Influence of alkaline conditions on the ettringite formation of a Mayenite‐rich binary system

Abstract

To reduce carbon emissions from construction, low‐clinker cements like LC3 are wider used worldwide, while it brings the weakness in early strength. Mayenite (C12A7) is a calcium aluminate mineral with high solubility and reactivity amongst calcium aluminates. A binder designed with a Mayenite‐rich cement and gypsum has been proven in increasing early strength by forming ettringite in a type of low‐clinker cement. To investigate the mechanism of its accelerating effect, isothermal calorimetry is applied to observe the hydration heat of the Mayenite‐rich binder in various conditions, i.e., 1) the neutral environment with only DI H2O, 2) the pore solution simulating the alkaline environment of Portland cement paste, 3) the lithium‐ionic environment with Li2CO3 by 0.5 wt.%, and 4) the acidic environment achieved by citric acid (0.5 wt.%). As a result, the hydration heat in the pore solution environment is highest amongst. This result indicates the reactivity of mayenite in the environment with alkali can surpass the one with Li2CO3, which is a common accelerator to calcium aluminates. Furthermore, quantitative analyses of XRD and TGA on the hydrated samples unveil the phase assemblage evolution of the binary system. In conclusion, a synergetic effect is achieved via high alkalinity due to cement hydration accelerating the Mayenite reaction, which in return creates an Ettringite structure in the low‐clinker cementitious matrix to increase the strength in the early age.