Modeling early age hydration kinetics and the hydrated phase of cement paste blended with chloride and sulfate

Although chloride and sulfate salts have been widely used to efficiently improve early strengths of cement, rare research has been focused on modeling the hydration reaction process. This work proposes an integrated method to describe the early hydration process of cement mixed with chloride and sulfate. The hydration degree, heat release rate and various hydration products of this compound cement paste are predicted by using the proposed model. In addition, the isothermal calorimetry experiment of cement paste mixed with NaCl, Na2SO4, CaCl2 and CaSO4 was carried out to verify and validate the proposed model. The results show that chloride and sulfate salts accelerate early cement hydration except CaSO4, which can be shown from the hydration heat release rate and early compressive strength. Based on the degree of hydration obtained from the hydration model, the hydration products are calculated through the thermodynamic model with time. Friedel's and Kuzel's salt are generated in presence of NaCl or CaCl2, and the formation of Friedel's salt precedes Kuzel's salt with hydration. Finally, the proposed model has been validated against early compressive strengths. The simulated results are in good agreement with the measured results. The cement hydration products evolution and porosity obtained by the integrated models are is quite effective and potentially useful to predict the early age hydration blended with chloride and sulfate salts. (C) 2020 Elsevier Ltd. All rights reserved.