## 6 Critical Evaluation of the Utilisation of PCMs in the Concrete Industry and Their Improvements

Table 3: Cont. temperature control, PCMs have the capacity to store and release thermal energy during phase transitions. The illustration of the associated research on utilising PCMs in the concrete industry (Sections 3-5) introduced the fact of experiencing different types of PCMs. Specifically, microencapsulated PCMs (MPCMs), macroencapsulated PCMs, and PCM-embedded concrete are common categories that have been widely elucidated. MPCMs are tiny capsules that spread throughout the concrete matrix and can withstand mechanical pressure. However, macroencapsulated PCMs are larger capsules that are implanted in the concrete and affixed to the surface. Although they provide simple installation and replacement, the effectiveness of heat transfer may be constrained. The third type involves the direct addition of PCM into the concrete mixture to substitute for cement or aggregate. Nevertheless, the discussed studies assure the capability of PCMs to efficiently store thermal energy during the day and release it at night. In other words, PCMs can assist in maintaining indoor temperatures and lessen the demand for extra heating and cooling systems. In terms of energy efficiency and comfort for users, the use of PCMs in the concrete industry delivers substantial benefits. Undoubtedly, the utilisation of PCMs in concrete mixtures would result in energy savings and a reduction in carbon emissions due to a reduction in the heating and cooling energy requirements of buildings. Furthermore, there are a number of signs that PCMs can enhance the mechanical characteristics of concrete, increasing its longevity and reducing cracking. However, it should be realised that PCMs can be rather expensive. Thus, adding them to concrete may raise the entire cost of a building project. In addition, the PCM type and distribution inside the concrete can directly affect the efficiency of thermal energy storage and release and thus may retard the heat transfer rate. There is also a possibility of experiencing a volume shift throughout the phase transitions of organic PCMs. This, in turn, would cause microcracking in the concrete. The structural stability and long-term performance of the concrete depend on the PCM and concrete mix being compatible. Lastly, restoration and replacement of deteriorated or damaged PCM containers can be difficult and expensive in the case of macroencapsulated PCMs. With reference to the points raised in this review, the authors are able to list a number of advancements made in PCMs in relation to their use in the concrete industry for the period between 2018 and 2023. These developments are meant to improve the thermal performance, energy effectiveness, and general sustainability of concrete structures. A few of the significant upgrades include:  
1. Microencapsulation and macroencapsulation technology advancements have improved PCM leakage and degradation protection. The consistency and endurance of PCMs within the concrete are ensured via encapsulation, making them more appropriate for long-term uses. 2. PCM decreases concrete's mass density by almost twice its weight. The higher quantities of Microencapsulated PCM added to denser concrete walls were also shown to improve the energy efficiency of buildings. As the paraffin concentration rises, so does the heat conductivity, reducing the insulating properties of otherwise perfect autoclave-aerated concrete. 3. The mechanical strengths of the thermal energy storage cement-based composites have been reduced by raising the content of the form-stable hydrate salt PCMs. Nevertheless, they can still be used as covering subtractions for construction elements. The quantity of thermal energy saved and released also increased with PCM integration, doubling at the highest PCM integration percentage simulated (40%). 4. Integrated PCM and a bio-based hygroscopic material (hemp concrete) have strong thermoregulation abilities, with an ultimate period shift of 30 min and a discrepancy in temperature of about 4.6 \({}^{\circ}\)C between the reference and PCM hemp concrete.