Hydration inhibition mechanism of gypsum on tricalcium aluminate from ReaxFF molecular dynamics simulation and quantum chemical calculation

To understand the hydration inhibition mechanism of gypsum (CaSO4·2H2O) on tricalcium aluminate (C3A), the very early hydration process of C3A in the presence of CaSO4·2H2O was investigated by ReaxFF molecular dynamics simulation and quantum chemical calculation. The adsorption propensity of H2O to the surface of CaSO4·2H2O and C3A, the penetration of H2O into CaSO4·2H2O and C3A, the diffusion of CaSO4·2H2O and C3A to H2O, and the structural changes at the interface of C3A were investigated by analyzing the adsorption configuration, penetration depth, diffusion distance, and the radial distribution function, respectively. The results showed that two forms of associative adsorption and dissociative adsorption were found on the surface of CaSO4·2H2O and C3A. The internal structure of CaSO4·2H2O was more conducive to the movement of H2O than that of C3A. The diffusibility of overall C3A was weaker than that of overall CaSO4·2H2O due to the cage-like structure of C3A. The sensitivity of the C3A structure was greater than that of CaSO4·2H2O structure to hydrolysis.