Utilization of lauric acid-myristic acid/expanded graphite phase change materials to improve thermal properties of cement mortar

Lauric acid-myristic acid/expanded graphite (LA-MA/EG) composite phase change materials (PCMs) were prepared by absorbing the binary eutectic mixtures into expanded graphite (EG) with high absorbability, in which LA-MA binary eutectic mixtures act as latent heat storage materials while EG serves as the supporting material. LA-MA binary eutectic mixture was prepared according to low eutectic phase transition point theory, which is proper to apply in constructions due to the high latent heat and suitable phase transition temperature. The proper firing technology and absorption content of EG were determined according to the temperature sensibility and the long-term durability. Inner morphology of the prepared LA-MA/EG composite PCMs was observed through scanning electron microscopy (SEM). Alkali resistance, thermal stability and thermal properties of the LA-MA/EG composite PCMs were analyzed through differential scanning calorimeter (DSC), thermogravimetry analysis (TGA) as well as melting point apparatus, respectively. In addition, PCM-based mortar was prepared by mixing LA-MA/EG composites into cement mortar. Thermal performance of PCM-based mortar was studied through temperature simulation, and the temperature fields of thermal control model were performed. Results show that LA-MA/EG composite PCMs, prepared with EG fired at 800 °C for 20 s, absorbing 600% LA-MA eutectic mixtures, possess the optimal thermal properties. The LA-MA eutectic mixtures can well disperse inside the EG porous structures due to the capillary and surface tension forces. Thermal storage time and thermal release time of LA-MA/EG composite PCMs are shorter than that of LA-MA binary eutectic acids due to the increased heat transfer rate, caused by the combination with the EG that has a high thermal conductivity. The thermal stability of LA-MA/EG composite PCMs improves in comparison with LA-MA eutectic mixtures. The PCM-based mortar shows proper temperature controlling effects, with decreased effective heat value, delayed temperature peak time and larger cooling extent.