## 5 Studies on Using other Types of PMC in Concrete for Thermal Energy Storage
Heat transmission and temperature change over a single curing session were simulated using a numerical model. When preparing the aggregate of PCM-CLSC as well as the blocks of PCM-concrete thermal storage with various weight percentages (0%, 2%, 4%, and 6%) of PCM, [PERSON] et al. (2021) [93] used Elastic Light Shale Ceramsite (CLSC) to absorb paraffin, which increased the PCM-concrete's heat storage capability, solved the PCM leakage problem,  
Figure 11: Air temperature variation with PCM thickness [90]. and decreased the heat storage cost. The research showed how an active thermal storage system's efficiency changed depending on the PCM weight percentage and the HTF features. The experimental findings demonstrated the high absorbency and compatibility of the PCM-CLSC aggregate. The average specific heat capacity of PCM-concrete thermal storage blocks rose via 12.54% (2 wt.% PCM), 31.60% (4 wt.% PCM), and 41.23% (6 wt.% PCM), whereas the compressive strength and thermal conductivity decreased with the weight percent increase of PCM. Activated silica fume (ASF) was first used as a tumble machine surface coating by [PERSON] et al. (2021) [94]. The experimental series examined the effects of heat and cold cycling on the characteristics of PCMA and ASF-coated PCMA, as well as the effects of mixing PCMA and ASF-coated PCMA with rubberized concrete (RC). After being put through 100 heat/cool cycles, the ASF coating was shown to significantly decrease PCM leakage by about 5.4 times. Mixing RC with ASF-PCMA somewhat improved its mechanical qualities compared to mixing it with PCMA alone. Depending on the condition of the PCM, the ASF coating may have either a positive or negative influence on the thermal conductivity (K) of RC. Mixing RC with ASF-PCMA reduced the loss in latent heat storage capacity compared to mixing with PCMA. The thermal performance of concrete bricks containing PCM was investigated experimentally by [PERSON] and [PERSON] (2021) [95]. The thermal performance of four concrete bricks (three with macroencapsulated PCM and one without PCM, representing the reference) was evaluated in a hot environment. At a constant PCM concentration, the research analysed how increasing the heat transfer area of the PCM encapsulation affected the thermal performance of the brick. There were three distinct configurations of PCM capsules in PCM bricks: (1) one large capsule (Brick-B, 4 \(\times\) 4 \(\times\) 10 cm\({}^{3}\)), (2) two capsules (Brick-C, 4 \(\times\) 4 \(\times\) 5 cm\({}^{3}\)), and (3) five capsules (Brick-D, 4 \(\times\) 4 \(\times\) 2 cm\({}^{3}\)). The highest PTR (peak temperature reduction), HTRc (conductive heat transfer reduction), and TD (time delay) were achieved by Brick-D, relative to the reference brick, at maximum outside temperatures of 156.5%, \(-\)61%, and \(-\)133%, respectively. Using a hollow steel ball (HSB), [PERSON] et al. (2022) [96] obtained PCM-HSB aggregates by macro-encapsulating the PCM. In addition, steel fibres were inserted into the PCM-HSBs to boost the thermal and mechanical qualities of the material. The mechanical and thermal qualities of the steel fibre-strengthened PCM-HSB concrete were studied in relation to the volume content of the steel fibre (0.35, 0.7, and 1.05 vol.%) as well as the HSB thickness (0.3 and 1 mm). The results of the tests showed that the steel fibre content and HSB thickness greatly influenced the PCM-HSB concrete's thermal conductivity and compressive strength. Owing to the dispersed steel fibres' bridge function in the matrix of concrete, the 0.35% steel fibre inclusion increased the PCM-HSB concrete's heat conductivity by 71%. By increasing concrete's heat capacity and bearing capacity, the suggested fibre-reinforced PCM-HSB may secure energy piles' future uses. To make use of the benefits of both materials, [PERSON] et al. (2022) [97] suggested integrating PCM and a bio-based hygroscopic material (hemp concrete) into a unique multilayer building envelope.