Study on the Thermal and Rheological Properties of Nano-TiO₂-Modified Double Phase Change Asphalt

In this paper, paraffin-44H (PW-44H) and paraffin-5 (PW-5) were respectively selected as the high/low-temperature phase change core material, and expanded vermiculite (EVM) was selected as the phase change carrier matrix. A high-temperature composite phase change material (CPCM), 44H/EVM, and a low-temperature CPCM, 5/EVM, were prepared by combining melt blending with vacuum adsorption. Nano-TiO₂ was incorporated as a thermal conductor into the CPCMs to enhance the heat transfer efficiency between the CPCM and asphalt. The heat storage performance, chemical stability, microstructure, and thermal stability of the two CPCMs were studied. The results show that when the dosage of nano-TiO₂ is 2%, the critical temperature range and heat storage performance of the CPCMs reach the optimum. Among them, the enthalpy value of the phase transition of the high-temperature PCM 44H-nTiO₂/EVM is 150.8 J/g, and the phase transition occurs over a temperature range of 37.3 °C to 45.9 °C. The enthalpy value of the phase transition of the low-temperature PCM 5-nTiO₂/EVM is 106.6 J/g, and the phase transition range is -7.9-0.4 °C. Moreover, the incorporation of nano-TiO₂ increased the thermal conductivity of the high- and low-temperature CPCMs by 47.2% and 51.6%, respectively. Finally, the high- and low-temperature CPCMs were compounded in a 1:1 ratio and mixed into asphalt to obtain a composite double PCM asphalt. The heat storage performance of the original sample asphalt and the double phase change asphalt was investigated by DSC, DSR, and an environmental chamber. The results show that when the dosage of PCM is 20%, compared with the original asphalt, the high-temperature extreme value and the low-temperature extreme value of the double phase change asphalt are reduced by 3.4 °C and 2.1 °C, respectively. The heating rate and cooling rate decreased by 8.5% and 5.6%, respectively, and the rheological properties can meet the requirements of the specifications. It can be seen that the addition of double PCMs can effectively slow down the heating/cooling rate of asphalt, thereby improving the temperature sensitivity of asphalt.