Ultrasonic measurements as an in situ tool for characterising the ageing of an aluminous cement at different temperatures

In situ ultrasonic measurements have been done to characterise the ageing of a calcium aluminate cement, namely Secar 71, between 24 to 3500 h (5 months) after mixing the constituents. The longitudinal velocity, VL, has been measured on pastes prepared at 5, 20, 40 and 60 °C with a water over cement weight ratio, W/C, equal to 0.33. These in situ and real time data are compared with ex situ measurements such as DTA, XRD and porosimetric characterisations. DTA and XRD permit to follow the chemical and crystallographic changes occurring in the material during hydration. The variations of VL as a function of porous volume fraction, P, show that the relation between these two parameters is linear if P<0.15 and VL>4300 m/s. When P>0.15 and VL<4300 m/s, the relationship between VL and P is no longer linear; the variations of VL as a function of P depend on many other parameters such as chemical nature of interfaces, nature of hydrates, morphology of crystals.