از زباله های شیشه به مصالح ساختمانی – راه حل پایدار نوآورانه برای زباله های شیشه From waste glass to building materials – An innovative sustainable solution for waste glass

1. Introduction Over the past century, the total global consumption of materials has increased eightfold and per capita consumption has risen from 4.6 tonnes to 10.3 tonnes a year (Krausmann et al., 2009), matched by the generation of vast volumes of waste. Recycling technologies and numerous national and local regulations intended to drive the recovery of resources from waste have failed to keep pace with this accelerating consumption, resulting in ever-increasing volumes of waste to landfill (EPA, 2017). One major waste stream emerging as a serious challenge worldwide is glass, despite its ideal properties for recycling and its unsuitability for landfilling. Although glass can repeatedly be recycled with no loss of quality, large volumes of glass are ending up in the landfill. In Australia, for example, in the five years to 2015, glass consumption increased but the national glass recycling rate fell from 49% to 42% (IndustryEdge Pty Ltd and Equilibrium OMG Pty Ltd, 2016; Adaway et al., 2015), leaving almost 800,000 tonnes of waste glass requiring disposal every year (FEVE, 2017). Glass recycling rates in European Union nations are the world’s highest, averaging 73% (Glass Packing Institute, 2016), but other countries are trailing much further behind, such as the US (34%) and Singapore 20% (National Environment Agency, 2017). One major barrier to conventional recycling is the need to both separate glasses into its various types. Some speciality glasses like window panes, tempered glass, Pyrex, borosilicate glass and broken glass are usually not considered recyclable (Gautam et al., 2012). As the melting points and characteristics of different glass types are precisely matched to their uses, mixed glass cannot be remelted in one batch. If heat treated glass is mixed with bottle and jar recycling process, it can result in a different viscosity of the glass melt and prevent the molten glass to be extruded properly (Planet Ark Environmental Foundation, 2010). Forming, cooling rate and an annealing temperature of mixed glass are also harder to control. Additionally, different types of glass have different coefficient of thermal expansion which might expand and contract at a different rate. Mixing these glasses results in cracking or shattering of the piece during cooling (University of Delaware, 1843). Besides, contaminations are also the major problem in conventional glass recycling. Demolition sites are a major source of waste window glass, but an effort to recycle old window glass cullet to new glass has not been done. Unlike container glass which allows a small amount of impurities of 20- 50 ppm, production of flat window glass tolerate no ceramic and ferrous metal impurities (Vieitez et al., 2011). Also, various types of window glass ranging from standard, tempered, silver-based varnish (mirror) to laminated glass have a different chemical composition and impurities, preventing conventional recycling to be done. To increase glass recycling rates, alternatives means of reprocessing waste glass without remelting are needed. Previous studies have reported the use of the waste glass powder (GP) as a filler for asphalt, concrete pavements and sidewalk slabs and as an alternative to both fine (Glass packing Institute, 2016; Hyperphysics, 2014) and coarse aggregates (Kenneth et al., 2013) in concrete. However, as waste glass can be used to replace only 10-30% of the original materials in these applications, they can absorb only modest volumes of this bulk waste (Glass packing Institute, 2016; Hyperphysics, 2014).