Phase Change Material-Based Lightweight Concrete Using Expanded Clay Aggregate: A Review of Materials, Incorporation Techniques and Performance

Phase Change Materials (PCMs) have emerged as promising thermal energy-storage materials for improving the energy efficiency of buildings. Their incorporation into lightweight concrete can reduce heat transmission, regulate indoor temperature and decrease dependence on mechanical heating and cooling systems. This review examines the development of PCM-based lightweight concrete, with particular emphasis on Expanded Clay Aggregate (ECA) as a porous carrier material. Organic PCMs, including paraffin, polyethylene glycol, fatty acids and esters, provide chemical stability and reliable thermal cycling, whereas inorganic salt-hydrate PCMs offer higher volumetric storage capacity and thermal conductivity. Different incorporation techniques, such as direct mixing, immersion, vacuum impregnation, microencapsulation, macroencapsulation and shape stabilization, are critically reviewed. Vacuum impregnation of ECA is considered particularly effective because it provides high PCM loading while reducing leakage and limiting direct interaction between PCM and cement paste. Previous investigations indicate that PCM incorporation can lower concrete thermal conductivity, delay peak temperature, increase cooling duration and improve indoor thermal comfort. However, reductions in compressive strength, increased water absorption, PCM leakage, phase segregation and long-term cycling stability remain important concerns. The review concludes that PCM-impregnated ECA can produce multifunctional structural lightweight concrete when PCM content, pore characteristics, impregnation conditions and protective treatments are carefully optimized.