An appraisal of the mechanical, microstructural, and thermal characteristics of concrete containing waste PET as coarse aggregate

Abstract

This study assessed the workability, mechanical, microstructural, and thermal behaviours of concrete composed from recycled waste polyethylene terephthalate (PET) as a partial or full replacement for natural coarse aggregates. Workability and Compressive/Split tensile strength tests alongside microstructural and thermogravimetric analysis were performed. Results disclosed that the concrete’s workability increased with increasing percentages of PET. The compressive strength increases with extended curing but decreases as the percentages of waste PET increased at different curing lengths. The PET-modified blends could not yield the target design strength for grade 25 concrete after 28 days. However, the 20% PET-modified mix reached the target strength for concrete grade 20. For all blends, increase in split tensile strength with curing lengths was observed, only the 20% PET-modified blend achieved suitable split tensile strength values. Microstructural analysis revealed that the 100% PET sample has a relatively irregular surface pattern with pores of about 2–4 µm, high quantities of Ca, and minor traces of O, C, Al, Si, Mg, and Na. While PC-20 had a much denser interface between the PET aggregates and the cement matrix with high percentage of Si, O, and Ca, and moderate to minor percentage of Al, Au, Na, and Mg. Thermal analysis showed that the 100% PET sample endured three transition stages. The research outcomes prove that heat-processed PET-modified concrete is suitable for structural applications due to its acceptable fresh, mechanical, microstructural, and thermal properties. Moreover, this alternative is eco-friendly and sustainable as it substitutes natural aggregates with waste plastics.