Performance of packed-bed thermal energy storage using recycled aggregate: From a lab-scale prototype to a 1 MWh module

Recycled aggregate (RA) is produced during construction and demolition activities, but its reuse is limited by residual mortar content and the energy-intensive thermal treatment required. Using RA as a filler in packed-bed thermal energy storage (PBTES) offers a dual function: acting as a sensible heat-storage medium and supporting RA thermal treatment, which enhances material recovery and circularity. This study explores a concept of concrete circularity-renewable energy symbiosis through a case study of RA-PBTES with dual functions. Laboratory experiments assessed the thermal response, pressure drop, cyclic repeatability, and structural behaviour of RA-PBTES under repeated heating and cooling. Results showed RA maintained stable thermocline development, good heat storage, and acceptable hydraulic resistance, though some thermal ratcheting occurred at 250°C, emphasising the need to consider particle movement and bed structure for long-term design. Repeated thermal cycling made RA particles more brittle, suggesting benefits for crushing and residual mortar removal. To explore scalability, a one-dimensional heat-transfer model based on the Schumann formulation was developed and validated, accurately predicting temperature and thermocline development obtained from the experiments. Applying this model to a 1 MWh storage module assessed large-scale thermal performance, fan energy, and system behaviour, revealing trade-offs among heat transfer, resistance, energy use, and material utilisation. The use of waste-derived RA further offers potential sustainability benefits through material reuse and subsequent thermal upgrading.