Cementitious materials are porous medium. During the hydration of cement, the porosity is continuously reduced with the continue increase of reaction products. A better understanding of the development of microstructure during cement hydration is very important in view of its significant influence on the physical and mechanical behaviors of cement-based materials. This work is focused on the utilization of electrical resistivity measurement for monitoring the hydration process and characterizing the microstructure properties of cementitious materials....[ Read more ]

Cementitious materials are porous medium. During the hydration of cement, the porosity is continuously reduced with the continue increase of reaction products. A better understanding of the development of microstructure during cement hydration is very important in view of its significant influence on the physical and mechanical behaviors of cement-based materials. This work is focused on the utilization of electrical resistivity measurement for monitoring the hydration process and characterizing the microstructure properties of cementitious materials.

A non-contact electrical resistivity measurement method is used in the present work to continuously and accurately detect the resistivity evolution of cementitious system. The resistivity measurement is very sensitive to the change of ambient temperature. This influence has been successfully corrected by using the empirical equation and Arrhenius-based equation in this work. Thus, the resistivity is only affected by the internal change of specimen and a fair comparison of the resistivity data obtained at the varying temperatures can be carried out. After correcting the temperature influence, the non-contact resistivity measurement has been applied to monitor the hydration processes of different types of cement and to study the compatibility of superplasticizing admixtures with different cements. More details about hydration behavior of cement mixtures can be obtained by this measurement. The correlation and comparison between resistivity and ultrasonic methods in monitoring cement hydration have also been conducted. It concludes that the non-contact resistivity method provides a non-destructive and objective way to study the cementitious materials.

Finally, a simple model based on the general effective media theory is proposed to realistically predict the microstructure parameters of cementitious materials using the resistivity results. The major parameters in the proposed model are the microstructural properties such as capillary pore threshold and pore structure parameter, capillary pore phase and solid-gel phase resistivities. To validate the model, an experimental relationship between the resistivity formation factors and the phase volume fractions of a series of cement pastes has been built up with the assistance of mercury intrusion porosimetry techniques. The good agreement between the model and experimental data shows that it is feasible to obtain better understandings of the evolving microstructure of cementitious materials during the hydration using electrical resistivity measurement. Furthermore, based on the log-linear increase of resistivity with time, the porosity in mature stage can be predicted by the proposed model.