Thermal storage kinetics of phase-change modified asphalt: The role of shell design and asphalt influence

The feasibility of using phase change materials (PCMs) in asphalt pavements has been well-supported by research, whereas their actual cooling effect often falls short of expectations. To better understand the interactions between asphalt and PCMs, and to enhance thermal storage efficiency of PCM-modified asphalt systems, this study employs three non-isothermal crystallization kinetic models: Jeziorny, Ozawa, and Mo models. The thermal storage behaviors of microencapsulated phase change materials (MPCMs) with organic and inorganic shell (ORMPCM and INMPCM), and their corresponding modified asphalts (ORMA and INMA), were systematically investigated under the combined effects of temperature, cooling rate, and time. The thermal storage mechanisms of MPCMs in asphalt are further explained through crystallization activation energy and interfacial thermal resistance effects. The results show that the shell significantly impacts the thermal conductivity of MPCMs. Optimizing the shell's thermal conductivity can mitigate the effect of cooling rate on the crystallization process of paraffin. Analysis based on the Jeziorny model reveals that the crystallization of paraffin in the modified asphalt involves both one-dimensional and two-dimensional crystal structures. This suggests that asphalt inhibits the crystallization of paraffin and alters its crystal structure, resulting in a more diverse range of crystal forms. Further analysis of cooling functions using the Ozawa and Mo models indicates that differences in thermal properties between the core, shell, and asphalt, along with interfacial thermal resistance effects, influence the crystal growth rate of the paraffin to varying degrees. Finally, the crystallization activation energy results imply that the energy barrier for crystallization in modified asphalt is significantly higher than that of MPCMs, further confirming asphalt's hindering effect on the thermal storage behavior of MPCMs. Consequently, when MPCMs are applied to asphalt, asphalt partially impedes the crystallization of PCMs. This inhibition is a key factor affecting thermal storage efficiency and a major reason for the suboptimal cooling effect of PCMs in asphalt pavements.