Validation and refinement of mixture volumetric material properties identified in superpave monitoring project II : phase II.
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2015-02-01
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Abstract:This study was initiated to validate and refine mixture volumetric material properties identified in the
Superpave Monitoring Project II. It has been found that differences in performance are primarily controlled
by differences in gradation and resulting volumetric properties between the mixtures. A set of performancerelated
parameters and associated criteria have been developed based on analysis of the aggregates in the
Dominant Aggregate Size Range and the Interstitial Component (DASR-IC). These parameters include
DASR porosity, disruption factor (DF), effective film thickness (EFT), and the fine aggregate ratio (FAR).
The porosity relates to the DASR, which has been found to be beneficial to improving both rutting and
cracking resistance while DF, EFT, and FAR relate to the IC. This study focused on EFT and FAR
parameters, which have not been validated. The study was to assess the effects of changes in interstitial
volume (IV) characteristics on cracking performance. The main goal was to establish through extensive
laboratory study clear implementable gradation and volumetric criteria for purposes of mixture design and
construction specifications that will lead to consistently enhanced cracking performance. Laboratory test
results from Superpave Indirect Tension Test (IDT) clearly showed that changes in IC gradation have an
effect on mixture performance. The effect of changes in IC gradation on mixture properties were dependent
on aggregate type and the characteristics of the aggregate. The two unmodified granite mixtures that met the
preliminary established criteria exhibited the best mixture performance while all other granite mixtures
exhibited marginal performance. Modification, however, helped to improve the underperforming granite
mixtures except for excessively fine ICs. All the limestone mixtures had adequate performance and were
relatively unaffected by modification. It was concluded that the preliminary volumetric criteria were
effective, and their implementation would help to ensure consistently enhanced cracking performance. It
may be possible to relax criteria if modified binder is used.
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