CAIT project no.: NYSDOT RU8883 (FHWA-NY02010-001)
Fiscal Year: 2007/2008
Rutgers-CAIT Author(s): Thomas Bennert
External Author(s): Zoeb Zavery, NYDOT
Sponsor(s): USDOT, FHWA
The research conducted in this study evaluated the asphalt mixture performance of various gravel and crushed stone sources consisting of different levels of crushed face counts, as determined by ASTM D5821. Along with ASTM D5821, two additional aggregate angularity tests were conducted to evaluate the angularity and texture of the coarse aggregates; 1) AASHTO T326, Uncompacted Void Content of Coarse Aggregates, and 2) Aggregate Imaging System (AIMS). Each of the asphalt mixtures designed and tested during the study used three different asphalt binders; 1) Neat PG64-22, 2) Polymer Modified PG64-22 meeting NYSDOT Elastic Recovery specifications (called PG64-22 ER), and 3) Polymer Modified PG76-22. The permanent deformation properties of the different asphalt mixtures were measured using the Asphalt Pavement Analyzer (AASHTO TP63) and the Asphalt Mixture Performance Tester, AMPT (AASHTO TP79) with confining pressure applied to the specimens.
The aggregate testing concluded that ASTM D5821 correlated poorly to both AASHTO T326 and the AIMS system. There were also situations when aggregates had identical crushed counts but different levels of uncompacted voids contents. Meanwhile, the asphalt mixture testing demonstrated that the AMPT using confining pressure correlated well to the uncompacted void content results of AASHTO T326. Unfortunately, stresses applied in the APA did not mobilize the asphalt mixtures enough to differentiate the differences in aggregate angularity. Both asphalt tests were sensitive to asphalt binder high temperature stiffness, as determined by AASHTO TP70, Multiple Stress Creep Recovery Test. The final statistical analysis of the data resulted in a table that would allow NYSDOT to interchangeably “swap” aggregate angularity, as determined by AASHTO T326, and the non-recoverable creep compliance (Jnr), as determined by AASHTO TP70 to ensure gravel aggregate HMA mixes perform as well as crushed stone aggregate HMA mixes.