Comparison of 9.5 mm SuperPave and Marshall Wearing I Mixes in ...

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31Table 2.10 Results of Huber’s APA testsAggregate Source FAA Avg. Rut DepthGeorgia granite 48 3.96Alabama limestone 46 3.04Indiana crushed sand 42 4.17Indiana natural sand 38 2.81supports the concept of using a test method to restrict use of round materials with low texture,but questions the validity of Superpave's current method and specification.Casanova et. al. Studied the FAA of nine aggregate types. Each aggregate type was evaluatedwith methods A, B and C of AASHTO T304-96. These methods require different gradationblends. Method A is specified by Superpave. The aggregate were also evaluated under amicroscope to achieve a visual measure of angularity and texture. Direct shear tests were usedto assess the strength of each aggregate type and gradation. The results showed the FAA testcorrelated well with the visual assessment of angularity and texture. However, there was not agood correlation between FAA and the shear strength. The FAA would reject aggregates withhigh shear strength and vice versa. The researchers suggested supplementing the FAA test withdirect shear measurements (Casanova, 2000).2.4 VOIDS IN THE MINERAL AGGREGATEVoids in the Mineral Aggregate percentages have been considered one of the major indicatorsof asphalt concrete quality since the development of volumetric analysis for mix design.Recently, concern as been expressed with designers not being able to achieve the currentminimum VMA values specified in the Superpave design method (Coree, 1999 and Kandal,1998). These minimum values range from 11% for pavements with a nominal maximumaggregate size of 37.5 mm to 15% for a 9.5 mm nominal maximum aggregate size asphaltconcrete. In 1992, Aschenbrener set out to better quantify the relationship between the VMAvalue and the placement of the gradation curve in relation to the maximum density line(Aschenbrener, 1992). For this study, 101 mixes used by the Colorado Department ofTransportation were examined to find the most appropriate method for placing the maximumdensity line in reference to the Fuller curve.It was found that the reference gradation line, the line drawn from the origin to the actualpercent passing on the nominal maximum aggregate size, gave the best indication of themeasured VMA values. It was found that by staying away from the maximum density line at the#30 sieve and the fourth largest sieve to retain material would yield higher VMA values. This is
32theoretically correct in that the farther the gradation curve is kept from the maximum densityline, the more voids that would be in the mix.Twenty-four laboratory samples were also made up for this project to study the effects ofgradation, quantity of material passing the #200 sieve and the FAA value of the fine aggregate.The researchers hypothesized that these variables have the greatest effect on VMA. Gradationhad the largest effect on VMA. The quantity of material passing the #200 and FAA hadsignificant affects on VMA. One interesting finding of this study was that FAA affected the VMAof coarse mixes more than the fine mixes, but the amount of minus #200 material affected theVMA of the fine mixes more than the coarse mixes.Coree and Hislop examined the historical aspect of the VMA criteria (Coree, 1999). Coree foundthat a minimum VMA value was not used until the 1950s and in the 1960s it was specified as amix design parameter in Marshall mix design. They stated that many researchers haveidentified problems meeting the current Superpave VMA specifications. These researchers feelthat they often have to “fail” mixes that would have been acceptable in pavement performancebecause of the VMA criteria. Also changing the gradation to get an improved VMA value willsometimes increase the optimum asphalt content leading to higher construction costs.During Coree’s research several problems were encountered with the VMA, including:no field data could be located that was used to set the original VMA values,the original and current VMA values are based on Marshall mix design, andthe precision of tests used to determine the VMA values is not good enough to allow forstrict enforcement of the minimum VMA values.Recommendations of this research are: (a) the minimum VMA values need to be validatedagainst pavement performance, including factors such as particle shape, texture and gradation,(b) since there is a lack of precision of the tests used to determine the VMA criteria, rigidenforcement should be discouraged at this time, and (c) minimum average film thickness needsto be verified and correlated to pavement performance.There has also been concern expressed about the relationship between the VMA values, theSuperpave restricted zone and asphalt film thickness. It was found that the decreased VMAvalues, as compared to Marshall VMA values, while designing under Superpave could beattributed to the higher compactive effort of the Superpave gyratory compactor as compared tothe Marshall compaction hammer. This in turn has led to the use of coarser mixes in order toachieve the required VMA percentage. The problem arises in that this VMA requirement forSuperpave’s coarser mixes is the same as those for Marshall’s mixtures.Experiments during this research indicate that average film thickness yields a better picture ofthe mix being developed and encompasses more mix types (Kandal, 1998). This allows forhigher pavement durability since film thickness is optimized. The method for achieving the
Page 1 and 2: COMPARISON OF 9.5 MM SUPERPAVE ANDM
Page 3 and 4: iNOTICEThe contents of this report
Page 5 and 6: iiiasphalt concrete wearing courses
Page 7 and 8: vMixing Procedure 78Appendix B Fine
Page 9 and 10: viiTable C-7 Marshall Medium 13% NS
Page 13 and 14: 4Table 1.1 Mix Design Types in Expe
Page 15 and 16: 6CHAPTER 2 LITERATURE REVIEW2.1 INT
Page 17 and 18: 82. determine aggregate stockpile b
Page 19 and 20: 10SieveAllowable PercentPassing Sie
Page 21 and 22: 12Stability is recorded as the maxi
Page 23 and 24: 14The WVDOH procedure for determini
Page 25 and 26: 16sieve. This is somewhat different
Page 27 and 28: 18G sb = bulk specific gravity of a
Page 29 and 30: 20theoretical gravity at the initia
Page 31 and 32: 22D/B est = adjusted dust to binder
Page 33 and 34: 24P b,est - 0.5%,P b,est ,P b,est +
Page 35 and 36: Percent Passing261009080Superpave U
Page 37 and 38: 28Table 2.6 WVDOH Marshall and Supe
Page 39: 30Table 2.9 Habib Marshall Analysis
Page 43 and 44: 34the machine. This variability was
Page 45 and 46: 36CHAPTER 3 EQUIPMENT3.1 INTRODUCTI
Page 47 and 48: 38Hose PressureWheel Load100 psi100
Page 49 and 50: 40mouth. This jar rests on a holder
Page 51 and 52: problematic, as the saturated surfa
Page 53 and 54: 44Mechanical Laboratory Sieve. Afte
Page 55 and 56: Percent Passing4610090100% Limeston
Page 57 and 58: 48Maximum specific gravity is a req
Page 59 and 60: 50gradation. This allowed for direc
Page 61 and 62: Percent Passing521009080Light 100%
Page 63 and 64: 54percentage of aggregate from the
Page 65 and 66: 56Table 5.4 Summary of Volumetric a
Page 67 and 68: 58Table 5.5 Calculated and Adjusted
Page 69 and 70: 60Table 5.6 Results of APA TestsAir
Page 71 and 72: 62exhibit lower rut depths than any
Page 73 and 74: design had significantly more rutti
Page 75 and 76: 66SP L 100LS SP L 64NS -10.335 2.77
Page 77 and 78: 68percent air voids and percent lim
Page 79 and 80: Air Voids (%)Uncompacted Voids (%)7
Page 81 and 82: 72than the Marshall mixes. Table 6.
Page 83 and 84: Voids in the Mineral Aggregate. As
Page 85 and 86: 76REFERENCESAmerican Association of
Page 87 and 88: 78APPENDIX A BUCKET MIXER INSTRUCTI
Page 89 and 90: 80APPENDIX B FINE AGGREGATE ANGULAR
Page 91 and 92:
82Table B-3 Uncompacted Void Conten
Page 93 and 94:
84AGGREGATE DESIGN DATATable C-1 St
Page 95 and 96:
86Table C-3 Computed Blend Gradatio
Page 97 and 98:
88Table C-7 Marshall Medium 13% NS
Page 99 and 100:
90%G mm%AC VMA VTM VFA @ N ini @N d
Page 101 and 102:
92Table C-14 Superpave Light 64% NS
Page 103:
946 2979.3 1696.7 2988.1 2.307 7.09
Page 106 and 107:
971 2912.7 1620.8 2917.9 2.246 7.65
Page 108 and 109:
992 8.40 10.80 7.402 7.90 9.90 7.80
Page 110 and 111:
1011 9.50 6.90 11.502 9.79 7.15 10.
Page 112 and 113:
1032 8.55 5.20 5.95L R RDate Tested
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