Hydration Mechanism of Cement Pastes with the Addition of Dry Ice through Electrochemical Impedance Spectroscopy

The addition of dry ice as an admixture to cement pastes has many advantages such as improving the compressive strength and sequestration of CO2. However, its effect on the hydration mechanism of cement pastes is still unknown and will be investigated using electrochemical impedance spectroscopy in this paper. Based on the linear correlation of cumulative hydration heat from the isothermal calorimetry test and the logarithm of high-frequency resistivity, a modified Knudson equation is derived. Corresponding hydration kinetic parameters are calculated by applying the boundary nucleation and growth theory and kinetics model, including Avrami, geometrical contraction, and diffusion equations. The boundary area per unit volume (OvB) for the control specimen and specimens with 0.2% and 0.5% cement weight dry ice addition is 0.1171, 0.1250, and 0.1562, respectively, indicating that the dry ice addition increases the surface area of the nucleation process. In addition, the results show that the Avrami equation for monitoring the nucleation process is limited. Regarding the hydration curves, the transition from the nucleation and growth stage to the interaction of phase boundaries (I) stage is delayed by adding dry ice to the mixture.