A Review of Aggregate and Asphalt Mixture Specific Gravity ...

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2 BACKGROUNDAir voids (V a ), voids in the mineral aggregate (VMA), voids filled with asphalt (VFA),and volume of effective binder (V be ) are calculated from the following well knownequations: GmbVa1 x100G (1) mm GmbPsVMA 100 (2) GsbVMAVVFA a x100(3) VMA V VMA (4)beV awhere:G mbG mmP sG sb= bulk specific gravity of the compacted sample= maximum specific gravity of the asphalt mixture= percentage (by mass) of aggregate in the total mixture= aggregate bulk specific gravityWith these equations, the effects of the specific gravity results can be analyzed moreclosely, and the following approximate relationships can be determined.From Equation 1, if G mb is held constant, the following relationship between AirVoids and G mm is established:when G mm changes by +0.01, V a changes by +0.4%. (5)Likewise, if G mm is held constant in Equation 1, the following relationshipbetween Air Voids and G mb is established:when G mb changes by +0.01, V a changes by -0.4%. (6)From Equation 2, when G sb and P s are held constant, the following relationshipbetween VMA and G mb is established:when G mb changes by +0.01, VMA changes by -0.4%. (7)And also from equation 2, when G mb and P s are held constant, the followingrelationship between VMA and G sb is established:when G sb changes by +0.01, VMA changes by +0.3%. (8)2
3 BULK SPECIFIC GRAVITY OF AGGREGATEBulk specific gravity is defined as the ratio of the weight of a given volume of aggregate,including the permeable and impermeable voids in the particles, to the weight of an equalvolume of water. Bulk specific gravity of aggregate is important information fordesigning HMA because it is used to calculate VMA and VFA. Since differentprocedures are used to determine the G sb of coarse and fine aggregate, this section isdivided into two parts, one for coarse aggregate and one for fine aggregate.3.1 Coarse Aggregate Bulk Specific Gravity3.1.1. Standard Test MethodsThe standard test methods used for the determination of specific gravity of coarseaggregate are described in AASHTO T 85 and ASTM C127. The methods are essentiallythe same, except for the required time in which a sample of aggregate is submersed inwater to essentially fill the pores. While the AASHTO standard requires the sample beimmersed for a period of 15 to 19 hours, the ASTM method specifies an immersed periodof 24 ± 4 hours. After the specimen is removed from the water, it is rolled in an absorbenttowel until all visible films of water are removed. This is defined as the saturated surfacedry(SSD) condition. Three mass measurements are obtained from a sample: SSD mass,water submerged mass, and oven dry mass. Using these mass values, the G sb of anaggregate can be determined.3.1.2. Precision Estimates of Standard Test MethodsEven though the two standard methods require different saturation periods, the precisionindices are the same, as shown in Table 1.TABLE 1 AASHTO T 85 and ASTM C127 Precision EstimatesAcceptable Range ofStandard Deviation(1s)Two Results(d2s)Single-operator precision:Bulk specific gravity (dry) 0.009 0.025Multilaboratory precision:Bulk specific gravity (dry) 0.013 0.038Precision estimates for the standard coarse aggregate G sb test methods are alsodetermined annually by the Proficiency Sample Programs and reported on the AMRLwebsite (1). These precision indices are shown in Table 2. The precision estimates from1998 through 2005 vary significantly from year to year due partially to the use ofdifferent aggregate sources in the program. The precision estimates from the proficiencyprogram are greater than the precision estimates cited in the standard test methods (Table1). Since 2006, the Proficiency Sample Programs have used a different method of3
Page 1 and 2: NCAT Report 12-06A REVIEW OF AGGREG
Page 3 and 4: Objective and Process of the Review
Page 5 and 6: warranted in these methods at this
Page 7 and 8: Table of Contents1. Introduction ..
Page 9: 1 INTRODUCTIONCurrent practices for
Page 13 and 14: TABLE 3 Advantages and Disadvantage
Page 15 and 16: TABLE 4 AASHTO T 84 and ASTM C128 P
Page 17 and 18: TABLE 6 Modifications of Standard T
Page 19 and 20: In 2000, Kandhal et al. (7) conduct
Page 21 and 22: angular fine aggregate with higher
Page 23 and 24: ASTM does not specify an absorption
Page 25 and 26: 4.3. Alternatives to Current Standa
Page 27 and 28: 5 BULK SPECIFIC GRAVITY OF COMPACTE
Page 29 and 30: TABLE 15 Advantages and Disadvantag
Page 31 and 32: inaccurate sample volumes caused by
Page 33 and 34: For G sb , the specific gravity val
Page 35 and 36: line). Since it may be more desirab
Page 37 and 38: Both standard test procedures, incl
Page 39 and 40: 8 RECOMMENDATIONSBased on the revie
Page 41 and 42: REFERENCES1. The Proficiency Sample

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