Early Hydration Process and Kinetics of Concrete Based on Resistivity Measurement

The resistivity of fresh concrete was obtained for the period from casting to the age of 72 h by a non-contact electrical resistivity measurement. Early hydration process of three types of concrete with the ratio of water to binder in mass of 0.4, including ordinary Portland cement concrete (OPC), concrete with fly ash of 30% (FAC) and concrete with silica fume of 5% (SFC), were analysed and compared. Based on resistivity data and Krstulovic-Dabic model, parameters of kinetics model were obtained, and hydration kinetics process was characterized. Results show that early hydration process of concrete can be characterized by the development of resistivity. Early hydration process is divided into five stages, which are ion dissolution, induction, acceleration, transition and deceleration. Incorporation of fly ash reduces the peak of hydration rate and delays the second hydration acceleration, whereas addition of 5% of silica fume has little effect on the early hydration of concrete. The compressive strength and electrical resistivity of three types of concrete show a good linear correlation at early age. The parameters of Krstulovic-Dabic kinetic model can be fitted well by using resistivity data of concrete.