Lightweight aggregates with shape-stabilized graphene and phase change material for energy storage concrete

In this study, a novel thermal energy storage lightweight aggregate (TSA) composite based on butyl stearate (BS), a low-cost, commercially available phase change material (PCM), and graphene nanoplatelets (GNs), as a highly conductive filler, was investigated. The least amount of liquid state graphene-enhanced PCM was shaped stabilized in the surface-coated porous medium of expanded clay (EC) aggregates. The performance of the TSA was evaluated by combining experiments and finite element analyses, the results of which demonstrated that the TSA composite with 2 % GN by weight of PCM exhibits the best behavior. The thermal analysis, at ≤5 % relative humidity, of the thermal energy storage concrete (TSC) containing TSA with 3.5 % (wt.) of GN-PCM showed the maximum peaks smoothed by up to 4 ◦C when compared to concrete containing PCM-EC and up to 5.1 ◦C when compared to control concrete with pristine EC, while this decrease was around 3.6 ◦C and 5.2 ◦C for the tests in 50 % relative humidity condition. In addition, TSC containing TSA with 2 % GN by weight of PCM exhibited enhanced heat transfer, with its thermal conductivity increasing by 244 % and 67 % when compared to concretes containing pristine EC and PCM-EC, respectively. Additionally, the ultrasonic wave propagation velocity increased by approximately 20 %, thereby demonstrating the higher degree of homogeneity of the media. Finally, the leakage measurements demonstrated that the TSA is thermally stable, and the temperature history demonstrated its potential to maintain thermal performance after at least 500 cooling-heating cycles. The results indicated that the novel-designed TSA composites pave the way for a practical and effective solution to improve indoor comfort and energy efficiency in buildings.