Thermal accumulation mechanism of asphalt pavement in permafrost regions of the Qinghai-Tibet Plateau

This paper monitors and calculates the hydrothermal data in an “atmospheric-pavement structure-permafrost” system of an asphalt pavement from 2010 to 2014 and compares the data with that observed from an adjacent natural surface system. Asphalt pavements have small albedo and low transfer coefficients, showing an increase in shortwave absorption and a decrease in heat dissipation. In comparison with the natural ground, the asphalt pavement absorb an additional 17.07 MJ/m2 of shortwave radiation and 10.97 MJ/m2 of longwave radiation, while the monthly upward shortwave, latent heat, and sensible heat were less than 5.46, 19.7, and 30.5 MJ/m2, respectively. According to the theory of energy balance, the heat absorption of an asphalt pavement was 8.56 times greater than that the natural surface, leading to the water-heat change in the subgrade. Given the horizontal and vertical movements of water in the subgrade, a high aquifer formed under pavement with depth of 10-30 cm and average volume moisture content of 22-26% with vapor-water phase transition. The increase of moisture in the subgrade promotes heat accumulation in the soil. As results, the average ground temperature increased by 0.32 °C/a in an asphalt pavement structure and could reach 0.8 °C/a near the permafrost table. Pavement properties, pavement-surface radiation and energy balance, and subgrade's water-heat accumulation generally constitute the thermal accumulation mechanism of asphalt pavement in cold regions.