The Use of Recycled Polyethylene Terephthalate as a Partial Replacement for Sand on the Mechanical Properties of Structural Concrete

Abstract

Negative environmental impacts caused by the over-extraction of sand have arisen due to the high demand of global concrete production. Subsequently, the need to find an adequate replacement for sand in concrete production is paramount. Additionally, the mismanagement of plastic waste in Southeast Asia has resulted in large quantities being sent to landfill. This could otherwise be used as a viable alternative. Several studies have investigated the effect of Polyethylene Terephthalate (PET) aggregate as a partial replacement for sand on the mechanical, durability and physical properties of concrete. Nevertheless, due to the broad number of variables affecting the properties of concrete, gaps remain in the literature suggesting the necessity for a more comprehensive approach. The aim of this research was therefore to investigate the impact on strength when using Polyethylene Terephthalate (PET) flakes in concrete. The effects of substituting 10 % and 20 % of sand by volume with recycled PET flakes were investigated, with the results compared to reference mix samples. 20 cube samples, of sizes 100 mm3 and 150 mm3, were cast for compressive strength tests; 20 cylinder samples, of sizes 100 ømm x 150 mm and 150 ømm x 300 mm, were manufactured for splitting tensile strength tests; and 9 prism samples, of size 100 mm x 100 mm x 500 mm were cured for flexural strength and modulus of elasticity tests. All 49 samples were tested for dry density. A constant curing age of 28 days and a water-to-cement ratio of 0.5 were applied to this experiment. The size of the PET flakes used in the concrete mixes were between 0 and 10 mm. The results indicated that an initial decrease in the compressive strength and modulus of elasticity for 10% replacement level was seen before an increase in strength for 20% replacement. Contrastingly, an initial increase in flexural strength for 10% replacement was exhibited, before a decrease in strength for 20% replacement. The splitting tensile strength and hardened density showed a growing decrease in values for increasing replacement percentage. The conventional reference concrete mixes underwent brittle failure; whereas ductile behaviour was shown by the mixes containing PET flakes. Accordingly, it was concluded that there is significant potential for the use of up to 20 % replacement of PET in a suitable mix design for structural and non-structural applications.