An Advanced Single Particle Model for C₃S and Alite Hydration

Abstract

The hydration behavior of portland cement phases continues to be debated with new insights fueling the controversy. What causes the induction period? What initiates acceleration? What causes the onset and rapid decrease in reaction rate post peak? Does diffusion play a role and what causes low, but sustained reaction rates for long periods of time? Recent modeling efforts suggest that boundary nucleation and growth can explain at least some of the observations and that such occurs in a “limited reaction volume” accounting for about 30% of the initial cement mass. Yet, other efforts offer an alternative theory that would suggest that densification occurs in two steps. In an effort to resolve these and other questions, a single particle model for alite/Ca3SiO5 hydration has been developed using a mass continuity‐based continuum approach as an alternative to the Avramian basis used in most recent studies. Such single particle models are relevant starting points for fast model‐based experimentation, more elaborate single particle models, and simulation platforms that act on ensembles of particles. The present model includes transport effects, solution phase chemistry, and incorporates intraparticle nucleation.

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

“…Compared to many recently published models [6,26,31] , the model proposed in this study is rather simplified with a minimum number of independent parameters. Biernacki and Xie have extracted a much larger number of parameters (12 fixed and eight adjustable) by adopting a mass continuity-based continuum approach to model C 3 S hydration [31] .…”

“…Such behavior may imply that nucleation at new sites is less likely to happen during the " growth period " as it seems easier for the ions to attach to C-S-H surfaces than C 3 S surfaces. Even if new nucleation does occur, it has been demonstrated that early hydration kinetics is much more sensitive to the amount of instantaneously formed nuclei than the subsequent nucleation rate [31] . The model presented here only investigates the case of site-saturated nucleation.…”

“…Biernacki and Xie have extracted a much larger number of parameters (12 fixed and eight adjustable) by adopting a mass continuity-based continuum approach to model C 3 S hydration [31] . While the model presented here may lack certain degree of flexibility in considering all the possible influencing factors of C 3 S/cement hydration, the results of this study suggest that it is not possible to independently determine all the parameters by fitting hydration kinetics data only.…”

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

“…The large CH crystals formed in alite paste may completely stop the hydration of certain C 3 S particles enclosed inside. It should also be noted that the method used here to account for inter-particle interactions is different from that introduced in [12] , though they are based on similar principles.…”

“…If one assumes particles of all sizes behave like the system average, as suggested by Biernacki and Xie [12] , then Equation (8) can be applied to individual cement particles and becomes compatible with the particle-based models. Hence, for Portland cement paste hydration, Equation (2) becomes…”