In situ nano-scale observation of C3A dissolution in water

Abstract Historically, sparingly soluble mineral dissolution in aqueous solutions is measured at macroscopic scales, mostly by indirect methods that track the solution composition over times ranging from minutes to years. Relatively fewer measurements have been made of dissolution rates of highly soluble minerals and their variability at microscopic length scales and shorter times prior to the products precipitation. Here, we report in-situ, real-time measurements of the initial absolute dissolution rate of an extremely reactive mineral, cubic tricalcium aluminate (C3A), in pure water, by monitoring its surface retreat with nanometer resolution. The data reveal that C3A has an extremely fast dissolution rate within the instantaneous contact with water, in the range of (0.5 to 2) mmol·m−2·s−1 and several orders of magnitude greater than that of gypsum or calcite. Soon after that initial dissolution, nucleation and rapid growth of calcium aluminate hydrate would occur, leading to a dramatic decrease of the C3A dissolution rate by blocking its access to the solution. To our knowledge, this is the first time the real dissolution rate of C3A is measured in water, which is urgently needed for the fundamental modelling of the reaction mechanisms, kinetics, and microstructure development during cement hydration.