Assessment of mechanical properties and environmental impacts of eco-friendly lightweight geopolymer concrete using popcorn aggregates from recycled plastic waste

Abstract The increasing challenges in natural resource consumption and cement production have intensified interest in recycling and sustainable construction materials. In this study, an environmentally friendly lightweight geopolymer concrete (LWGPC) was developed by integrating two recycled components: fly ash (FA) as the primary binder and a novel lightweight coarse plastic aggregate (LCPA), produced from locally recycled plastic waste and commonly referred to as “popcorn aggregates”, which was used to fully replace natural coarse aggregates. Fourteen mixes were prepared with varying sand-to-LCPA ratios, while maintaining constant fly ash content and a fixed alkaline activator. Fresh, physical, and mechanical tests, as well as SEM and EDX analyses, were conducted alongside environmental and economic assessments after curing for 7 and 28 days under direct sunlight. The experimental results revealed that workability improved with increasing LCPA content, with the 1S:2LCPA mix achieving a 54% increase in slump. Dry density decreased gradually, with the 1S:1LCPA mix achieving a 23.1% weight reduction while maintaining structural integrity. Although compressive strength decreased with higher LCPA content, the 1S:1LCPA mix demonstrated a favorable balance between density reduction and strength, recording 30.6 MPa at 28 days. Moreover, the 1S:1.5LCPA mix improved tensile and flexural performance up to the optimal ratio, beyond which reductions occurred. Importantly, these mixes reduced energy consumption by 41.09%, CO 2 emissions by 40.52%, and overall cost by 31.58% compared to the control. The results highlight the potential of LCPA as an innovative aggregate, enabling sustainable, cost-effective, and lightweight geopolymer concrete production, with promising applications in non-structural blocks, partition walls, and energy-efficient lightweight panels. Graphical abstract