Fly ash-based geopolymers containing added silicate waste. A review

This review summarizes different types of industrial wastes such as biomass ash, red mud, recycled glass and heavy metals waste, in their application for geopolymer production. These wastes, which are currently abundant and urgent to dispose of, cannot be used alone in the geopolymer process because they do not provide a suitable SiO2/Al2O3 molar ratio for this technology. For this reason, these by-products are commonly used in addition to other aluminosilicate sources such as fly ash or metakaolin. Important parameters which affect the properties and performance of fly ash based geopolymers with addition of a variety of wastes are discussed based on a comprehensive literature review.