Experimental Study on Adaptability of Neutral Aggregates for Asphalt Concrete Panels in Severe Cold Regions

[Objective] Asphalt concrete is widely favored as an impermeable panel in pumped-storage power station design due to its excellent impermeability, deformation adaptability, self-healing ability, and ease of construction. At present, research on the application of neutral aggregates in asphalt concrete panels is limited, especially regarding experimental results on their key performance. This paper aims to promote the application of neutral aggregates in asphalt concrete panels in severe cold regions of western China. [Methods] Laboratory mix design and performance tests of asphalt concrete panels were carried out using neutral aggregate diabase. Thirteen groups of specimens were prepared to analyze porosity, 48 h Marshall flow value, splitting tensile strength, and splitting failure strain of asphalt concrete with different mix proportions. The optimal mix proportion was proposed as: gradation index 0.4, asphalt content 7%, and filler content 12%. To verify the adhesion between diabase coarse aggregate particles and asphalt, the boiling test was conducted. [Results] After 5 minutes of boiling, the asphalt film coating on the surface of diabase coarse aggregate particles was completely preserved, with the percentage of stripped area approaching zero and an adhesion level of Ⅴ. To compare the performance differences between neutral and alkaline aggregate asphalt concrete, comparative performance tests were conducted on asphalt concrete with diabase and limestone aggregates. The results showed that asphalt concrete with diabase aggregate exhibited better slope flow value and maximum flexural strain than that with limestone aggregate, while other mechanical and deformation properties showed no significant difference. [Conclusions] Under the recommended mix proportions, the permeability coefficient, water stability, slope flow value, splitting test, small beam bending test, direct tensile test, and bonding strength with cement concrete of the diabase aggregate asphalt concrete impermeable layer all meet the relevant technical requirements for asphalt concrete face dams. The freezing temperature of the recommended asphalt concrete mix is lower than -37 ℃, enabling it to withstand the local minimum temperature of -31.9 ℃ and satisfy design specifications. Based on the results of the static triaxial test, the Duncan-Chang model parameters of the asphalt concrete impermeable layer material with the recommended mix proportion are obtained, which can be applied to numerical calculations of dam stress-strain.