Potential transition to a circular economy for plastics in developing countries: recycling plastic waste into plastic-bonded aggregate composites for construction

Abstract

Due to inadequate recycling systems, developing countries (DCs) are major contributors to ocean plastics. Producing plastic-bonded aggregate construction composites (PBAC) is a low-cost recycling option for DCs. There is, however, limited scientific research on PBAC properties. The PhD aimed to provide an understanding of the production, properties, and competencies of PBAC and assess barriers to implementing a circular economic plastic recycling model in DCs. Using heat-mixing techniques, water sachets and bottle caps were used to bind sand and quarry dust to form the PBAC samples. The effects of the temperature, binder (PWB), and aggregate (FA) type on the PBAC properties were analysed using thermal analysis, DMA, SEM, and mechanical testing techniques. The mechanical property correlations were also established. The durability and failure mechanisms of PBAC interlocking block (PIB) units and wall panels were researched for the first time. The circular economic transition barriers were assessed using a novel contextualised assessment framework. PBACs are lightweight materials with a 1.3 to 1.8 g cm-3 density range. The maximum compressive, flexural, and splitting tensile strength of PBAC with unsieved sand were 28.4 MPa, 21.0 MPa and 5.3 MPa, respectively. The compressive strength increased to 37.1 MPa with FA particle sizes below 300μm. The optimum properties of PBAC were achieved when 65 to 75 wt.% dense graded soil was mixed into PWB with high binding capacity. The maximum storage modulus of the optimised PBAC recorded between 38 to 48℃ ranged between 1.4 to 4.5 GPa. PBAC failure was mainly due to FA-PWB matrix debonding or the pull-out and tearing of the PWB strands. The compressive strengths of the PIB walls ranged between 4.2 to 5.7 MPa, depending on the PWB type. The failure mechanisms of the PIB wall panels were similar for all variations of the PBAC, but the extent of wall damage varied.