0000000001072443
AUTHOR
Sandrine Garrault
showing 12 related works from this author
Mechanisms and parameters controlling the tricalcium aluminate reactivity in the presence of gypsum.
2007
International audience; To understand the mechanisms and the parameters controlling the reactivity of tricalcium aluminate in the presence of gypsum at an early age, a study of the hydration of the “C3A–sulphate” system by isothermal microcalorimetry, conductimetry and a monitoring of the ionic concentrations of diluted system suspensions have been carried out with various gypsum quantities. The role of C3A source and its fineness were also studied. This work shows the fast initial formation of AFm phase followed by ettringite formation during the period when the sulphate is consumed. It has been highlighted that the time necessary to consume all the gypsum varies with the type of C3A and i…
Hydration of tricalcium aluminate in the presence of various amounts of calcium sulphite hemihydrate : Conductivity tests.
2006
Abstract Hydration of calcium aluminate C3A (3CaO·Al2O3) in the presence of calcium sulphite hemihydrate (CaSO3·0.5H2O), with the molar ratio of substrates close to 1, produces the C3A·CaSO3·11H2O calcium monosulphite aluminate phase. Small amounts of calcium sulphite added to calcium aluminate (the ratio of CaSO3·0.5H2O / C3A equalling 0 : 1) change the rate of C3A hydration and influence the whole reaction. Reaction processes for various ratios of the C3A–CaSO3·0.5H2O mixture were examined in pure distilled water with a considerable amount of liquid W / S = 38–50 (constant W / C3A). Processes in the liquid phase were monitored with conductivity equipment, and the XRD analysis was used to …
Influence of orthophosphate ions on the dissolution of tricalcium silicate
2008
International audience; Tricalcium silicate dissolution in the presence of orthophosphate ions was monitored by measuring the concentrations of calcium and silicate ions in dilute suspensions using a special dissolution cell coupled to an optical emission spectrometer. Results show that increasing adsorption of orthophosphate ions slows down the dissolution of Ca3SiO5 and that a calcium-phosphate precipitate may form at certain orthophosphate concentrations. These observations are correlated with results of calorimetric experiments carried out during the hydration of silica-rich cement pastes in the presence of the same salts.
Hydration of alite containing aluminium
2011
Abstract The most important phase in Portland cement is tricalcium silicate, which leads during its hydration to the nucleation and growth of calcium silicate hydrate [referred to as C–S–H, (CaO)x–SiO2–(H2O)y]. The development of this hydrate around the cement grains is responsible for the setting and hardening of cement pastes. The general term for designating the tricalcium silicate in cements is alite. This name relates to all polymorphs containing various foreign ions inserted in their structure. These ions may influence the intrinsic reactivity, and once released during the dissolution, they may interact also with C–S–H. One of the most likely species to be inserted in the alite struct…
Hydration process and rheological properties of cement pastes modified by orthophosphate addition
2005
Abstract The use of cement by nuclear industry for confining low radioactive waste knows a constant increase. The interest bore to this material is due to its mechanical and chemical properties. However, these properties may be modified by the nature and the amount of wastes introduced with the mixing solution especially with large amount of phosphate. Precipitation of hydroxylapatite in the cement paste at the very beginning after mixing was emphasized from a particular concentration of orthophosphate. It was also found that this phenomenon leads to an early rigidification of the cement paste. From a kinetics point of view, the evolution of hydration was both delayed and slowed down accord…
Formation of the C−S−H Layer during Early Hydration of Tricalcium Silicate Grains with Different Sizes
2005
Portland cement is a mixture of solid phases which all react with water. Tricalcium silicate (Ca3SiO5) is its main component and is often used in model systems to study cement hydration. It is generally recognized that setting and hardening of cement are due to the formation, by a dissolution-precipitation process, of a calcium silicate hydrate (C-S-H) on anhydrous grains during Ca3SiO5 hydration. The purpose of this paper is to study the effect of Ca3SiO5 particle size on the nucleation-growth process of C-S-H. An experimental study of the rate of hydration by using different grain sizes under controlled conditions has been performed. The experimental data have been compared with results o…
The influence of an ion-exchange resin on the kinetics of hydration of tricalcium silicate
2010
The addition of a finely-ground ion-exchange resin makes it possible to modify the hydration kinetics of C3S pastes. Analyses of the liquid phase in pastes and more dilute suspensions show that the resin exchanges calcium ions for sodium ions very rapidly during the early stage of hydration and therefore the concentration of silica in solution increases. The resin impacts the hydration of C3S by other mechanisms which depends on the resin quantity added. For a high resin quantity, the induction period is very short, but the longer-term hydration is enhanced compared to a reference sample without resin. We hypothesize that the surface of the resin can provide sites for the nucleation and gro…
Study of alite containing aluminium hydration
2008
International audience
Hydration of alite containing alumimium
2009
International audience; The most important phase in cement is tricalcium silicate which leads during its hydration to the nucleation and growth of calcium silicate hydrate (referred to C-S-H (CaO)x-SiO2-(H2O)y). The development of this hydrate around the cement grains is responsible for the setting and hardening of cement pastes The general term for designating the tricalcium silicate in cements is alite. This name relates to all polymorphs containing various foreign ions inserted in their structure. These ions may influence the intrinsic reactivity and once released during the dissolution, they may interact also with C-S-H. The melt phase during clinkering is rich in aluminium and moreover…
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…
UNDERSTANDING OF REACTIONAL SEQUENCES AND LIMITING STAGES DURING TRICALCIUM ALUMINATE HYDRATION WITH AND WITHOUT GYPSUM.
2007
International audience; The tricalcium aluminate reacts very quickly with water to form calcium hydroaluminates while the addition of calcium sulphate, leads to the formation of ettringite, with a slower process. The systematic study of the systems: “C3A” and “C3A-sulphate” by isothermal microcalorimetry and a follow up of ionic concentrations of diluted system suspensions made it possible to understand the sequence of the reactions and the limiting stages in both systems. In all cases, as it is in contact with the solution, the C3A dissolves what leads to the instantaneous precipitation of a certain quantity of calcium hydroaluminate. In case of only C3A hydration, there is then a decrease…
The materials saga: sintering
2007
In ICV no 1010, we inaugurated our materials saga with the classification and shaping of ceramics. This second and short chapter deals with sintering and its different forms: non reactive or reactive sintering, natural or pressure sintering as well as two essential parameters: density and porosity.