Structural control and performance evaluation of polyurethane-based solid–solid phase change materials for thermal regulation of asphalt pavements in high-temperature climate conditions

Phase change materials (PCMs) hold promising potential for regulating asphalt pavement temperatures during the summer. To enhance the suitability of polyurethane-based solid–solid phase change materials (PUSSPCMs), this study focuses on optimizing their structure and performance. A series of PUSSPCMs were synthesized with varying soft-to-hard segment ratios and soft segment molecular weights. Their high-temperature leakage resistance, phase change behavior and thermal stability were systematically evaluated, to identify the optimal formulations. Subsequently, a SMA-13 phase change asphalt mixture incorporating a selected PUSSPCM was designed. The effect of the PUSSPCM, as a functional filler, on both the pavement and thermal properties of the mixture was evaluated. Results indicate that the PUSSPCM structure critically affects leakage resistance at elevated temperatures. Increasing the hard segment content significantly improves leakage resistance, enabling the PUSSPCM to maintain structural integrity during the high-temperature paving of phase change asphalt mixtures. A higher molecular weight of polyethylene glycol (PEG) requires a correspondingly higher proportion of hard segments for leakage prevention. An increase in PEG molecular weight or soft-to-hard segment ratio usually leads to elevated phase change temperature and enthalpy. Irrespective of the composition, PUSSPCMs can perform excellent volumetric, chemical, and phase transition stability during hot-mix asphalt construction. P8000–6 as a preferred PUSSPCM enhances high-temperature stability and low-temperature crack resistance, but reduces the moisture resistance of the asphalt mixture. The phase change asphalt mixture exhibits a reduced heating rate, maintaining a temperature difference of over 3 °C for up to 250 min, with a maximum difference of 3.7 °C. The addition of P8000–6 functional filler has minimal impact on the thermal conductivity of the asphalt mixture. However, it effectively moderates temperature fluctuations during heating by increasing the heat absorption capacity.