Study on the mechanical performance damage in laboratory-simulated periodic salt environment for asphalt concrete

The phenomenon of sustainable salt damage caused by soluble salt solutions in salt environments has raised concerns in asphalt pavement. However, the evaluation methods for salt erosion damage in asphalt concrete are limited, and there is a lack of comprehensive analysis of the composition of asphalt concrete. In this study, asphalt concrete specimens immersed in NaCl solution were subjected to dry-wet cycles and freeze-thaw cycles to analyze the erosion mechanisms of NaCl solution on their mechanical properties. The chemical stability and microstructure of asphalt after immersion in NaCl solution, as well as the microstructure and mechanical properties of aggregates after NaCl solution immersion and dry-wet cycles, were investigated. The results showed that NaCl solution has a softening effect on asphalt, promoting the intrusion of NaCl crystalline salt into the asphalt. The salt crystallization of NaCl solution altered the surface roughness of the aggregates, resulting in a decrease in skid resistance but an improvement in compressive strength. Specifically, limestone exhibited more stable mechanical properties than basalt. Meanwhile, the NaCl solution concentration has no significant impact on the mechanical performance of asphalt concrete initially, but its domination over mechanical performance gradually increases as the salt environment's cyclic effects intensify. The mechanisms of salt damage in asphalt concrete by NaCl solution mainly involve dry-wet cycles (crystal volume expansion), freeze-thaw cycles (ice volume expansion), and asphalt softening and viscosity reduction. The findings of this study provide a basis for the durability research of asphalt pavements in salt environments.