An Investigation of Partial Replacement of Fine Aggregate with Recycled Plastic Supported by Silica Fume and Its Effect on Compressive Strength and Weight

Abstract

Concrete is one of the main construction materials used in the building industry where it is projected that the revenue of manufacture of ready-mix concrete will amount to approximately 37.5 million dollars by 2022 in the local sector. In addition, plastic waste is another important contributor to the waste pollution since locally only 7% of such waste is recycled. This study is based on the partial replacement of aggregate by means of recycled polycarbonate plastic bottles while attaining the required structural compressive strength. Dolomite, which is an imported aggregate, and silica fume, which is a cementitious material, were used to attain a more appropriate concrete mixture.A total of six concrete mixtures were designed for the purpose of the research by varying the proportion of polycarbonate and fine aggregate. A uni-axial compressive strength test was performed after 7 and 28 days from the cube casting where a maximum of 63.2N/mm2 was attained with a control mixture made of dolomite as the coarse aggregate. Results also showed that the compressive strength decreased with the addition of plastic as a partial replacement of fine aggregate.Statistical analysis by means of an independent sample T-test showed that no significant difference in compressive strength was present between the silica fume mixture and the 5% fine aggregate replacement mixture. The results also showed that compared with the control mixture, the silica fume mixture was significantly weaker at 7 days, but no significant difference resulted at 28 days. Considering the results attained, one may easily note that there was a significant relationship between the percentage of plastic and the compressive strength. A regression analysis was used to observe such a relationship. Moreover, the result showed that a replacement percentage of 48% results in a suitable compressive strength of 10.19N/mm2, where such concrete can be utilised for non-structural purposes.From the results obtained, it was also observed that the final mass of the concrete blocks decreased as the plastic percentage increased. In relation, by maintaining a constant volume between all the samples, the hardened density of the samples also decreased with the increase in plastic percentage.