An Alternative Approach for the Determination of Bulk Specific Gravity and Permeability of Hot Mix Asphalt (HMA)

Abstract

The objective of this study was to investigate the use of an alternative method for determination of bulk specific gravity and estimation of water permeable voids of dense graded HMA mixes. As a part of an ongoing study on evaluation of permeability of HMA, several dense graded mixes with coarse and fine gradations from three New England states were compacted to produce mixes at different air voids. The bulk specific gravities of these mixes were determined using both the saturated surface dry method and the vacuum seal method. Theoretical maximum densities of these mixes were also determined. Air voids of the different compacted mixes were estimated from the bulk specific gravity and theoretical maximum density values. Porosity and permeability tests were also conducted on the mixes. The results showed that for coarse graded mixes and fine graded mixes with high air voids, the vacuum seal method provided a better estimation of air voids in a compacted HMA mix. For coarse graded mixes, porosity can provide a good indication of inter-connectivity of air voids in a compacted HMA mix. Analysis of the data showed that porosity could provide an excellent indication of permeability of HMA. A porosity of 7% seemed to be critical--mixes with porosity greater than 7% showed significantly higher permeability than mixes with porosity lower than 7%. Charts have been provided for selection of proper gradation and air voids to avoid mixes with excessive permeability.