Long-term heat absorption of asphalt pavement and its effects on permafrost subgrade

Under the combined influence of climate warming and long-term heat absorption by asphalt pavement, highway stability in permafrost regions is progressively deteriorating. As asphalt pavement ages, its long-term thermal effects remain insufficiently understood. This study conducted in-situ monitoring of heat and mass exchange within the ‘atmosphere–asphalt pavement–permafrost subgrade’ system along a high-grade highway test section from 2009 to 2020. The investigation focused on long-term heat absorption in asphalt pavement structures through radiation and energy balance, water migration, vapor diffusion, and hydrothermal accumulation processes. The results indicate that increases in downward shortwave radiation (0.5 W/m 2 per year, p < 0.05) and longwave radiation (0.3 W/m 2 per year, p < 0.05), along with a decrease in upward longwave radiation (−0.43 W/m 2 per year, p < 0.05), contributed to sustained heat absorption. The pavement continued absorbing heat and reached thermal stabilization approximately seven years after construction, after which heat absorption declined. Temperature gradients drove water migration and vapor diffusion within the pavement structure. Water changes were positively correlated with surface and base layer temperatures during the thaw period, promoting water and heat accumulation in the base and cushion layers. In the permafrost subgrade, water accumulated at depths of 50–150 cm and 250–400 cm, while ground temperatures increased by 0.01 and 0.13 °C per year on the shady and sunny sides, respectively. Based on the rate of change in ground temperature, the influence depth of heat absorption of asphalt pavement exceeded 15 m during 2010–2017. This study reveals that temperature regulation alone is insufficient to maintain subgrade stability in permafrost area. It recommends implementing integrated water–temperature regulation measures to mitigate the thermal impact of asphalt pavement.