## 3 Studies on Using Organic PCM in Concrete for Thermal Energy Storage
GPC with a PS-(DVB/RT27) core (Paraffin Rubitherm\({}^{\text{\textregistered}}\)RT27 core with a Polystyrene cross-linked shell with the divinylbenzene) and a PMMA/PCM26 shell (Paraffin mix core with a shell of cross-linked polymethyl methacrylate) can reduce the consumption of power to maintain the indoor temperature (23 \({}^{\circ}\)C) to about 18.5 \({}^{\circ}\)C. In addition, as can be seen in Figure 3, for GPC with an MF/PCM24 core (paraffin mixture core), the compressive strength can be reduced if MPCM is incorporated into the GPC because it causes a higher number of air pockets. Figure 3: (**a**) Compressive strength of GPC-containing microcapsules below (20 \({}^{\circ}\)C) and above (40 \({}^{\circ}\)C) PCM’s melting range; and (**b**) Compressive strength reduction between solid and liquid states of PCM [51]. A novel cement composite including n-octadecane (OC)/diatomite shape-stabilised composite PCM was investigated for the first time by [PERSON] and [PERSON] (2018) [PERSON] and [PERSON] (2018). Due to its hierarchical porosity microstructure and appealing crystallisation character, diatomite coated with carbon nanoparticles and calcined at 800 \({}^{\circ}\)C for 3 h (DC) was regarded as the optimal supporting matrix. These suborbicular thermal storage media are uniformly distributed throughout the cement matrix, showing good compatibility and having no discernible impact on the mortar's apparent density or porosity. Furthermore, the cement mortar containing 30% OC/DC could still achieve flexural and compressive strengths of 3.5 MPa and 18.3 MPa, respectively. Notably, the cement's chemical, mechanical, and thermal dependability remained almost unchanged even after being exposed to a 400 melt-freeze cycle when more OC/DC was included in the mix. It has been discovered that the heat-storage cement mortar produced can lessen the fluctuations in interior temperature and has great potential for energy savings and thermal comfort in the built environment. Experimental research on the thermo-physical properties and heat storage characteristics of an organic PCM for waste heat recovery applications was introduced by [PERSON] and [PERSON] (2018) [PERSON] and [PERSON] (2018). Based on experimental data, it can be stated that organic PCM has desirable properties for use in thermal management systems, including a low phase transition temperature of 60.8 \({}^{\circ}\)C, a high latent heat capacity of 164.28 kJ/kg, good thermal conductivity, and a high degree of thermal stability. The findings implied that the PCM's thermo-physical characteristics and heat storage potential significantly affect the rate at which energy is exchanged between the PCM and the surrounding fluid throughout the heating and cooling cycles. Heat transfer rates ranged widely from a few watts to over 1 kilowatt, depending on the operating circumstances. Thus, PCM has been deemed a potentially useful and energetic component in waste heat recovery systems. Autoclave aerated concrete (AAC) and paraffin were combined by [PERSON] et al. (2019) [PERSON] et al. (2019) [PERSON] et al. (2019) to create innovative composite construction materials with enhanced heat storage capability. The composite specimens were made via the impregnation of 3 AACs with RT28 paraffin, with varying degrees of porosity. Both solid and liquid paraffin were used to determine the paraffin/AAC composites' active thermal conductivity at 20 \({}^{\circ}\)C and 35 \({}^{\circ}\)C. In addition, the active composites' thermal conductivity was calculated using a fractal model. Figure 4 depicts the correlation between the thermal conductivity and paraffin content, showing that the experimental data, as well as the predictions from the model, reveal that the thermal conductivity rises by increasing the level of paraffin, leading to a decrease in the pure AAC's thermal insulation capability. Additionally, the thermal diffusivity of the AACs, a measure of the composites' thermal storage ability, was derived from their volumetric heat capacities.