Rheology, mechanics, microstructure and durability of low-carbon cementitious materials based on circulating fluidized bed fly ash: A comprehensive review

Fly ash collected from the flue of a power plant’s circulating fluidized bed furnace is referred to as circulating fluidized bed (CFB) fly ash. The high pozzolanic activity of CFB fly ash has potential benefits for the production of environmentally friendly building materials. To actualize the sustainable and large-scale utilization of CFB fly ash in the field of building materials, this paper reviews the pertinent domestic and international literature and introduces the fundamental characteristics of CFB fly ash, including its phase composition and chemical composition. In terms of fresh mixing properties, mechanical properties, and durability, the research advancement of CFB fly ash-based cementitious materials (CFBFACM) was reviewed. Particularly, the influence of unstable factors f-CaO and SO3 in CFB fly ash on the various properties of ecological building materials is examined, because, in the early stage, f-CaO and SO3 will react to promote the dissolution of active silicon and aluminum and generate hydration products that are conducive to the development of strength. The internal tension is insufficient to withstand the crystallization pressure as gypsum and ettringite become increasingly abundant. Consequently, macro strength loss and inadequate durability are brought about. By calculating the ratio between the elements of AFt and C-(A)-S-H gel, CFBFACM with high strength, good volume stability, and good durability can be designed. In addition, in the collaborative treatment of multi-component solid waste, full consideration of bulk density and particle size distribution is beneficial to the performance of CFBFACM. The method of adding nanomaterials or modifying CFB fly ash may become the way of large-scale utilization of CFB fly ash. In the future, it is still necessary to evaluate the cost and sustainability of the life cycle of CFBFACM to fully understand the economic value, ecological value, and social value of the large-scale utilization of CFB fly ash.