Self-healing analysis of steel slag asphalt mixture under microwave heating through laboratory fatigue-healing test and microscopic characterization method

Abstract

Steel slag is an eco-friendly low-carbon building material that has been widely used for pavement construction in recent years. In this study, the steel slag aggregate (SSA) is used to replace a part of the basalt aggregate in the porous asphalt mixture to improve its microwave absorption ability. Microwave heating promotes the self-healing capability of steel-slag asphalt mixture. We designed and conducted 16 groups of fatigue-healing tests based on an orthogonal experimental design to analyze the influence of various factors, including the degree of damage, healing temperature, and rest time, on the self-healing ability of the steel slag asphalt mixture. The ratio of the number of cyclic loads after healing (N1) to the number of cyclic loads before healing (N0) is defined as the healing index. The results of the range analysis demonstrate that the healing temperature presents the greatest impact on the healing rate of fatigue damage, followed by the degree of fatigue damage; the rest time has the least impact. The fatigue damage healing rate gradually decreases with the increase in the degree of damage. It first increases and then decreases with the increase in the healing temperature. It increases with the rest time. The optimal healing state of the steel slag porous asphalt mixture involves heating to 80℃ with 60 % degree of damage followed by resting for 8 hours. CT scanning technology is used to observe the crack distribution before and after healing. The CT images and a 3D reconstruction of the asphalt mixture demonstrate that obvious healing of cracks can be observed after microwave heating, and microwave heating does not significantly affect the porosity of the asphalt mixture. The nano-indentation indicates that the Young’s modulus and hardness of the asphalt mortar in the cracking area increased by 16.8 % and 22 %, respectively, after healing due to microwave heating, which can be attributed to the ageing of the asphalt.