Cementitious materials based on fluidised bed coal combustion ashes

This paper summarises work aimed at developing cementitious materials based on fluidised bed coal combustion ashes. It was found that such ashes, unlike most conventional fly ashes, exhibit distinct hydraulic properties and – if mixed with appropriate amounts of water – set and harden spontaneously at ambient temperature, yielding a C—S—H phase and ettringite as main products of hydration. Under hydrothermal conditions the hydrogarnet phase is formed as the main reaction product, together with tobermorite and anhydrite. Depending on the composition of the ashes, the strength of the hardened material can be enhanced by the addition of some other cementitious constituents, particularly blast furnace slag. Due to the favourable strength-to-bulk density ratio, the hardened material may be considered a lightweight cementitious product.