Correlation between hydration mechanism and ultrasonic measurements in an aluminous cement: effect of setting time and temperature on the early hydration

Early hydration (0–24 h) of Secar 71, a calcium aluminate cement, has been examined in-situ by ultrasonic testing for pastes prepared at 20 °C (W/C=0.33, 0.38 or 0.40) and at 5 °C, 40 °C and 60 °C (W/C=0.33). The ultrasonic measurements consist of following the velocity of the longitudinal ultrasonic wave, VL (frequency=1 MHz), transmitted inside the specimen and also the reflection coefficient, R, at the interface between the cement and the container of the paste, which is a polymethylmethacrylate mould. The variations of VL as a function of setting time can be described by a dissolution-precipitation mechanism. Lastly, the changes in R can be linked with morphological changes occurring inside the cement paste, especially the progressive formation of crystallised hydrates.