Concrete properties incorporating fine Polyethylene Terephthalate aggregates after microwave irradiation pretreatment

Natural resource depletion and inadequate plastic recycling pose significant environmental and waste management challenges. The substitution of natural aggregates with recycled plastic waste in concrete presents a potential solution for mitigating these issues. While lower replacement ratios are generally linked to improved strength, this study focuses on examining the upper limit of plastic utilization to advance understanding of its material properties and to fill the gap in current knowledge. However, the incorporation of high replacement ratios of plastic aggregates into fine natural aggregates (FNA) often results in reduced concrete strength due to poor interfacial bonding. To address this issue, the current study examined the potential of using microwave irradiation pretreatment (MP) of fine polyethylene terephthalate aggregates (FPET). Four concrete mixtures were analyzed: FNA, untreated fine PET aggregate (FPET), and treated fine PET aggregates with low and high MP exposure (FPET 500-5 and FPET 500-10, respectively). A volume of 30% of the aggregate was replaced with FPET with a water-to-cement ratio of 0.40. The results showed that low MP exposure can effectively modify the FPET surface, leading to an improvement in the interfacial transition zone (ITZ), a 4% increase in compressive strength, a 10% increase in splitting tensile strength, and a 25% decrease in the chloride diffusion coefficient compared with FPET. Additionally, the MP-treated FPET concrete exhibited about a 20% reduction in thermal conductivity compared with FNA, indicating improved thermal insulation. This study novelly identifies an optimum microwave energy-time combination (500-5) for FPET. Therefore, MP offers a promising pretreatment technique for enhancing recycled plastic aggregate use in construction materials and contributing to waste management.