Kinetics of hydration of tricalcium aluminate in the presence of gypsum

Abstract

Based on a conceptual model for the stages of hydration of tricalcium aluminate in the presence of gypsum, a mathematical model was developed for the kinetics of hydration. The model was solved, illustrated and compared to experimental heat release data. Analytical equations were presented for the first two stages, while the last stages of hydration reduced to a previously developed model for the hydration of tricalcium aluminate in the absence of gypsum. Results suggested that pore diffusion through a thickening ettringite barrier layer controlled the first stage of hydration, while pore diffusion through a thinning ettringite barrier layer controlled the second stage. After the ettringite layer disappeared, the reaction of the remaining tricalcium aluminate proceeded more rapidly, but by a similar mechanism, than in the absence of sulfate containing species.