Elastic properties of concrete at early age: monitoring of the e-modulus and the poisson's ratio with cyclic loadings and ultrasonic measurements

Knowledge of early age evolutions of the concrete properties is of a great interest for predictions of cracking risks. In this period, from the time of setting, disorders govern the future durability of concrete. Numerical computations coupled with Experimental investigations on samples are common strategies to predict the behaviour of structures. Heat release, strength evolutions, autogenous and thermal strains, time of setting, elastic and delayed deformations have to be taken into account. Among these properties, the Poisson's ratio is scarcely evaluated. Measurements are tricky even on hardened materials. At early age, accurate determinations are even more delicate. Some results can be found in the literature on early age evolutions of Young's modulus and Poisson's ratio either with static testing (e.g. [De Schutter & Taerwe, 1996], [Boulay et al. 2010]) or ultrasonic measurements ([Boumiz et al. 1996] for example). In this paper a comparison is achieved between these two techniques applied to an ordinary concrete (CEM I, w/c: 0.5). The comparison between static and dynamic Poisson's ratio show a linear relationship. Static and dynamic Young's modulus evolutions are also compared. Classically, on hardened concrete, it is reported that dynamic values are greater than static values. It is naturally confirmed here and it is observed that the Edyn/Estat ratio decreases during the hardening process of the material. This evolution is attributed to the water content linked to the hydration process.