Mechanical and thermal characterizations of various thermal energy storage concretes including low-cost bio-sourced PCM

Abstract

Abstract In this study, a thermal energy storage concrete (TESC) was developed by adding composite lightweight aggregates (cLWA), made of LWA impregnated with a low-cost bio-based phase change material (PCM), to a cement mortar. Three types of mineral LWAs were used (bentonite, sepiolite and silica gel), together with two methods of impregnation, namely direct impregnation and vacuum impregnation. The retained PCM is a vegetable oil, whose phase change is centered around 23-26°C. The micro-structure and morphology of the cLWA were analyzed with scanning electron microscopy (SEM), while the chemical bonding and compatibility were determined with Fourier transformation infrared (FTIR). The TESCs were prepared either by simple addition or by replacing a basic component (sand or gravel) by the cLWA. To further improve the reliability of the characterization, several specimens were produced for each kind of possible sample. For the thermo-physical properties of the PCM, they were obtained by means of differential scanning calorimetry (DSC), while the thermal characteristics of the TESC were evaluated with an in-house set-up that measured both temperature fluctuations and heat fluxes. The best impregnation rates were obtained with silica gel, but the mechanical tests showed that sepiolite should be preferred due to legal considerations. In both cases, the behavior of bentonite was extremely bad. Despite a loss of mechanical resistance, it is demonstrated that TESCs with a compressive strength greater than 7-10 MPa are feasible. It is also shown that an improvement of 24.4% and greater than 13.5% is achievable for the energy storage capacity and thermal conductivity respectively.