Recent advances in alkaline cement binders: A review

Alkaline cement binders offer innovative and ingenious solutions to combat global energy demand, waste generation, and greenhouse emissions. In their production, alkaline binders consume waste materials with less energy and emit less carbon dioxide compared to ordinary Portland cement. In this review paper, a prime materials-based classification method was used to summarize the recently reported alkaline binders which comprised with the types of coal ash-based, clay-based, slag-based, and mine waste-based. These alkaline binders were further sub-divided into co-binder types, depending on the additional binder incorporated to modify and enhance the cementitious properties. This paper summarises the key properties of recent alkaline binders in terms of their rheological, mechanical and microstructural aspects, highlighting the composition of the binding and alkaline materials with curing conditions in the processing of cement paste, mortar or concrete. The publications reviewed emphasize the potential of alkaline cement to consume various waste precursors such as ashes, clays, industrial slags, and mine tailings along with different waste additives to improve the fresh and hardened characteristics of alkaline cement by reducing the adverse cost and environmental impacts. The classified alkaline binders reveal some vital results which can be used for optimum mix design combinations for actual field applications. The physicochemical properties of the precursors and alkaline materials and the curing regimes mainly affect the fresh and hardened properties of various alkaline binder compositions. Finally, the potential for substituting waste alkaline sources instead of commercial alkaline solutions is highlighted to make the alkaline binders completely waste-based.