Mechanical, environmental, and cost evaluation of concrete using recycled polypropylene

This study investigates the mechanical, environmental and cost of concrete incorporating recycled polypropylene (PP) granules as partial fine aggregate replacement at 0 %, 10 %, 20 %, and 30 %, with water-to-cement (W/C) ratios of 0.45 and 0.55. The addition of PP granules reduced workability and density due to their hydrophobic and lightweight nature, leading to compressive strength reductions of up to 48 % at 30 % PP content. The optimal substitution level was identified at 10 %, achieving a balance between mechanical performance and environmental benefits. A strong exponential correlation between ultrasonic pulse velocity (UPV) and compressive strength was established (f'c = 0.045e^0.0016v, R² = 0.793), enabling reliable non-destructive strength prediction. Life cycle assessment (LCA) revealed that incorporating PP granules increased the global warming potential (GWP) by approximately 2–6 % at a 0.45 W/C ratio and 3–8 % at 0.55, primarily due to the energy-intensive recycling process. Additionally, the embodied energy (EE) increased by 5–15 % and 7–21 % at 0.45 and 0.55 W/C ratios, respectively. Although PP integration contributes to reducing natural aggregate consumption, its environmental benefits are constrained by higher embodied energy and costs, indicating its application is best limited to non-structural concrete where sustainability trade-offs can be justified.