Utilization of coal fly ash from a Chinese power plant for manufacturing highly insulating foam glass: Implications of physical, mechanical properties and environmental features

This research focuses on the potential use of fly ash (WAf) from a Chinese pulverized-coal combustion (PCC) power plant for manufacturing foam glass. The influences of fly ash properties, fly ash/recycled glass proportion in the raw materials, addition of fluxing and foaming agent, firing temperature, and residence time at the peak temperature on the final properties (apparent density, compressing strength and leachable potential of major and trace elements) of the foam specimens are investigated. The optimal foaming products were obtained consuming up to 33.3-43.3% fly ash, adding 9-11% Na2CO3 fluxing agent and 0.5% SiC foaming agent, firing at 865-915 °C during 15 min residence time at the peak temperature. The obtained fly ash-based product revealed comparable compressive strength but slightly higher densities than commercial foam glass, with low CO2 emissions and low leachable potential for environmentally relevant trace elements within the limits for inert/no-hazardous material established by the European Council Decision 2003/33/EC for land waste disposal. The large porosity of the foam glass indicates a high potential of thermal and acoustic insulation. The foaming behavior and the final properties the foam glass are strongly influenced by properties of fly ash (mainly fluxing temperature and organic C content), fly ash/recycled glass proportion in the raw materials, addition of Na2CO3 fluxing agent and SiC foaming agent, firing temperature, and residence time at the peak temperature. The low C content and high refractory character of WAf give rise to poor foaming of the specimens when only fly ash and Na2CO3 mixtures are used. The consumption of relatively high proportions of recycled glass and SiC is essential to produce foaming.