Modelling early age hydration kinetics of alite

The modelling platform μic [1] has been used to investigate the mechanisms occurring during the hydration of alite. It is shown that it is possible to obtain a good simulation of the hydration kinetics through the implementation of two mechanisms: a dissolution mechanism combined with nucleation and growth of products. The dissolution rate is varied according to the ratio β, between the ion activity product and the equilibrium solubility product according the theory published by Juilland et al. [2]. The solution concentrations are computed directly from the amount of alite dissolved taking into account the amount of water present and the amount of products formed, with activities and complex ion formation calculated according to standard methods. Saturation index calculations are implemented to compute the time of precipitation of C–S–H and portlandite (CH) individually. For the main heat evolution peak, the rate controlling mechanism switches to a modified form of boundary nucleation and growth. C–S–H grows in a diffuse manner in which the density of packing of the C–S–H phase increases with hydration [3]. The rate of heat evolution obtained from the simulations is compared with isothermal calorimetry data and good agreement is found.