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 degreesC (W/C = 0,33, 0.38 or 0.40) and at 5 degreesC, 40 'C and 60 degreesC (W/C = 0.33). The ultrasonic measurements consist of following the velocity of the longitudinal ultrasonic wave, V-L (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 V-L 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. (C) 2002 Elsevier Science Ltd. All rights reserved.