Functionalization of lightweight two-stage concrete composite (LTSCC) for thermal energy storage

Integrating phase change material (PCM) in concrete can enhance building energy efficiency. This study functionalized lightweight two-stage concrete composites (LTSCC) for thermal energy storage by incorporating PCM-loaded foam glass aggregates (PFGA), which eliminated the damage and segregation issues of the PCM carriers that frequently occurred in existing methods. The PFGAs physically loaded with PCM were first preplaced and infiltrated with a highly flowable lightweight slurry to produce LTSCC. By adjusting the volume ratios of the PFGA, functionalized LTSCC of varying strength grades was produced, achieving a maximum 28-day compressive strength of 52.6 MPa at an air-dried density of 2077.6 kg/m³, with thermal conductivity under 1.547 W/(m·K). With the incorporation of the PFGA, room model tests revealed the superior temperature regulation performance of the fabricated LTSCC, achieving a significant reduction in indoor temperature difference (down to ∼10 °C). Finally, a long-term reliability test was conducted, in which geometrical, mechanical, and thermal properties were characterized before and after 360 thermal cycles, along with microstructure observations. The comparative analysis demonstrated the stable performance of the functionalized LTSCC, with self-desiccation identified as the primary cause of the minor property changes. The radar chart analysis of the collective results indicated that the functionalized LTSCC effectively balanced lightweight properties, strength requirements, and thermal energy storage, with an optimal PFGA volume ratio of 2/3.