The heterogeneity and mechanical response of hot mix asphalt laboratory specimens

Many pavement distresses, including rutting, fatigue cracking and low-temperature cracking, are influenced by the air void distribution in hot mix asphalt (HMA). This study investigated the influence of the type of Superpave gyratory compactors (SGCs) and specimen preparation/geometry on air void distribution and its manifestation on mechanical response. X-ray computed tomography along with image analysis techniques was used to capture and characterise the air void distribution within HMA microstructure. The mechanical response was characterised using the dynamic modulus test and static creep test. An index called heterogeneity index was developed to quantify the air void distribution in vertical and lateral directions. The study revealed that laboratory compacted specimens are heterogeneous and there is a need to prepare laboratory specimens with homogeneous air void distribution for accurate interpretation of results. In addition, the study revealed that the type of the SGC used influenced the dynamic modulus of compacted HMA specimens.