A novel graphene-enhanced phase change material based composite aggregate for energy storage concrete applications

Phase change materials (PCMs) are increasingly regarded as promising candidates for thermal energy storage (TES) in buildings. However, their low intrinsic thermal conductivity significantly limits their effectiveness. In this study, a novel thermal energy storage aggregate (TSA) was developed by integrating butyl stearate (BS) as a cost-effective organic PCM with high-conductivity graphene nanoplatelets (GN) embedded into expanded clay (EC) aggregates. The composite demonstrated improved thermal conductivity, with 2% GN by weight of PCM yielding the best results in terms of heat transfer and phase change performance. The TSA coated in a dual-layer system exhibited long-term stability and no leakage during thermal cycling. When incorporated into a concrete matrix, the thermal energy storage concrete (TSC) containing EC aggregates with 3.5 wt% 2GN-PCM effectively reduced peak ambient temperature fluctuations by up to 5.2 °C compared to concrete with EC at ≤5% and 50 % humidity. Thermal conductivity increased by 244% compared to normal concrete. Moreover, ultrasonic wave speed rose by ~20%, confirming improved homogeneity. These findings demonstrated that the proposed TSA is a robust and efficient solution for energy storage concrete that improves indoor comfort and energy savings in next-generation buildings.