Thermal energy storage cement mortar containing encapsulated hydrated salt/fly ash cenosphere phase change material: Thermo-mechanical properties and energy saving analysis

Solar passive house equipped with thermal energy storage cement mortar (TESCM) containing encapsulated phase change material (PCM) has showed great potential in terms of energy saving. However, TESCMs are universally behaved as deteriorated mechanical strength and high cost, limiting their applications. This study developed a novel TESCM by integrating cement mortar with polyethylene glycol@SiO₂-coated eutectic hydrated salt/fly ash cenosphere encapsulated PCM, in order to improve the mechanical property and cost-effectiveness. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and attenuated total reflection Fourier transform infrared (ATR-FTIR) results showed that the synthetic encapsulated PCM possessed satisfying encapsulation ability, latent heat and chemical compatibility. The encapsulated PCM was incorporated into cement mortar by partial replacement of sand. It turned out that the prepared TESCM containing 20% encapsulated PCM exhibited 28d compressive and flexural strengths of 36.5 MPa and 6.2 MPa, merely presenting slight decreases of mechanical strengths compared to the control cement mortar. Moreover, X-ray diffraction (XRD), thermal gravimetric (TG) and backscattered electron (BSE) were conducted on TESCM to analyze the hydration products, hydration degree and interface transition zone between cement matrix and the encapsulated PCM, and the influence on mechanical strength was deeply analyzed. Besides, thermal performance test confirmed that the prepared TESCMs had good heat storage capacity. In the heating test, the peak temperature in the test chamber equipped with TESCM was reduced by 3.1 °C when 20% encapsulated PCM was contained in TESCM. Furthermore, economic evaluation indicated the low cost and prominent energy saving performance of the prepared TESCM. This work provides insights into the developing structural-functional building materials with high mechanical strength and thermal energy storage for efficient solar energy utilization in passive buildings.