Simulations of diffusion-controlled and dissolution mechanisms with respect to the deceleration period of tricalcium silicate hydration

Abstract

The macroscopic properties of concrete are largely determined by the deceleration period of cement hydration. Tricalcium silicate (C3S), a major component of Portland cement clinker, is usually utilized as a material model to investigate hydration controlling mechanisms. However, there still exist debates on the controlling mechanisms during different hydration periods. Lack of complete knowledge of hydration controlling mechanisms would lead to incorrect predictions about the macroscopic properties of cement or concrete. The diffusion-controlled and dissolution mechanisms are utilized to explain the occurrence of the deceleration period. However, in terms of the diffusion-controlled mechanism, the analysis on the occurrence of the deceleration period which is affected by the coupled effects of factors remains lacking. In addition, in terms of the dissolution mechanism, the effect of the evolution of the interfacial dissolution rate or reactive surface area on the occurrence of the deceleration period is still not clear. The purpose of this study was to analyze the above issues and to verify the two mechanisms through a simulation analysis. A new simulation model considering the diffusion-controlled and dissolution mechanisms was proposed. The obtained results indicated that: (1) The simulation considering the dissolution mechanism alone would lead to a higher degree of hydration under practical water to cement ratio during the deceleration period, compared with the experiment. (2) The anisotropic dissolution of C3S particles would transform into the isotropic dissolution when the hydration entered the deceleration period. (3) The initial fall in the hydration of C3S could be reproduced by the simulation model proposed in this study under the consideration of the dissolution mechanism. (4) If the deceleration period was caused by the dissolution mechanism, the dominant factor would be the decrease of the reactive surface area rather than the evolution of the interfacial dissolution rate. (5) The occurrence of the deceleration period should not be ascribed to the diffusion-controlled mechanism, because the time when this mechanism worked was later than the time when hydration rate started to decrease.