Study of "alite-tricalcium silicate-gypsum"complex system

2007

International audience; The systematic study of “alite-C3A-gypsum” systems by using simultaneously the dynamic mode rheometry and the isothermal microcalorimetry made it possible to specify interactions between the different components and to quantify the effect of the mixtures on the cohesive properties of C-S-H. In the system “alite-C3A”, the presence of aluminate ions decreases both the growth rate of C-S-H and the ratio dG' /dQ which represents the increase in the elastic modulus dG' corresponding to the formation of a certain quantity of C-S-H, estimated by released heat dQ; for the great quantities of C3A, there is a positive effect of the surface developed by calcium hydroaluminates …

Hydration of Ferrite Phase

2009

Apports de la rhéométrie dynamique et du couplage rhéométrie-microcalorimétrie pour l'étude de la cohésion des pâtes de ciment

2008

National audience; Le passage de la pâte de ciment d'un matériau mou à un solide dur se produit en plusieurs étapes successives. Tout d'abord, les grains anhydres coagulent pour former une structure connectée, puis, les hydrosilicates de calcium (noté C-S-H) qui sont les principaux produits d'hydratation du ciment précipitent sur la surface des grains en particulier aux points de contact préalablement formés et vont ainsi former la phase percolante de la matrice cimentaire. Ces hydrosilicates, particules nanométriques, renforcent la structure en augmentant la surface de contact entre les grains. La cohésion de la pâte de ciment augmente alors avec la quantité d'hydrates formée. Une fois que…

Retardation mechanisms of sodium gluconate for hydration of pure tricalcium silicate and alite in cement

2009

Sodium gluconate is known to be a strong set retarder of cement. Many studies have been devoted to the interactions between cement and gluconate at early ages but the true mechanisms of this retardation is not yet elucidated. The most important phase in cement is alite which is a tricalcium silicate containing impurities. Tricalcium silicate hydration leads to the nucleation and growth of calcium silicate hydrates which are responsible for setting and hardening of cement paste. This work is devoted to the influence of sodium gluconate on the early hydration, period during which calcium silicate hydrates should nucleate and begin to grow on anhydrous grains. Previous studies have shown that …

Hydration of silicate phase and mechanical evolution in 'alite-tricalcium aluminate-gypsum' complex system

2007

International audience; Using simultaneously the dynamic mode rheometry and the calorimetry, it has been possible to specify interactions between the components of “alite-C3A-gypsum” system. The concept of "mechanical efficiency of calcium silicate hydrates" (R = dG' /dQ, is the increase in the elastic modulus dG' corresponding to the formation of a certain quantity of CSH, estimated by released heat dQ) was introduced to quantify the effect of the mixtures on the cohesive properties of C-S-H. For the system alite-C3A : the presence of aluminate ions decreases both the growth rate of CSH and R; for the great quantities of C3A, there is a positive effect of the surface developed by AFm on R.…

Influence of high nitrate salts concentration on dimensional variations of mortars under wet curing

2008

Cementation is a widely applied technique for the conditioning of low- and intermediate-level radioactive wastes. In particular, the use of cement is an attractive procedure to immobilize evaporator concentrates from aqueous effluents treatment. This study is devoted to bring information on the influence of concentrates mixing solution on the dimensional variations under wet curing of simulated solidified waste forms with high ionic strength. In this study, the salinity of the evaporator concentrates was simulated by adding sodium or potassium nitrates. The length changes were measured, with displacement gauges consisting in linear variable differential transducers. Mortars prepared with so…

Alite hydration modelling and numerical simulations

2008

Tricalcium silicate modeling and numerical simulations

2010

International audience; In order to identify and quantify what is modified when tricalcium silicate hydration rate varies, we have developed a model to simulate experimental evolution of reaction advancement versus time. It is experimentally observed that the hydrates formation consists of a primary heterogeneous C-S-H nucleation leading to the formation of clusters followed by the anisotropic growth of these clusters. In our model, C-S-H nucleation is described by a random distribution of clusters on a surface. We split the growth step into two processes corresponding to the clusters growth on the surface (parallel growth) and the increase of the cluster thickness (perpendicular growth). E…