No abstract

The developed tools are used to create a representative volume element (RVE) of cementitious materials and then assess the diffusive properties. The algorithms developed in Combs target a fast placement of the inclusions and a fast generation of the RVE shape and its mesh. Two application cases are considered: the unaltered material diffusivity and the degraded material diffusivity. The first case of application focuses on the description of the capillary porosity. The second application case focuses on the description of the degradation of cementitious material (mineral and porosity) and the diffusive properties associated. The reliability of the analytical effective medium approximations (MT and SC) is confirmed from 3D finite elements (FE) calculations performed on a matrix-inclusions microstructure obtained by RVE generation with Combs. The results also show the need to take into account the percolation behavior.

An experimental campaign was carried out to study the passivity of steel embedded in Ordinary Portland mortar. Mockup samples made of steel coupons (roughly polished or pre-corroded) embedded in mortar were tested under a relative humidity of 80, 90 and 95% or in a solution simulating the ground water of the French site of Bure (at 25 and 50uC) and under aerated and deaerated conditions, during up to 3 years. The results of gravimetric measurements show that the average corrosion rates determined on polished coupons are typical of passive conditions (,1 mm/year) and vary from 0?2 to 2?3 mm/year for pre-corroded coupons. Moreover, characterisation (Raman spectroscopy and SEM-EDS) of the samples tested in aerated conditions points out a stable state in term of the nature of the corrosion products and of the composition of the steel/mortar interface. In de-aerated conditions, magnetite is observed in the corrosion products.

We have focused on the test conditions influence on accelerated degradation of cementitious materials using ammonium nitrate. PH-buffering and renewal of the leaching solution were studied. PH-buffering appeared not to be very important when the renewal pH remains under eight. Renewal appeared to be the most influential feature. Its absence leads to calcium accumulation in the leaching solution inducing aggressiveness fall. Degradation is then less marked in terms of depth, flux and mineralogy. The resulting porosity increase is also smaller.Nous nous sommes intéressés à l'influence des conditions expérimentales sur la dégradation accélérée au nitrate d'ammonium (6M). Le renouvellement périodique et le maintien du pH de la solution lixiviante ont été étudiés. Il en ressort que le maintien de pH n'est pas important lorsque le renouvellement est effectué jusqu'à pH=8. Le renouvellement est l'élément le plus important. Son absence entraine l'accumulation d'ions calcium dans la solution et la diminution de son potentiel agressif. La dégradation est alors moins marquée en termes d'épaisseur dégradée, de flux lixivié et de minéralogie. L'augmentation de porosité correspondante est aussi plus faible.