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Secondary aggregate can be made from industrial waste by treatment with carbon dioxide gas (accelerated carbonation). Trials were conducted on bauxite waste, biomass ashes, metal dusts, quarry fines, steel-making waste, and the ashes arising from municipal incineration, paper recycling, sewage sludge incineration, and coal fired power stations. The wastes were formed into pellets using a combined pelletising and accelerated carbonation process with patent pending. The manufactured pellets conformed to the bulk density requirements for lightweight aggregate specified by British Standard. Specification for lightweight aggregate is limited, and two commercial lightweight aggregates were tested alongside the manufactured pellets for comparison. Compressive strength, water absorption and apparent density of the materials were comparable to that of the commercial aggregate. Furthermore, the finished product contained up to 11% of its own weight in carbon dioxide gas, permanently bound as solid minerals. In a series of on-site pilot scale demonstrations, aggregates have been produced in bulk and used in commercial product trials. The aggregates produced by accelerated carbonation appear to be suitable for use in a wide range of applications including concrete, construction blocks, and substrates for green roofs.

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