PHOTOACOUSTIC STUDY OF THE WATER IN HYDRATED CEMENT PASTE

The photoacoustic signal strength was measured on a series of similar portland cement pastes dried to different water contents. Under appropriate conditions this signal is a function of only the paste's specific heat capacity and thermal conductivity. Because of this, inferences can be made about the state of water held in the paste by examining the manner in which the signal strength changes with water content. The water content-signal strength relationship has an abrupt change at a location related to the degree of hydration and corresponding to the D-dry state. The results indicate that there are two thermally distinct states of water detected by the method in cement paste. These two types of water are apparently sequentially removed upon first drying. The first type of water to be removed may be physically bound water and the second type chemically bound water. The results show that the D-dry condition corresponds to the water content that separates the removal of these two types of water. © 1979.