Durability of concrete made with waste glass: a South African perspective

Abstract

The surge in urban development has driven extensive industrial growth and spurred numerous construction projects, particularly in the provision of affordable housing for low- and middle income communities. Urbanisation has brought about an increase in the demand of concrete and its constituent materials such as sand. This has resulted in a reduction in the quantity of available natural sand. Urbanisation brings about a demand for concrete and its constituent materials. However, the supply of constituent materials such as sand is limited. Places such as Cape Town have limited resources. As a result, glass has to be sourced from far. And because Glass has to be sourced from fire and is limited, it means that the cost of construction and producing concrete is going to increase. However, something like glass has the same properties as sand, so glass can be used as a partial replacement. In addition to that, glass is also non-biodegradable, therefore incorporating it into concrete as a partial replacement for sand also will help to address municipal solid waste management challenges. A controlled experiment using laboratory-made concrete mixes was conducted. Three replicates were used throughout the testing. Waste glass was used as a partial replacement for sand – at replacement levels of 10% and 20% – in concrete mixes with w/c ratios of 0.50 and 0.66. Fresh concrete properties that were investigated comprised slump, flow, and vebe time. The hardened properties that were investigated comprised compressive strength at 3, 7, 14, and 28 days, surface resistivity, accelerated drying shrinkage and durability indexes (oxygen permeability index and water sorptivity index). Microstructural and mineralogical analyses of the hardened concrete were also undertaken using scanning electron microscopy, X-ray fluorescence, and X-ray diffraction. The effect of glass content on the workability of concrete is dependent on w/c ratio. An increase in glass content resulted in a corresponding reduction in slump, a reduction in flow and an increase in vebe time in mixes with a w/c ratio of 0.50; and an increase in slump, an increase in flow, and a reduction in vebe time in mixes with a w/c ratio of 0.66. An increase in glass content also resulted in a corresponding reduction in density (fresh and hardened), and compressive strength of the density of concrete at all ages and drying shrinkage. Glass did not result in a significant increase in the surface resistivity of concrete. The effect of glass on OPI, WSI and macroporosity was not well-defined. The addition of glass in concrete improved the density of the interfacial transition zone and the overall microstructure of the matrix. Glass was observed to densify the concrete microstructure, with a glass content of 10% producing the best microstructure. The matrix of concrete mixes containing glass was also characterised by microcracks. The incorporation of waste glass in concrete holds much potential for use in concrete and would significantly reduce overdependence on natural sand in concrete production, contribute to efficient municipal solid waste management, and promote environmental sustainability. However, further research on the effect of waste glass – at various water/cement ratios – on hydration, durability, reinforcement corrosion, alkali silica reaction and an in-depth life cycle analysis and life cycle costing is required to evaluate the economic, environmental and long term performance of glass in concrete.