Characterization of Air Void Distribution in Asphalt Mixes using X-ray Computed Tomography

TLDR

The study aims to quantify the structure of air voids in asphalt mixes using experimental and analytical methods. The authors used X‑ray computed tomography and image analysis to measure void sizes at various depths, then applied Weibull statistical modeling to assess how compaction effort, compaction method, and aggregate size affect void distribution. The void size distribution exhibited a bathtub shape with larger voids at specimen top and bottom, a pattern that intensified with higher compaction effort, and varied significantly with compaction method and aggregate size.

Abstract

This study describes experimental and analytical methods to quantify the structure of air voids in asphalt mixes. An x-ray computed tomography system along with image analysis techniques were used to measure air void sizes at different depths within asphalt mix specimens. The statistical analyses performed validated the applicability of the Weibull model for describing the air void distribution. Consequently, the Weibull model was used to quantify the effect of the compaction effort, method of compaction, and aggregate size distribution on air voids. The air void size distribution in Superpave gyratory compacted specimens was found to exhibit a "bathtub" shape, whereby larger voids were present at the top and bottom parts of a specimen. This shape was more pronounced at higher compaction efforts. The method of compaction was significant in influencing the air void size distribution. Specimens prepared using the Superpave gyratory compactor with different aggregate sizes were found to have noticeably different air void sizes.