Influence of aggregates' spatial characteristics on air-voids in asphalt mixture

Air-void is the main structure in asphalt mixture; it significantly affects the strength and durability of asphalt mixture. To better understand the influencing factors of air-voids, one group of specimens with different aggregate gradations were fabricated at the same experimental situations and evaluated at first, then, another group of specimens with the same aggregate gradation were drilled from test track and used to investigate the effect of compaction energy on air-voids. The internal structures can be obtained by X-ray computed tomography (X-CT) device, and digital image processing (DIP) technology was used to extract and reconstruct the spatial models of aggregates and air-voids based on original CT images. Influence of aggregates and compaction energy on air-voids were studied; the results show that the improved extracting and segmenting program, which divides the original CT image into a serial of annular regions firstly, can effectively identify different microstructures; 3D fractal dimension provides a quantitative value of presenting the complexity of microstructures' morphology, it comprehensively reflects the volume, shape and distribution of aggregates and air-voids; aggregates' angularity has a significant effect on air-voids, and compaction energy causes different characteristics of air-voids as well. Methodologies developed in this paper are effective to evaluate the influence of aggregate particles on air-voids.