In-depth understanding the hydration process of Mn-containing ferrite: A comparison with ferrite

Manganese (Mn) is inevitably incorporated into cement from raw materials, and is mainly incorporated into the ferrite phase of cement. In this paper, the hydration kinetic was investigated for Mn-containing ferrite and unmodified ferrite. The evolution of the solid phases, aqueous species, and both conductivity and pH were investigated for unmodified ferrite and Mn-containing ferrite by a diluted suspension experiment. Isothermal calorimetry, transmission electron microscopy, and mechanical property measurements were conducted to explore the influence of Mn on the hydraulic activity of ferrite. The results showed that the incorporation of Mn enhances the hydraulic activity, alleviates the influence of gypsum on the retardation of ferrite, and improves the early strength in the presence of gypsum. Mn-containing ferrite also accelerates dissolution, influencing the initial sulfate adsorption. Mn ions eventually incorporate into (Al, Fe)-AFt and (Al, Fe)-AFm. During the first several hours of hydration of ferrite, there is no sulfate consumption after the initial adsorption, accompanied by a decrease of Ca2+ and Al3+ concentration. And an "adsorption-barrier" hypothesis is proposed to explain the dormant period of sulfate consumption.