Enhanced thermo-mechanical properties of cementitious composites via red mud-based microencapsulated phase change material: Towards energy conservation in building

Integrating microencapsulated phase change materials (PCMs) into cement-based materials can endow building with huge heat storage capacity. Nevertheless, cement-based materials containing microencapsulated PCMs universally behave deteriorated mechanical and heat transfer properties. In this study, a capric acid and paraffin eutectic PCM (CA-PA) was prepared, and it had a large latent heat (143.4 J/g) with the suitable melting point (27.1 °C) used for building applications. Then, a novel microencapsulated PCM was proposed by the three-step method including the construction of red mud-based geopolymer hollow microsphere (RMHM), the impregnation of CA-PA and the surface grafting of nano-SiO₂. A comparative study was performed to unveil the influence mechanism of different surface properties of the synthetic red mud-based microencapsulated PCMs (namely CA-PA/RMHM and CA-PA/RMHM@SiO₂) on the microstructure, mechanical and thermal properties of cement mortar. It turned out that the 28d compressive strength and thermal conductivity of the cement mortar with replacing 20 % sand by CA-PA/RMHM were 26.7 MPa and 0.7165 W/m·K, which were increased by 41.6 % and 14.7 % due to introducing nano-SiO₂ coating. Besides, energy and environmental assessment indicated that using mortar with CA-PA/RMHM@SiO₂ in building had good energy saving performance and great potentials for emission reduction.