A Study Of Air Voids And Effective Air Voids In Hot Mix Asphalt (hma)

Air voids are a fundamental parameter in the mix design of Hot Mix Asphalt (HMA), as they directly influence performance characteristics such as durability, permeability, and aging. Typically estimated using bulk and maximum specific gravity measurements, accurate determination of air voids is critical, given that laboratory samples are compacted to target void levels. This study investigates the influence of aggregate gradation and asphalt content on air voids, effective air voids, and specific gravity parameters - including bulk, apparent, and maximum specific gravities - in both fine- and coarse-graded HMA mixtures. Experimental testing included the determination of bulk, apparent, and maximum specific gravities, as well as performance metrics such as the Rutting Tolerance Index (RTIndex) and Cracking Tolerance Index (CTIndex). The findings reveal significant discrepancies between air voids calculated using different methods and effective air voids, with greater variability observed in coarse-graded mixes. Apparent specific gravity values exhibited considerable sample-to-sample variation, diverging notably from assumed generic maximum specific gravity values, thereby affecting the accuracy of air void estimations. A strong correlation was found between the ratio of effective air voids to total air voids. Given the demonstrated relationship between effective air voids and key durability indicators, this study recommends incorporating effective air voids into routine HMA mix design practices for improved performance prediction and quality control.