Distribution of air voids in compacted Hot-Mix Asphalt samples – laboratory vs field

Abstract

The research work presented in this paper investigated the spatial distribution of air voids in compacted Hot-Mix Asphalt (HMA) core samples under different compaction levels and layer/briquette thicknesses. A medium-graded HMA mix was used to investigate the vertical and radial or diametrical distribution of air voids in asphalt samples compacted using the Superpave Gyratory Compactor (SGC). The spatial distribution of air voids in asphalt cores extracted from two road sections constructed using the standard South African Bituminous Treated Base (BTB) and High Modulus Asphalt (HiMA) mixes were also investigated to supplement the study. Findings of the study indicate that the vertical distribution of air voids of the compacted HMA samples differs, with the top and bottom parts exhibiting relatively high air voids content (i.e., low density). The middle part of the HMA samples appears to possess fairly uniform air voids distribution, which confirms the current procedure of coring samples for HMA performance testing from the middle part of the compacted HMA specimens. On the other hand, the radial distribution of air voids was uniform for both the gyratory compacted samples and the field cores. The study has demonstrated that the spatial distribution of air voids may serve as a potential indicator of problems such as aggregate segregation, and temperature variation with depth during compaction, which influence compaction efficiency, as well as the future performance of the asphalt mix layer.