PERMEABILITY OF SUPERPAVE MIXTURES: EVALUATION OF FIELD PERMEAMETERS

i DISCLAIMER The contents of this report reflect the views of the authors who are solely responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views and policies of the National Center for Asphalt Technology of Auburn University. This report does not constitute a standard, specification, or regulation. CHAPTER 1-INTRODUCTION BACKGROUND Within the hot mix asphalt (HMA) community, it is a generally accepted notion that the proper compaction of HMA pavements is vital for a stable and durable pavement. For dense-graded mixtures, numerous studies have shown that the initial in-place air void content should not be below approximately 3 percent or above approximately 8 percent (1). Low air voids have been shown to lead to rutting and shoving while high void contents are believed to allow water and air to penetrate into the pavement resulting in an increased potential for water damage, oxidation, raveling, and cracking (1). In the past it has been thought that for most conventional dense-graded HMA, increases in in-place air void contents have meant increases in permeability for pavements. Zube (2) performed an insightful study during the 1950s and early 1960s that indicated dense-graded HMA pavements become excessively permeable to water at approximately 8 percent air voids. This was later confirmed by Brown et. al. (3) during the 1980s. However, due to problems associated with Superpave designed mixtures in Florida, the size and interconnectivity of the air voids within the pavement have been shown to greatly influence the permeability of HMA pavements (4). A study conducted by the Florida Department of Transportation (FDOT) indicated that Superpave mixtures designed on the coarse side of the restricted zone can be permeable to water at air void contents below 8 percent. As part of this study, the FDOT developed a laboratory permeability device utilizing a falling head concept for cores cut from HMA pavements. FDOT also developed a standard method of test for this laboratory permeameter (5). The question that arises as a result of the experiences of FDOT is " Why are the coarse-graded Superpave mixtures more permeable than conventional dense-graded mixtures? " The probable answer to this question is that the coarse-graded Superpave mixtures have a different void structure than the dense-graded mixtures used prior to Superpave. The 1990 Georgia Department of Transportation gradation band for an " E " mix had as the lower gradation …