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Expert Task Group on Asphalt Mixtures & Construction; Asphalt Binders; and Models Technology August 2001 Attachment F - Recommendations for Changes to AASHTO T-209
The Expert Task Group (ETG) for Superpave Mixtures and Aggregates is recommending changes to be made to AASHTO T-209, "Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures". These changes, with accompanying rationale, are detailed below.
Change: Eliminate provision for manual agitation of the specimen (Section 9.4); require continuous mechanical agitation. The suggested change is shown below.
Rationale: Data from AMRL proficiency samples #31 and #32 were analyzed to determine the relative variability of test results obtained using manual and mechanical agitation. Table 1 shows the results of the analysis.
An analysis of variance (ANOVA), or "F" test, showed that the differences in mean Gmm values obtained using the two agitation methods are not statistically significant. However, a two-sample "F" test for sample variance showed that the difference in the variance (or standard deviation) obtained from data representing each agitation method is statistically significant at a 0.05 level of significance (α = 0.05). Based on these findings, it is recommended that manual agitation be eliminated to improve testing precision in AASHTO T209.
Change: Change the minimum sample size table in Section 7.2 to conform to standard Superpave mixture size terminology; reduce entries to streamline table. A suggested format is shown below.
Rationale: The left column heading in the existing table is ambiguous and not consistent with standard Superpave terminology for mixture designation. The change would simplify and standardize the terminology and streamline the table by reducing the number of minimum size entries. A suggested format is shown below