Quantifications of growth rate and particle size of magnesium silicate hydrate cement using small‐angle X‐ray scattering

Abstract The focus of recent research on cement binders has shifted to alternatives such as magnesium silicate hydrate (M‐S‐H) to mitigate the environmental impact of conventional concrete production. However, a detailed understanding of the morphology and growth rate of M‐S‐H, which informs its applicability as a cementing agent, is lacking. These properties are important as they influence cement hydration and consequently the development of macroscopic properties. In this study, the particle size distribution and growth rate of M‐S‐H synthesized by mixing aqueous stock solutions were analyzed using synchrotron‐based small‐angle X‐ray scattering. The reaction solutions contained dissolved magnesium and silicon with concentrations ranging from 2 to 500 mM, corresponding to saturation indices with respect to M‐S‐H endmembers, M 0.75 ‐S‐H and M 1.50 ‐S‐H, between 5.8 and 10.3. The precipitation rates of M‐S‐H align with affinity‐based kinetic models and can be described by the following equations: For M 0.75 ‐S‐H: , and for M 1.50 ‐S‐H: , where is the rate in mol/L/s, and represents the saturation ratio with respect to M‐S‐H. Moreover, we observed that changing the [Mg]/[Si] ratio affects particle size, a trend that cannot be fully explained by changes in the saturation index alone. These insights are critical for improving the predictability and control of cementation in concrete that utilizes M‐S‐H‐based binders.