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Laboratory and industrial projects
Two major projects, funded by the Waste and Resources Action Programme (WRAP) are taking place at the University of Sheffield to explore the huge potential for the use of waste glass in concrete aggregate.
It has been estimated that over three million tonnes of waste glass are generated annually in the UK(1). Key sources are waste containers, flat glass (windows, wind-screens and process scrap), fibres and lighting glass (71%, 23%, 1.6% and 0.3% respectively). The Packaging and Landfill Waste Directives(2,3) have imposed fiscal measures to control recovery and recycling of packaging wastes in the European Union. The UK government implements these via the Producer Responsibility Obligations Regulations(4) and Landfill Tax Regulations(5) respectively. In addition, the End-of Life Vehicle (ELV)(6) and Waste Electrical and Electronic Equipment (WEEE) directives(7) have further increased the pressure on the industry to recover and recycle waste glass (see Table 1).
The UK Packaging Recovery Notes (PRN) scheme(9) promotes recycling and reuse of packaging waste by supporting the chain of collectors, processors, re-users and recyclers, using levies imposed on packaging waste producers. Nevertheless, the UK failed to meet its 50% recovery target in 2001(1). To achieve these targets, The Waste and Resources Action Programme (WRAP) was established in response to the UK Government's Waste Strategy(10) to promote sustainable waste management for selected materials, including glass.
Waste glass for concrete construction
In 2002, the Aggregates Levy(11) on virgin aggregates was introduced to encourage the use of alternative materials in construction. Whilst some markets for recycled waste glass already exist as aggregate (170,000 tonnes)(1), there is huge potential for this to increase in the concrete construction sector.
Glass pozzolan
Finely ground glass has the appropriate chemical composition to react with alkalis in cement (pozzolanic reaction) and form cementitious products(12-15) Table 2 gives the oxides of common glass types(16) and widely used concrete pozzolans(17) and shows that pozzolanic properties are likely to be derived from the high SiO^sub 2^ content of glass.
Glass aggregate
Waste glass could also be used as a concrete aggregate, either as a low-value direct replacement for normal concrete aggregates or as an exposed, decorative, high-value aggregate in architectural concrete products. However, the fundamental problem of alkali-silica reaction (ASR) between glass particles and cement paste...