| Voids in the mineral aggregate (VMA) is a volumetric property of hot-mix asphalt mixture design that is subject to meeting regulatory requirements in both the mixture design process and in the quality control/quality assurance of in-place pavements. The conventional philosophy on VMA is that increasing VMA improves performance. Recent research has suggested that higher values of VMA, especially in coarse-graded Superpave mixtures, may actually be detrimental to performance.;In this research, twenty-four (24) asphalt mixture designs were created using the Superpave method. The mixture designs consisted of four aggregate sources (sandstone, limestone, syenite, and gravel), two gradation types (coarse-graded and fine-graded), and three levels of VMA (low, medium, and high). These mixtures were then tested in the Evaluator of Rutting and Stripping in Asphalt (ERSA), a Hamburg-type wheel-tracking device, and the Rotary Asphalt Wheel Tester (RAWT), a laboratory performance evaluator developed by Pine Instruments. The data collected during the laboratory testing was compiled and the performance of each mixture was evaluated with respect to rutting and stripping.;Permanent deformation performance results indicated that trends related to VMA and gradation type were highly dependent upon aggregate type. In some aggregate types, fine-graded mixtures performed better than coarse-graded mixtures. In others, VMA appeared to be a more significant factor in rutting and/or stripping performance. Further, in some cases, combinations of VMA and gradation were significant such that increasing VMA was beneficial for the performance of fine-graded mixes, but detrimental to the performance of coarse-graded mixes. In summary, it was determined that increasing VMA was not necessarily beneficial to the rutting and/or stripping performance of the mixes, and that aggregate type was a more significant factor. Thus, mixture performance may be optimized if the VMA requirements include a consideration of aggregate source. |
