Evaluation of eco-friendly concrete having waste PET as fine aggregates

Abstract

This study assesses the impacts of recycling waste polyethylene terephthalate (PET) plastic bottles as a partial substitute for fine natural aggregates on the workability, mechanical, microstructural, economic, and thermal properties of concrete. The mix design adopts a concrete mix ratio of 1:2:4 for grade M25, 0.55 water/cement ratio, ordinary Portland cement (OPC) as the binder, varying proportions of heat-processed waste PET and river sand as fine aggregates, and granite as coarse aggregate. Results indicate that workability increased with increasing percentages of waste PET plastics until the 40%PET level, beyond which workability reduces. Compressive and split tensile strength decreased with increasing percentages of waste PET plastics. However, 10% to 40%-PET-modified mixes achieved the recommended strength for M20 concrete. Microstructural analysis on the 30%PET indicates higher quantities of O and Ca, and trivial percentages of Mg, Si, C, Al, and Au. Whereas 100%PET indicates the presence of only C, O, and Au. 100%PET endures three transition stages during heat flow. A glass transition, an exothermic peak below decomposition temperature during cooling at a temperature of 199.88 °C from PET crystallization, and a baseline shift after the endothermic peak at 243.22°C. Thermogravimetry revealed that 100%PET suffers a dual-stage decomposition, an initial stage accounting for an 87.41% reduction in sample mass and a second stage accounting for a further mass loss of 12.79%. Highly significant statistical correlations and regressions developed variations between PET% and the workability and mechanical parameters. The study shows that heat-processed PET-modified concrete is appropriate for structural applications due to its suitable fresh, mechanical, microstructural, and thermal properties. Besides, this practice is eco-friendly and sustainable as it conserves natural resources.