Deriving early hydration cement paste phase assemblage, microstructure development and elastic properties using thermodynamic simulation and multi-scale material modeling

Many hydration models focus on predicting the long-term hydration process and resulting material changes without specifically addressing early hydration within the first day. Here, we present a new approach for predicting early hydration cement paste phase assemblage, microstructure development and elastic properties by applying thermodynamic modeling and simulation as input to a multi-scale material model. Cement dissolution for implementation within the thermodynamic simulation is derived by fitting the five-parameter logistic function (5PL) to experimental data from quantitative X-ray diffraction. Results are compared with simulations using the modified Parrot & Killoh model for cement dissolution. Further, the influence of variations in the calcium sulphate and calcite content of the initial cement phase assemblage is investigated accounting for errors in experimental determination. The proposed model for hydrating cement paste accounts for all phases predicted by the thermodynamic simulation output, two types of C-S-H, as well as concentric growth of hydrates from the surface of the clinker grains. The stiffness of the hydrating cement paste is derived by upscaling the microscopic properties using a multi-level continuum micromechanics homogenization scheme. Model predictions are compared with experimental results from penetration tests and ultrasonic Young's modulus determination. It is shown, that 5PL dissolution modeling in combination with thermodynamic simulation is able to describe early hydration cement phase alterations. The 5PL approach thereby captures initial ettringite formation and accurately describes portlandite precipitation. However, the results are highly dependent on the quality of the experimental data. The results further illustrate, how cement paste stiffness development can be derived by application of low-cost computational methods. The proposed approach enables investigations of state-of-the-art questions of cement hydration including the influence of individual hydrate phases on the solidification process.