Recycling of glass waste by converting it to aggregate not only saves landfill space but also reduces the demand of extraction natural raw material for construction activity. Glass as a hard, brittle, and commonly transparent substance, white or coloured, made by melding sand or silica together with lime, potash, soda or lead oxide. Glass is a completely recyclable material, it is assessed that glass recycling rate in the United States is about 40% and that of Brazil is around 50% of the total glass waste produced in their respective countries (Environment and Community Organizing, 2010).The European’s glass recycling (Letsrecycle, 2010) reported that since 1996, most of the European countries recycled more than 50% of their glass wastes.
In India, 0.7% of total urban waste comprises of glass (Pappu et al, 2011). 1.
2. Behaviour of Glass Aggregates in Concrete 1. Alkali Silica Reaction with Glass Aggregate (ASR) It is generally believed that glass is unstable in the alkaline environment of the concrete. When Portland cement and glass aggregates are mixed together, the silica content of glass aggregates react with the alkali content of the Portland cement and produce a gel-type substance which increases in volume as it absorbs water. The alkalis in the concrete pore react with reactive siliceous minerals and form an alkali-silica gel product which swells and gives additional internal pressures in the presence of water; thereby resulting to failure of concrete (Rear et al.1994).
Use of up to 30% glass aggregate in concrete might not cause any deleterious effects, particularly if the alkali content of the concrete is below 3 kg/m3 (Shayan and Xu , 2004).1. Effect of Waste Glass on Unit Weight and Density of Concrete The addition of waste glass as an aggregates caused a slight weight reduction and it is because of the lower specific gravity of glass aggregates as compare to fine aggregates (sand), also dry density of the concrete mixes having glass aggregates showed decreasing tendency and this again because of the lower density of glass