Search results for "Material chemistry"

Intrinsic Elastic Properties of Calcium Silicate Hydrates by Nanoindentation

2007

International audience; To understand the mechanical properties of cement materials is obviously one of the main purposes of the material science. But the mechanical properties measures of a cement piece by conventional methods (vibration, compression, etc.) are largely dependent on the sample porosity. Hence, the result gives information about the sample density rather than on the intrinsic mechanical properties of the material itself. This work aims to present results on cement materials (alite and C-S-H) mechanical properties obtained by nanoindentation using an atomic force microscope (AFM). The material Young modulus in the z-direction is obtained by applying a force perpendicular to t…

Hydration of a CEM V Blended Cement: Characterization of PFA and BFS Reactivity and Evolution of the Porosity

2007

The long term behaviour of cement based materials is strongly influenced by the internal chemistry and the paste microstructure. The industrial byproduct additives like pulverised fly ash (PFA) or blastfurnace slag (BFS) used in blended cement influence together the paste microstructures and the chemistry. A blended cement, designated CEM V in the European standard, containing PFA and BFS has been studied in order to understand processes involved during hydration. Several techniques as Xrays diffraction (XRD), solid-state NMR, thermogravimetry analysis (TGA) have been used to characterize the hydration of the PFA, BFS and the components (C2S, C3S) of the clinker. Such types of characterizat…

Effect of temperature on the development of C-S-H during early hydration of C3S

2007

International audience; It is known that accelerating or retarding hydration of OPC by temperature has consequences on the final properties of concrete, the lower the temperature the higher the final compressive strength. It seems that this effect is related to the properties of the hydration layer formed at early age. Early hydration of C3S has then been studied at temperature ranging from 5 to 45°C in isothermal conditions. The percentage of hydration is estimated from calorimetric measurements and the surface developed by the growth of C-S-H is estimated from Nuclear Magnetic Relaxation Dispersion method. Both data are numerically simulated according to a C-S-H growth model described pre…

Hydration of Ferrite Phase

2009

Impact of Titanium Dioxide Nanoparticle Dispersion State and Dispersion Method on Their Toxicity Towards A549 Lung Cells and Escherichia coli Bacteria

2014

International audience; Titanium-dioxide nanoparticle (TiO2-NPs) dispersion for toxicological studies is classically achieved by high power sonication. The aim of this study was to compare the dispersion state resulting from different dispersion techniques, and to correlate dispersion state and dispersion method to in vitro toxicity in a final view to contribute to the very active field of establishing protocols for reliable NP toxicity testing. To achieve this objective, several dispersion methods were applied to Evonik P25 TiO2-NPs. The dispersion state, as well as the stability of these TiO2-NP suspensions were evaluated by photon correlation spectroscopy (PCS) and turbidimetry. A549 hum…

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…

Influence of PC superplasticizers on tricalcium silicate hydration.

2007

International audience; The influence of polycarboxylate superplasticizers with variations of content of anionic groups was studied on pure tricalcium silicate hydration. The hydration in diluted suspension has been investigated by conductimetry, calorimetry, and ionic and total organic carbon analysis of the liquid phase. The tricalcium silicate hydration is always delayed in presence of polycarboxylate superplasticizer. Moreover, the delay can be correlated with the number of carboxylate groups which are on the adsorbed superplasticizer molecules. This effect seems to be due to a decrease of the C3S dissolution rate. Namely the pure C3S dissolution was studied by ICP with or without a car…