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

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ASTM D 2041 precision estimates for mixtures containing aggregate withabsorption of less than 1.5% or between 4 to 5% were evaluated in NCHRP 9-26 (2,11).The precision estimates for D 2041 from NCHRP 9-26 are presented in Table 10 and aremuch smaller than the corresponding values shown in Table 9.TABLE 10 Precision Estimates for ASTM D2041 Evaluated in NCHRP 9-26StandardDeviation(1s)Acceptable Range ofTwo Results(d2s)Single Operator Precision:Without supplemental dryback foraggregate with less than 1.5% absorptionWith supplemental dryback for aggregate0.0020.0050.0060.0013with 4 to 5% absorptionMultilaboratory Precision:Without supplemental dryback foraggregate with less than 1.5% absorptionWith supplemental dryback foraggregate with 4 to 5% absorption0.0040.0100.0110.027The Proficiency Sample Programs also publish precision estimates for AASHTOT 209 and ASTM D2041 annually. These precision indices are shown in Table 11.Information about whether absorptive or non-absorptive aggregate mixtures used andhow many laboratories used supplemental dryback for absorptive aggregate mixtures wasnot published on the AMRL website (1) at the time of this writing.TABLE 11 AASHTO T 209/ASTM D2041 Precision Indices Published by AMRLYear Sample No. of Labs Single Operator MultilaboratoryNo. Participated* Data Used** 1s d2s 1s d2s2007 21/22 475 430 0.0037 0.0105 0.0057 0.01602006 19/20 435 415 0.0060 0.0170 0.0083 0.02342005 17/18 405 398 0.0072 0.0203 0.0115 0.03252004 15/16 358 352 0.0059 0.0166 0.0086 0.02442003 13/14 305 300 0.0041 0.0117 0.0080 0.02272002 11/12 281 271 0.0043 0.0123 0.0073 0.02072001 9/10 235 230 0.0053 0.0151 0.0070 0.01982000 7/8 221 214 0.0048 0.0135 0.0080 0.02251999 5/6 152 148 0.0052 0.0148 0.0078 0.02211998 3/4 53 51 0.0059 0.0166 0.0077 0.0216*Total number of laboratories participated in the program each year**Number of laboratories whose data were used to determine precision estimatesAlmost all of the annual precision estimates are smaller than the D2041 precisionstatements shown in Table 9. This suggests that the D2041 precision statements should bere-established.16
4.3. Alternatives to Current Standard Test MethodsThere are two additional procedures for the determination of G mm worthy of discussion:1) the CoreLok and 2) the pressure meter method. The CoreLok is a vacuum-sealingdevice that has been discussed previously and has been adapted for the determination ofG mm . The pressure meter concept for asphalt mixtures is based on the pressure meterused for determining the air content of concrete mixtures. The advantages anddisadvantages of each of these alternate methods are shown in Table 12.TABLE 12MethodVacuum Sealingor CoreLok(Instrotek) (6)Pressure Meter(Franko andLee) (12)Advantages and Disadvantages of Alternate Methods for G mmAASHTOand/orASTMAdvantagesDisadvantagesDesignationD 6857 Simple to perform Equipment and bag cost Less time consuming than No dryback procedurecurrent AASHTO or Not accurate for mixturesASTM procedurescontaining porous Potential for reduced aggregatevariability with moreexperienceNone Similar results to Cumbersome piece ofAASHTO T 209 for mean equipment (large andand standard deviation heavy) Fast test Equipment needs designchanges to be more userfriendly Relatively unknownmethod in asphalt testing Limited research hasbeen conductedRecent research related to G mm testing has focused on the evaluation of alternativemethods for determining the G mm and not on improving the accuracy or precision of thecurrent AASHTO or ASTM methods. As shown in Table 12, Franko and Lee (12)adapted the pressure meter test for asphalt mixtures. This test, similar to that used for themeasurement of air content in concrete mixtures, was successful at matching AASHTO T209 with respect to accuracy and precision. The main drawback is the excessive weightand size of the equipment. The test procedure, with additional refinement, appears to bea viable alternative to the current AASHTO and ASTM procedures.Sholar et al. (6) evaluated a vacuum-sealing device, commercially known as theCoreLok, for the determination of G mm for HMA containing porous limestone aggregateand mixtures containing non-porous granite aggregate. The CoreLok produced resultssimilar to AASHTO T 209 for non-porous aggregate mixtures. However, the CoreLok17
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 and 10: 1 INTRODUCTIONCurrent practices for
Page 11 and 12: 3 BULK SPECIFIC GRAVITY OF AGGREGAT
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: ASTM does not specify an absorption
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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