Abstract
Efficient and accurate cement hydration simulation is an important issue for predicting and analyzing concrete’s performance evolution. A large number of models have been proposed to describe cement hydration. Some models can simulate the test results with high accuracy by constructing reasonable functions, but they are based on mathematical regression and lack of physical background and prediction ability. Other models, such as the famous HYMOSTRUC model and CEMHYD3D model, can predict the hydration rate and microstructure evolution of cement based on its initial microstructure. However, this kind of prediction model also has some limitations, such as the inability to fully consider the properties of cement slurry, or being too complicated for use in finite element analysis (FEA). In this study, the hydration mechanisms of the main minerals in Portland cement (PC) are expounded, and the corresponding hydration model is built. Firstly, a modified particle hydration model of tricalcium silicate (C3S) and alite is proposed based on the moisture diffusion theory and the calcium silicate hydrate (C-S-H) barrier layer hypothesis, which can predict the hydration degree of C3S and alite throughout the age. Taking the hydration model of C3S as a reference, the hydration model of dicalcium silicate (C2S) is established, and the synergistic hydration effect of C3S and C2S is calibrated by analyzing the published test results. The hydration model of tricalcium aluminate(C3A)-gypsum system is then designed by combining the theory of dissolution and diffusion. This model can reflect the hydration characteristics of C3A in different stages, and quantify the response of the hydration process of C3A to different gypsum content, water–cement ratio, and particle size distribution. Finally, several correction coefficients are introduced into the hydration model of the main mineral, to consider the synergistic hydration effect among the minerals to some extent and realize the prediction of the hydration of PC.
Highlights
The hydration model of the first stage is established by applying the dissolution theory, and the hydration models of the remaining two stages are controlled by water passing through the monosulfide hydrated calcium sulphoaluminate (AFm) and calcium aluminates hydrate (C3 AH6 ) barrier shell
The metastable barrier hypothesis, proposed by Stein et al [48] and perfected by Jennings et al [49] and Mehta [50], suggests that in the initial period, the unhydrated C3 S surface will gradually form a continuous but thin metastable layer composed of calcium silicate hydrate phase with high Ca/Si, which can effectively passivate the surface by limiting its contact with water, reducing the hydration rate of C3 S
H (t) − Hc rout (t) − rin (t) where, rin is the radius of unhydrated particle; rout is the outside radius of particles after hydration; H is the relative humidity in pores; Hc is the relative humidity at the interface between unhydrated particles and calcium silicate hydrate (C-S-H) shell
Summary
Modern mass concrete projects have the characteristics of high strength and fast construction speed, which leads to an increase of the dosage of cementitious materials in concrete, accompanied by the high heat of hydration and high shrinkage. Van breugel [15] and Bentz [16] proposed the famous HYMOSTRUC model and CEMHYD3D model respectively, which appear to be the most accepted ones Both models can accurately predict the influence of particle size distribution, water state and reaction temperature on hydration rate based on the real initial microstructure of cement, and can describe the microstructure evolution during hydration. The hydration model of the first stage is established by applying the dissolution theory, and the hydration models of the remaining two stages are controlled by water passing through the monosulfide hydrated calcium sulphoaluminate (AFm) and calcium aluminates hydrate (C3 AH6 ) barrier shell This threestage hydration model can reflect the influence of gypsum content, water cement ratio (w/c) and particle size distribution on the hydration rate of C3 A. A series of correction coefficients are introduced into the model to quantify the influence mechanism between each mineral during cement hydration, and the prediction of Portland cement (PC) hydration with the composite model is realized
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