Investigating the impact of porous steel slag aggregates on the low-temperature crack resistance of asphalt concrete

The macroscopic and microscopic mechanisms of the impact of the porous characteristics of steel slag aggregates on the low-temperature crack resistance of asphalt concrete are not yet fully understood, which is detrimental to the effective maintenance of the durability of asphalt pavement containing steel slag aggregates. To address this deficiency, various index property tests were first conducted on steel slag aggregates, and the basic shape features of steel slag particles were captured and quantified through blue light laser scanning. Subsequently, the gradation of steel slag asphalt concrete (SSAC) was optimized, and two new preparation techniques for steel slag asphalt concrete were proposed. Finally, based on the laboratory low-temperature three-point bending (TPB) test, a refined discrete element method (DEM) model of the SSAC beam that can characterize various microscopic groups was constructed. The experimental research results show that controlling the heating temperature of steel slag aggregates according to their moisture content can ensure the full evaporation of pore moisture. Concurrently, extending the wet mixing time can ensure that the asphalt mortar fully fills the surface pores of the steel slag aggregates, and the low-temperature crack resistance of the SSAC specimens treated as above all satisfies the specification requirements. The numerical simulation results show that stress concentration occurs near the pores of the steel slag aggregates, which directly explains why cracks tend to appear near such pores. The higher the porosity of the steel slag aggregates, the greater the decrease in the comprehensive index of low-temperature crack resistance (up to a decrease of 6.5 %), and the easier it is for cracks to develop from the pores of steel slags. Whether or not the pores of steel slags are filled with asphalt mortar has a greater impact on the low-temperature fracture performance of SSAC. When the pores of steel slags are not filled with asphalt mortar, as the porosity of steel slags increases, the degree of decrease in u_0 increases (up to a decrease of 22.7 %), and the internal damage of steel slags also increases. In actual engineering applications, it is recommended to control the content of large-pore steel slag aggregates and ensure that the asphalt mortar fully fills the pores of the steel slag aggregates to improve low-temperature crack resistance of SSAC.