ASPHALTmlECHNOLOGY

NEWSA Publication of the National Center for Asphalt Technology, Auburn University Volume 6, Number 1 SPRING 1994

NCAT BEGINS MAJOR RESEARCHPROJECTS ON SMA AND AGGREGATESThe National Cooperative Highway

Research Program (NCHRP) of theTransportation Research Board hasawarded research contracts to NCAT fortwo major research projects: NCHRPProject 9-8, “Designing Stone MatrixAsphalt (SMA) Mixtures” and NCHRPProject 4-19, “Aggregate Tests Relatedto Asphalt Concrete Performance inPavements.” The background andobjectives of these two research projectsare as follows.

Designing Stone Matrix AsphaltMixtures

Stone Matrix Asphalt (SMA) isdefined as a gap-graded aggregate-asphalt hot mix that maximizes theasphalt cement content and coarseaggregate fraction. This provides a sta-ble stone-on-stone skeletal structureheld together by a rich mixture ofasphalt cement, filler, and stabilizingagent.

(Continued on page 2)

SHRP gyratory compactor in use at NCAT by Jack Weigel of Payne and Dolan,Inc. during SHRP Binder and Mix Workshop.

/n this kwie

PJCAT Begins MajorResearch Projects

- Page 1

St-/f?P BinderTests andSpecifications

– Page 3

Putting ResearchInto Practice

- Page 7

Asphalt Forum- Page 10

SpecificationCorner

- Page 12

ResearchIn Progress

- Page 14

Page 2

NCAT’S NEW SMA ANDAGGREGATES RESEARCH

(Continued from page 1)

SMA was developed in Europe and appears to have sig-nificant potential as a durable and rut-resistant pavementlayer. Several states in the U.S. have recently placed SMAprimarily to minimize rutting in hot mix asphalt (HMA)pavements subjected to high traffic volume, heavy wheelloads, and high tire pressures. The approach to date hasbeen to duplicate SMA mixtures developed in Europe,using domestic materials, equipment, and HMA industryexpertise. More than 20 SMA pavement projects have beenconstructed successfully in the U.S. and are now beingmonitored for their performance. Following European prac-tices, Marshall mix design (50 blows) was primarily usedfor designing SMA mixtures for the American projects.

The Federal Highway Administration, state highwayagencies, and HMA industry have identified the need forbetter definition of the currently specified components andproperties for SMA mixtures and the need to consider newtest procedures. Better information is also needed regard-ing type and amount of stabilizer(s), required compactiveeffort, and mixture volumetric for design and placement.

The primary objectives of this $500,000 two-yearresearch project are: (a) to define the materials and theirproperties to maximize durability and rut resistance ofSMA mixtures, and (b) to recommend a SMA mix designprocedure consisting of tests which can predict durability,performance, and moisture susceptibility of SMA mixtures.Dr. Ray Brown, NCAT director, is the principal investigatorof the SMA project.

Aggregate Tests Related to Asphalt ConcretePerformance in Pavements

Approximately 85 percent of the total volume of HMAconsists of mineral aggregates. The performance of HMA isthus significantly influenced by the properties of coarse andfine aggregates. HMA pavement distresses such as strip-ping, rutting, and lack of good friction properties can oftenbe attributed to improper aggregate selection and use.

Current aggregate tests are primarily based on exper-ience with their use in various applications such as unboundbase courses, portland cement concrete and hot mix asphalt.The empirical characterization of aggregates through thesetests does not consider their specific end use or the perfor-mance of the specific final product. For example, it is logi-cal to assume that certain aggregate properties desirable inunbound base courses may not be necessary when aggre-gates are used in HMA applications. Many aggregate testsand specified criteria, therefore, have no relationship to theperformance of the final product such as HMA.

It is evident from the literature available that research onthe relationship of aggregate properties to HMA perfor-mance has been very fragmented. No comprehensive norcoherent research effort has been made to evaluate theexisting aggregate tests, nor to develop new tests that relateto HMA performance. The recently completed StrategicHighway Research Program (SHRP) for asphalt—a $50-million, five-year research effofi&-did not include aggre-ga te research. Al though SHRP has developed aperformance-based asphalt binder system and SUPER-PAVE mix design system, it did not include performance-based characterization of aggregates. SHRP simplyconvened a meeting of an Aggregate Expert Task Group(ETG) which considered the existing aggregate tests andcriteria. Through the Delphi process the ETG recommend-ed guidelines for aggregate testing to be used in theSUPERPAVE mix design system.

This NCHRP project on aggregates is a $500,000 three-year research effort which is expected to result in the rec-ommendation of a set of aggregate tests that relate to theperformance of HMA mixtures. The research will includethe evaluation of existing aggregate tests (such as LosAngeles abrasion, soundness, sand equivalent, flat andelongated particles, and polishing) to assess their ability topredict HMA pavement performance and, where this pre-dictive ability or clear relationship to performance is lack-

(Continued on page 13)

Page 3

SHRP ASPHALT BINDER TESTS AND SPECIFICATIONS

The SHRP binder grading system was discussed in thefall, 1993, issue of Asphalt Technology News. Now, wewill discuss the SHRP asphalt binder tests and specifica-tions.

The following binder tests have been proposed bySHRP to measure various properties:

● High/intermediate temperature properties—Dynamic shear rheometer (DSR)—Rotational viscometer (RV)

● Low temperature properties—Bending beam rheometer (BBR)—Direct tension tester (DTT)

● Durability properties—Rolling thin film oven (RTFO)—Pressure aging vessel (PAV)

SHRP TESTS

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PAVEMENT TEMPERATURE, “C

Figure 1

Figure 1 shows the new SHRP binder tests in relationto conventional binder tests in use today. At high con-struction temperatures such as 135°C (275”F), the viscos-ity of the binder is measured with a rotational viscometer(RV) in lieu of the kinematic capillary tube viscometer. Athigh summer pavement temperatures such as 60”C(140”F) which are critical for rutting, the viscoelasticproperty of the binder is measured with a dynamic shearrheometer (DSR) in lieu of measuring only the viscosityof the binder with a vacuum capillary viscometer. At aver-age pavement service temperatures such as 20”C (68°F)which are critical for fatigue cracking or durability, theviscoelastic property of the binder is measured with adynamic shear rheometer (DSR) in lieu of measuring thepenetration of the binder at 25°C (77”F). At low pavementservice temperatures such as -20”C (-4”F) which are crit-ical for low temperature cracking, SHRP has proposedtwo test methods: bending beam rheometer (BBR) and

direct tension tester (DTT). No tests are being used at thepresent time to measure low-temperature properties of theasphalt binder.

SHRP has proposed the rolling thin film oven (RTFO),which is already in use in some western states, to simulatethe aging of the asphalt binder during mixing and con-struction operations. No accelerated laboratory aging pro-cedure was available prior to SHRP to simulate the agingof the asphalt binder in service.

The pressure aging vessel (PAV) was developed bySHRP to simulate binder aging during five to ten years ofservice life.

A brief discussion of each SHRP binder test and its rel-evance to the SHRP performance graded asphalt binderspecification (given on page 6) follows. It should be notedin the specifications that the test criteria (minimum ormaximum limits) for all grades of binder remain thesame, and only the test temperature is varied according tothe grade selected.

Rotational Wscometer (RV)This is also referred to as Brookfield viscometer. This

test has been used by the polymer industry for many years(ASTM D4402). The rotational viscometer will be used toevaluate the handling and pumping properties of asphalt

applied torquefrom momr

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spindle

asphaltsample

sample chamber

Figure 2

binders (including modified binders) during construction.It will also be used to establish the mixing and com-paction temperatures of the hot mix asphalt (HMA) byconducting the test at two temperatures. Figure 2 shows aschematic of the rotational viscometer.

The asphalt binder sample is poured in a sample cham-ber which is placed in a therrno-container to control thetest temperature. A standard spindle is inserted in the sam-ple chamber. Torque is applied from a motor to the spin-dle to rotate it within the asphalt binder. The torquerequired to achieve 20 rpm speed of the spindle is mea-sured and the viscometer shows the binder viscosity as adigital read out. The rotational viscometer is more suit-able for testing modified asphalt binders (such as asphalt-rubber) than a capillary tube viscometer, which is likely to

get plugged. SHRP asphah binder specifications permit amaximum viscosity of 3 Pa ● s (pascal-second) or 3,000centipoises at 135°C (275°C) to insure that the binder canbe adequately pumped and mixed with the aggregates.

Dynamic Shear Rheometer (DSR)Asphalt binders exhibit viscoelastic behavior, especial-

ly at intermediate temperatures such as 25°C (77”F).Unlike capillary viscometers which only measure the vis-

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cosity, the dynamic shear rheometer (DSR) measures boththe viscous and elastic properties of the asphalt binders. Asample of asphalt binder is sandwiched between twoplates as shown in Figure 3. The bottom plate is fixed.Torque is applied to the top plate so that it oscillates backand forth at a rate of 1.6 cycles per second (representing55 mph speed of vehicles on the highway). As shown inthe figure, one cycle is completed when the top plate goesfrom A to B, back to A, A to C, and back to A.

The DSR measures the complex shear modulus G* (G-star) and the phase angle 8 (delta). G* is a measure ofoverall stiffness which includes both viscous and elasticeffects. Phase angle 8 is used to separate the viscous andelastic components in G*. The higher the elastic compo-nent in G*, the greater is the binder resistance to ruttingand fatigue cracking.

SHRP specifications specify a minimum value of 1.0and 2.2 kilo pascals at the designated test temperature forG*/sin 8 (G star over sin delta) for the original (neat)binder and RTFO residue, respectively. G*/sin 8 is analo-gous to viscosity at 60”C ( 140”F). It can be considered asthe rutting factor. However, it should be realized that theaggregate structure, rather than the asphalt binder, has adominant role in resisting rutting.

SHRP specifications specify a maximum value of5,000 kilo pascals for G* sin 8 (G star times sin delta) ofan asphalt binder which has been aged in the rolling thinfilm oven (RTFO), and the pressure aging vessel (PAV).G* sin 8 can be considered as the fatigue factor. Valuesover 5,000 kilo Pascals are likely to cause fatigue crack-ing. G* sin 6 is analogous to the penetration test which isconducted at 25°C (77°F). However, the penetration test

is an empirical test, whereas G* sin 5 gives test values infundamental engineering units.

Bending Beam Rheometer (BBR)HMA pavements develop low-temperature thermal

cracking when the asphalt binder is too stiff at low pave-ment temperatures. SHRP has recommended the use ofbending beam rheometer (BBR) to evaluate low tempera-ture stiffness properties (creep stiffness and m-value) of

Creep Lmd

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deflection

Load

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Engineering Creep Stiffness

,,mc /, Pr!n~les

m-value

Beam Geometry/

Figure 4

the asphalt binder which has been aged in RTFO and PAV.As shown in Figure 4, a beam of asphalt binder is loadedat mid point and the deflection is noted. By the use ofengineering beam principles, the creep stiffness and m-revalue (slope of loading time versus creep stiffness) aremeasured after a loading period of 60 seconds. The test isconducted at the designated low test temperature to main-tain the integrity of the asphalt binder beam. SHRP spec-ifications specify a maximum value of 300,000 kiloPascals and a minimum value of 0.30 for the m-value tominimize low temperature thermal cracking.

Direct Tension Tester (DTT)Some modified asphalt binders may be stiff at low tem-

peratures but do not develop low temperature thermalcracking, since compared to neat asphalt cement bindersthey can stretch more when pulled. As shown in Figure 5,a direct tension test was developed primarily to accom-modate modified binders. A small dogbone shaped speci-

clongation

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test—

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Page 5

men is loaded in tension at a constant rate until it breaks.Since the failure strains are relatively very small, a laserbeam is used to measure the strain at failure. According tothe SHRP specifications, the failure strain should be atleast 1.0 percent.

Pressure Aging Vessel (PAV)As mentioned earlier, the pressure aging vessel was

developed by SHRP to simulate long-term (5-10 years)aging of the asphalt binders in service. A schematic of thetest equipment is shown in Figure 6. Asphalt binder sam-ples which have been subjected to RTFO aging are pouredin flat sample pans. These pans are placed in a samplerack which is placed in a pressure vessel. The air pressurein the vessel is increased to 2.1 mega pascals or about 300psi to accelerate the aging process. The temperature insidethe vessel is maintained at 90°C (194°F) or 10O°C

(212”F) depending on the binder grade. The samples aresubjected to 20 hours aging in the pressure vessel andthen tested for properties specified in the performancegraded binder specifications.

—Ken Kandhal

pressure v.,,.] sample rack w@. pm

Figure 6

I

Visit of German engineers to NCAT and laboratories in Decembez

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Original Binder

lash Point Temp,

AASHTO T48: Min, “C 230

‘iscosity, ASTM D 4402: b

Max, 3 Pa-s (3000 cP),Test Temp. “C

135

)ynamic Shear, AASHTO TP5: c

52 58 64G*/sin ~, Min, 1.0 kpa

70

Test Temperature @ 10 rad/s, ‘C

dh‘hysical Hardening Index , Report

Rolling Thin Film Oven Test Residue (AASHTO T 240)

4ass Loss, Max, percent 1.0

)ynamic Shear, AASHTO TP5:52 58 64

G*/sin 5, Min, 2.2 kpa70

Test Temp @ 10 rad/see, “C

Pressure Aging Vessel Residue (AASHTO PP1 )

‘AV Aging Temp. “C 90

)ynamic Shear, AASHTO TP5:G“sin 6, Max, 5,000 kpa 25 22 19 16 13 10 7Test Temp @ 10 rad/see, “C

keep Stiffness, AASHTO TP1: f

S, Max, 300,000 kpa,m-value, Min, 0.30 0 -6 -12 -18 -24 -30 -36Test Temp, @ 60 see, “C

)irect Tension, AASHTO TP3: f

Failure Strain, Min, 1.0 % o -6 -12 -18 -24 -30 -36Test Temp @ 1.0 mrrr/min, ‘C

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Pavement temperatures can be estimated from air temperatures using ao algorithm contained in the SUPERPAVE software program or may be provided bytbe specifying agency.

This requirement may be waived at the discretion of the specifying agency if the supplier warrants that the asphalt binder can be adequately pumped andmixed at temperatures that meet all applicable safety standards.

For quality control of unmodified asphalt cement production, measurement of the viscosity of the originaJ asphaft cement maybe substituted for dynamicshear measurements of G*/sin 5 at test temperatures where the asphalt is a Newtonian fluid (generally above 55° C). Any suitable standard means ofviscosity measurement may be used, including capillary or rotational viscometry.

The physical hardening index h accounts for physical hardening and is calculated by h = (S24/S 1) m 1 /m24 where 1 and 24 indicate 1 and 24 hours ofconditioning of the tank asphalt. Conditioning and testing is conducted at the designated test temperature. Values should be calculated and reported. S is~h~ Creep stiffness after 60 seconds loading time and m is the slope of the log creep stiffness versus log time curve after 60 seconds loading time.

The PA’v’ aging temperature is 100° C, except in desert climates, where it is 110° C.

If the creep stiffness is below 300,000 kPa, the direct tension testis not required. If the creep stiffness between 300,000 and 600,000 kPa the direct tensionfailure strain requirement can be used in lieu of the creep stiffness requirement. The m-value requirement must be satisfied in both cases.

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PUTTING RESEARCH INTO PRACTICE

1. LABORATORY EVALUATION OF THEADDITION OF LIME TREATED SANDTO HOT MIX ASPHALT(Hanson, Shields and Brown)

Hydrated lime has proven to be an effective additivefor reducing moisture damage susceptibility of HMAmixtures. The current method most often used to addlime to HMA is to add it to the entire aggregate stream.Recent field trials have shown that it is feasible to addhydrated lime just to the sand fraction in amounts thatare equivalent to the desired concentration on the totalaggregate basis. This would allow set up of a centralfacility for adding lime to the sand fraction of a HMAaggregate. The lime/sand mixtures could then be trans-ported to a HMA facility and mixed with the remainingaggregate fraction.

The objective of this study was to conduct a labora-tory study to determine whether adding the lime just tothe sand fraction and then adding the sand/lime mixtureto the remainder of the aggregate would produce thesame results as when the lime is added to the entireaggregate stream.

This study consisted of mixing a known strippingaggregate (Georgia granite) with three sand types (gran-ite, quartz, and limestone fine aggregates) which result-ed in three different HMA mix types. The lime wasmixed into the aggregates by the following four meth-ods: (a) dry lime added to the entire moist aggregatemixture, (b) dry lime added to the moist sand fractiononly, (c) lime slurry added to the entire aggregate frac-tion, and (d) lime slurry added to the sand fraction only.Four lime contents (0.0, 0.5, 1.0 and 1.5 percent) byweight of the total dry aggregate, were used. HMA mix-tures were evaluated for moisture susceptibility usingthe modified Lottman and Root-Tunnicliff procedures.

The following conclusions can be drawn from thisstudy:●

●

The two methods of lime addition (lime to sand andlime to total aggregate) produced HMA mixtures thathad equivalent reductions in moisture damage sus-ceptibility.

The greatest reduction in moisture susceptibility of

●

the HMA mixtures studied occurred from increasingthe lime content from 0.5 to 1.0 percent, with lesseffect resulting from a 1.0 to 1.5 percent increase.

The addition of lime in the form of a slurry, in mostcases, proved to be better (in terms of higher retainedstrengths) than the addition of lime to a moist aggre-gate.

z. RATIONAL METHOD FOR LABORATORYCOMPACTION OF HOT MIX ASPHALT(Blankenship, Mahboub and Huber)

This paper is based on a study titled, “Gyratory Com-paction Characteristics: Relation to Service Densities ofAsphalt Mixtures,” conducted as Task F of the SHRPContract AOO1. A SHRP gyratory compactor with thefollowing specifications was used:●

●

●

●

Angle of gyration, 1.000

Speed, 30 rpm

Vertical pressure, 0.6 MPa (87 psi)

100-mm and 150-mm diameter molds

The primary objective of this study was to determinethe number of gyrations (N~e,l,n) required to representvarious traffic levels in different climates.

N~,,i,n is defined as the compactive effort (number ofgyrations at a specified pressure) at which the air voidlevel of the compacted HMA mixture is measured forvolumetric design and mix characterization in SHRPSUPERPAVE mix design.

Cores were obtained from existing HMA pavementswhich had more than 12 years of traffic exposure to rep-resent pavements that have densified to their design per-cent air voids. It was assumed in this experiment that thepavements were designed to have final air voids of 3-5percent, and the pavements were placed at 7-9 percentair voids. The testing matrix incorporated 18 cores rep-resenting three climates (hot, warm and cool), three traf-fic levels, and upper and lower layers.

Air void contents of the pavement cores were deter-mined by measuring the bulk specific gravity and max-imum specific gravity of the cores. The aggregate wasrecovered from the cores by solvent extraction. The

Page 8

recovered aggregate was mixed with a neat AC-20asphalt cement. The mixture was subjected to short termaging and then compacted in the SHRP gyratory com-pactor to obtain compaction curves (number of gyra-tions versus air void content). The field air void contentswere used to establish the design number of gyrations(N~e,l,n). Again, it was assumed that the air void contentwas 8 percent for the gyration level at zero traffic. Thelower layer data (more than four inches from the sur-face) showed no real relation to traffic (gyrations).Hence a total of 30 data points (two data points x 15cores) were used to obtain three regression lines (forhot, warm and cool climates) of traffic in ESALS versusnumber of gyrations. These regression lines were usedto prepare the table for determining N~e,,,n for a specifictraffic category and climatic conditions to be used inSHRP SUPERPAVE Level I mix design. It should benoted that only 15 cores were used to develop this tableand, therefore, additional work is needed to increase theprecision of N~e,,,n.

3. INVESTIGATION OF AASHTO T283 TOPREDICT THE STRIPPING PERFORMANCEOF PAVEMENTS IN COLORADO(Aschenbrener and McGennis)

Moisture damage to HMA pavements has been a spo-radic but persistent problem in Colorado even thoughlaboratory testing is performed to identify moisture sus-ceptible mixtures and liquid antistripping additives areused if needed. The laboratory conditioning (AASHTOT283) was often less severe than the conditioning theHMA pavements encountered in the field.

Twenty sites of known field performance with respectto moisture susceptibility, both acceptable and unac-ceptable, were identified. Materials from these siteswere tested using several versions of AASHTO T283.The standard AASHTO T283 procedures includedshort-term aging (16 hours at 60”C for loose mixtureand 72 to 96 hours at 25°C for compacted specimens),limits on air voids (6-8 percent), limits on saturation(55-80 percent), and freezing. The variations to AASH-TO T283 included: (a) no freeze, (b) vacuum saturationfor 30 minutes regardless of the saturation levelachieved, and (c) no short-term aging. The followingconclusions and recommendations are drawn from thisstudy:

“ Generally, AASHTO T283 is a reasonable predictorof moisture susceptibility of HMA mixtures. Known‘~ t- i; performing mixtures (Sites 1-7) exhibited high-er retained tensile strength (TSR) values. Poor per-forming mixtures (Sites 13-20) exhibited lower TSRvalues. For these sites showing well and poor per-forming mixtures, any of the variations in the AASH-

●

●

TO T283 procedures (that is, freeze, no freeze, 30-minute vacuum saturation with freeze) would haveadequately predicted observed moisture susceptibili-ty.

Marginally performing HMA mixtures (Sites 8-12)were not as well identified by the standard AASHTOT283 test, with or without a freeze cycle. However,the standard procedure modified to include a 30-minute vacuum saturation period was more effectivein predicting the performance of these marginal sites.

Use two test severity levels. For HMA pavementsexperiencing high traffic, high temperature-s and highmoisture, Severity Level 1 should be used, whichincludes no short-term aging, vacuum saturation for30 minutes with 610 mm of mercury, and a freezecycle. For HMA pavements with low traffic or areaswithout extremely high temperatures, a SeverityLevel 2 should be used, which corresponds to ASTMD4867 (Root-Tunnicliff procedure) w i t h o u t t h eoptional freeze cycle.

4. EVALUATION OF LONGITUDINAL JOINTCONSTRUCTION TECHNIQUES FORASPHALT PAVEMENTS (Kandhal and Rae)

Common problems associated with longitudinaljoints in HMA pavements are the formations of cracksalong the joint, ravening, and widening of cracks due tosubsequent ingress of water. It is believed that theseproblems occur when there is a substantial difference indensities on either side of the joint or overall low jointdensity. Although several longitudinal joint constructiontechniques are specified and practiced in different states,the relative effectiveness of these methods has not beenestablished. This study was undertaken to evaluateseven techniques in a project in Michigan and eighttechniques in a project in Wisconsin. Both projectsinvolved a dense-graded HMA surface course overlay.Each technique was used on a 500-foot (152-m) test sec-tion. The following different techniques were used inboth projects:●

●

●

●

●

●

●

Rolling the joint from the hot side (Technique A).

Rolling the joint from the cold side (Technique B).

Rolling the joint from the hot side six inches (152mm) away from the joint (Technique C).

Michigan wedge (1: 12 slope) joint without tack coat.

Michigan wedge (1: 12 slope) joint with tack coat.

Restrained edge compaction with a hydraulicallypowered wheel which rolls alongside the compactor’sdrum (Wisconsin project only).

Use of a cutting wheel to cut off 1 1/2-2 inches (38-51 mm) of the unconfined, low density edge of the

Page 9

initial lane after compaction while the mix is still ●

plastic.

● Use of a AW-2R joint maker, which consists of adevice attached to the side of the screed at the corner. .The device forces extra material at the joint throughthe extrusion process prior to the screed.

The edge restraining device and the cutting wheelsections appear to be the best on the Wisconsin pro-ject.

Among the three rolling techniques attempted, Tech-nique A gave the highest density at the joint followedby Technique C, on both the Michigan and Wisconsinprojects.

The visual evaluation of joints on both projects will

Based on the density data at the joint and visualinspection of the joints after the first winter the follow-ing conclusions were drawn: be continued for at least five years. It is quite possible● The cutting wheel and Michigan wedge joint sections that the tentative rankings reported in this paper may

appear to be the best on the Michigan project. change based on the long-term field performance.

Attendees and instructors at NCATk Binder and Mix Workshop in December Left to right: (Row I) Ken Kandhal, Hussain Bahia,Jay Winford, Sarah Williams, Randy Mountcastle, Doug Hanson, Jack Weige[, Hugh Gal[ivan, (Row 2) Mark Ishee, Jim Davis, Mor-ris Steward, Jeff Frani, Richard Maddox, Mike Novak, Darren Phillips, (Row 3) Timothy Saue< Gene Danicich, Jeff Bar~ Earl Ru.Y -sell, Trent Baldwin, Larry Shively, Stephen Russell, Kevin Suite< (Row 4) Mikael Thau, Ray Brown, and Bob McGennis. Not pictured:Dale Gifford.

Page 10

ASPHALT FORUM

NCAT invites your comments and questions. Questions and responses are pubIi8kd ~ each issue ofAsphtdl Technology News. Some are edited for consistency and space.

k

Australia (John Bethune, AustralianAsphalt Pavement Association)

Six different asphalt surfacing types have beenplaced on a rigid plain concrete pavement on a majorMelbourne metropolitan arterial road. The followingsurface characteristics will be measured initially andat regular intervals thereafter for comparative pur-poses: (a) noise, (b) skid resistance, (c) spray gener-ation, (d) roughness, (e) texture, and (f) durability.

Virginia (John Muhlke, Q/C Resource)The modified Rice test developed for SHRP by

NCAT for determining maximum theoretical specif-ic gravity of HMA mixtures, requires maintaining 30~ 1 mm vacuum for 15 minutes. I have found that a

vacuum bleed-off valve installed in the line betweenthe pump and the vapor trap helps to maintain thevacuum consistently while the pump is running fulltime. Also, the use of a vibrating table (availablecommercially) gives repeatable results and frees up15 minutes of the technician’s time that would other-wise be spent agitating the pycnometer every twominutes.

Kentucky (Dwight Walker, KentuckyTransportation Cabinet)

We intend to work with available SHRP binderand mixture equipment to gain experience. We areplacing a trial project using hydrated lime as an anti-stripping additive.

Texas (Maghsoud Tahmoressi, Texas DOT)

We have developed a new HMA mixture designcalled Coarse Matrix High Binder (CMHB) which isconsidered ideal for designing crumb rubber modi-fied (CRM) mixtures and stone matrix asphalt(SMA) mixtures.

Does any DOT have specifications or approvalprocesses on hot mix truck release agents?

Rhode Island (Francis Manning, Rhode IslandDOT)

Has anyone looked into snow plow damage to

pavements and their markings? Do any states useskid blocks to raise plow blades off the pavement?

Hawaii (Frank Uyehara, Hawaii DOT)The disposal of rubber tires in landfills will be pro- %

hibited after July 1, 1994.

The following responses address the questionfrom Samuel Miller of the Maryland State HighwayAdministration, “What experience do other stateDOTS have using crushed gravel in hot mix asphaltsurface mixtures ?”

Ontario, Canada (Kai Tam, Ontario Ministry ofTransportation)

Crushed gravel surface mixes are mainly used insecondary highways with traffic less than about3,000 AADT. This is because of the poor friction andmix stability characteristics of gravel aggregate.Also, there could be a need for an antistripping agentin the HMA mixture. Performance of the crushedgravel mixtures has been good when mixes are prop-erly designed.

New Jersey (Eileen Connolly, New Jersey DOT)The New Jersey DOT has used crushed gravel in

friction course mixes for about 20 years. The gravelis required to have less than 20 percent carbonatesand have at least one crushed face. The frictioncourses have performed well in increasing the fric-tional characteristics.

Texas (Maghsoud Tahmoressi, Texas DOT)The Texas DOT allows the use of crushed gravel

in HMA mixtures provided that the gravel has a min-imum of 85 percent particles retained on the No. 4sieve with two or more mechanically producedcrushed faces. According to our experience, gravelmixtures have a tendency to be tender and suscepti-ble to moisture damage.

The following responses addressfrom Eileen Connolly of New Jersey

the questionDOT, “Have

Page 11

other states which have constructed SMA pavementsexperienced post-construction bleeding ?”

Georgia (Ronald Collins, Georgia DOT)

The Georgia DOT has not experienced post-con-struction bleeding on SMA projects, but we haveexperienced some loss in surface friction for ourcoarse SMA used as an intermediate layer in a testsection placed in 1991. As a result, we typicallyselect optimum asphalt content corresponding to 3.5to 4.0 air voids based on the 50-blow Marshall com-paction. We are also convinced that the field verifi-cation of the mix design is just as critical for SMAmixtures as it is for conventional dense-graded HMAmixtures.

Wisconsin (Stephen Shober, Wisconsin DOT)

Wisconsin placed its first SMA in 1991 on I-94near Waukesha. Since then we have constructedseven other SMA projects using different mixtures.We have not experienced any “post-constructionbleeding” in any of these projects. However, wehave experienced flushing during construction onseveral occasions. This problem has been limited tothe polymers and seems to be temperature related,except for one instance that can be traced to prob-lems with the feed mechanism for the additives atthe HMA facility.

Virginia (Bill Maupin, Virginia ‘IYansportationResearch Council)

Virginia’s SMA pavement constructed in 1992started to bleed at stop lights in 1993. An investiga-tion by NCAT revealed no obvious causes. However,slight changes were made in the job mix formula gra-dation (less material passing the No. 4 and 200sieves) and AC-30 asphalt cement was substitutedfor AC-20 for a SMA placed by Virginia DOT in1993.

Connecticut (Charles Dougan, Connecticut DOT)We have been using a solvent called Premium Safe

Solv in extraction tests for the past two years as analternative for chlorinated solvents. This is a productwhich does not require rinsing with water and, there-fore, does not increase testing time.

Warren Foster of the Maine DOT had asked, “Areother states having flushing problems when usingAC-10 asphalt cement in hot weather?” We use AC-10 only in mixes containing reclaimed asphalt pave-ment (RAP) material so that the resulting recycled

asphalt cement meets the specified penetration rangeof 60 to 100.

South Carolina (Milt Fletcher, South CarolinaDOT)

Richard Downs of Hughes Asphalt Companyasked the question, “Many states are adopting thespecifications that have reduced the amount of mate-rial passing No. 200 (P200). With this practice,should not the design air voids in the total mix beincreased to reduce the rutting potential becausereplacing the P200 material with asphalt cementcould result in an unstable mix?” The reduction inP200 does not necessitate that the asphalt content beincreased to fill air voids. Air voids can be adjustedby changing the VMA (voids in the mineral aggre-gate) of the HMA mixture. The VMA can be changedby using different proportions of coarse and fineaggregates.

Georgia (Ronald Collins, Georgia DOT)Eileen Connolly of the New Jersey DOT asked the

question, “Are there HA4A quality control proceduresbeing used that allow the contractors to obtain sam-ples and test them for acceptance ? What testing isdone by the state to verifi the contractor’s testresults ?”

Georgia has established a procedure to allow forcontractor acceptance sampling and testing of hotmix asphalt. Nineteen projects where the contractoris required to perform extraction acceptance testinghave been let to contract. While all the projects havenot been completed yet, early indications are that asignificant savings in manpower can be realizedwithout sacrificing quality.

The contractor’s technician must pass a writtenexamination as well as demonstrate, by hands-ontests, a proficiency in the perfm-mance of the requiredsampling and testing pr~dure. The contractor’slaboratory is certified to assure that all equipmentused is in calibr~icm and meets departmental testingstandards.

Companion samples are taken during the day’soperation and are randomly selected by departmentpersonnel for testing, and these are compared to thecontractor’s results. When the sample selected com-pares favorably with the contractor’s results, thedepartment accepts the contractor’s results for thatlot of material. When the results do not compare,additional companion samples are tested and DOTresults are used for acceptance, and an investigationis made to determine why the results varied.

Page 12

SPECIFICATION CORNERVermont-The Vermont Agency of Transportation (VAOT)is moving forward with the QC/QA (quality control/qualityassurance) concept based on the mutual desire by both theHMA industry and VAOT to produce the best product possi-ble. HMA compaction specifications, which include bonuspayments as well as reduced payments based on compaction

quality, have been developed. Specifications which willinclude a surface tolerance (ride) criterion and the HMA mixquality (based on air voids) are being developed.

Georgia-The Georgia DOT has let to contract its first pro-

ject (I-95 near Savannah) using SHRP binder specifications.Performance grade (PG) 70-22 was specified for the open-graded friction course, and PG 76-22 was specified for theSMA mixtures. These paving grades are higher than can bemet with our conventional asphalt cements. However, they arerecommended by SHRP for high-traffic situations in Geor-gia’s climatic conditions.

Wisconsin-Asphalt cements will be specified in 1994 basedon a dual specification for either penetration-graded or viscos-ity-graded materials. Beginning in 1994, the Wisconsin DOT(WisDOT) will specify, by special provision, an optionalnotched and tapered (12: 1) longitudinal joint for HMA pave-ments. Depending on the results, this method could become astandard, possibly by 1995. The WisDOT has implemented apolicy to pay contractors for the asphalt cement contained inthe reclaimed asphalt pavement (RAP) used in hot-mix recy-cling to encourage the use of RAP in mix designs.

Ontario, Canada—The new end result specification forpavement compaction developed in 1993 has been discussedwith the HMA industry, and is being implemented on select-ed contracts in 1994.

.,Hawaii-State law now re&-es the use of glass in HMAbase course mixtures when the cost is. less. Hawaii DOTaccepts alternate bids for base course mixtures: virgin mix-tures, recycled mixtures with 50 percent maximum RAP, andmixtures with 10 percent maximum glass.

Texas-Implementation of QC/QA specifications will beginthis year with 50 projects anticipated to be let. Full imple-mentation will take place in 1995. More than 10 projects willbe built this year using the coarse matrix high binder (CMHB)mix design philosophy; About ten projects will also be con-structed in 1994 incorporating crumbhibber modified (CRM)in HMA by the wet and dry procesl++i!

Kentucky-An extensive training and certification programfor contractors and state personnel involved with controllingand accepting HMA has been initiated. Work is being done toachieve greater stone-to-stone contact in large stone basecourse mixtures. It has been planned to use effective specificgravity of the aggregate in VMA calculations.

Maine-Specifications are being developed for crumb rubbermodified HMA mixtures. A committee has been formed todevelop QC/QA specifications.

Nevada—An end result specification for HMA will be imple-mented on three projects this year. Specifications have beendeveloped for a polymer-modified asphalt cement, designatedAC-30R which will be used on one project this constructionseason.

Indiana—SHRP specifications for asphalt binder andHMA mixture will be used for three projects to be con-structed in 1994. One project will require SUPERPAVELevel 1 mix design procedure and field verification of thedesign. The other two projects will also use Level 1 mixdesign procedure to further verify the mix designs using theMarshall method. The SHRP asphalt binder grades to beused on these projects are PG 58-28, PG 58-34, and PG 64-34.

ansas-The NAA (National Aggregate Association) flowKtest was modified to measure the particle shape and surfacetexture of the fine aggregate (material passing No. 4 sieve). Avolumetric flask will be used in lieu of the bulk specific grav-ity test as an input in the test method. This new test and spec-ification has been implemented to replace the percent crushedfaces test (for fine aggregate) which was not indicative of themix performance in the field.

Montana-Specifications for hot-mix recycling have beenrevised to allow up to 50 percent RAP in base mixtures, 35percent RAP in low-volume road surface mixtures, and 10percent RAP in high-volume road surface mixtures. The useof polymer-modified asphalt cements, which are specifiedgenerically, is on the increase especially for highways carry-ing heavy traffic.

Oregon-The Environmental Conditioning System (ECS)developed by SHRP will be used in 1994 in lieu of the Indexof Retained Strength (IRS) (modified AASHTO T 165) tomeasure the moisture susceptibility of open-graded mixtures.A minimum ratio of 0.80 after ECS will be specified. Dense-graded mixtures will continue to be designed using the IRS.

Page 13

NCAT’S NEW SMA ANDAGGREGATES RESEARCH

A wide variety of aggregates will be evaluated in thisproject. Prithvi (Ken) Kandhal, NCAT assistant director, is

the principal investigator. NCAT would like to identify

aggregates which do not meet conventional aggregate(Continued from page 2)

specifications but otherwise give satisfactory performance

ing, to develop new tests. The characterization of mineral in HMA pavements, and vice versa. If you have such infor-fillers including baghouse fines will also be attempted. mation please contact NCAT at (205) 844-6228.

Engineers, technicians, and instructors at SHRP Binder and Mix Workshop at NCAX January, 1994. Left toRight: (Row 1) Jerry Hancock, E d w a r d D. Brummitte, R o b e r t D. Bistoc M i k e Bailey, W i l l i a m R. Coy;(Row 2) M i c h a e l Bambrick, K e n Kandhal, F r a n k Butler; (Row 3) Hamad Abdul- Wahab, Hussain Bahia,Ibrahim Asi, Doug Hanson; (Row 4) Ray Brown.

RESEARCH IN PROGRESS

The following research projects pertaining to hot mix asphalt (HMA) pavements are currently in progress.

STATE PROJECT RESEARCHER(S) COST COMPLETION OBJECTIVESDATE

%Iaska Rutting of Asphalt Pavements Esch, Alaska DOT $190,000 December ’94 Evaluate the contribution of studdedtire wear and displacement to rutdevelopment.

Performance Based Asphalts Sterley, Alaska DOT 45,000 December ’94 Determine the ability of modifiersto produce different PBA and SHRPgrades from Alaskan North Slopecrude oil.

~rkansas AIJ~rp Additives: Ulrich, University of Arkansas 45,000 April ’95 Quantify the presence of anti-stripadditives in HMA.

New Martial Equipment Austin, Arkansas DOT 50,000 July ’95 Evaluate the new SHRP equipment,Technology procedures, and products.

Georgia Round Robin Testing of Lai, Georgia Tech and Caylor, 130,000 February ’97Modified Georgia Loaded Georgia DOT

Title self-explanatory

Wheel Tester

Evaluating Methods of Brown, Georgia DOT 64,600 December ’96 Evaluate the performance of HMAModifyin HMA Pavements

tUsing Ru ber Modifierspavements containing crumbrubber of different gradation andconcentration and mixeddifferently.

Kansas Full Depth Bituminous Fager, Kansas DOT 75,000 December ’99 Evaluate various additiveRecycling of 1-70 combinations in hot and cold

recycling.

Oklahoma Engineering Properties of Ayers, Oklahoma State 70,000 1994Blended Asphalt Cements University

Determine the effects of mixingdifferent asphalt cements.

Oregon Implementation of SHRP Oregon State University 91,600 January ’95Asphalt Binder Tests

Evaluate SHRP binder test in termsof repeatability, reliability andrelation to mix performance.

Crumb Rubber Modifiers in Hunt, Oregon DOT 150,000 June ’99 Determine the most cost effectiveAsphalt Concrete Pavements crumb rubber modified HMA

mixture.

I

STATE PROJECT RESEARCHER(S) COST COMPLETION OBJECTIVESDATE

Oregon Porous Pavements Hicks, Oregon State University 114,000 September ’94 Develop improved guidelines forthe use,of porous pavements.

Overlay Design for Unstable Bell, Oregon State University 83,100 July ’94 Evaluate the effectiveness ofI-IMA Mixes overlays of rutted HMA pavements

and develop criteria for theirdesign.

Rhode Island Viable Use of Crumb Rubber for Lee, Kovacs and Marcus, 158,000Highway Construction

November ’94 Laboratory evaluation of HMAUnwersity of Rhode Island mixtures containing different

amounts and types of crumbrubber.

South Carolina Utilization of Waste Tires in Amirkhanianf 333,800 December ’95 Investigate the use of waste tiresAsphaltic Materials Clemson Unwersity in HMA and develop a generic,

rubber modified mix designsystem.

Texas Re cling Second GenerationT

Crockford, 200,000 August ’94 Title self-explanatoryAsp alt Rubber Pavements Texas A & M

Wisconsin Development of Safety Based Berg, University of Wisconsin 70,200 January ’95 Determine the de ree of rutting atStandards for Rutting and Schmiedlin, Wisconsin f?which safety is a ected and

DOT maintenance is required.

Performance Evaluation of Rut- Johnson, Wisconsin DOT 100,000 December 2000Resistant Asphaltic Concrete

Monitor the long-term

Pavementsperformance of rut-resistant HMAmixtures on interstate highways.

Transportation Field Procedures and Equipment Cominsky, Brent Rauhut 900,000 September ’96Research Board to Implement SHRP Asphalt Engineering ;:$%:z:;s;%!%;r

Specifications HMA mixture production.

Design and Evaluation of Large Button, 300,000 November ’94Stone Mixtures

Title self-explanatoryTexas A & M

Australia Asphalt Fatigue Sharp, A $250,000 June ’96 Develop a simple fatigue testAustralian Road Research Board method to enable ranking of

conventional and modified HMAmixtures.

Australian Precision Study Oliver A .$120,000 September ’95 Determine the precision of theAustralian Road Research Board dynamic creep test and resilient

modulus test for Iaboratoysamples.

(

NCAT’S 1994 Asphalt Technology Course Attendees and Instructors

Row 1: Mark Swanlund, Wi l l iam C. Quillin, Burean E HuE Frank M. Kreis, Brian Egczn, James Cravens.Row 2: Terry Hughes, Larry Steven Moore, Dan Wegman, Ken Kandhal, Gary L. Owens, John Haddock, Stan Graczyk,Doug Hanson.

National Center for Asphalt Technology211 Ramsay Hall Non-Profit Organization

Auburn University, AL 36849-5354 U.S. PostagePAID

PERMIT NO. 9Auburn University, AL 36849