Thermodynamic Behavior and Freeze-Thaw Resistance of Phase Change Recycled Aggregate Concrete

To address the freeze-thaw damage issues in concrete structures in cold regions and promote the application of recycled aggregate concrete (RAC), this study integrates low-temperature phase change material (PCM) n-tetradecane with recycled aggregates to develop phase change recycled aggregate concrete (PCRAC). Through thermodynamic performance and temperature response tests, the material characteristics and temperature regulation mechanisms of the PCM were analyzed. Freeze-thaw cycle tests were conducted combining with fractal theory and computed tomography (CT) technology. The fractal dimension was integrated into a uniaxial compression damage model, and regression analysis of fractal damage variables was performed. Ultimately, a freeze-thaw damage model for PCRAC was established to investigate its freeze-thaw resistance. The results indicate that as the PCM dosage and the recycled aggregate replacement ratio increase, the compressive strength and thermal conductivity of PCRAC decrease, while the specific heat capacity increases. The PCM significantly delays the internal temperature response near its phase transition temperature of 5°C. Freeze-thaw cycles exacerbate mechanical damage in both RAC and PCRAC, with failure occurring after 100 and 150 cycles, respectively. Postfreeze-thaw, the internal pore volume and quantity of PCRAC increase by 19.09% and 34.32%. Freeze-thaw damage increases exponentially with the number of cycles. The PCM mitigates ice expansion stress, thereby enhancing the maximum freeze-thaw cycle resistance and freeze-thaw durability of concrete. The established freeze-thaw damage model captures the progression of freeze-thaw damage in PCRAC, providing a basis for advancing its applications in cold regions.