CALPHAD formalism for Portland clinker: thermodynamic models and databases

International audienceThe so-called CALPHAD method is widely used in metallurgy to predict phase diagrams of multi-component systems. The application of the method to oxide systems is much more recent, because of the difficulty of modelling the ionic liquid phase. Since the 1980s, several models have been proposed by various communities. Thermodynamic databases for oxides are available and still under development. The purpose of this article is to discuss the distinct approaches of the method for the calculation of multi-component systems for Portland cement elaboration. The article gives a state of the art of the most recent experimental data and the various calculations for the CaO-Al2O3-SiO2 phase diagram. A literature review of the three binary sub-systems leads to main conclusions: (i) discrepancies are found in the literature for the selected experimental data, (ii) the phase diagram data in the reference books are not complete and up to date and (iii) the two-sublattices model and the modified quasichemical model can be equally used for the modelling of the aluminates liquid. The predictive feature of the CALPHAD method is illustrated using the CaO-Al2O3-SiO2 system with the two-sublattices model: extrapolated (predicted) and fully-assessed phase diagrams are compared in the clinkering zone of interest. The recent application of the predictive method for the calculations of high-order systems (taking into account Fe2O3, SO3, CaF2, P2O5) shows that the databases developed with the two-sublattices model and the modified quasichemical model are no longer equivalent

Tricalcium silicate Ca3SiO5 superstructure analysis: a route towards the structure of the M1 polymorph

International audienceIn this paper, we present a structural model for the M1 polymorph of tricalcium silicate Ca3SiO5 from Powder X-Ray Diffraction (XRD) data, including weak intensity superstructure Bragg lines. As no single crystal is available, this structural model has been deduced using the structural relationships found between the previously known triclinic and monoclinic M3 polymorphs. We find that the better starting set of atomic positions for Rietveld refinement is the triclinic set and not the monoclinic set. A key observation is that the monoclinic M1 structure is closer to the low temperature triclinic T3 structure (within the Golovastikov model) than to the higher temperature monoclinic M3 structure. The unit cell and the set of atomic positions of the two best models, called 3Pc and 3Pn models, are provided. We prefer the 3Pc model for it better reproduces the weak characteristic Bragg lines of the superstructure

Extrudable Reactive Powder Concretes Hydration, shrinkage and transfer properties

International audienceThe behavior of five reactive powder concretes (RPC), with four of them being extrudable, has been studied since the first minutes up to more than 90 days. The extrusion force, hydration rate, free autogenous shrinkage at early age, mechanical properties and durability parameters were measured. The performance analysis showed the benefits of a partial substitution of silica fume with crushed quartz on the RPC properties. The cost/performances analysis highlighted that the main advantage of using RPC lies in their potential of durability, which is 10 to 100 times higher than that of ordinary or high-performance concretes, according to the property considered

Oil-Based Mud Cutting as an Additional Raw Material in Clinker Production

Oil-Based Mud (OBM) cutting is a hazardous by-product generated during oil-well drilling. Its chemical composition suggests that it might be suitable as a raw material in cement manufacturing. It is rich in calcium oxide, silica, and aluminium oxide, which are the major oxides in raw materials for cement manufacturing. In this research, OBM cutting is used as a constituent of the raw meal for cement clinker production. Raw meal mixtures were prepared by mixing different ratios of raw materials increasing OBM content. The impact of the addition of OBM cutting on the resulting clinker has been investigated. The results demonstrate that OBM cutting could be recycled in the manufacturing of Portland cement clinker. Clinker prepared using OBM cutting had very similar properties to that prepared from limestone. This result could represent an opportunity for solving an environmental problem. The addition of OBM cutting lowers the calcination temperature, and increases the rate of carbonate dissociation. However, it also leads to a higher free lime in clinker, which is a result of the presence of trace elements, such as barium. Overall, its use as a raw material in cement production could provide a cost-effective, environment-friendly route for the management of OBM cutting

Jean-Gilbert Bourras, La querelle des vacants en Aquitaine - pour en finir avec sept siècles de féodalité, 1995

De Noirfontaine Françoise. Jean-Gilbert Bourras, La querelle des vacants en Aquitaine - pour en finir avec sept siècles de féodalité, 1995. In: Annales de démographie historique, 1996. Morbidité, mortalité, santé. pp. 449-450

Etude structurale et cristallographie des composés du ciment anhydre.

This structural study on the anhydrous cement compounds primarily focused on the major component, the alite (tricalcium silicate impure), which hydration produced the largest fraction of the effect of hydrated cement paste. The tricalcium silicate C3S, this polymorphism depends on both temperature and the impurities it contains. The seven varieties of polymorphs are triclinic symmetry (forms called T1, T2, T3), monoclinic (M1, M2, M3) and rhombohedral (R). In the industrial clinkers, the bedridden are essentially stabilized symmetries monoclinic. The identification of this polymorph is hard diffraction X-rays because the powder patterns are very similar. Why do some impurities they stabilize one form over another? Is there a link between the observed structure and reactivity of the clinker? It must rely on a good structural knowledge of different polymorphs attempt to answer these questions.Cette étude structurale sur les composés du ciment anhydre a principalement porté sur le composé majoritaire, l'alite (silicate tricalcique impur), dont l'hydratation produit la fraction la plus importante de l'effet de colle du ciment hydraté. Le silicate tricalcique, C3S, présente un polymorphisme dépendant à la fois de la température et des impuretés qu'il contient. Les sept variétés de polymorphes sont de symétries tricliniques (formes appelées T1, T2, T3), monocliniques (M1, M2, M3) et rhomboédrique (R). Dans les clinkers industriels, les alites stabilisées sont essentiellement de symétries monocliniques. L'identification du polymorphe présent est difficile par diffraction des rayons X parce que les diagrammes de poudre sont très semblables. Pourquoi certaines impuretés stabilisent-elles une forme plutôt qu'une autre ? Y a-t-il un lien entre la structure observée et la réactivité du clinker ? Il faut s'appuyer sur une bonne connaissance structurale des différents polymorphes pour tenter de répondre à ces questions

Jean-Gilbert Bourras, La querelle des vacants en Aquitaine - pour en finir avec sept siècles de féodalité, 1995

De Noirfontaine Françoise. Jean-Gilbert Bourras, La querelle des vacants en Aquitaine - pour en finir avec sept siècles de féodalité, 1995. In: Annales de démographie historique, 1996. Morbidité, mortalité, santé. pp. 449-450