Non-contact resistivity measurement for characterisation of the hydration process of cement-paste with excess alkali

A non-contacting electrical resistivity measurement device was used to investigate the influence of excess alkali on the hydration process of cement paste. The experiment was conducted with several specimens with different water/cement ratios and alkali contents. It was found that the resistivity curves measured using the method can be used to identify different hydration stages, such as dissolving period, competition period, setting period and hardening period. To verify the results of the resistivity measurement, hydration heat rates of cement pastes were measured using a JAF calorimeter. It was found that the resistivity curve and the curve of heat evolution rate of cement were closely related and thus can be used to examine a hydration process. The study showed that the hydration process of a cement paste could be influenced significantly by alkali content and caution must be exercised to control its influence on the early age properties of cement-based materials.