Further, extended curing reduced the permeability significantly.

However, porosity and water sorptivity were similar for both the control and limestone cements.

Sprung and Siebel (1991) found that in general concretes made with portland limestone

cement showed reduced resistance to frost damage as compared to those made with portland

cement, even when the strengths were the same. However, they concluded that it is possible to

make concretes from limestone-portland cement that are as frost resistant, provided the limestone

meets the criteria for composition limits specified by ENV 197-1. Clay content is probably the

most important criterion for limestone quality related to frost resistance. In another instance,

Siebel and Sprung (1991) reported that not all limestones are suitable for portland limestone

cement. Concrete with water/cement ratio less than 0.60 are adequately frost resistant except for

the cement having 11 percent limestone. Schmidt (1992) demonstrated that the concrete

specimen made from portland cement (13 to 17 percent limestone) performed as well as or

slightly better than those made from portland cement. Baron (1988) suggested that 15 percent

limestone cement requires smaller air void spacing factor than portland cements in order to

provide good frost resistance.

Soroka and Stern (1976) illustrated the beneficial effect of CaCO3 on sulfate resistance of

portland cement mortars. Though there was no substantial increase in 28-day compressive

strength, time to cracking for mortar prism exposed to 5 percent NaSO4 increased from 6 to 14

weeks after 30 percent CaCO3 inclusion in the portland cement. Soroka and Setter (1980)

concluded that the use of limestone improves the sulfate resistance of mortars, but not to such an

2.12

extent as to produce sulfate resistant mortar. Hooton (1990), however, saw no clear trend

regarding the effect of carbonate addition on sulfate resistance. He rather concluded that sulfate

resistance is not affected by carbonate additions but is primarily determined by C3A content. A

similar trend was obtained by Matthews for his study (1993).

Ramachandran et al. (1990) monitored length and modulus of elasticity of mortar

specimens containing precipitated CaCO3 which were hydrated in lime water or in laboratory

prepared “seawater” (2.7% NaCl, 0.32% MgCl2, 0.22% MgSO4, and 0.13% CaSO4). Exposure to

seawater generally lowered the moduli, with more reduction in the higher water/cement ratio

mortars. Feldman et al. (1992) examined limestone portland cement mortars exposed to NaCl

and MgCl2 solution, concluded that the moduli are reduced and expansions increased compared

to controls exposed to Ca(OH)2 solution. Deja et al. (1991) reported that chloride exposure is

equally deleterious to the strength of mortars with or without limestone. However, they noted that

limestone is effective in protecting the steel from corrosion. Baron and Douvre (1987)

recommended 10 percent limit of limestone content for marine exposure; at higher limestone

content strength may be severely affected.

Hobbs (1983) reported on the affects of 5 percent limestone addition on expansion due to

alkali-silica reactivity of 25×25×250 mortar bars made from Thames Valley sand and a Beltane

opal rock having particle 150 - 300 :m in size. He concluded that 5 percent limestone addition

to cement did not increase the susceptibility of mortars to ASR. Research by Detwiler (1996),

and Nehdi et al. (1996), suggests that the performance of mineral admixtures is unaffected by

limestone addition to cement. However, for blended cements, it may be possible to optimize the

strength for different ages by blending different amounts of limestone addition and mineral

admixtures.

Sprung and Siebel (1991) pointed out that natural limestones contain clay minerals,

which above a certain proportion cause increase in water demand and significantly reduce the

frost resistance of concretes. European prestandard, ENV 197, specifies limits on the

composition of the limestone:

2.13

CaCO3 content $ 75% by mass

Clay content (prEN 933-12) # 1.20 g/100g

Total organic carbon # 0.20 % by mass

Spring and Siebel (1991) recommended that ENV 197 criteria for limestone composition are

suitable for frost resistance of concrete. The methylene blue test has been seen to be an effective

means of detecting deleterious quantities of clay in limestone. Yellepeddi et al. (1993)

considered X-ray fluorescence to be less than adequate to determine the limestone content of

cement because it does not directly measure the phase such as CaCO3. The better method they

proposed is quantitative X-ray diffraction which analyzes the CaCO3 content directly.

An in-depth study of fines was performed in France [Cochet and Sorrentino, 1993], where

use of 10 percent limestone filler as partial replacement for cement is permitted on a national

level. Assuming that a normal concrete mixture contains around 350 kg/m3 cement as opposed

to 700 kg/m3 of fine aggregate, an arbitrary replacement figure of 10 percent would be

represented as 35 kg/m3 in the case of cement and 70 kg/m3 in the case of sand. Because of the

greater quantities involved, it may more profitable to the aggregate industry to replace sand than

cement by a mineral filler, but the underlying advantages of replacing cement by mineral filler

were underscored by Cochet and Sorrentino (1993).

Research conducted in the Ciments Lafarge laboratory in France (Cochet and Sorrentino,

1993) found that strengths of concretes containing limestone fines-filled cement are comparable

to the strengths of concrete without fines replacement. As a matter of fact, concretes containing

these fines behave much the same as normal concretes with respect to freeze-thaw and seawater

resistance, and chloride diffusion properties. They observed that some of the important factors

which influence the rheological behavior of limestone-filled cement include the quality of the

filler and its fineness. If the quality of limestone rock is good, rheology of the mortar or concrete

remains unaffected. On the other hand, the presence of clay in limestone increases the water

demand, thus negating the beneficial effect of limestone filler. The fine particles of fillers have a

favorable action; in the case of finely ground fillers, the water-reducing action is greater for W/C

<0.40, though the effect may be opposite if clay is present.

2.14

According to Cochet and Sorrentino (1993), the strength gain achieved by using

limestone filler comes from (a) the water-reducing effect of filler, (b) better use of hydraulic

potential of clinker, and (c) optimization of quality of clinker at a given strength class.

Furthermore, the optimum amount of filler in a concrete mixture depends on the maximum size

of aggregate, grading of aggregate, mineralogical composition, and particle shape. Cochet and

Sorrentino claim that the percentage of limestone filler to be added depends on the clinker itself.

For example, to achieve a strength of 45 MPa at 28 days, the filler content varies from 22 to 32

percent, though the exact amount to be added depends on the intrinsic properties of each clinker.

The researchers specified that a higher fineness of filler cement is required to achieve the same

strength at 28 days.

Since the principal objective of producing filler cement is to make concrete, Cochet and

Sorrentino (1993) attempted to develop a model to determine the optimum amount of filler

requirement. In their analytical method, for example, the activity index (Ai) is defined as the

ratio of strength of filler cement to that of plain cement. From the activity index they defined an

activity factor K, where K = 2.12 x Ai - 1.42 for fly ash, and K = 2.60 x Ai - 1.74 for filler.

From this coefficient one can determine the optimum quantity of filler for a given strength.

An important outcome of Cochet and Sorrentino’s study (1993) was that they were able to

demonstrate the importance of carboaluminate formation when normal hydration of cement is

modified in the presence of limestone powder in a cementitious system.

In Japan, cement produced by substituting a large quantity of particle-size adjusted

limestone powder for portland cement is already used for high-fluidity concrete (Uchikawa and

Okamura, 1993). The beneficial properties of this type of concrete are amply demonstrated by

Uchikawa and Okamura (1993). In another recent study on replacement of fine aggregate by

mineral powders, Uchikawa et al. (1996) took a slightly different approach to evaluate these

concretes. Their results show that the hydration reaction, hydration products, and the

microstructure of the hardened concrete prepared by substituting mineral powders for part of fine

aggregate, are not substantially different from those of concretes prepared by using slag or fly

ash. They claim that in all these concretes, densification of the hardened structure by the filling

action of mineral powder or mineral admixture is the primary reason for its enhanced properties.

2.15

The mineral powder, which is uniformly distributed in the paste, succeeds in filling up the pores,

prevents the materials from separating, reduces the size of hydration products, and restricts the

growth of Ca(OH)2. Another French study (Regourd, 1976) focused on the particle size

distribution and the chemical makeup of concretes when limestone fines are used as a

replacement of cement. She reported that the substitution of fines serves to fill the gaps in the

finer portion of the particle size distribution curve. This, in turn, improves workability,

shrinkage, density, and strength of the concrete. It was observed that if the fines are calcareous in

composition, the bond formation between the cement paste and the aggregate is enhanced,

possibly due to calcium carboaluminate crystallization.

Jackson and Brown (1996) in comparing natural sand versus manufactured sand, drew

similar conclusions. They found that in most applications, use of a higher amount of fines in

manufactured sand helps to improve workability, increase density, reduce w/c, and therefore

achieve higher strength. Their experience, however, demonstrated that if the fines content

exceeds 10 - 12 percent, plastic shrinkage is likely to occur; if the bleeding rate is lower than the

evaporation rate, then this is quite possible. Furthermore, Jackson and Brown (1996) assert the

importance of differentiating between fines representing the dust of fracture and naturally

occurring fines which typically contain a high amount of clay. They attribute the beneficial

properties of fines in concrete to its filler action, that is, fines help to reduce the voids

and lubricate the coarse aggregate particles without the need for additional water. According to

them, use of fines in concrete can result in a more economical and superior performing concrete

mixture.

Implications of the Literature Review

It is clear from the literature review that a consensus has not yet been reached on the use

of aggregate fines in cement and concrete. The wide range of research approaches adopted by

different research groups to the applications of aggregate fines in the construction sector, and the

broad scatter in results ensuing from these studies suggests that the prospect of using aggregate

fines in concrete on a commercial scale needs further research particularly with respect to their

effect on concrete workability and finishability.

2.16

French researchers advocate the use of limestone fines as a partial replacement of

portland cement (Cochet and Sorrentino, 1993). They have presented research data to support

this type of application. Actually, the implementation of this concept has been quite successful

to date, and a number of European countries now market fines-filled portland cement (Ramirez et

al., 1990). Proposals are also under way to incorporate fines-filled cement as a part of the

European cement standards. Incorporation of up to 5 percent limestone fines in portland cement

is under consideration by ASTM C 150. Although the Japanese have been using aggregate fines

in a number of their cements, they have focused attention on developing ternary and quaternary

component blended cements in which aggregate fines forms an essential component, while

portland cement and other fine materials such as silica fume, slag, or fly ash represent the other

constituents (Uchikawa et al., 1996). Researchers in Canada have studied the possibility of

replacing sand with quarry fines in concrete (Malhotra and Carrette, 1993). One group has

demonstrated that the use of fines in conjunction with silica fume may be the most cost-effective

way of producing high-performance concrete (Nehdi et al., 1996).

In addition to the segmented nature of research on fines, none of the researchers have

addressed the critical need to establish a proper characterization protocol for aggregate fines,

which in several respects is just as essential as the tests on aggregates such as particle size

distribution according to ASTM C 33, water absorption, etc., that are performed before an

aggregate can be approved for use in concrete. Besides, it is clear that quarry fines represents an

untested class of material for use in concrete, and therefore, a much fuller understanding of its

behavior is required for it to be universally accepted by the concrete industry as a viable material

with potential for either cost reduction or improved performance of concrete, or both.

Ahn and Phelan (2001) carried out a research study to determine guidelines for

proportioning concrete with higher levels of crushed fines. Specially, the objectives were to:

• Develop a classification of crushed fines based on their suitability for use,

• Develop guidelines for mix proportioning of concrete higher fines contents,

• Determine the effect of higher amounts for several types of crusher fines on concrete

including fresh and hardened properties,

• Develop modifications to existing construction specifications.

2.17

Based on test results, the authors concluded that microfines with high quantities of quartz usually

had low absorption; however, a low quantity of quartz did not always result in high absorption

capacity, tip speed, significantly affected the aggregate particle shape and amount of micro fines

produced. Most samples had 5 ro 20% micro fines content. The percentage of micro fines

definitely increased with increased crushing speed. The gradations of most MFA used in their

study did not meet the ASTM C33 specification. ASTM C1252 is not an adequate test to

differentiate particle shape and texture of MFA. The particle size distribution showed that the

highest volume was for the particle size range from 56 to 73:m.

Summary of State of the Practice

After having discussed at some length, the previous results on the use of fines in concrete,

it emerges that different researchers have opted to choose their own parameters for

characterization purposes, depending on the focus of their study. For example, Malhotra and

Carrette (1985) selected a broad range of w/c’s and concrete mixtures with and without

HRWRA, using only one set of fines to conduct tests for compressive and flexural strengths,

freezing and thawing resistance, and drying shrinkage. Thus, their area of interest was on

establishing a correlation between mechanical strength and durability of filler-concrete. Ramirez

et al. (1990) called attention to the significance of clay when using quarry fines in concrete. They

concluded that the three parameters that influence the mechanical properties of concrete

containing limestone fines most are fines content, clay content, and cement content. Their use of

the sand equivalence test to estimate the clay content in a filler, however, may not be valid. The

methylene blue dye technique appears to hold greater potential of identifying clay in a mineral

filler. Nehdi et al. (1996) added a third component, silica fume to work on limestone filler

concrete. Their study yielded the highest strengths so far. Nonetheless, the only products they

tested were low W/C concretes with the objective to market the most viable option available in

the field of high-performance concrete. Their mathematical equation indicates higher cost

effectiveness for limestone-silica fume cement concrete than HPC containing only silica fume.

An interesting aspect of all these studies on the use of fines in concrete has been the fact

that while one school of researchers considers replacement of fine aggregate by fine filler to be

the practical method, the other school has focused its attention on limestone-filled cement to

2.18

produce concrete. On viewing this concept from a broader perspective, it denotes the

development of a more energy-efficient product, which causes less emission of greenhouse gases

into the atmosphere, yet succeeds in maintaining the fundamental characteristics of hydraulic

cement. The lead in this domain of research has long been taken by a group of French

researchers who have not only carried out advanced work on the more fundamental aspects but

have successfully transferred their laboratory research to industrial applications; the French and

several other European specifications now allow the addition of up to 18 percent filler materials

in their cements.

Though the volume of research on the use of fines in concrete by no means has been

insignificant so far, the segmental nature of research intensifies the need for a unified system for

characterization of fines and a characterization-based classification framework, such that a

particular application of fines from a specific source can be predicted from this framework. An

attempt has been made in the proceeding two chapters to set up this much-needed classification

framework. The functionality of this framework is also demonstrated through examples of two

fines from different sources.

3.1

CHAPTER 3

DEVELOPMENT OF CLASSIFICATION

FRAMEWORK METHODOLOGY

Approach to Classification of Fines Protocol

It is hypothesized that variation in size and mineral constituents may be associated with

the properties of fines from different sources. These, in turn, can be expected to lead to

differences in the performance of concretes containing higher amounts of fines. Therefore,

classification of aggregate fines relative to usage in concrete will need to be structured on the

basis of the relationship between the materials properties of the aggregate fines and the factors

which affect the performance of concrete both in its fresh and hardened states.

The factors governing the performance characteristics of concrete can be divided into the

following categories:

C Workability of fresh concrete

C Strength - hardened concrete

C Durability - hardened concrete

A concrete in which workability can be controlled may not necessarily achieve a high

strength. A high-strength concrete is not always workable or the most durable concrete. A

concrete in which all three factors are optimized would be desirable. This optimization becomes

critical when higher than normal amounts of aggregate fines is to be used in concrete.

The material properties of any constituent of concrete influences the performance of

concrete. The important properties that need to be examined when considering the use of

additional aggregate fines in concrete, are:

C Surface area

C Absorption

C Clay content

3.2

Material Properties Performance Factor

Surface area Strength/workability

Water absorption Workability

Clay content Workability, durability, strength

Particle size distribution Workability

Particle shape Workability

Chemical composition (high alkali sulfate andother soluble salts)

Durability

Mineralogy (stability, reactivity, crystal shapeeffects)

Durability

Table 3.1 Influence of Material Properties of Minus No. 200 Aggregate Fineson Performance Factors of Concrete.

C Particle size distribution

C Shape of particles

C Chemical composition and/or

C Mineralogy

The influence of material properties of aggregate fines on the performance of concrete are

tabulated below in Table 3.1. Complex interrelationships may develop when additional

aggregate fines are incorporated in a concrete composed of variable amounts of cement, coarse

aggregate and fine aggregates, admixtures, air entraining admixture and water.

For example, when surface area increases, water demand increases and unless

adjustments are made, workability is reduced; if adjustment to water is made but no water-

reducing admixture is used, strength is reduced. When absorption increases, additional water is

needed but it does not affect either workability or strength if the amount is correctly determined

3.3

Figure 3.1 Schematic of Proposed Classification Framework.Note: HPC-High Performance Concrete; SC-Structural Concrete;

CLSM-Controlled Low Strength Material.

and is hence only the amount needed to satisfy the aggregate absorption capacity. However, the

rate that is absorbed may be an issue. Clay mineral content is an example of a material that if

present in fines will increase surface area due to fineness and flat plate-like crystals.

Proposed Classification Framework

An overview of the classification framework which is proposed for use in describing

aggregate fines is presented in Figure 3.1 in a schematic form.

In this framework, following the identification of a source of fines, screening tests are

proposed. The practicality of these test are discussed in the proceeding section. For example, if

fines from a particular

source exceed an

arbitrary value then

their applicability for

use in either

structural, paving or

high performance

concrete is

established. Some

additional factors may

need to be considered

to determine the

optimum amount that

can be used. Fines

which fall short of

this arbitrary value would be subjected to further tests for their application to some other cement-

based material. Tests conducted on the fines themselves are referred to as level 1 tests (Tests of

Fines). Tests pertaining to concrete mixtures containing high-fines contents are referred to as

Level 2 tests (Tests of Concrete). Specific applications can be most effectively evaluated through

actual tests on concrete incorporating fines material as is demonstrated later in Chapter 4. Based

3.4

on the test results at these levels, the most likely application, (high performance concrete (HPC),

structural concrete (SC) or controlled low strength materials (CLSM)), may be proposed.

Although amounts of fines are only preliminarily suggested, in the case of structural concrete

(SC), the optimum amount that can be incorporated in concrete would probably not exceed 20

percent as percent of the sand. The amount for HPC may be 10 percent or less, and the amount

for CLSM could be 50 percent or more of the fine aggregate depending upon the effect on the

placing and engineering properties of the CLSM mixture.

It must be noted that the classification framework of aggregate fines proposed in this

research study is intended to be applicable when the material is batched into the concrete as a

separate ingredient or incorporated in the fine aggregate. Use of fines as a portion of the

cementitious materials will be considered in later phases of research, an outline of such research

is presented in Chapter 6.

Proposed Testing Protocol

The classification framework lays the groundwork for consideration of the importance of

different testing and analytical methods that have been used to determine how aggregates fines

may qualify for use in a specific type of concrete such as HPC, SC, or CLSM.

The types of tests that were considered most practical for a framework that is capable of

accommodating a wide range of variations in materials properties are:

C Physical characterization

C Chemical characterization

C Mineralogical characterization

Figure 3.2 shows potential tests in these categories and outlines the relationship between

the material properties of aggregate fines and performance factors of concrete. Table 3.2 outlines

the performance factors described in the following paragraphs and suggests proposed criteria as

to the types of concrete that are suitable for the given quality of fines indicated from the test

results. These suggested criteria limits require further verification to determine their

3.5

appropriateness for the noted applications and must only be considered to be preliminary at this

stage.

Screening Tests

The screening tests intended to be guide tests for fines or fine aggregate containing the

fines are organized into physical, chemical, and mineralogical categories. For the time being,

only one test procedure was identified for screening purposes which fit under the physical

category. The other categories are provided in anticipation that other screening tests may

eventually be found to make the screening procedure more effective. Currently, there are no test

procedures that can be suggested as screening tests in the chemical or mineralogical areas. It

should also be noted that although specific gravity is not shown in Figure 3.2 it is listed in Table

3.2 for possible consideration in the classification protocol.

Figure 3.2 Details of the Different Levels of Proposed Testing.

3.6

Level/Type

Test Unit of measure Performance Factors SuggestedCriteria

Screening/Physical

Sand equivalent Percent (for fines only). Toestimate clay size particles inquarry fines.

Clay particles adversely affect strength >90 - HPC>70 - SC<70 - CLSM

1/Physical Absorptioncapacity

Percent by dry weight Affect on water demand andworkability

Low - HPC; Med - SC;High - CLSM

1/Physical Specific gravity Absolute To determine if very heavy mineralsare present in fines

Normal - HPC, SCOthers - CLSM

1/Physical Particle sizedistribution

Shape of the % retained atindividual sizes

Affect on particle packing; strengthdevelopment

Well - HPC, SCGap - CLSM

1/Chemical Oxide analysis Percent of element or oxide To determine presence of potentiallyexpansive compounds (i.e. alkalies,metals, sulfate, etc.)

None - HPC, SCOthers - CLSM

1/Mineral-ogical

XRD Qualitative To identify deleterious mineralspresent in fines

None - HPC, SCn/a -CLSM

1/Mineral-ogical

Petrography Qualitative To determine potentially reactive ornon-reactive minerals, shape factor,and aspect ratio of particles

None - HPC; Some -SC; Others - CLSM

2/Physical Rheology Slump High water content may reducestrength (without use of SP’s).

1-6" - HPC; 3-6" - SC>6" - CLSM

2/Physical Porosity Volume of intruded mercury High porosity may cause highshrinkage and low strength

Low - HPC; Med - SCHigh - CLSM

2/Durability ASR, ACR Amount of expansion (%) Expansions over 0.2% will causeundesirable cracking

<0.04% - HPC; <0.10%- SC; <1.00% - CLSM

2/Durability ChemicalResistence

Permeability of hardened cementpaste -m/s

High permeability yields lower strength <10-18 - HPC; <10-13-SC; >10-10 - CLSM

2/Durability Freeze/thaw Loss of stiffness Level of durability factor >90 - HPC; >70 - SC<70 - CLSM

2/Durability Cl ion penetration Resistence to penetration -coulombs

Corrosion of reinforcing at lowresistences

<1000 C - HPC; <6000 C - SD; >6000 C CLSM

2/Mechanical Strength Structural strength (psi or MPa) High strengths tie to lowerpermeability and better durability

>12,000 psi - HPC> 3,000 psi - SC< 3,000 psi - CLSM

2/Mechanical Shrinkage Volumetric shrinkage Amount of shrinkage to cause cracking < 600 :, - HPC;

<800:,-SC; >1000:,CLSM

Table 3.2 Parameters to Classify Fines.

3.7

Figure 3.3 Sand Equivalent Results of Fines No. 1 and No.2, and Sand with 10% Fines No. 1 and 2.

Physical Characterization

Among the several physical attributes of fine aggregate which can influence the

performance of concrete, the sand equivalent, particle size distribution, density, and water

absorption are possibly the most important in terms of concrete’s behavior in the fresh state. The

sand equivalent (SE) test which is intended to serve as a rapid test to measure the relative amount

of clay-size in graded aggregates, was used as the screening test in the proposed classification

system for aggregate fines. As the name implies, this test is applicable when blending of fine

aggregate with appropriate mineral fines is being considered. It is possible that another entirely

different screening test, such as the acid insoluble residue test (a test for CaCO3 in dust of

fracture), may have to be introduced for use of fines as cementitious materials.

That the sand

equivalent of fines can vary

from one source to another is

illustrated in Figure 3.3. It is

postulated that if the sand

equivalent test for a sample of

fines yields a value higher

than the California limit of

70%, then it can be considered

a candidate for use in normal

or structural concrete. On the

other hand, a low sand

equivalent value (say less than

60) would tend to direct its

use towards other applications

where specifications for

water-cementitious materials ratio, and/or strength, are less demanding, such as, in low strength

concrete or controlled low strength material (CLSM) as noted in Table 3.2.

3.8

The sand equivalent test was chosen as an example of screening criterion is because the

test is rapid and simple to perform. Additionally, it is one of the least expensive tests in the

entire series and does not require expensive equipment.

Level 1 Tests (Tests of Minus No. 200 Fines)

Similar to the screening tests, Level 1 tests are organized into three categories of physical,

chemical, and mineralogical types of tests. Further research will be needed for specific test

procedures to use for Level 1.

Physical Characterization

Particle Size Distribution

Particle size distribution when measured by laser, X-ray beam method or -200 wash tests,

may acquire some significance when it is correlated to the porosity of the hydrated cement paste.

Proper grading of cement as well as fine aggregate are important for filling voids in the paste. In

this respect, change in the particle size distribution that occurs as a result of using fines either as

fine aggregate or cementitious material can have a detrimental effect or it can be beneficial.

Therefore, this test is important for understanding the filler mechanism of fines in concrete. This

test has been assigned at a Level 1 within the framework of the testing protocol. .

Absorption Capacity

Since water demand is a function of the specific surface area of the particles, it may be

implied that the finer the particles, higher will be the water demand because of the higher amount

of water required to wet each individual particle. Additionally, water absorption can also be high

if the original rock was porous. Whatever the reason, higher water demand leads to an increase

in water-cement ratio of the concrete. It is likely that there is an inverse relationship between

sand equivalent and water demand. However, a high sand equivalent does not necessarily imply

that the water demand will be low or within an acceptable limit. It may be possible to establish

an acceptance level based on the physical characteristics of fines. Although actual measures for

3.9

absorption capacities are not indicated, the framework of the criteria is listed in Table 3.2 based

on dry weight.

Chemical Characterization

Oxide analysis of elements present in fines may be carried out using x-ray fluorescence

(XRF) or energy dispersive x-ray analyzer (EDXA). Though it requires sophisticated

instrumentation, most chemical, metallurgical, and materials testing or research laboratories are

equipped to perform this test fairly rapidly and accurately. The advantage of chemical analysis is

that it allows the user to obtain foreknowledge of the amount of alkalies and other potentially

deleterious chemicals that may be present in the fines.

Furthermore, chemical analysis can reveal whether or not a source of fines is rich in

metals such as iron. If so, its generous incorporation in concrete could produce a

discoloration/stain over a period of time due to oxidation. This can affect the appearance of

concrete particularly in structural or architectural applications. Additional research of these

characteristics is needed since it is only subjectively indicated in Table 3.2 relative to suitable

types of concrete.

Mineralogical Characterization

X-Ray Diffraction Analysis

An x-ray beam is directed to a powder sample; diffracted x-rays from the crystalline

constituent(s) are then collected as planar reflections, characteristic of crystalline phases present

in the sample. Interpretation of the XRD data, however, requires competent personnel. Once the

phases present in the fines have been identified, they can be correlated with the chemical

composition obtained from chemical analysis. For example, a chemical analysis may provide the

percentages of magnesium and calcium present in the fines, but to distinguish whether it is

composed of magnesian dolomite or dolomite + calcite, it is essential to run an XRD of the fines.

Performance criteria is noted in Table 3.2 on a subjective basis relative to the amount of

undesirable minerals. Further definition will require more research.

3.10

Petrography

Petrographic examination requires the services of a trained petrographer. Each

constituent is identified from its characteristic set of optical properties. Its usefulness in the

classification chain can be best explained through an example. The percentage of silica (SiO2)

may be disproportionately high (from chemical analysis) compared to the amount of crystalline

quartz actually identified from XRD. It is petrography which helps to identify the other

constituents containing silica, such as chert or chalcedony.

Morphology of particles plays an important role in terms of rheology. For example,

elongated particles are known to cause workability problems as opposed to near-spherical

particles which improve workability. Morphological data obtained from petrographic

examination of fines can be very useful in predicting the water demand of a concrete mixture. A

format for considering these factors on performance is provided in Table 3.2 but as in the case

with most of the level 1 tests, further development is required to specifically indicate limits

associated with each type of concrete.

Level 2 Tests (Tests of Fines Used in Concrete)

Level 2 tests are categorized according to physical, durability, and mechanical tests that

are used for concrete. Many of these test measures are empirical in nature and their relationship

to field performance is not clearly delineated. However, based on experience and documented

knowledge of performance mechanisms, a test criterion is listed in Table 3.2 for specific tests

where sufficient information is available to do so. Otherwise, further research is recommended

to define test measure and performance relationships.

Physical Characterization of Fresh and Hardened Concrete

Concrete Workability and Consistency

Workability can be best defined as the amount of useful internal work necessary to

produce full compaction. The ASTM C 125-93 definition of workability is somewhat more

qualitative: "property determining the effort required to manipulate a freshly mixed quantity of

concrete with minimum loss of homogeneity". The ACI 116R-90 definition of workability is:

3.11

"that property of freshly mixed concrete or mortar which determines the ease and homogeneity

with which it can be mixed, placed, consolidated, and finished".

The slump test is by far the oldest and the most widely used test of consistency or

wetness. ASTM C-143, "Standard Test Method for Slump of Portland Cement Concrete",

describes the scope of the test as: "This method covers determination of slump of concrete, both

in the laboratory and in the field". This test is extensively used in sites work all over the world.

For the vast majority of those working with concrete, the slump test has taken on a much

more important connotation. To them it is a reflection of the amount of water in a mixture, and

may be used as an indicator of expected strength. However, there are a number of difficulties

associated with the slump test. The test is completely empirical and is not related to our earlier

definition of workability, which involved a measure of the amount of energy required to compact

concrete. With different aggregates or mix properties, the same slump can be measured for very

different concrete consistencies. In addition, the slump test cannot differentiate between different

low workability concretes, which may all give no slump. Concretes with slumps less than 25

mm should be tested by another procedure, preferably one involving vibration. The slump also

vary considerably depending on how long after mixing the test is carried out.

The slump test can best be an indicator of performance of concrete for a given mixture

only when the aggregate gradations and properties, chemistry and fineness of cementitious

materials, air entrapped and entrained, time / temperature, and water content are exactly the same

from batch to batch and from day to day. It may be possible to keep these factors constant in a

laboratory where materials and mixing are controlled and batches are relatively small. Under

these conditions, changes in slump have been shown to affect strength and other characteristics

important to the performance of concrete. However, this may not hold true under field

conditions.

Despite these limitations, the slump test is useful on the construction site as a check on

the batch- to batch or hour-to-hour variation in the consistency of the mixture as an indicator of

variation of materials being batched into the mixer. Changes in slump on a given job generally

indicate that a change has occurred in the aggregates or in the amount of water or admixture

3.12

being used. Too high or too low a slump gives immediate warning and enables the mixer

operator to explore reasons and remedy the situation.

High range water reducing admixtures complicate interpretation of the slump since these

can be used to reduce water but increase slump to make a concrete more workable lending itself

to improved placement properties and enhanced finishability - which yields a less permeable and

more durable concrete. These would only be used for high-performance concrete, precast

concrete, and for high-strength structural concrete.

Paste Porosity

Porosity is a component of the microstructure of hydrated cement paste. Capillary

porosity is defined as the total volume of pores larger than gel pores, expressed as a percentage of

the overall volume of the hydrated paste. The strength of concrete is influenced by the volume of

all voids in concrete: entrapped air, capillary pores, gel pores, aggregate pores and entrained air,

if present. In addition to total paste porosity, the effect of pore size distribution on strength must

also be considered. Generally, at a given porosity, smaller pores lead to a greater strength in the

cement paste.

Shrinkage is another important phenomenon which is related to porosity of the cement

paste. One type is autogenous volume change, which is the consequence of withdrawal of water

from the capillary pores by the hydration of the hitherto unhydrated cement. Another type is

drying shrinkage which occurs when the adsorbed water and capillary water is lost to the exterior

of the concrete. Porosity also dominates the permeability of cement paste. Pastes with high

capillary porosities have high permeability, as water or vapor can flow easily through the larger

pores. Well hydrated pastes with low water/cement ratios have permeability that may be three

order of magnitude lower than a paste with a high water/cement ratio.

Mercury intrusion porosimetry can be used to determine the pore structure of the cement

paste. This method gives a better appreciation of the larger capillary pore system, which has an

important influence on permeability and on shrinkage at high humidities. This method assumes

that pores become narrower with depth while, in fact, some pores have a constricted entrance;

this distorts the value of porosity measured by mercury intrusion porosimetry.

3.13

Durability Characterization

Alkali-Silica Reaction (ASR)

An understanding of the expansion mechanisms resulting from the alkali-silica reaction is

essential to the assessment of the susceptibility of a concrete structure to deterioration by these

processes and to the planning and implementation of preventive measures. As a result of alkali-

silica reaction between certain reactive aggregates and the highly alkaline pore fluids in a cement

paste, a reaction-product gel develops that, in the presence of water, expands and may cause

cracking of mortar or concrete.

The potential for ASR has gained a lot of attention from product suppliers and state

highway departments in nearly every state. Even though the problem has had worldwide

attention for the past 50 years, effective measures for inhibiting the alkali-silica reactions other

than the use of low alkali cement and fly ash have not been available until recently. To prevent

deleterious expansion the following three options are available:

• use low alkali cement,

• avoid reactive aggregates

• include in the cementitious material a finely divided material reactive with alkalies

such as with with fly ash or other fine siliceous materials

• use a lithium-based admixture

Alkali-silica reaction can be disruptive and manifest itself as cracking. The crack width

can range from 0.1 mm to as much as 10 mm in extreme cases. The cracks are rarely more than

25 mm, or at most 50 mm, deep. Hence, in most cases, the alkali-silica reaction adversely affects

the appearance and serviceability of a structure, rather than its integrity; in particular, the

compressive strength of concrete in the direction of the applied stress is not greatly affected.

Nonetheless, cracking can facilitate the ingress of harmful agents and may shorten the life of the

structure.

An accelerated test method (ASTM C 1260) can be used to detect potentially deleterious

expansion of mortar bars due to ASR. Using this method, it is possible to detect within 16 days

3.14

potentially deleterious expansion of mortar bars due to alkali-silica reactivity. The test method is

used to determine the effectiveness of mineral additives, such as fly ash, silica fume, and blast

furnace, but its success rate is not established. One drawback is that it also indicates expansions

for some nonreactive aggregates. Thus, it always advisable to further investigate using ASTM

C227 (or ASTM C 289 and C 856 - petrographic analysis), and by examining field service

records. Aggregate fines if rapidly reactive may help mitigate ASR.

According to Tonma, et al. (2000), even though there exist conflicting results about the

effectiveness of some of the mitigation alternatives, it is possible to mitigate ASR in concrete.

The effectiveness of an alternative depended upon the degree of reactivity of aggregates, the type

of alternative used, and the dosages used. They noticed that there is a lack of specifications for

the use of mitigation alternatives, which is mainly caused by the large variety of aggregate

reactivity and by the lack of accurate testing procedures capable of predicting the degree of

aggregates’ reactivity and determining the effectiveness of a proposed alternative. It is possible

however, to develop guidelines and recommendations to be used for minimizing concrete

damage due to ASR. These guidelines and recommendations need to be formulized and proven.

Alkali-Carbonate Reaction (ACR)

It is not known how aggregate fines from these type of rocks may affect ACR.

Chemical Resistance (Acids, Sulfate and Others)

Concrete is generally well resistant to chemical attack, provided an appropriate low-

porosity mixture is used and the concrete is properly compacted. Generally, portland cement

concretes are not durable in acidic environments. Numerous laboratory and field investigations

have shown that mineral admixtures, by virtue of their ability to reduce porosity by reducing the

calcium hydroxide content of the cement paste, can improve the chemical resistance of concrete.

Chemical attack of concrete occurs by way of decomposition of the products of hydration

and formation of new compounds which, if soluble, may be leached out and, if not soluble may

be disruptive in situ. The attacking compounds must be in solution. The most vulnerable cement

3.15

hydrate is Ca(OH)2, but C-S-H can also be attacked. Calcareous aggregates are also vulnerable

to acids.

External chemical attack occurs mainly through the action of aggressive ions, such as

chlorides, sulfates, or of carbon dioxide, as well as many natural or industrial liquids and gases.

The damaging action can be direct or indirect. Expansion and cracking due to alkali-silica

reaction, sulfate attack, corrosion of steel in concrete due to chloride ion penetration are some of

the good examples of chemical attack in concrete.

There are various physical and chemical tests developed to assess the deterioration of

concrete due to various forms of chemical attacks. It is essential that tests are performed under

realistic conditions, and care is required in interpreting the results of accelerated tests. Use of

blended cements which include ground granulated blast furnace slag, pozzolans, and especially

silica fume, is beneficial in reducing the ingress of aggressive substances. The reduction in

permeability associated with the lime-consuming pozzolanic reaction seems to make an

important contribution to the overall durability of products containing mineral admixtures.

Freezing and Thawing

The most common method to assess the deterioration of concrete due to freezing and

thawing is to measure the change in dynamic modulus of elasticity and/or length of a wet

concrete specimen exposed to freezing and thawing cycles.. The reduction in the modulus after a

number of cycles of freezing and thawing expresses the deterioration of the concrete. The most

commonly used procedures in the United States are AASHTO T 161 (ASTM C 666), which

prescribes two procedures. In Procedure A, both freezing and thawing take place in water; and in

Procedure B, freezing takes place in air but thawing takes place in water. A modification of this

test method, is referred to as Procedure C. The concrete specimen is wrapped in absorbent cloth

to keep the specimens wet during freezing and (2) non-rigid containers to prevent damage to

either the container or the specimen. Procedure C resulted in a more severe test than either

Procedure A or B. This procedure should be investigated further to determine its ability to

predict field performance.

3.16

The effects of freezing and thawing can also be assessed from measurements of the loss

of compressive or flexural strength, from observations of the change in length, or in the mass of

the specimen. Measurement of a decrease in the mass of the specimen is appropriate when

damage takes place mainly at the surface of the specimen, but is not reliable in cases of internal

failure. Another test method determines the dilation of concrete subjected to slow freezing, and

is prescribed by ASTM C 671-94.

One of the main objects of laboratory tests is, of course, to predict the frost behavior of

concrete under field conditions. Natural exposure conditions, however, are so varied and

complex that they are difficult to reproduce in the laboratory. Freezing rate, the minimum

temperature, and the length of the freezing period are certainly the most obvious differences

between laboratory and field conditions.

Whatever anomalies occur between the field and laboratory condition, durability of

concrete under field conditions is often better than the durability measured in the laboratory. The

importance of air entrainment to protect the cement paste against frost action has been

demonstrated a very large number of times. The increase in durability with the decrease of the

water/cement ratio has also been well documented. And the relationship between the

characteristics of the aggregate pore system (as well as the maximum size of the particles) and

the resistance of concrete to freezing and thawing cycles has been established. Therefore, when

the results of field tests, (or of field observations) are not in agreement with those of laboratory

tests, it is often because laboratory tests are more severe. Test results are presented in the form of

the durability factor.

There are no definite values of the durability factor for acceptance or rejection of the

concrete subjected to freezing and thawing test. As general guidance, durability factor smaller

than 40 means that the concrete is probably unsatisfactory with respect to freezing and thawing,

40 to 60 is the range concretes with doubtful performance, and above 60, the concrete is probably

satisfactory; and around 100, the concrete can be expected to be satisfactory.

3.17

Chloride Ion Penetration

Chloride-induced corrosion in the reinforcing steel is a major deterioration mechanism

for reinforced concrete structures. Design of concrete structures based on material strength rather

than durability, the growing use of deicing salts and chloride containing admixtures, and

construction in increasingly aggressive environments are some of the factors that have lead to the

surge of concrete experiencing reinforcement corrosion.

When internal steel reinforcement corrodes, the strength of the reinforced concrete

member is undermined in several ways. Since corrosion products have a greater volume than the

parent steel, internal tensile stresses will develop in the cement mortar at the steel/mortar

interface. As a result, the surrounding concrete cracks and will eventually spall away as

corrosion of internal steel advances. In addition, under tensile stress developed during corrosion,

existing fine cracks and microcracks in the surrounding concrete tend to enlarge and coalesce to

form a network of interconnected cracks, providing increased ionic transport between the surface

of the concrete and the surface of the reinforcing steel, effectively promoting corrosion process.

Crack growth decreases concrete stiffness and tensile strength, while the formation of a network

of cracks increases concrete permeability. And, as the steel is progressively lost to corrosion, the

reinforcing bar cross-section is reduced, decreasing the member's tensile strength. Furthermore,

as corrosion advances, the bond between the steel and surrounding concrete is weakened,

adversely affecting the load transfer between the two materials.

To ensure that reinforced concrete members perform according to their design capacity

and design service life, it is important to prevent or delay the occurrence of corrosion. The

standard rapid test method to measure the chloride permeability is prescribed by ASTM C 1202.

There is a controversy concerning whether or not the Rapid Chloride Permeability Test is a

reliable way of measuring the chloride permeability. It has been pointed out that the RCPT may

give a misleading result when chemical and mineral admixtures are incorporated into concrete, as

it is primarily a electrical conductivity measurement. The standard static ponding test (AASHTO

T259) is generally accepted for the evaluation of chloride penetration into concrete under

continuous immersion in salt water. It has been recommended however, that to determine

3.18

differences in rates of chloride penetration in low permeable concretes, this test must be

continued for longer than 90 days.

The diffusion of coefficient of cement pastes or mortars for chloride ions has often been

estimated by the static diffusion cell method, but this method is considerably time consuming and

not applicable for a large variety of concrete mixtures. Charge passed in the RCPT is one of the

most effective indicators for the evaluation of the chloride permeability of a large variety of

concrete mixtures, and that the simple measurements of initial direct current or electrical

resistivity is also effective in estimating the charge passed in RCPT. Usually, high performance

concrete is expected to have extremely low chloride ion permeability of less than 1000

Coulombs, and for structural concrete is usually around 5000 Coulombs.

Mechanical Characterization

Strength

Strength of concrete is commonly considered its most valuable property, although, in

many practical cases, other characteristics, such as durability and permeability, may in fact be

more important. Thus, concrete strengths alone may be misleading in terms of choosing an

appropriate mix design for a particular job. Nonetheless, strength usually gives an overall picture

of the quality of concrete because strength is directly related to the structure of the hydrated

cement paste.

The factors that can affect the strength of concrete can be classified into four categories:

constituent materials, methods of preparation, curing procedures, and test conditions. The

paramount influence of voids in concrete on its strength has been a universal fact. And it is

possible to relate this factor to the actual mechanism of failure. For this purpose, concrete is

considered to be a brittle material, even though it exhibits a small amount of plastic action. High

strength concrete is more brittle than normal strength concrete.

There are several means of assessing the strength of concrete, of which compressive

strength is commonly considered in structural design. However, for some purposes tensile,

flexural, shear, bond strengths are also equally important for design considerations. And it is

3.19

generally true that there are no simple unique relationships among the various measures of

concrete strength.

Specification of quantities almost invariably includes associated tolerances on the various

quantities. Exact determination of mix proportions by means of tables or computer data

generally is not possible: the materials used are essentially variable and many of their properties

cannot be assessed truly quantitatively. In consequence, all that is possible is to make an

intelligent guess at the optimum combinations of the ingredients. It is not surprising, therefore,

that the distribution of strength of test specimens can be described by the mean and standard

deviation. In selecting a concrete mix we must, therefore, aim at a mean strength higher than the

minimum. Usually compressive strength of high performance concrete is in excess of 80 MPa

(12,000 psi) and the normal structural concrete is more than 20 MPa (3000 psi).

Shrinkage

Among several types of shrinkage that can occur in concrete due to different reasons, and

at different times in the life cycle of a concrete, which one of the shrinkage strains would be

more dominant depends on several factors. Temperature and humidity of the atmosphere are two

prominent elements, while the size of the concrete structure, temperature of the concrete, mixture

proportions (water/cement ratio, aggregate factors, cement proportion, admixture influence), and

thermodynamic conditions of curing are some of the other important parameters governing

shrinkage, and thus cracking in concrete.

Drying shrinkage is perhaps the most important among the deformations unrelated to

load. The loss of mixing water from newly cast concrete during exposure to air at less than 100

percent relative humidity causes drying shrinkage. It is the contraction of concrete on removal of

water to outside. A part of this movement is irreversible. For example, if a concrete dries and

then is wetted again, it will not resume its original dimensions, but a part if it is reversible and is

simply called moisture movement.

The shrinkage of new concrete occurs in two phases. In the first phase, free water

evaporates and a relatively small amount of shrinkage occurs. Then, during the second phase,

adsorbed water in capillary and gel pores is lost, and a large amount of shrinkage occurs. The

American test method to measure the magnitude of shrinkage is prescribed by ASTM C 157-93;

3.20

the air movement past the test specimens is carefully controlled and the relative humidity is

maintained at 50 percent. The relation of ACI 209-92 can be used whenever shrinkage at a given

relative humidity is needed to be estimated on the basis of a known value of shrinkage at some

other relative humidity.

Concrete surfaces exposed to air dry and shrink quicker than interior locations.

Theoretically, the shrinkage profile is parabolic, with drying proportional to the square of the

distance from the surface. Similarly, the evaporation rate of water in concrete depends on the

environment and the surface-to-volume ratio of the concrete section. Concretes with a high

surface-to-volume ratio dry and shrink quicker. Members with rapid surface drying and slow

diffusion (from either low permeability or large thickness) develop large strain differentials as

the surface dries and shrinks while interior portions remain at a high moisture content and shrink

much less. Shrinkage differentials initially can produce compressive stresses in the interior and

tensile stresses in the exterior portions, contributing to cracking. Drying shrinkage of

unreinforced, unrestrained newly cast concrete in a 23°C (73°F), 50 percent RH environment can

range from about 500 to 1000 :,.

Some types of cement cause more shrinkage than others; for example, concrete made with

portland cement that is deficient in gypsum will shrink more than a nearly identical concrete with

cement that has an optimum gypsum content. ASTM C 596 can be used to determine the effect

of portland cement on the drying shrinkage. However, the drying shrinkage of paste or mortar

may not be a good predictor of the drying shrinkage of concrete.

Careful selection of concrete materials can reduce drying shrinkage. Aggregate type and

grading, water content, cement content, concrete placement temperature, and curing all affect

performance. To reduce the overall shrinkage, designers should specify the largest practical

maximum aggregate size should be used, the aggregate and cement should have low shrinkage

characteristics, fines and clay material passing the 200 mesh should be a minimum, and the least

amount of cement or cementitious materials to achieve the required compressive strength should

be used. Shrinkage-compensating cement can also be used to reduce shrinkage and shrinkage

stresses.

3.21

Summary

Following the sand equivalence test, other physical, chemical, and mineralogical tests

proposed in the foregoing classification protocol, are considered adequate from the standpoint of

decision making as to the most appropriate application of a particular set of aggregate fines. The

result of the screening test will permit a decision as to whether aggregate fines from a specific

source can be used in HPC, SC, or CLSM, failing which Level 1 tests must be carried out. The

data obtained in the first level tests will enable us to select the most practical alternative

application, based upon test results on the actual aggregate fines. Testing of concrete mixtures

containing fines at Level 2 will be necessary if level 1 test criterion is not met for a certain

category of concrete. The amount of fines used in each type of concrete has only been

preliminarily defined and further testing and development is needed to determine the optimum

amount of fines that can be incorporated in concrete mixtures.

4.1

Sample S.E.

Fine aggregate (sand only) 95

Fines No. 1 87

20% replacement with No. 1 fines 94

Fines No. 2 8

20% replacement with No. 2 fines 67

Table 4.1 Sand Equivalent Results..

CHAPTER 4

APPLICATION OF CLASSIFICATION FRAMEWORK

Introduction

The results of a test run of the classification process described earlier, are presented in

this chapter. Two samples of fines from different sources, labeled No. 1 and No. 2, were used for

the classification. The test results at different levels are presented.

Screening Test

Sand Equivalent Test

The objective of the sand equivalent (SE) test was to ascertain if it can be used as an

effective screening parameter when incorporation of quarry fines as a replacement for sand is

being considered. Ramirez et al. (1990), however, used this test to determine the clay content in

fines. The test was performed in accordance with AASHTO T 176-86 on the fine aggregate

(sand) before and after replacement with aggregate fines. The results in Table 4.1 show that even

after replacing 20 percent sand by fines No. 1, the SE value changes only marginally. In contrast,

the SE decreases substantially when the sand is replaced with a corresponding amount of fines

No. 2.

4.2

Discussion

The SE test is actually designed to limit the use of dirty aggregate particles in concrete,

which can be coated with a layer of fine clay. This type of clay coating tends to create a

debonding failure at the paste-aggregate interface, and thus, weakens the concrete. The presence

of clay can also increase the water demand of a concrete mixture.

Petrographic examination revealed neither the presence of dirty sand particles nor clay

balls that may be associated with aggregates. If indeed clay is present, it must be dispersed in the

matrix, although clay was not identified from XRD analysis. The results, however, do indicate

that the SE can greatly vary from one set of fines to another.

Nonetheless, the SE was integrated as the screening test in this classification system

because of its simplicity, low cost, and rapid results. The test, run on two samples of aggregate

fines, indicates that it may be advantageous to perform the SE test on fines independent of either

sand or cement to get a more realistic representation of the amount of clay size or extremely fine

particles present. This will facilitate the prediction of its application at the very outset rather than

subjecting each and every sample of fines to a battery of tests. Undoubtedly, the SE of fines by

itself, will be lower than that of a standard concrete sand. Therefore, a compromise must be

made to allow for a lower value of SE for fines than for sand.

When discussing applications of aggregate fines in different types of concrete, whereas a

SE of arbitrary lower limit in the 70s (for example, fines No. 1) may be acceptable for structural

concrete; a low SE of only 8, as in the case of fines No. 2 will most definitely require additional

testing, as proposed in our classification framework, before it can be considered for use as sand

replacement in concrete. Failure on its part to be incorporated in normal concrete as a partial

replacement of sand, does not necessarily imply total rejection of a particular set of fines. On the

contrary, the present classification has been conceived to take into account fines with a wide

range of properties, including the ones with low SE. It is quite possible that once tests have been

completed, fines No. 2 may prove to be suitable for replacement of sand either in normal

concrete or in a controlled low strength material (CLSM).

4.3

Sample/Class No. 1 No. 2

Sand (4.75mm - 75:m) 79% 51%

Clay (< 2:m) 10% 10%

Silt (75:m - 2:m) 11% 39%

Table 4.2 Classification of Particles in Fines.

Level 1 Tests

Particle Size Classification

Table 4.2 presents the particle size classification (according to ACI 111R) of the two

samples of fines (No. 1 and 2).

It is evident from this classification that fines sample No. 2 contains distinctly more

particles that are finer than 75 :m. It is interesting that though this type of material is termed

fines, particles finer than 75 :m (passing the 75 :m sieve) in sample No.1 are less than 25

percent, while the rest are greater than 75 :m. This underscores the need for a better definition

of quarry fines.

Absorption

Water demand of aggregates is a property that must be known before a concrete mixture

can be properly proportioned. Several attempts to determine the water demand of these two fines

using ASTM C 128 method were not successful because of their fine particle size. If the method

of using aggregate fines is to blend a quantity with a fine aggregate, the absorption of the blend

can be determined by ASTM C 128 method. If, however, the fines are to be used as a separate

ingredient of concrete at the batch plant, then a testing procedure needs to be developed in a

follow-on phase of research to estimate the absorption capacity.

4.4

Petrography of Fines

Aggregate fines consist of rock fragments, which in turn are composed of minerals. Each

mineral has characteristic optical properties that can be determined from examination of thin

sections by a trained petrographer using appropriate microscopes. Besides mineralogical

identification, determination of particle size, shape and surface texture can also be made. These

data are useful in evaluating use of aggregate fines in concrete. The two samples were examined

by light microscopy.

Sample No. 1

The optical micrographs of this sample are presented in Figures A.1 through A.4. Figure

4.1 shows that the majority of the particles are less than 0.1 mm in size. One occasionally

encounters a few coarse grains ( 0.5 mm or greater) as shown in this figure. The morphology of

the grains can be best described from Figure A.2; they are mostly subrounded (nearly round);

some are subangular (some, not all sides are angular). Elongated grains with a high aspect ratio

as shown in Figure A.3 are rare. From the mineralogical standpoint, the ‘fines’ are composed of

calcite (CaCO3) and dolomite [CaMg(CO3)2] (Figure A.4). Other minerals, such as quartz (SiO2),

are limited in quantity in this sample. The mineral dolomite is readily recognizable from its

rhomb shape, while the characteristic cleavage planes in calcite are rather indistinct. Since the

primary mineral is calcite and dolomite is the secondary mineral, the rock is a dolomitic

limestone. Fossils were not observed.

Sample No. 2

Compared to sample No. 1, the percentage of coarse as well as elongated particles is

higher in this sample (Figure A.5). The sample contains a fairly high amount of quartz, along

with calcite (Figure A.6). Extremely fine grains of feldspars were also identified. Other silicate

minerals are possibly present in small amounts. The reddish-to-brownish tint of this sample is

suggestive of the presence of iron-bearing mineral(s). The grains are not as rounded as those in

sample No.1. In general, the particles are subangular. This sample contains finer particles than

sample No.1 (see Figures A.7 and A.8). The size classification also yielded similar results. In

4.5

view of the range of minerals present in this rock, it is difficult to assign a specific name to it

without chemical data. One possibility is to term this rock siliceous limestone.

Mineralogical Analysis

X-ray diffraction (XRD) is used to identify crystalline phases. In several respects, it

complements other techniques such as optical microscopy and scanning electron microscopy. A

more positive identification of a mineral can be obtained from petrographic examination,

followed by XRD.

The mineralogical analysis of these two samples presented in the X-ray diffraction

patterns (Figures B.1 and B.2) shows that sample No. 1 is mainly composed of calcite with a

small amount of dolomite and still lower amount of quartz (Figure B.1). In contrast, sample No.

2 contains a much lower amount of calcite. The minerals identified are present in the following

order:

Quartz >> Dolomite > Calcite >> Feldspar

Thus, the nomenclature of the first sample would be ‘dolomitic limestone,’ whereas the second

would be classified as a mixture of ‘siliceous and dolomitic limestone.’ From petrographic

analysis also, these minerals were identified, but their relative abundance was difficult to

estimate from petrographic examination.

Chemical Analysis

The bulk chemical analysis of the two samples were carried out using energy dispersive

X-ray (EDX) analyzer, attached to the scanning electron microscope. Although normally it is

used to analyze the object under view, fairly accurate bulk analysis of powder can be obtained

rapidly from EDX. The elemental compositions (average of five analysis) given in Table 4.3

confirms the previous XRD and petrographic results that sample No. 1 definitely contains more

calcite than the counterpart No. 2 fines, whereas its silica (quartz) content is much less than that

of No. 2. That fines No. 1 is dolomitic limestone is evident from its high Mg content. The Si is

high in sample No. 2. Part of it is the contribution of quartz, and the rest is due to feldspar

4.6

Sample/Element No. 1 No. 2

Ca 80.7 45.3

Si 2.3 35.3

Mg 18.6 1.9

Na 1.7 0

Al 1.0 7.0

K 0 4.7

Fe 0.8 1.0

Table 4.3 Elemental Composition (Percent by Mass) of Aggregate Fines.

present in this sample. The non-negligible amount of potassium in this sample suggests that the

feldspar is potassium feldspar (orthoclase, sanidine, microcline).

Inferences

A series of inferences can be made from this characterization procedure carried out under

the screening and Level 1 tests. First, as anticipated, fines from different sources present

different properties, which are likely to affect the performance characteristics of concrete quite

distinctly and possibly its durability also. For example, while aggregate fines from one source

are siliceous, the others are calcareous. The mineralogical compositions of the two fines under

study are also quite different. One mainly consists of dolomitic limestone, and the other mainly

contains quartz. Additionally, fines from one source are finer than the other. The subrounded

grain shape, uniform particle size distribution and good grading, compositional and

morphological homogeneity of the dolomitic limestone sample (No. 1) are some of the properties

that can be best utilized to improve the rheology of structural concrete. These beneficial

properties of this set of fines would go unattended if used in a controlled low strength material.

4.7

In the second sample, although the overall distribution of particles appears to be finer

than its counterpart sample No. 1, a non-negligible portion is composed of very coarse and

elongated particles. The medium fraction appears to be lacking. As a result, the particle size

distribution is gap-graded. Workability and finishing problems are liable to arise if the amount

of ‘fines’ substitution is high in concrete. Additionally, water demand of the concrete mixture

can increase. Therefore, rather than considering this fines for structural concrete, it may be more

effectively used in controlled low strength material, where flowability rather than workability is

the prime criterion when designing such a mixture.

Level 2 Testing Program

Although Level 1 tests had already indicated that only one set of fines needed further

testing, whereas the other could be directly incorporated as a replacement of sand in HPC or

structural concrete, both samples were subjected to the same series of tests to evaluate the

validity of the proposed classification system.

Mixture Proportions

Following the characterization phase, tests on optimization of these fines in concrete

started in the laboratory with trial mixtures. Initially, it was decided to proportion the mixtures

on the basis of 1-in. slump. Only replacement of sand with equivalent amount of fines was

included in this phase of study. The proportion of replacement ranged from 0 to 30 percent in

increments of 10 percent (Table 4.4). It was not always possible to maintain 1-in. slump in all

the experimental batches. Nonetheless, every effort was made to ensure that the slump did not

exceed 1½-in. It was possible to obtain a slump mostly ranging from 1 to 1¼-in. The water

demand of these mixtures is seen to vary significantly from siliceous to calcareous fines (Figure

4.1). The higher water demand of the siliceous fines is consistent with its greater fineness. This

figure also illustrates that in the case of the siliceous fines, the W/C of the concrete increases

with increase in the replacement percent in order to maintain a constant slump of 1-in.,

suggesting that this set of fines (fines No. 2) may be better suited for application in controlled

low-strength materials.

4.8

Material/No. 1 2 3 4

Cement (lb) 13.4 13.4 13.4 13.4

Water (lb) 6.6 7.0 5.9 6.6

CoarseAggregate (lb)

41.5 41.5 41.5 41.5

Fine Aggregate(lb)

31.7 28.5 25.4 22.9

Fines 0 3.2 6.3 9.5

% Replacement 0 10 20 30

W/C ratio 0.49 0.46 0.44 0.48

Slump (in) 1.0 1.0 1.25 1.25

Table 4.4 Mixture Design for Limestone Fines Concrete.

Figure 4.1 Water Demand of Reference Concrete, and Concretes Containing 10 Percent Fines.

4.9

Figure 4.2 Compressive Strength at 7 and 28 Days, where LS = Limestone,N2 Siliceous.

This trend in W/C, however, is reversed when limestone fines (No. 1) are incorporated in

concrete. At 30 percent limestone fines replacement, its W/C was noted to be nearly the same as

that of the reference concrete containing 0 percent fines. Thus, it appears that besides higher

surface area of fines No. 2 (siliceous), it is most likely more absorptive than No. 1 (limestone),

although siliceous fines are normally less absorptive. Nevertheless, this large difference in water

demand when these two fines are used needs to be investigated further.

Compressive Strength

The 7 and 28-day compressive strengths of concretes containing 0, 10, 20, and 30 percent

fines replacement for sand are presented in Figure 4.2. Despite the lower W/C of the limestone

fines concretes, their compressive strengths are slightly lower than that of the reference concrete

both at 7 and 28 days, implying that it may be necessary to reduce the W/C still further, possibly

through the use of a HRWRA, to achieve comparable strength. Interestingly, the concrete

containing 20 percent limestone fines gains higher strength than its counterpart 10 percent

limestone fines concrete, and this is attributable to its lower W/C. The concrete mixtures

containing siliceous fines show a steady reduction in strength as function of replacement

4.10

percentage, which can be directly related to the increasing W/C of this series of concretes,

illustrated in Figure 4.1.

Porosity

The porosity of these concretes at 28 days were studied using a mercury porosimeter. The

pore diameter versus total intruded mercury is plotted for each replacement value for the

siliceous and limestone fines concretes respectively in Figures 4.3 and 4.4. Figure 4.3 shows that

the cumulative intrusion of mercury increases from 0.050 to 0.095 mL/g of Hg as a function of

replacement percentage. Additionally, pores with larger diameters also increase in frequency.

Once again, this is attributable to the additional amount of water the siliceous fines concrete

requires to maintain the same slump as the reference concrete. The limestone fines concrete

mixtures also display an increase in pore volume and pore radius (Figure 4.4). Nonetheless, at 20

percent replacement, the volume of intruded mercury is slightly lower for limestone fines

concrete, 0.070 mL/g vs 0.085 mL/g for siliceous fines concrete.

Shrinkage

The shrinkage data for concretes containing 0, 10, 15, and 20 percent limestone fines (No.

1) over a period of 14 days are plotted in Figure 4.5. The reference concrete at the end of the

testing period has the lowest shrinkage of 0.0018 in. The concrete with 10 percent fines records

the same amount of shrinkage, but when the replacement amount increases to 15 percent, an

upsurge in shrinkage was observed. Shrinkage in the concrete with 20 percent fines is lower than

that with 15 percent fines. This discrepancy cannot be explained at this stage. Interestingly

though, Malhotra and Carrette (1985) also obtained higher shrinkage in concrete in which 20

percent sand had been replaced with limestone fines.

4.11

Figure 4.3 Porosity of Reference Concrete, and Concretes Containing 10, 20, and 30Percent Siliceous Fines.

Figure 4.4 Porosity of Reference Concrete, and Concretes Containing 10, 20, and 30 PercentLimestone Fines.

4.12

Figure 4.5. Shrinkage vs. Time for Concrete Samples Containing Limestone Fines.

Inferences

It is well known that the porosity of concrete, which is a function of its W/C, can be

undesirably high at higher W/C. This, in turn, can lead to loss of durability of the concrete due to

environmental or chemical attack, which occurs from permeation of solution into the concrete.

This study shows that in order to preserve the microstructural and mechanical

performance-related integrity of concrete containing quarry fines, it is essential to reduce the W/C

within practicable means. Refinement in pore structure can be expected to be achieved if the

matrix is densified as a result of W/C reduction. Consequently, higher strength and enhanced

durability will ensue.

The optimum percentage of sand replacement with fines is yet to be established, but

there are strong indications that the optimum will vary, subject to the source of fines. So far, the

study shows that the water demand is distinctly different for different fines. This, in turn, affects

4.13

the W/C of concrete. If the precise reason for this difference can be determined, then predicting

the behavior of a particular set of fines in terms of W/C will be easier.

Conclusions

Among all the tests performed on the fines and concretes, the sand equivalent is possibly

the simplest test. This justifies its assignment to the screening test category. It appears to be quite

effective in estimating the amount of clay size particles in quarry fines, but clay minerals as such

cannot be identified from a sand equivalent test. X-ray diffraction analysis coupled with chemical

analysis is required to identify clay minerals, if any. The two fines used in the test run, however,

do not contain a significant amount of clay.

Petrography of fines and their particle size analysis, which are two other tests proposed in

the Level 1 testing sequence, help to predict a particular application of fines, that is, whether it is

more suitable for use in structural concrete, high-performance concrete, or controlled low-

strength materials. Sand equivalent test data indicated that only one set of fines may be suitable

for use in structural concrete as a sand replacement material. This being a test run, both the fines

were subjected to Level 1 tests. The results confirmed the findings of the screening test.

As all the required durability and performance tests on concretes containing fines have not

been carried out in Level 2, the results have been inconclusive. Thus, the optimum

percentage of fines required for structural concrete is yet to be established. Nonetheless, those

Level 2 tests which were carried out have been highly instructional in the sense that the results of

these tests have identified the need to reduce the water/cement ratio to obtain satisfactory

performance related data.

Of the two fines that were tested, the limestone fines (No. 1) holds strong potential for use

in structural concrete, provided the porosity of the concrete can be refined by reducing the

water/cement ratio. The siliceous fines (No. 2), has the possibility of being used in a controlled

low strength material where strength and porosity are not major considerations in designing the

concrete/mortar mixture. Flowability of the mixture is more important in this type of material.

Several aspects of the test program reported in this chapter were beneficial in assessing the

suitability of most of the tests included in the protocol. However, it is clear that further

4.14

verification is needed with respect to the criterion limits noted in Table 3.2 associated with each

test in order to confidently designate a particular fines source to a particular concrete use.

5.1

CHAPTER 5

POTENTIAL APPLICATIONS OF AGGREGATE FINES

As previously indicated, an integral part of the aggregate fines classification process is the

categorization of a particular source of fines relative to its potential use. The end result of

implementation of the classification system previously described is intended to yield the most

appropriate category of use for a given source of fines based upon measured characteristics.

A highly promising and emerging use for aggregate fines appears to be in the construction

of energy efficient residential structures utilizing a new technology referred to as insulated

concrete forms (ICF). Additionally, Europe, Canada, and Japan have accepted the technological

challenge to commercialize filler-cement in the most satisfactory way possible. Thus, one sees

increasing amounts of limestone fines being introduced in portland cement in several of these

countries. However, prior to an in-depth discussion regarding the background of these potential

applications of fines in cement and concrete, it will be well to point out and discuss the general

use areas or categories of aggregate fines as suggested by the classification procedure. These

general categories of potential uses are listed as follows:

Cement

C Limestone-filled cement,

Concrete

C High performance concrete mixtures,

C Structural concrete mixtures, and

Controlled Low Strength Materials (CLSM)

C Insulated concrete forms

Limestone-Filled Cement

Ground limestone is the principal calcareous component in the manufacture of portland

cement. Nonetheless, the use of limestone fines as a raw material is unsuitable because it tends

to generate a high volume of dust inside the kiln. Addition of fly ash, granulated blast-furnace

5.2

slag, or silica fume to portland cement is well accepted and has become a standard practice in

several countries. The main problem with the addition of so-called fillers, principally limestone

or sand, is that they are considered to be inactive. In Norway, a type of calcareous filler called

“Aktivitt” was developed to increase the strength of concrete. Although a relatively high

percentage of limestone powder is added to masonry cement, this type of specialty cement

occupies only a small portion of the global market. Even Type III cement, though its sale is not

as brisk as that of a general purpose Type I cement, is produced in much larger volume than other

specialty cements.

Concrete users, for all practical purposes, prefer to use fillers to fill the gap in the finer

portion of the particle size distribution (PSD) curve. This correction in PSD improves rheology,

density, and strength of the concrete and reduces its shrinkage. These benefits are further

enhanced if the filler is calcareous in composition. It is claimed that improvement is achieved

mainly because of the formation of carboaluminate at the paste-aggregate interface, which

replaces the conventional and weak Ca(OH)2 crystals in the interstitial zone and also helps to

refine the paste microstructure. According to Cochet and Sorrentino (1993), using limestone-

filled cement, within specific limits on bleeding, is a reliable way of achieving rheologically and

physically improved concrete. Furthermore, filler-cement is particularly advantageous for

producing a desired concrete strength and is capable of achieving adequate durability by using a

more economic material than energy-intensive portland cement.

The French standard, AFNOR NF P15-301, introduced in 1979, was responsible for two

major changes. First, strength classes were no longer defined by their minimum values but by an

average. The second was the possibility of adding fillers in cement in the same proportion as

slag, fly ash, or pozzolans up to a maximum content of 35 percent. Whereas the first concept

was well received, customers were critical of the second. The skepticism for cement containing

fillers stems from the fact that its effective w/c is higher than that of a cement containing only

clinker and gypsum. Consequently, the porosity, strength, durability, and other related properties

of filler cement may deteriorate. This reasoning, however, does not take into consideration that

to produce filler cement for a given strength class, the clinker present in the cement is more

finely ground to compensate for the higher w/c. Finally, with the acceptance of the concept of

5.3

filler-cement comes the choice of filler. In this respect, limestone filler may be the most

favorable, at least from previous reports on performance criteria of fillers.

High-Performance Concrete

The possibility of partially replacing cement by a limestone or siliceous filler with well-

adjusted particle size, in conjunction with silica fume, slag, or fly ash for producing high-strength

concrete has been examined by Canadian and Japanese researchers (Malhotra and Carrette, 1985;

Uchikawa and Okamura, 1993). It is evident from their results that partial replacement of cement

by combined pozzolanic materials and unprocessed mineral dust such as quarry fines, which

effectively represents a triple-blend cement, may provide not only a more efficient use of cement

but also the practical and cost-effective means of making high-performance concrete. The

compressive strength of this class of concrete far exceeds that of conventional concrete both at

early and late ages. Additionally, a refined pore structure is said to be generated in the hardened

paste due to the presence of a pozzolanic or cementitious admixture and mineral dust. As a

result, the durability of high-performance concrete is significantly higher. Taking into

consideration the fact that a generous dosage of HRWRA is needed to reduce the w/c, for high-

performance concrete to compete with normal concrete in the future, it is essential to use, for

example, microfillers such as industrial by-products and unprocessed materials such as quarry

fines.

Structural Concrete

This class of concrete typically represents normal-strength concrete, with compressive

strength in the range of 3,000 to 5,000 psi. It is in structural concrete that quarry fines may find

the maximum use and application. Finishing and pumping characteristics will, in many

instances, be enhanced in these mixtures due to the addition of fines. A feature that is

characteristic of pumpable concrete mixtures is sufficient mortar to provide a coating or an

envelopment of the aggregate particles such that the mixture will move through the pump line

under minimal pumping pressure. Keeping pumping pressures below certain limits will facilitate

placement of concrete in a timely manner and the development of an adequate air-void system.

5.4

An important aspect of high-fines concrete is the improvement of the workability of concrete,

which can, in many instances, outweigh any reduction in strength that may be incurred from the

use of high quantities of aggregate fine materials.

Controlled Low Strength Material (CLSM)

The use of fines in a CLSM potentially will have many applications, particularly with

reference to insulated concrete forms (ICF) as they may pertain to residential construction. The

cementitious component of the wall sections cast with these types of forms is envisaged to be a

CLSM. The aggregate fines or filler makes up the major portion (up to 72 percent) of a typical

CLSM. Typically, much of the filler in these mixtures consists of sand as used in the production

of concrete. The material is used because of its ready availability. While sand is an excellent

filler for CLSM, by no means is it an economic material to use. Actually, materials such as

aggregate fines that do not meet the ASTM standard C 33, have proven to be more economical.

Materials of this nature, however, should possess adequate grading to insure high flowability

which is an important consideration in ICF technology. In this regard, an important factor will be

the shape of the particles of the fines. Angular particle shapes and sharp edges reduce

flowability. Fly ash has been used successfully as a filler material for CLSM to enhance the

workability and to counter the effect of particle shape and angularity. It is anticipated that use of

quarry fines holds greater potential as a partial replacement, if not a total replacement, of sand for

CLSM as it would pertain to its use in ICFs.

Current Status of ICF Technology

The development and implementation of alternative designs in residential concrete

construction relative to ICFs has recently experienced rapid growth. The emergence of insulated

concrete form (ICF) technology, as a viable alternative to the standard wood-frame construction,

has in fact demonstrated a high potential to provide energy savings for several parts of the United

States. While ICFs accounted for only a small portion of all above-ground wall systems, they

show promise in establishing themselves as the focal point of an emerging industry, that being,

5.5

Figure 5.1 Residential Concrete Building Systems. Left to Right: Hebel Block, Rastra ICF,and Polystyrene ICFs

residential concrete building systems (RCBS). This section describes some important aspects

relative to RCBSs, and how aggregate fines might be utilized in this field of application.

Residential Concrete Building System

It is well established that energy consumption can be as much as 15 percent of the total

life-cycle costs associated with owning a home, and that the design and materials used to

construct a structure play the predominant roles in determining the consumption pattern the

dwelling will ultimately experience. The long-term behavior and performance for a given set of

construction materials, wall sections, and structural configurations may combine to escalate the

situation, making improved building energy design a paramount endeavor.

Current state of the art in RCBS is polystyrene-based insulated concrete forms (ICF)

(Figure 5.1). The ICF is a stay-in-place concrete form that is used as part of the exterior wall

system. It is composed of expanded polystyrene, recycled plastics, and in some cases, metal

structural support members. Individual ICFs are used as interlocking building blocks that define

a solid, post and beam or modified post-and-beam wall system, which is subsequently filled with

5.6

a cement-based mixture. Typically, a 3000-psi concrete mixture, containing a 9.5-mm (3/8-in.)

sized-gravel as the coarse aggregate, is placed into the form’s center region. Most placing

operations use pumping as the preferred method of conveyance. In these types of applications, a

low-strength material will meet the structural requirements of a residential building. Since a high

compressive strength concrete is not the primary criterion which needs to be achieved with an

ICF structure, it should be possible to use controlled low-strength materials (CLSM) containing a

high quantity of aggregate fines in place of conventional concrete.

ICF Types. Various types of ICF’s are illustrated in Figure 5.1. Rastra markets an ICF

that is made of polystyrene concrete, with 25 ft x 10 ft panels being produced in three separate

plants. Generally these panels are cut into smaller dimensions, which ease shipping and

installation. The cost of the Rastra system is about 20 percent less than the standard ICF, and a

stucco coating can be applied directly to the external surfaces, further reducing the expense of the

completed system. The current Rastra system has a 2-hour fire rating, but attempts are under way

to increase it to a 4-hour rating. It is expected that a polystyrene concrete ICF will provide

superior performance, and that the Rastra design could act as the precursor.

Hebel is an aerated autoclaved concrete design of German origin, with some 50 plants

worldwide. A $35-million dollar facility was opened in Atlanta last year, and they have plans to

begin construction on another facility in Texas this year. The Hebel system is not specifically an

ICF, but rather a pre-cast building block which is marketed as a free-standing structural system.

Hebel prepackages their units, including roof assembly, and offers a cost-effective product to the

residential market, which also has a 4-hour fire rating.

All of these RCBSs represent departure from the standard wood frame, pink insulation,

and conventional construction methodology. Building energy conservation is the major reason

supporting this departure. Claims in ICF industry literature state that RCBS can lower energy

consumption by as much as 70 percent over conventional designs. This has been accomplished

while maintaining cost competitiveness with existing wood frame systems (single family housing

units +10 percent, and commercial is +2 percent ).

5.7

Commercial Application of Aggregate Fines in ICF

There are many areas associated with current designs of polystyrene ICF wall systems

which can be streamlined or optimized from several different perspectives. Typical ICF wall

systems may be as much as 15 times stronger than conventional wood frame construction

perhaps even rivaling the strength and stiffness of normal-strength concrete products such as tilt

wall and masonry block construction. While this may have allayed some of the fears of

engineers and building officials, when confronted with the novelty of the product, in some

respects it has also adversely impacted the marketability of ICF. The factors associated with this

issue have been a primary technical concern of the ICF industry.

The Hebel building system has shown that a free standing 350-psi wall system can pass

the scrutiny of perceived regulatory compliance, and several ICF manufacturers have started to

reduce the steel reinforcing standards and to review the mixture requirements of their individual

systems. Also, by reducing the mass and improving the thermal properties of the ICF filler

material, the energy performance of the composite system is expected to improve. This tends to

suggest that if an ICF wall system with lower mass and structural requirements were to be

introduced into ICF technology, that it would have high market appeal.

Concrete mixtures for ICF wall systems can be improved in terms of the coarse aggregate

type and content, particularly relative to the flowabililty and the method of placement of the

material in the forms. Where concrete pumps have been the primary mode of conveyance,

improvement such as this should allow for smaller pump and less labor intensive equipment to be

used or even a low-cost worm gear pumping station that the building contractor could actually

own, versus paying the rental fee for such services.

In order to improve the marketabililty of ICF wall systems as a competitive building

component, the role of quarry fines in the mixture in the ICF should be fully investigated and

taken advantage of. Therefore, the course of action that is being suggested is to pursue research

to develop CLSMs specifically for ICF’s containing optimal amounts of aggregate fines to be

used to fill the central void of an ICF form.

All of these indicators support the commercial development of ICFs made with aggregate

fines, expanded polystyrene beads, and a host of other lightweight materials, which can be used

5.8

as a structural filler material in ICFs, and also semi-flat roof systems, composite cement blocks,

railings, overhangs, and basements, etc. With the advent of new RCBSs, the commercial

development of structural lightweight ICF using aggregate fines seems extremely feasible. Areas

of research are recommended to improve upon its application to reduce residential energy usage

and improve construction efficiency. Addressing these areas of research will only not addresses

the technical issues but also assist in creating the infrastructure necessary to support the

implementation of residential concrete building systems in a timely manner and provide a new

market for aggregate fines. Conservatively speaking, this could translate into the use of perhaps

as much as 20 million tons of fines per year - most of which would be sizes passing the 75-:m

(#200) size sieve.

Summary

The purposes of this study were to identify the feasibility of the using aggregate fines in

concrete and determine possible applications for high-fines concrete that could possibly lead to

new markets for the use of these materials. A review of the literature on fines revealed the

definite possibility of using more fines than are currently being used in concrete across the U.S.

However, the use of fines needs to be implemented in a controlled and consistent manner due to

the variability of fines sources. To facilitate such a process, a framework to classify aggregate

fines was proposed in this report to provide some guidance on the use of fines in concrete as a

function of the properties of the fines themselves and to indicate the direction of further

development of a classification procedure. As a result of this framework, certain characteristics

of fines were identified as key to performance of the concrete and the criteria associated with

different types of concretes that contain high fine contents. The types of concretes fell into HPC,

SC, and CLSM categories which indicated the markets where fines could be sold. A use was

also identified relative to limestone-filled cements. In order for the industry to fully realize the

benefit of this research, each of these feasible alternatives for the use of fines and should be

pursued and simultaneously developed along with the classification framework into full

implementation.

6.1

CHAPTER 6

AREAS OF FUTURE RESEARCH

Introduction

The research objective was to develop guidelines for using fines in concrete. The results

have been quite encouraging, and based on the innovative approach taken by the researchers, it

has been possible to propose a performance classification framework methodology for using

aggregate fines in concrete. Further research, however, is required to refine the classification

protocol so that it can become universally acceptable both in the aggregate industry and

construction industry.

For future research, aggregate fines from additional sources must be incorporated in the

classification program to obtain more statistically reliable data and to validate the proposed

classification. These aggregate fines must also be subjected to the same tests that were applied to

the two reference fines under study. A review of all the data acquired on these fines must then be

carried out to ascertain the feasibility of establishing the classification framework in its final

form. That there exists a need for such a classification procedure is well recognized by the

aggregate and ready mix concrete producers. It is anticipated that as the use of aggregate fines

increase in the construction industry, the need for such a classification system will become

significant.

Having described at some length the potential applications of aggregate fines in concrete

in the previous chapter, which by any conservative estimate can be said to be great, the necessity

to conduct an exhaustive research study on the effects of partial replacement of cement by fines

becomes apparent. Taking this dual approach, that is, study the role of fines as a sand as well as

a cement replacement, is expected to yield a more efficient use of cement for making concrete,

with less energy consumed but without compromising the properties of concrete. Although

global cement production is expected to increase in order to meet the demands of a steadily

growing world population, there is an increasing concern to optimize cement production to

conserve natural resources and maintain a cleaner environment. Since fines are generated in all

aggregate quarries, it constitutes an interesting option as a filler in cement.

6.2

The concept of producing filler-cement is now employed by a number of European and

Japanese cement manufacturers, who by use of a filler with the cement clinker, attempt to

improve the hydraulic potential of the cement and contribute towards energy conservation. The

production of filler cement, however, is not as simple as it appears; merely adding a fixed

amount of quarry fines to the cement will rarely achieve the purpose for which it is being

incorporated. Thus, arises the need for a systematic study of the important parameters that

influence the optimization of fillers in cement.

In the same vein, it can be stated that the effect of using powder filler, either by blending

with fine aggregate or cement or for the production of low W/C concrete using an HRWRA is

not fully understood. Yet, it is well known that concrete users prefer to use fillers to fill the gap

in the finer portion of the particle size distribution (PSD) curve of solid particles. This correction

in PSD is said to improve rheology, density and strength of the concrete, and reduce its

shrinkage, but definite proof is still lacking. Admittedly, some coarse and fine gradings can be

improved. These benefits are further enhanced if the filler is calcareous in composition, although

Cochet and Sorentino (1993) add that provided the quality of limestone is good, the rheology of

the concrete is neither affected adversely nor improved significantly by the addition of limestone

filler. Regourd (1976) demonstrated that it is the fine particles that have a favorable action, so

the coarse fraction must be limited. When the filler particles are finely ground, the water-

reducing action of the filler is greater for W/C less than 0.40. It has been claimed that

improvement is achieved mainly because of the formation of a mineral called carboaluminate at

the paste-aggregate interface, which replaces the weak Ca(OH)2 crystals in the interstitial zone

and also helps to refine the paste microstructure.

Several researchers have commented that the quality of limestone filler is very important.

A limestone filler originating from a soft or porous rock or one containing a lot of clay can have

an unfavorable influence on the rheology of concrete. The presence of clay can lead to increase

in the water demand and thus negate the beneficial effect of limestone. This reiterates the need

to develop a sound classification framework which will not only characterize the properties of

fines, but also address the specific application of fines from a particular source.

6.3

The materials which can be added to cement, including industrial by-products, do not

behave in the same way during hydration in the presence of cement. Some such as slags have a

genuine hydraulic potential; others have pozzolanic effect (fly ash or silica fume), while some are

of low chemical reactivity (quartz sand). As for the role of limestone fillers in cement, their

influence on the rheology, strength, and durability must be thoroughly appraised.

Research Needs

Influence of C3A

Limestone powder is not inert but can react with C3A to form carboaluminate, which is a

stable compound. The advantage of limestone filler over silica is that it can even be used in a

high-C3A cement where it will form more carboaluminate in place of the less desirable

sulfoaluminate hydrate phases such as ettringite or monosulfate. Theoretically, this implies a

diminution in the possibility of internal sulfate attack. Therefore, limestone-filled cements will

most likely prove to be a viable alternative to existing commercial portland cements for the

precast industry where the durability of the precast elements is believed to have been

compromised by excessive amounts of sulfate in cement.

Influence of Particle Fineness:

It is well established that finer cement particles tend to generate heat of hydration more

rapidly. Nevertheless, fine particles have a positive effect on the paste-aggregate interface; they

tend to improve the bonding between the paste and aggregate. To date, this has been achieved

through the use of ultrafine silica fume, an industrial by-product of the ferrosilicon industry, or

through the combined use of fly ash/granulated blast-furnace slag + HRWRA. Once this is

accomplished, chances of chemical attack on the concrete decreases exponentially because of the

refined paste-aggregate interface. Since part of the diffusion of chloride ions occurs through the

interficial transition zone, its migration to the rebar in reinforced concrete can be reduced.

The incorporation of a reactive filler, such as limestone fines, to replace or even dilute the

finest fraction of the cement is anticipated to have a positive effect on the durability. Not only

6.4

will it reduce amounts of C3A and gypsum that react in the early stages, but this will also reduce

the heat evolved.

Some fines, limestone powder for example, can react with C3A of the cement to form

stable calcium carboaluminate phases.

Selection of Cements

In order to perform this study in a systematic manner, it is imperative that we include four

sets of cements, based on their fineness and C3A contents:

(1) Two coarse ground commercial cements (equivalent to Type I cement) with high

and low C3A

(2) Two fine ground commercial cements (equivalent to Type III cement) with high and

low C3A

The final selection of four cements will made after reviewing the mill certificates of some

of the locally available cements. Their C3A contents will be verified from x-ray diffraction

analysis and PSD pattern determined by laser granulometry or Coulter counter.

Optimization of Particle Size Distribution

As discussed earlier, the particle size distribution has a significant influence on the final

properties. Optimization of particle size distribution will include computerized construction of

grading patterns from PSD curves cements replaced with fillers. Two approaches should be used

to generate these patterns. In the first, a steep gradient factor will be considered as the idealized

distribution. The second approach will consist of an increment in the amount of fine fraction so

that this end of the PSD curve approaches a skewed configuration. The water demand,

rheological, and related properties of fresh concrete will be evaluated against these particle size

distribution patterns. This optimization process can have a critical impact on the development of

guidelines for use of aggregate fines in concrete.

6.5

The Mechanism of Filler Action

The questions that will be posed repeatedly, as this research involves the incorporation of

a non-pozzolanic or non-hydraulic substance, include:

C Do the properties of concrete change only due to a filler action leading to a

mechanical effect in the PSD, filling the space by substituting fine particles of either

cement or sand?

C Does an acceleration in the hydration process take place?

C Does limestone filler modify the thermodynamic assemblage of the hydrates?

C What is the role of carboaluminate?

C Does this type of filler modify the morphology of hydrates?

In order to better understand the hydration behavior of fines concrete, it is necessary to

study the microstructure at different ages, ranging from Day 1 to later ages such as 28 days.

Scanning electron microscopy, X-ray diffraction analysis, and thermal analysis are some of the

techniques which must be employed to establish the mechanism of filler action.

Concrete Testing

It is well known that most of the cement which is manufactured is used in concrete; part

of it is consumed in the precast industry, while a significant amount is used for the production of

ready-mixed concrete. Therefore, it is imperative to study the performance characteristics of

concrete made with limestone filler cement.

The rheological properties of concretes in fresh state and their strength in the hardened

state will be tested and correlated. Additionally, attention will be focused on the durability

aspect of concrete. Test samples of fines concretes will be subjected to tests to represent

different exposure conditions.

The complete concrete testing program is enumerated below:

6.6

Physical

ASTM C403 Time of setting of concrete mixture by penetration resistance

ASTM C642 Specific gravity, absorption, and voids in hardened concrete

ASTM C138 Unit weight, yield, and air content

AASHTO T119 Slump and workability

ASTM D4404 Pore volume in mortar

Mechanical

ASTM C39 Compressive strength of cylinder

ASTM C496 Tensile strength (Diametral compression)

Durability

AASHTO T227 Rapid chloride ion permeability

AASHTO T161/ Resistance to freezing and thawing

ASTM C672 Scaling resistance

ASTM C293 Potential alkali aggregate reactivity

Summary

The influence of partially replacing cement by quarry fines needs to be studied not only

from the fundamental standpoint, but the industrial applicability of limestone filler-cement also

must be critically examined. The first will help us better understand the mechanism of filler

action, while tests carried out for the purpose of introducing the concept of filler cement in the

construction industry will include physical, chemical, mechanical, and durability properties of

concrete.

The need for parallel research on the feasibility of developing filler cement using

aggregate fines becomes more explicit as vast quantities of quarry fines generated by the

aggregate industry continue to stockpile. Besides confirming the classification framework for

quarry fines, which will form an integral part of guidelines for use of fines in concrete, there is a

need to introduce fines in portland cement in order to produce a more energy efficient cement

without compromising the inherent properties of concrete. All tests and analyses must be

performed with the objective to evaluate whether the performance and properties of fines filled

cement comply with those of normal portland cement or if some improvements in properties can

be achieved through the incorporation of a less reactive powder. The microstructure of fines

cement will help to better understand the hydration process and mechanism of filler action. The

influence of fines on the durability of concrete has to be tested in accordance with the standard

test procedures.

6.7

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R-4

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A.1

APPENDIX A

MICROGRAPHS OF AGGREGATE FINES

A.3

Figure A.1 Showing the Distribution of Fine and Coarse (A)Particles.

Figure A.2 Subrounded and Subangular Morphology of Grains.

Sample No. 1

A.4

Figure A.3 An Elongated Particle (A) with a High AspectRatio of 8:1.

Figure A.4 Distribution of Dolomite Rhombs (A) andSubrounded Calcite Crystals (B).

A.5

Figure A.5 Distribution of Elongated (A) and Coarse (B)Particles.

Figure A.6 Quartz (A) and Calcite (B) Grains in the Sample.

Sample No. 2

A.6

Figure A.7 Overall Particle Size Distribution is Finer ThanThat of Sample No. 1 Shown in Figure A.8.

Figure A.8 Particle Size Distribution of Sample No. 1.

B.1

APPENDIX B

X-RAY DIFFRACTION PATTERNS OF AGGREGATE FINES

B.3

Fig

ure

B.1

X-r

ay D

iffr

acti

on P

atte

rn o

f F

ines

No.

1 (

Lim

esto

ne).

B.4

Fig

ure

B.2

X-r

ay D

iffr

acti

on P

atte

rn o

f F

ines

No.

2 (

Sil

iceo

us).

C.1

APPENDIX C

APPLICATION OF HIGH-FINES CONCRETE

C.3

Materials HVFAC Concrete + 10% Fines

Cement (lb) 362 660

Fly ash (lb) 261 0

Total cementitious (lb) 623 660

Coarse aggregate (lb) 2140* 2203**

Fine aggregate (lb) 1438 1455

Fines (lb) 0 159

Total fine aggregate 1438 1614

Air entraining agent (mL) 131 139

Superplasticizer (mL) 887 1572

Water (lb) 155 255

W/(C+FA) 0.25 0.39

W/C 0.59 0.39

Slump (in) 5 Flowing

*River gravel **Crushed limestone

Table C.1 Compositions of Concrete Mixtures.

Field Testing Program

A field testing program has been initiated in the campus of Texas A&M University,

College Station, Texas. Under this program two non-conventional concretes have been placed

side by side as a part of a sidewalk. The total volume of concrete used in this sidewalk was 48

ft3. One of these concrete mixtures contains 10% limestone fines by mass, and the other

represents high-volume fly ash concrete (HVFAC) with 58% Class F fly ash by mass.

Mixture Designs

The mixture designs of these concretes are presented in Table C.1.

C.4

Figure C.1 Temperature Curves for Limestone Fines Concrete and High Volume Fly AshConcrete up to 120 Hours.

Temperature Data

The temperatures of these two concretes measured at regular intervals up to 120 hours are

plotted in Figure C.1. From this figure it is evident that the amplitude of both theses curves is

nearly the same, that is, 8 0C for HVFAC and 90C for the concrete containing 10% fines. The

peak for the HVFAC temperature curve, however, is delayed by nearly 34 hours. This strong

retardation is not unusual considering that 58% cement has been replaced by Class F fly ash,

which is known to develop its pozzolanicity only at a late age. In contrast, since 10% limestone

replaces sand, but the quantity of cement remains constant in this concrete, neither reduction in

heat evolution nor any retardation has occurred.

C.5

Figure C.2 Compressive Strength of Limestone Fines Concrete and High Volume Fly AshConcrete at 3, 7 and 28 days.

Compressive Strength

The compressive strengths of these two concretes at 3, 7 and 28 days have been plotted in

Figure C.2. The concrete containing 10% fines develops higher strength than the HVFAC at all

ages up to 28 days, although this situation is expected to change at a later age when the fly ash

gradually begins to become more reactive, and contributes towards strength enhancement.

Interestingly enough, despite 58% lower cement content in the HVFAC, its strength, however,

does not show a corresponding decrease.

Porosity

The porosity of the field two concretes at 28 days are plotted in Figure C.3. The porosity

of the HVFAC is comparable to that of a high W/C neat cement concrete. The inflexions in the

curve for the 10% limestone fines concrete is due to a high dosage of superplasticizer used in the

C.6

Figure C.3 Porosity of Field Concretes at 28 Days.

concrete. Its

overall high

porosity cannot be

explained at this

stage of study.

Nonetheless, it is

noteworthy that

the strength of this

concrete is higher

than its counterpart

HVFAC.

Microstructure of Field Concretes

For a better understanding of the mechanistic behavior of these two concretes, their

microstructure at the age of 28 days were studied under a transmitted polarized light optical

microscope and a scanning electron microscope (SEM).

Concrete Containing 10% Limestone Fines

The air voids were observed to be small in diameter (<0.1 mm) and uniformly distributed

in the paste (Figure C.4). The entrained air content was estimated as 4+1%. At least 10 to 15%

cement grains were still unhydrated (Figure C.5), thus implying that further increase in strength

is likely as these cement grains hydrate to form more calcium silicate hydrate (C-S-H) or the

binder matrix of the concrete. The paste-aggregate interface appeared to be well bonded (Figure

C.6). A thin rim of calcium hydroxide (CH) crystals had developed around fine aggregate

particles, as shown in Figure C.7. Limestone fines that had been incorporated as a partial

replacement of sand, were not identifiable under the optical microscope due to the low resolution

of the instrument; under the SEM, however, these fine particles were seen to be embedded in the

C-S-H matrix (Figure C.8). Crystallites of CH of about 10 :m in size, seen earlier (Figure C.7)

at the paste-aggregate interface from optical microscopy, were also identifiable in the paste

C.7

Figure C.4 Small, Circular Air Voids Uniformly Distributedin the Paste.

Figure C.5 Unhydrated Cement Particles (º) in the Paste.

Optical Micrographs: Concrete containing 10% limestone fines.

C.8

Figure C.6 Paste-Aggregate Interface, where A = Aggregate,B = Paste.

Figure C.7 CH (ö) Around a Fine Aggregate Particle.

C.9

Figure C.8 A Particle of Limestone Fine (A) in the Paste (B).

Scanning Electron Micrographs: Concrete containing 10% limestone fines

(Figure C.9). Figure C.10 illustrates the characteristic paste-aggregate interface with some ettringite

needles and CH crystals formed at the interface. The paste mostly consists of C-S-H (Figure C.11).

Fairly large pores have developed, as seen from porosity results also (Figure C.3), but the concrete

is by no means permeable.

High Volume (58%) Fly Ash Concrete

The air voids in this concrete are similar in size and amount as its counterpart concrete

containing fines (Figure C.12).The paste-aggregate interface is well developed (Figure C.13). The

paste contains an abundant amount of unreacted fly ash particles (Figure C.14). Figure C.15 shows

the paste microstructure under the SEM. The paste is not as porous as the counterpart concrete. This

is attributable to its low water-cementitious ratio. Nonetheless, its strength is not as high as the

concrete containing fines because of the lack of C-S-H binder in the paste. Although the W/(C+FA)

of this concrete is only 0.25, the calculated effective W/C is = 0.59. The massive CH seen in the

paste (Figure C.16) may be due to the hydration of cement at such a high W/C. The fly ash particles

in Figures C.16 and C.17 suggest that CH is not related to the reaction of fly ash. It is possible that

C.10

Figure C.9 CH (A) in the Paste.

Figure C.10 Paste-Aggregate Interface. A = Aggregate, B = Ettringite, C = CH.

C.11

Figure C.11 Paste Microstructure, where A = Pore.

Figure C.12 Small, Circular Air Voids Uniformly Distributedin the Paste.

Optical Micrographs: HVFAC

C.12

Figure C.13 Paste-Aggregate Interface, where A = Aggregate,B = Paste.

Figure C.14 Fly Ash Particles in the Paste.

C.13

Figure C.15 Paste Microstructure Showing an Abundance ofUnreacted Fly Ash.

Figure C.16 CH (A) in the Paste.

Scanning Electron Micrographs: HVAC

C.14

Figure C.17 Reacted and Unreacted Fly Ash Particles.

Inferences

Though the paste microstructure of these two concretes is similar in some respects, the lower

strength of the high-volume fly ash concrete is due to (a) the presence of such a large volume of as-

yet unreacted fly ash particles, as opposed to 90% cement by weight in the other concrete containing

10% fines, and (b) its relatively porous paste-aggregate interface. The concrete containing fines has

developed a porous paste due to its higher water-cement ratio. None of these concretes, however,

exhibit any deleterious features such as cracks or segregation of particles.

C.15

Figure C.18 Porous Paste- Aggregate Interface, where A =Aggregate, B = Paste.