Sustainable lightweight concrete using waste-derived heavy fuel oil ash as a phase change material carrier: Thermal energy storage and structural performance in buildings

Lightweight concrete systems made by employing PCMs and natural waste aggregates are a promising material to minimize heating and cooling needs in buildings. But most systems utilize natural minerals or fly ash-based carriers with finite storage capabilities and are not validated under real-world conditions. There is, however, a dearth in the literature of waste-derived, carbon-rich ashes which can act as stable porous hosts for lightweight aggregates and organic PCMs. This study covers the gap by applying reclaimed heavy fuel oil ash as a new bifunctional carrier, impregnated with lauryl alcohol, and integrated into lightweight concrete to produce a 50:50 (heavy fuel oil ash-PCM):cement blended concrete composite. The impregnated ash showed thermal stability at approximately 150 °C and the absorbed lauryl alcohol was also about 20 °C in melting and has the latent heat capacity of 110–120 J/g. In concrete, the ash impregnated had a peak temperature of 1–3 °C reduction on the internal surface with direct sunlight, as compared to the diatomite control when both mixed. Outdoor cabin experiments indicated reduced daytime heat gain and delays in nighttime cooling, suggesting a significant thermal buffering effect. This implies that the composite obtained from waste could alleviate daily temperature variations, enhance its indoor thermal comfort, and decrease heat transfer through building envelopes. This work makes a solid foundation in the development of thermal performance and the sustainability of lightweight building materials by linking material-scale characterization to component-level outdoor testing and paving a way further from the aforementioned studies.