## 3 Studies on Using Organic PCM in Concrete for Thermal Energy Storage
When compared to GPC's U-value of 2 W/m\({}^{2}\) K, the U-values of GP-L-PCM and LECA are 0.9 W/m\({}^{2}\) K and 1.6 W/m\({}^{2}\) K, respectively, after a 75% capsule supplement of GP-L-PCM and LECA. The compressive strength of the LECA and GP-L-PCM slabs was significantly lower than that of the GPC in all cases. The walls of GPC with MPCM were studied by [PERSON] et al. (2019) [59] for their possible use in buildings subjected to a range of climates. Numerical studies using the finite differences technique and the energy balancing method were used to comprehensively examine the impact of climatic variables (solar radiation and temperature) and the design of MPCM (concentration and shell thickness) upon the construction's energy efficacy. The higher quantities of MPCM addition and denser walls of concrete were found to enhance the construction's energy efficacy. Moreover, the construction's energy efficacy is diminished if the ultimate solar radiation is increased when the external temperature is greater than the inside temperature. The use of a phase change composite as an aggregate substitute to control the temperature of porous asphalt concrete was studied by [PERSON] et al. (2020) [60]. After settling on the PEG, FT-IR spectroscopy and DSC were used to investigate its chemical and mass stability when exposed to a continuous high temperature, a high-temperature cyclic conditioning, and a low-temperature cyclic conditioning. The fine aggregate in porous asphalt concrete was replaced with a composite material made of SiO\({}_{2}\) as the shell and PEG as the phase transition material. Porous asphalt concrete may benefit from using a PEG/SiO\({}_{2}\) composite with a 70% PEG mass content, as has been found. The optimal replacement amount was found to be 1.4% of the total weight of aggregate, while the suitable particle size range for phase change composites was found to be between 0.6 and 1.18 mm. Concrete's thermal energy storage capability employing paraffin wax, silicon carbide, and slag aggregate-based PCM was studied by [PERSON] et al. (2020) [61]. The DSC curve demonstrated a phase transition and thermal energy storage in the PCM/SiC-based composite aggregate at 33-34 \({}^{\circ}\)C. The thermal heat storage ability of the PCM/SiC-based composite aggregate was shown by the internal temperature test, which revealed that the sample with PCM/SiC-based composite aggregate had a temperature that was about 2-10 \({}^{\circ}\)C higher. The surface temperature of the wall on both the inside and outside of the energy storage structure was found to be 42 \({}^{\circ}\)C. While the temperature inside the energy storage building was measured at 35 \({}^{\circ}\)C. The incorporation of PCM/SiC-based composite aggregate into the concrete led to a 3 \({}^{\circ}\)C reduction in both ambient and latent heat. To create a form-stable composite PCM, [PERSON] et al. (2020) [62] looked into the feasibility of using activated carbon made from oil palm kernel shell (OPKS) as the supporting material for paraffin. There was a mass retention of 31% for paraffin by the activated carbon that was manufactured. Paraffin-OPKS-activated carbon composite had melting and solidifying temperatures of 29.2 \({}^{\circ}\)C and 31.6 \({}^{\circ}\)C, respectively, and latent heat values of 57.3 J/g and \(-\)57.2 J/g, respectively, as determined experimentally. Incorporating paraffin-OPKS-activated carbon composite into concrete allowed the material to attain a compressive strength of up to 25 MPa after 28 days. Figure 5 shows that the thermal conductivity dropped from the A to B mix designs as the percentage of composite PCM rose. Figure 5: Properties of thermal energy storage concrete with mix designs: (**a**) thermal conductivity, (**b**) thermal diffusivity, and (**c**) specific heat. A= 1963 PCMA (kg/m\({}^{3}\)), A= 2096 PCMA-Al (kg/m\({}^{3}\)), B= 1844 PCMA (kg/m\({}^{3}\)), B= 1959 PCMA-Al (kg/m\({}^{3}\)) [62]. [PERSON] et al.