Early age deformations of hydrating cement systems: comparison of linear and volumetric shrinkage measurements

Low water/binder ratio systems can undergo significant deformations upon the first hours of hydration. In certain cases, these deformations can even lead to the premature failure (cracking) of the material. The quantitative determination of these deformations is important to better understand the mechanisms involved. It also provides essential information for the validation of degradation models. Linear and volumetric procedures have been developed in the last years to assess the early-age deformations of hydrating cement systems. The very few comparisons of the two types of procedures indicate that linear measurements tend to underestimate the early-age shrinkage of the material. In order to bring more information on this aspect of the problem, the autogeneous deformations of mortar mixtures were systematically investigated using three different experimental methods. The autogeneous deformation of the mortar mixtures was first determined by linear measurements carried out on prismatic samples cast in a free-shrinkage bench. The volumetric deformation was measured by means of the immersion technique. A third series of linear measurements was carried on prismatic samples of various sizes using extensometer and micrometer. Some of these measurements were performed in three directions. Finally, self-desiccation and temperature measurements and also chemical shrinkage tests were carried out. The discrepancies between the three series of measurements are discussed.