## 4 Studies on Using Inorganic PCM in Concrete for Thermal Energy Storage
Figure 6 shows that the cement-based composites' mechanical strengths used for thermal energy storage diminish as the concentration of form-stable hydrate salt PCMs increases, but that these materials may still be used as building envelopes. In addition, the results of thermal performance tests show that cement mortars containing form-stable hydrate salt PCMs have beneficial exothermic and endothermic qualities, as well as helping to moderate the maximum temperature within. Using a wooden box fitted with infrared radiators and a cooler, [PERSON] et al. (2018)[68] studied cuboid, cylindrical, plate-shaped, and spherical phase-change packages. Salt hydrate was stored in airtight containers, which were then placed within a regular concrete block. Modifying the PCM's thermal behaviour may be carried out without affecting the PCM's mass by altering the package's design. It was determined that the optimal layout for maximum heat transmission included a large number of thin packages arranged in a certain pattern. Reduced heat transfer into interior spaces was achieved by the use of thermal shading and uniform PCM dispersion inside the concrete blocks. To improve a building's energy efficiency, [PERSON] et al. (2018)[69] zeroed in on the creation of facade features. New textile-reinforced concrete panels with microencapsulated PCMs in a selection of mix patterns are offered as a potential solution. To compare the thermal efficiency of various setups, an experimental characterization was carried out across many scales. As predicted, the addition of PCMs to the textile-reinforced concrete increased its heat storage capacity and thermal inertia. Further, an experimentally validated numerical model was created. As can be seen from the findings, the thermal conductivity of concrete is improved by including PCM particles in its mass, and this improvement is proportional to the amount of PCM used. Additionally, a heating/cooling test was conducted using a guarded hot box to assess the panels' heat storage capacity and highlight their melting and solidifying temperature ranges, respectively. A melting point between 23 \({}^{\circ}\)C and 27 \({}^{\circ}\)C was determined. Lightweight concrete with high concentrations of PCM (up to roughly 7.8% by weight of concrete) was studied for its ability to store latent heat and energy by [PERSON] et al. in 2019[70]. Polymer-coated metal (PCM) and Polyethylene Glycol (PEG) were injected into porous lightweight aggregates with weights up to 24%. At volumetric substitution ratios of 0%, 25%, 50%, 75%, and 100%, PCM aggregates were utilised instead of conventional  
Figure 6: CM, EHS/EGO-CM, and EHS/P(AA-AA)-CM compressive strengths at 28 days with various contents of form-stable hydrate salt PCMs [67]. lightweight aggregates. At the age of 28 days, the samples were subjected to a battery of tests, including compression, flexure, thermal conductivity, and phase change material thermal storage. The presence of PCM aggregates has been shown to have varying impacts on the mechanical and thermal characteristics of concrete. As the percentage of PCM aggregate increases, the mechanical characteristics seem to improve. Figure 7 displays the relationship between the PCM aggregate replacement rate and the latent heat. Using thorough experimental tests and numerical simulations, [PERSON] et al. (2019) [71] introduced the idea of creating a low-priced Concrete-based Thermal Energy Storage (CTES) system. An independent test facility was built to investigate the efficiency of high-temperature thermal energy storage systems that work at temperatures of up to 500 \({}^{\circ}\)C using air as the heat transfer fluid. The CTES module was constructed using a shell and tube design; 22 air openings were located in the tubes, while the shell was filled with concrete.