Modeling cement hydration by connecting a nucleation and growth mechanism with a diffusion mechanism. Part I: C₃S hydration in dilute suspensions

Abstract

A particle-based C 3 S hydration model, which mathematically connects a nucleation and growth controlled mechanism with a diffusion controlled mechanism, is developed in this study. The model is first formulated and fitted with C 3 S hydration in stirred dilute suspensions in Part I where interactions between different particles can be ignored, and further developed and fitted with Portland cement paste hydration in Part II to account for inter-particle interactions. Excellent agreement was observed between experimental and modeled results. Three critical rate-controlling parameters, including a parallel growth rate constant, a perpendicular growth rate constant and a diffusion constant, were identified from the proposed model. The dependencies of these parameters on particle size and initial quantity of nuclei are investigated in Part I while their dependencies on cement composition, water-cement ratio, and curing condition are studied in Part II.

Modeling cement hydration by connecting a nucleation and growth mechanism with a diffusion mechanism. Part II: Portland cement paste hydration

“…Therefore, unless one believes cement hydration never becomes diffusion controlled, the low diffusivity values should not be used against the second hypothesis mentioned above. The diffusion constant obtained from the model proposed in this study also seems to be independent of particle size, at least for C 3 S hydration in dilute suspensions [8] . While it is not yet possible to prove or disprove either hypothesis, the current study lends additional support to the second one.…”

“…However, no modification to the model is necessary from this aspect as long as the hydration mechanism remains similar. This is especially true as it has already been shown that the shape of the growing nuclei does not significantly affect the fitting results [8] . For application to Portland cement paste hydration, the physical parameters (e.g., nucleation density, growth rate, and density of hydration product) shall be interpreted as the weighted average values of all hydration products growing on the surface of cement particles.…”

“…The detailed derivation and verification of this model are presented in Part I [8] . Only the main equations will be summarized here.…”

“…Second, the diffusion constant obtained from certain models seem to vary with C 3 S particle size by more than an order of magnitude, while in theory it should be independent of particle size [3] . However, as discussed in Part I [8] , many factors may contribute to the relatively low apparent diffusivity obtained from the models. The diffusivity obtained by modeling period 5 (from approximately 30 h up to 1000 h) alone is similar to that obtained by modeling both periods 4 and 5 [8 -10] .…”

“…By introducing a clear definition of the transition point, a new particle-based numerical model, which compatibly combined the NG and DC mechanisms, was developed in Part I of this study and successfully applied to C 3 S hydration in dilute suspensions (which would be impossible to model with the space restriction assumption) [8] . In this study, we attempted to demonstrate that with, some modifications, the proposed model can also be applied to the hydration of Portland cement paste.…”