Thermo-Mechanical Performance and Techno-Economic Assessment of Lightweight Cement Mortar Incorporating a Coconut Shell Activated Carbon/PCM Composite for Thermal Energy Storage

This study presents a sustainable, leakproof, shape-stable composite phase change material for Thermal Energy Storage (TES), created by incorporating a eutectic mixture of capric- and myristic-acid-based biobased PCMs into porous activated carbon derived from waste coconut shells (ACcs). The resulting ACcs/EPCM composite was embedded into cement mortar in varying ratios (10-30 wt%) to manufacture thermally enhanced building material. Comprehensive testing was conducted to assess the phase transition characteristics of composite PCM along with chemical, microstructural, physical, mechanical, thermal and thermophysical characterization, and thermoregulation performance evaluation of ACcs/EPCM incorporated mortar. The DSC analysis showed that ACcs/EPCM possessed a melting temperature of 21.8 °C and a latent heat capacity of 32.5 J/g with high thermal cycling stability. FTIR results confirmed good chemical compatibility of ACcs/EPCM within cement mortar and TGA indicated sufficient thermal stability below degradation temperatures (< 150 °C). Replacing 30 wt% of sand with composite PCM in mortar significantly enhanced its thermal insulating properties through reduction of thermal conductivity by 33% and thermal diffusivity by 26%. On the other hand, this modification led to a 75.3% decrease in compressive strength and an increase in water absorption from 7.6% to 24.7%. Further, pore size distributions of cement mortars were evaluated through mercury intrusion porosimetry indicated a reduction from 2.46 μm to 1.86 μm in critical pore diameter and increase in total porosity by 36.8% through inclusion of 30 wt% of ACcs/EPCM. Furthermore, techno-economic analysis of ACcs/EPCM incorporated cement mortar reveals an encouraging payback period of 2.33 years.