With any hot-mix asphalt (HMA) pavement, the applied loads ulti-mately must be carried by the aggregate. In addition to meeting mini-mum aggregate quality requirements, the proper aggregate gradingmust be used if the HMA is to perform satisfactorily in service. Theaggregate gradation is important for ensuring that the proper aggregatestructure and mixture volumetric properties are achieved. The findingsof an evaluation of aggregate size characteristics—namely, nominalmaximum aggregate size (NMAS) and gradation—in stone matrix as-phalt (SMA) and Superpave mixtures are described here. The studyobjectives were twofold. The first objective was to verify that the SMAmix design procedure developed for the NCHRP 9-8 project was ap-plicable to NMASs other than 19 mm. Second, mixture properties ofSMA and Superpave mixes with the same NMASs were compared.Mixture volumetric properties, wheel tracking tests, and permeabilitytests were used to make comparisons. The test data indicated that theNCHRP 9-8 mix design approach for SMA mixes was indeed appro-priate for various NMASs. Although differences in the wheel trackingresults of the SMA and Superpave mixes were observed, none of themixes experienced excessive permanent deformation. Permeabilityresults for the SMA mixes indicated that, for a given NMAS, mixeswith a smaller breakpoint sieve were less permeable. The SMA mixeswere relatively more permeable than the Superpave mixes. Overall, theSuperpave mix gradations above the restricted zone exhibited the leastamount of rutting and were the most impermeable.

Stone matrix asphalt (SMA) has been used successfully in the UnitedStates since 1991. However, it was not until 1995 that a standardmixture design procedure was developed by the National Center for Asphalt Technology for TRB under NCHRP Project 9-8 (1,2).This version of the procedure was applicable to SMA having a nominal maximum aggregate size (NMAS) of 19 mm. Thus, furtherstudy was warranted to extend the design procedure to include otherNMASs.

Hot-mix asphalt (HMA) mixtures with a large maximum aggre-gate size generally exhibit a resistance to permanent deformationthat is superior to that of mixes with a smaller maximum size (3–9).The effect of NMAS and particle size distribution of Superpavedesigned mixtures is of considerable interest. Significant aggregatestudies have been conducted since the conclusion of the StrategicHighway Research Program; however, research was needed toobjectively assess the role of NMAS and gradation in the overallperformance of HMA mixtures. NMAS and gradation of Superpavemixtures, in which SMA mixtures with the same NMAS were usedas the basis for comparison, are examined here.

TRANSPORTATION RESEARCH RECORD 1681 Paper No. 99-1429 19

OBJECTIVES

The objectives of the study were twofold. The first objective was toverify that the SMA mix design procedure developed for the NCHRP9-8 (1) project was applicable to NMASs other than 19 mm. Second,mixture properties of SMA and Superpave mixes with the sameNMAS were compared.

SCOPE

A hard, angular trap rock aggregate exceeding all the Superpaveaggregate quality requirements was selected for the investigation.SMA mixes were designed with five NMASs (25, 19, 12.5, 9.5, and4.75 mm). For each NMAS, SMA mixtures with different break-point (BP) sieves were investigated, providing a variance of grada-tion. The BP sieve is defined as the sieve size distinguishing therelative proportions of coarse and fine aggregate. Because the def-initions for coarse and fine aggregate vary with respect to NMAS,the BP sieve may be thought of as the separation point of the gra-dation so that the greatest concentration of aggregate exists abovethe division. Superpave mixtures with gradations above and belowthe restricted zone (ARZ and BRZ, respectively) were tested for the9.5- and 25-mm NMASs. A total of 15 mixes were evaluated (11SMA and 4 Superpave).

All mixture design and test specimens were compacted with theSuperpave gyratory compactor. The SMA and Superpave mixeswere compacted to Ndes= 100 and Ndes= 96 gyrations (Ndes= designnumber of gyrations), respectively. The volumetric properties foreach mix were evaluated. Six cylindrical wheel tracking test speci-mens were compacted at the optimum asphalt content to 4 percentair voids. Wheel tracking tests were conducted at 49°C and 64°Cwith an asphalt pavement analyzer (APA). Six cylindrical perme-ability test specimens were compacted at the optimum asphalt con-tent. Pairs of these were compacted at three different N gyrations toproduce a range of air void levels for each mix. Permeability testswere conducted by the falling-head method. The materials and testsdescribed were selected in an attempt to accentuate the effects ofNMAS and aggregate gradation on the response variables as muchas possible.

MATERIAL PROPERTIES

The trap rock aggregate source selected for this study was chosenbecause of its high quality. It was important to minimize effects ofaggregate properties other than NMAS and gradation. This trap rock

Evaluation of Aggregate Size Characteristics in Stone Matrix Asphalt and Superpave Mixtures

TODD A. LYNN, E. RAY BROWN, AND L. ALLEN COOLEY, JR.

T. A. Lynn, APAC Materials Services, 3005 Port Cobb Drive, Smyrna, GA30080. E. R. Brown and L. A. Cooley, Jr., National Center for Asphalt Tech-nology, 211 Ramsay Hall, Auburn University, Auburn, AL 36849.

has proven to be particularly suited for SMA, primarily because of itstoughness (low Los Angeles abrasion loss percentage). As a result,this aggregate does not experience excessive breakdown during mix-ing and compacting. The properties for the trap rock aggregate areindicated in Table 1. Aggregate stockpiles were separated into indi-vidual sieve size fractions for more controlled proportioning in thelaboratory.

The mineral filler and stabilizing fiber used throughout this studywere limestone and cellulose, respectively. The properties of bothare indicated in Tables 2 and 3. A PG 64-22 binder was used for allspecimens.

MIXTURE DESIGNS

Eleven SMA mixes were designed for the various NMAS and BPsieve combinations. Hereafter, the notation NMAS/BP is used to referto these mixes. The mixes are as follows:

• 25-mm NMAS/12.5-mm BP (25/12.5),• 25-mm NMAS/9.5-mm BP (25/9.5),• 25-mm NMAS/4.75-mm BP (25/4.75),• 19-mm NMAS/4.75-mm BP, Phase I gradation (19/4.75-IB),• 19-mm NMAS/4.75-mm BP, Phase II gradation (19/4.75-II),• 12.5-mm NMAS/9.5-mm BP (12.5/9.5),• 12.5-mm NMAS/4.75-mm BP (12.5/4.75),• 9.5-mm NMAS/4.75-mm BP (9.5/4.75),• 9.5-mm NMAS/2.36-mm BP (9.5/2.36),

20 Paper No. 99-1429 TRANSPORTATION RESEARCH RECORD 1681

• 4.75-mm NMAS/2.36-mm BP (4.75/2.36), and• 4.75-mm NMAS/1.18-mm BP (4.75/1.18).

Two different 19-mm mixes were included in this study for com-parison. The 19/4.75-IB mix was included because most of the test-ing for it had already been completed as part of another phase ofresearch. The shape of the gradation curve for this 19-mm gradationdiffered slightly from the 19/4.75-II mix that had a gradation curvesimilar to all the other SMA mixes.

The mix designs were done in accordance with the proceduredeveloped for NCHRP Project 9-8 (1). For each NMAS/BP combi-nation, a minimum of three trial blends were mixed and compactedat an estimated optimum asphalt content. The design gradation wasselected based on voids in the mineral aggregate (VMA) and voidsin the coarse aggregate (VCA). VCA of an HMA mixture is definedas follows:

where

VCA = voids in coarse aggregate of the mixture,Gmb = bulk specific gravity of the compacted mixture,Gca = bulk specific gravity of the coarse aggregate in the

mixture, andPca = percentage of coarse aggregate in the mixture.

The trial blend with a minimum VMA of 17.5 percent that satisfiedthe condition of stone-on-stone contact (VCA in the compacted

VCA mb

caca= −

×

100 GG

P

TABLE 1 Properties of Trap Rock Aggregate

mix less than the VCA in the dry-rodded condition) was chosen asthe design gradation. Once the design gradation was selected, theasphalt content was varied in order to determine the optimum amountof binder for the mix. Optimum asphalt content was selected on thebasis of voids total mix (VTM). The targeted design VTM was 3.75 percent. Although the actual mix VTM varied somewhat, thedesign VTM for each mix was between 3.5 and 4.0 percent in accor-dance with the design procedure. The final minimum design VMAwas 17 percent.

Four Superpave mix designs were developed for two differentnominal maximum sizes for comparison purposes. These mixes in-cluded two 9.5-mm mixes and two 25-mm mixes. ARZ and BRZ gra-dations were developed for each of these NMASs. These are referred

Lynn et al. Paper No. 99-1429 21

to here as 9.5ARZ and 9.5BRZ for the 9.5-mm mixes and 25ARZand 25BRZ for the 25-mm mixes. The Superpave mixes representtwo common nominal maximum sizes and were selected becausethey represent the endpoints of the Superpave NMAS range.

MIX DESIGN GRADATIONS

The SMA design gradations for each NMAS/BP combination areindicated in Table 4. Table 5 presents the design gradations for theSuperpave mixes. The mixture gradations were plotted on 0.45 powercharts as indicated in Figures 1 and 2. Each SMA gradation curve hadthe same general shape except for the 19/4.75-IB, which was slightlydifferent. The plots of Figures 1 and 2 indicate that the ARZ blendswere fine gradations. These were typical of traditional HMA mixturedesign gradations. The figures also indicate the similarities of the BRZand SMA gradations. The BRZ gradations had the same general shapeof the SMA gradations with the exception of having a much lowerdust content.

MIXTURE VOLUMETRIC PROPERTIES

SMA Mixtures

The optimum mix properties for the SMA mixes are presented inTable 6. The percent passing the BP sieve for each NMAS ranged

TABLE 2 Limestone Mineral Filler Properties

TABLE 4 SMA Design Gradations for Each NMAS/BP Combination, Cumulative Percent by Mass

TABLE 3 Cellulose Fiber Properties

from 21 to 32 percent and optimum asphalt contents ranged from 5.5to 8.3 percent (by weight of total mix). Design air voids (VTM)ranged from 3.5 to 3.8 percent. A minimum VMA of 17.0 percentwas achieved in all the SMA designs. The 4.75-mm NMAS mixesexhibited exceptionally high VCA values. This was attributed to thefact that the larger aggregate size or coarse fraction of these grada-tions actually consisted of material typically defined as fine aggre-gate (i.e., minus No. 4 material). It was also observed that the VCAwas higher for the mixes with the larger aggregate fraction composedof a single size (e.g., 12.5/9.5).

Superpave Mixtures

The optimum mixture properties for the Superpave mixes are pre-sented in Table 7. As indicated, the 9.5ARZ and 25ARZ had optimum

22 Paper No. 99-1429 TRANSPORTATION RESEARCH RECORD 1681

asphalt contents of 5.7 and 4.4, respectively. In addition, each mix sat-isfied the Superpave mixture criteria (i.e., those for a 3 to 10 millionequivalent single-axle load) for the various mix parameters.

The 25BRZ mix satisfied the Superpave mixture criteria; how-ever, the VMA value of 15.8 percent was considerably higher thanthe required minimum of 12 percent. This was the result of a com-bination of coarse gradation and the tough, breakdown-resistant traprock. A finer gradation would have resulted in lowering the VMAcloser to the limit, thereby lowering the optimum asphalt content;however, in the interest of time and because the mix satisfied alldesign criteria, this was not done.

The 9.5BRZ mix did not satisfy the Superpave mixture criteria forvoids filled with asphalt (VFA). As indicated in Table 7, the VFAof this mix was 79 percent. The 9.5BRZ mix also exhibited highVMA (19.3 percent). The high VFA observed was the product of thehigh VMA coupled with a constant design VTM of 4.0 percent. Like

TABLE 5 Superpave Design Gradations, Cumulative Percent Passing by Mass

FIGURE 1 The 0.45 power plots for 9.5-mm NMAS SMA and Superpave gradations.

the 25BRZ mix, a finer 9.5BRZ gradation probably would have low-ered the VMA so that the VFA criterion was satisfied. Despite thefact that it did not meet the Superpave VFA design criterion, wheeltracking and permeability tests results for the 9.5BRZ mix were usedin the SMA/Superpave comparison.

VERIFICATION OF SMA MIXTURE DESIGNPROCEDURE FOR VARIOUS NMASS

Seven of the 11 SMA mixes were successfully designed without anymodification to the 1995 version of the design procedure (2). Theseincluded the following: 9.5/2.36, 12.5/4.75, 19/4.75-IB, 19/4.75-II,25/12.5, 25/9.5, and 25/4.75. Based on these findings, it was con-cluded that the mix design procedure is applicable for designingSMA mixtures with NMASs other than 19 mm. However, someproblems were encountered in designing four of the NMAS/BP com-binations (4.75/2.36, 4.75/1.18, 9.5/4.75, and 12.5/9.5). The grada-

Lynn et al. Paper No. 99-1429 23

tion bands specified in the 1995 draft mix design procedure wereunnecessarily too narrow for some NMASs. The 1998 SMA mixturespecifications (10) and design procedure (11) have been modified sothat these problems are resolved.

It is recommended in the design procedure that at least three trialblends be evaluated initially. It is suggested that the three trial blendsconsist of the following: one each passing along the coarse and finelimits of the gradation band and one in the middle of the gradationband (11). In the 1995 draft version of the design procedure (2), theband limits for the different BP sieves were the same (20 to 28 per-cent passing by mass). Table 6 indicates that the 4.75/2.36, 4.75/1.18,and 9.5/4.75 mixes had optimum percentages passing the BP sieveof 31, 32, and 30 percent, respectively. These percentages were out-side the limits of the gradation band (>28 percent). However, Table6 also indicates that all the volumetric properties were acceptableaccording to the established mix design criteria (VTM between 3.5and 4.0 percent, VMA > 17 percent, and VCA ratio < 1). These dataindicated that modification of the gradation bands was warranted and

FIGURE 2 The 0.45 power plots for 25-mm NMAS SMA and Superpave gradations.

TABLE 6 Optimum SMA Mixture Properties

thus revisions were made in developing the 1998 version of thedesign procedure (11). The final gradations for these three mixeswere selected based on the limiting VCA ratio. Table 6 indicates thatthe VCA ratios for these mixes were 0.982, 0.996, and 0.932, respec-tively. The VCA ratio is obtained by dividing the VCA of the com-pacted mixture by the VCA of the dry-rodded coarse aggregate (orlarger aggregate size gradation). If the mixture VCA is less than theVCA of the dry-rodded coarse aggregate, the VCA ratio will be lessthan 1 and it can be concluded that stone-on-stone contact exists inthe mix. Gradations finer than those indicated in Table 4 for the threemixes in question (higher percentage passing the BP sieve) wouldhave resulted in VCA ratios greater than 1, indicative of a loss ofstone-on-stone contact. It should be noted that the 4.75 NMAS mix-tures might be considered undesirable in practice because of thehigher cost associated with the high optimum asphalt contents.

Table 6 also indicates the optimum properties for the 12.5/9.5mix. The design gradation established for this mix, presented inTable 4, had 26 percent passing the BP sieve. This represented thehighest percentage passing the BP sieve attainable without produc-ing a VCA ratio greater than 1. This coarse aggregate skeleton pro-duced a mix VMA of 22.0 percent. Consequently, a high optimumasphalt content (8.0 percent) was necessary to achieve the designlevel of VTM (3.5 to 4.0 percent). Despite the high asphalt content,stone-on-stone contact was preserved (VCA ratio < 1). Althoughthis mix satisfied design criteria, it provides evidence to suggest that,for economic reasons, some NMAS/BP combinations, particularlythose with predominantly single size or uniform coarse aggregategradations, may not be desirable for producing SMA mixtures.

Regarding the 19-mm mixes, the Table 6 data indicate no sig-nificant difference in optimum mixture properties between the two19-mm mixes. Both gradations had the same percent passing the BPsieve and essentially the same asphalt content, indicating no differ-ence between the traditional SMA gradation curve and the typicalgradation curve used for this study.

COMPARISON OF MIXTURE PROPERTIES AND CHARACTERISTICS OF SMA AND SUPERPAVE MIXES WITH THE SAME NMAS

Wheel Tracking Results

Wheel tracking tests were conducted on all the mixes with testspecimens compacted to design air voids. An APA was used to per-form the tests. The predecessor of the APA is the Georgia loadedwheel tester developed by the Georgia Department of Transportation

24 Paper No. 99-1429 TRANSPORTATION RESEARCH RECORD 1681

(GDOT). Testing was done at both 49°C and 64°C in accordance withGDOT standard testing procedures (12). The lower temperature wasselected because it is the temperature at which GDOT has establishedits specification criterion for high-performance mixes. Testing at thehigher temperature was done because all these mixes incorporated PG64-22 binder. The specimens were tested in the dry condition andaverage rut depths in millimeters were obtained after application of 8,000 cycles of a 100-lb (45.36-kg) load. This loading produces acontact pressure of about 100 psi (689.48 kPa).

APA wheel tracking results for all the mixes tested at 49°C arepresented in Table 8. It was observed that all the mixes rutted lessthan 5 mm. This is significant because this is the APA criterion usedby GDOT for design acceptance of high-performance surface mixes(13). Based on this criterion, one could expect good in-service rut-ting performance from all the mixes investigated. This was a par-ticularly interesting finding given that some of the mixes tested werebase/binder-type mixes.

Overall, the data in Table 8 do not indicate that better rut resistanceis achieved with increasing NMAS for SMA and Superpave mixes.The results of the 9.5- and 25-mm tests are presented in Figure 3. It isinteresting to note that the Superpave ARZ mixes performed betterthan the others tested. Also, Figure 3 indicates that generally the SMAand BRZ mixes exhibited the same amount of rutting. The 25BRZ,with an average rut depth of 2 mm, represents an exception. This mixrutted comparable to the 25ARZ. As would be expected, the rut depthsat 64°C are greater than the values obtained at 49°C. However, halfthe mixes tested at 64°C satisfied the GDOT rutting criterion.

Permeability Results

Permeability tests were also conducted on all the mixes. Specimensof the design gradation and asphalt content were prepared at differ-ent VTM levels. This was accomplished by varying the number ofgyrations when compacting with the Superpave gyratory compactor.Gyrations of 10, 30, and 50 were used to produce a range of air voids.A falling-head method was used to determine the coefficient of per-meability in centimeters per second. Test specimens were subjectedto a vacuum in accordance with AASHTO T-209 before testing toachieve saturation. The permeability results of the 9.5-mm mixturesare presented in Figure 4 and the results for the 25-mm mixes arepresented in Figure 5.

With the Florida Department of Transportation criterion of 100 ×10−5 cm /s established by Choubane et al. (14) used as a guidelinefor limiting permeability, the figures indicate that only the SuperpaveARZ mixes could be considered impermeable over the range of den-

TABLE 7 Optimum Superpave Mixture Properties

sities usually specified in the field (5 to 7 percent voids for SMAmixes and 6 to 8 percent voids for Superpave designed mixes). The9.5ARZ mix became permeable at about 8 percent voids or 92 per-cent of theoretical maximum density (TMD), whereas the 25ARZmix became permeable at about 7.5 percent voids or 92.5 percent ofTMD. All the other mixes were found to be permeable, according tothe FDOT criterion, regardless of the air void content.

Figures 4 and 5 indicate that the Superpave mixes were less per-meable than the SMA mixes. Of the Superpave mixes, the ARZ gra-dations were less permeable than the BRZ gradations. Figures 4 and5 also indicate that the 9.5-mm NMAS mixes were less permeablethan the 25-mm mixtures. It is also interesting to note that the9.5ARZ gradation satisfies the FDOT criterion at an air void contentof 9 percent.

Lynn et al. Paper No. 99-1429 25

It is important to note that the degree of permeability is a functionof both the level of air voids and the degree of interconnectivity ofthose voids. It also must be stated that the permeability test for HMAis currently in the developmental stages. Recent data suggest thatlarge stone mixes may exhibit erroneously high permeability be-cause of formation of flow paths at the specimen boundaries. Test-ing protocols to at least minimize the formation of these flow pathsmay be necessary to improve the accuracy of the test. This mayresult in lower observed permeability values for larger stone mixes.

Despite these considerations, the SMA mixes were determined tobe permeable over the range of void levels tested. It was especiallysignificant that the 9.5-mm mixes (compacted in the 5 to 7 percentvoid range) and the 25-mm mixes (compacted to design air voids)were found to be permeable.

TABLE 8 SMA and Superpave Wheel Tracking Results

FIGURE 3 APA wheel tracking results (tests conducted at 558C).

CONCLUSIONS AND RECOMMENDATIONS

The data generated by this study support the following conclusionsand recommendations:

1. In addition to 19 mm, the SMA mix design procedure devel-oped for NCHRP Project 9-8 is applicable for other NMAS mixtures.Based on the data for the trap rock aggregate, SMA gradation bandswere developed for the following NMASs: 25, 19, 12.5, 9.5, and 4.75 mm. These gradation bands have been submitted to AASHTOfor acceptance.

2. Wheel tracking results, determined with an APA, indicatedthat all mixtures rutted less than 5 mm when tested at 49°C. GDOTcurrently uses a maximum value of 5 mm as one of the design accep-tance requirements for high-performance surface mixes. Althoughall the mixtures exhibited good rutting resistance in the APA, it was

26 Paper No. 99-1429 TRANSPORTATION RESEARCH RECORD 1681

observed that Superpave mixes with ARZ gradations generally per-formed better than the others tested. An exception was the 25-mmBRZ gradation, which performed as well as the 25-mm ARZ mix-ture. These data suggest that ARZ gradations should not be ignoredwhen Superpave mixes are being designed.

3. Permeability results for the SMA mixes indicated that, for agiven NMAS, mixes with a smaller BP sieve were less permeable.The Superpave designed mixes were determined to be less perme-able than the SMA mixes. Of the two Superpave mix types, theARZ gradations were less permeable than the BRZ gradations.Also, the 9.5-mm NMAS mixtures were determined to be less per-meable than the 25-mm, NMAS mixes. These data suggest that, inorder to avoid potential moisture damage problems, SMA mixesand coarser graded Superpave mixtures (i.e., those with BRZ gra-dations) may require higher field density to produce an impermeableHMA layer.

FIGURE 4 The 9.5-mm NMAS SMA and Superpave mixture permeability (k = coefficient of permeability).

FIGURE 5 The 25-mm NMAS SMA and Superpave mixture permeability (k = coefficient of permeability).

ACKNOWLEDGMENTS

This work is part of a project sponsored by AASHTO in cooperationwith FHWA. It was conducted as part of NCHRP, which is adminis-tered by TRB, a unit of the National Research Council. The supportof NCHRP project officer E. Harrigan and the encouragement and feedback of the members of the project panel are gratefullyacknowledged.

REFERENCES

1. Brown, E. R., J. E. Haddock, L. A. Cooley, R. B. Mallick, and T. A.Lynn. Designing Stone Matrix Asphalt Mixtures.Final Report preparedfor NCHRP, TRB, National Research Council. National Center forAsphalt Technology, Auburn University, Auburn, Ala., Aug. 1998.

2. Brown, E. R., J. E. Haddock, T. A. Lynn, and R. B. Mallick. Design-ing Stone Matrix Asphalt Mixtures.Draft Final Report prepared forNCHRP, TRB, National Research Council. National Center for AsphaltTechnology, Auburn University, Auburn, Ala., Sept. 1996.

3. Kandhal, P. S. Large Stone Asphalt Mixes: Design and Construction.Journal of the Association of Asphalt Paving Technologists,Vol. 59,1990.

4. Kandhal, P. S., and E. R. Brown. Comparative Evaluation of 4-Inch and6-Inch Diameter Specimens for Testing Large Stone Asphalt Mixtures.Proc., 1990 Materials Engineering Congress,ASCE, Aug. 1990.

5. Kandhal, P. S., S. A. Cross, and E. R. Brown. Evaluation of BituminousPavements for High Pressure Truck Tires.Pennsylvania Department ofTransportation Report FHWA-PA-90-008-87-01, Dec. 1990.

Lynn et al. Paper No. 99-1429 27

6. Acott, M. The Design of Hot Mix Asphalt for Heavy Duty Pavements.NAPA QIP Series,Vol. 111, 1986.

7. Brown, E. R., and C. E. Bassett. Effects of Maximum Aggregate Sizeon Rutting Potential and Other Properties of Asphalt-Aggregate Mix-tures. In Transportation Research Record 1259,TRB, NationalResearch Council, Washington, D.C., 1990, pp. 107–119.

8. Mahboub, K., and D. L. Allen. Characterization of Rutting Potential ofLarge-Stone Asphalt Mixes in Kentucky. In Transportation ResearchRecord 1259,TRB, National Research Council, Washington, D.C.,1990, pp. 133–140.

9. Smith, R. D., R. P. Humer, and A. B. Webb. State DOTs Choose LargeAggregate Asphalt Mixes for Stability and Durability, Asphalt Institute.Asphalt,Fall 1989.

10. Standard Specification for Designing Stone Matrix Asphalt (SMA).AASHTO Draft, AASHTO, June 1998.

11. Standard Practice for Designing Stone Matrix Asphalt (SMA).AASHTO Draft, AASHTO, July 1998.

12. Standard Test Method for Rutting Susceptibility Using the GeorgiaLoaded Wheel Tester.Georgia Department of Transportation DesignationGDT-115, Georgia Department of Transportation, Aug. 1996.

13. Standard Specifications for the Construction of Transportation Systems,Department of Transportation, State of Georgia.Georgia Departmentof Transportation, 1995.

14. Choubane, B., G. C. Page, and J. A. Musselman. Investigation of WaterPermeability of Coarse Graded Superpave Pavements. Journal of theAssociation of Asphalt Paving Technologists,Vol. 67, 1998.

Publication of this paper sponsored by Committee on Characteristics ofNonbituminous Components of Bituminous Paving Mixtures.