Utilisation of bio-based acorn cupule aggregates in producing lightweight concrete: Influence of thermal treatment on performance characteristics

Environmental and climatic challenges necessitate careful consideration and strategic planning regarding the materials and techniques employed across all sectors. To reduce the depletion of non-renewable resources and to improve and achieve sustainable development, researchers have recently become interested in the trend of using bio-based materials as alternative resources in numerous fields. Given that the construction sector poses the main threat to environmental balance due to its high consumption of raw materials, such as fine and coarse aggregates widely used to create different concrete, and energy resources, particularly for building ventilation and cooling, this study aims to use acorn cupule (AC) waste as a low-cost and renewable lightweight bio-aggregate to develop green lightweight flowable sand concrete (FSC) with high insulation properties. Since such organic materials have a negative impact on concrete's mechanical performance, a heat treatment was applied to this AC aggregate to enhance its surface properties. For this purpose, the natural sand was volumetrically substituted with raw and heat-treated acorn cupule aggregates (RAC and HAC) at 10, 20, 30, 40, and 50% in FSC. The results showed that incorporating RAC aggregates decreased the concrete’s workability compared to the control one. The density, compressive strength, and flexural strength were reduced by up to 50%, 84%, and 68%, respectively, while the thermal conductivity was improved by approximately 24–89%. The heat treatment of RAC aggregates enhanced FSC flowability; reduced water absorption, reducing concrete porosity by 25%; and significantly improved the compressive and flexural strength by up to 41% and 45%, respectively. However, a slight decline in thermal performance was recorded. Finally, with up to 30% RAC and 40% HAC, AC was proven to be a highly recommended ecological alternative to natural aggregates in the concrete industry for developing lightweight-insulating-structural FSC.