Emmanuel Rozière

Influence of carbonation on ionic transport in unsaturated concrete: evolution of porosity and prediction of service life

Abstract In this paper, the effects of carbonation and moisture on chloride and ionic transport into concrete are studied. Based on the concrete composition and porosity as well as the physicochemical equilibrium, a comprehensive macroscopic model is proposed for this problem. The model features the chemical activity of ions, the interactions between chloride ions and concrete; and the ion–ion interactions in the solution. The governing equations of moisture and ionic transport into nonsaturated concrete are thoroughly described and solved numerically by the finite difference method in time and in space. Applications of the numerical model are demonstrated by predicting the evolution of the porosity and the service-life of a concrete specimen exposed to an aggressive environment containing chloride, carbon dioxide and moisture. A comparison of the model with a set of experimental data is finally proposed.

Influence of the initial water saturation of aggregates on concrete shrinkage

The study presented in this paper deals with the influence of the water saturation of natural aggregates on shrinkage and cracking sensitivity of concrete at early age. Limestone crushed gravels were specially chosen for this study due to their high porosity. The degree of water saturation of gravels varied, from a given concrete mixture, keeping the total water content constant. Significant variations of the plastic shrinkage and early age autogenous deformations were observed. Due to the kinetics of absorption of gravels, the water content remaining in cement paste was different from the effective water content. This was confirmed by the values of mechanical properties and porosimetry. The evolutions of elastic modulus and tensile strength were experimentally assessed and used to compare the cracking sensitivity of the three studied concretes by evaluating the self generated stresses.