In the quest for sustainable construction materials, researchers have turned their attention to an unlikely candidate: recycled polypropylene (PP) granules. A recent study led by Ade Okvianti Irlan from the Department of Civil Engineering at Universitas Hasanuddin in Indonesia has explored the potential of incorporating these plastic waste products into concrete, with intriguing results published in *Case Studies in Chemical and Environmental Engineering* (translated from Indonesian as *Studies in Chemical and Environmental Engineering*).
The research team investigated the mechanical, environmental, and cost implications of using recycled PP granules as a partial replacement for fine aggregates in concrete. They tested various substitution levels—0%, 10%, 20%, and 30%—alongside different water-to-cement (W/C) ratios of 0.45 and 0.55. The findings revealed that while the addition of PP granules reduced workability and density due to their hydrophobic and lightweight nature, the optimal substitution level was identified at 10%, striking a balance between mechanical performance and environmental benefits.
“At 10% substitution, we saw a compromise where the mechanical properties were still acceptable, and we could start to see the environmental benefits,” Irlan explained. However, higher substitution levels led to significant reductions in compressive strength, with up to 48% loss at 30% PP content.
One of the study’s notable achievements was establishing a strong exponential correlation between ultrasonic pulse velocity (UPV) and compressive strength. This correlation, expressed as f’c = 0.045e0.0016v with an R² value of 0.793, enables reliable non-destructive strength prediction, a valuable tool for quality control and safety assessments in construction.
The environmental impact of incorporating PP granules was also scrutinized through a life cycle assessment (LCA). The study found that while using recycled PP reduces natural aggregate consumption, it increases the global warming potential (GWP) by approximately 2–6% at a 0.45 W/C ratio and 3–8% at 0.55. This increase is primarily due to the energy-intensive recycling process. Additionally, the embodied energy (EE) saw a rise of 5–15% at 0.45 W/C ratios and 7–21% at 0.55.
“Although the environmental benefits are constrained by higher embodied energy and costs, the use of recycled PP in concrete can still be justified for non-structural applications,” Irlan noted. This suggests that while the material may not be suitable for high-strength structural components, it holds promise for other construction uses where sustainability trade-offs can be justified.
The study’s findings have significant implications for the construction and energy sectors. As the demand for sustainable building materials grows, the integration of recycled PP granules into concrete offers a potential solution for reducing plastic waste and conserving natural resources. However, the increased embodied energy and costs highlight the need for further innovation in recycling processes to enhance the environmental viability of this approach.
This research could shape future developments in sustainable construction by encouraging the exploration of alternative materials and recycling methods. As Irlan and her team continue to investigate these avenues, the construction industry may soon see a shift towards more eco-friendly practices, driven by the urgent need for sustainable solutions in the face of climate change and resource depletion.
In the meantime, the study published in *Case Studies in Chemical and Environmental Engineering* serves as a crucial stepping stone, offering valuable insights into the complexities of integrating recycled materials into construction and the delicate balance between performance, cost, and environmental impact.