Early chemical shrinkage due to dissolution and hydration of cement

New investigations into very early volume change of aqueous cement dispersions allow us to understand better what is meant by the general term 'chemical shrinkage'. In fact, early chemical shrinkage should be subdivided into dissolution shrinkage and hydration shrinkage, the latter taking place before as well as after the induction period. Shrinkage is evaluated by picnometry and by linear measurement carried out in three directions by means of an experimental set-up specially built to measure endogenous shrinkage right from the time after mixing. As expected, the volume of dissolved cement is a function of w/c-ratio, whereas the volume of early hydrated cement is independent of w/c-ratio. This relation, is linear and the slope as well as the intersection of the straight line with the ordinate vary depending on the cement composition. Therefore, these values may be considered to be indicating characteristic cement properties. In this way it becomes possible to classify cements and to predict the extent of early chemical shrinkage of mortar and concrete by just knowing their w/c-ratio.[PUBLICATION ABSTRACT]