Study on hydration process of early-age concrete using embedded active acoustic and non-contact complex resistivity methods

The microstructure development of early-age concrete during hydration process was investigated by means of embedded active acoustic and non-contact complex resistivity monitoring methods. Embedded active acoustic method utilized cement-based piezoelectric sensors and FEbLIN acoustic system to continuously emit and receive compressional acoustic wave. Signal-based parameters such as velocity, attenuation and frequency domain spectrum variation were evaluated to analyze the microstructure development of early-age concrete. Meanwhile, non-contact complex resistivity method was utilized to measure real-time electrical impedance of early-age concrete. These two innovative non-destructive testing methods have distinguished merit. Compressional acoustic wave is sensitive to the connectivity of the solid phase network in the fresh concrete. It continuously hunts for the shortest propagation path during monitoring. While the inducted current generated in impedance measurement is more sensitive to the liquid phase network conditions of the fresh concrete. It strictly adopts the transition path with lowest electrical impedance. In this study, the behaviors and properties of fresh concrete are interpreted based on the measurement results of these two methods. It is found that the hydration stages can be distinguished according to the characteristics of acquired parameters, and so does the maturity of concrete.