Properties and microstructure of lightweight aggregate produced from lignite coal fly ash and recycled glass

The effect of glass addition on the processing, physical properties and microstructure of lightweight aggregate made from lignite coal fly ash from the Megalopolis power station in Greece has been investigated. Fly ash/glass mixes have been rapidly sintered at temperatures between 1040 and 1120 °C in a rotary furnace, and the density, water absorption and pellet strength determined. Sintering 60:40 fly ash:waste glass mixes at 1120 °C produced lightweight aggregate with a mean density of 1.35 g/cm3, water absorption of ∼16% and crushing strength of 7.3 MPa. Major crystalline phases in sintered materials were quartz (SiO2), albite (NaAlSi3O8), moissanite (SiC), hematite (Fe2O3), wollastonite (CaSiO3) and diopside (CaMg(Si2O6)). The work indicates that Megalopolis fly ash combined with waste glass can be used to manufacture lightweight aggregate with properties comparable to commercially available products. Fly ash and glass are potential resources that are currently waste materials in Greece. The processing involving pelletising and sintering in a rotary kiln is similar to that required for other commercially available lightweight aggregates manufactured from shales, clays and slate, and therefore processing costs are expected to be similar. However, avoiding the costs and environmental impacts associated with importing lightweight aggregate or using pumice makes the production of FA/glass lightweight aggregate a viable option.