X-ray computed tomography analysis of internal voids in steel slag asphalt mixture under freeze–thaw damage and microwave healing process

Abstract

In this work, the variation characteristics of different scale voids under freeze–thaw damage and microwave healing were studied by X-ray computed tomography (CT). Firstly, the scale classification of voids was carried out to analyze the initial distribution state of voids. Then the distribution of the horizontal plane and vertical direction was quantitatively characterized, and the source of the damage-healing effect was analyzed by using iterative variation indexes. Finally, the critical void was judged by combining the total and relative iterative variation rates. The results show that the area of small voids (0.15 ∼ 2.0 mm2) accounts for 55.7 %, and the number accounts for 90.17 % of the whole, serious interference with overall development when voids are not classified. The initial distribution of voids at different scales is quite different. The void growth is relatively uniform in the horizontal plane. From the distribution of the number of voids, the inner region is more prone to coherent vertical cracks, and the outer region is more prone to discrete micro-cracks. The role of voids at different scales in the damage-healing process is different. Small voids are the critical voids in the freeze–thaw damage stage. Both small and big voids are critical voids in the healing stage. This work is helpful to better understand the damage-healing process of steel slag asphalt mixture at mesoscale and contribute to the sustainability of asphalt pavement.