Recycling of waste glass as aggregate in cement-based materials

Glass is a common material made from natural resources such as sand. Although much of the waste glass is recycled to make new glass products, a large proportion is still being sent to landfill. Glass is a useful resource that is non-biodegradable, occupying valuable landfill space. To combat the waste glass that is heading to landfill, alternative recycling forms need to be investigated. The construction industry is one of the largest CO₂ emitters in the world, producing up to 8% of the global CO₂ to produce cement. The use of sand largely depletes natural resources for the creation of mortars or concretes. This review explores the possibilities of incorporating waste glass into cement-based materials. It was found waste glass is unsuitable as a raw material replacement to produce clinker and as a coarse aggregate, due to a liquid state being produced in the kiln and the smooth surface area, respectively. Promising results were found when incorporating fine particles of glass in cement-based materials due to the favourable pozzolanic reaction which benefits the mechanical properties. It was found that 20% of cement can be replaced with waste glass of 20 μm without detrimental effects on the mechanical properties. Replacements higher than 30% can cause negative impacts as insufficient amounts of CaCO₃ remain to react with the silica from the glass, known as the dilution effect. As the fine aggregate replacement for waste glass increases over 20%, the mechanical properties decrease proportionally; however, up to 20% has similar results to traditionally mixes.