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

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

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

Polymorphism of Tricalcium Silicate, the Major Compound of Portland Cement Clinker: 1. Structural data : review and unified analysis

International audienceThis paper reviews the literature devoted to structural investigations, with a special concern to the various notations used by different authors. A unified analysis of the known T1, M1, M3 and R polymorphs is proposed. The superstructure relations between the various unit cells are discussed, together with the evidence of common 1D and 2D structural elements in all these polymorphs. These structural elements are related to the observed properties

Polymorphism of tricalcium silicate in Portland cement: a fast visual identification of structure and superstructure.

International audienceSo-called alite is a solid solution of tricalcium silicate Ca3SiO5 with a few percent of impurities. It constitutes the major phase of anhydrous Portland cement. In industrial compounds, alite crystallises into two monoclinic forms designated M1 and M3. The possibility of correlation between the crystallographic structure of the clinker and its reactivity is still an open question. The answer of such a question involves a proper quantitative analysis of the various phases –including the exact alite polymorph- of the industrial product. The rather similar structure of the two alites makes it difficult to distinguish them from their XRD patterns. This paper shows that five angular windows in the X-Ray diffraction patterns can be used with synthetic alites as well as industrial compounds, to identify the nature of the actual polymorph (M1 or M3) present and the structural model to be used (with or without superstructure) in subsequent Rietveld analysis of the data

Polymorphism of Tricalcium Silicate, the Major Compound of Portland Cement Clinker: 2. Modelling alite for Rietveld analysis, an industrial challenge

International audienceA comprehensive quantification of the various phases of clinkers by X-ray diffraction with a Rietveld-like analysis is an important industrial challenge. Various available structural models are used for the most frequent M1 and M3 polymorphs of alite usually found in industrial clinkers, referred to as M1- or M3-based clinkers. In this paper, the effect of C3S structural model is investigated. Four models are tested and compared using either synthetic M1 and M3 alites or M1- and M3-based clinkers. The comparison validates the available models for M1 and M3 alites and an average model, given here, derived from our recently proposed M1 structure as a catch-all model when the nature of the clinker is unknown. The latter model is meant to be used for industrial on-line quantification

An X-ray powder diffraction study of damage produced in Ca(OH)2 and Mg(OH)2 by electron irradiation using the 2.5 MeV SIRIUS accelerator

International audienceTwo isomorphous hydrous minerals, Mg(OH)2 and Ca(OH)2, were exposed to the 2.5 MeV electron beam of the SIRIUS accelerator platform. Both compounds remain stable under the beam up to high doses, in the range of 3–3.5 GGy. No decomposition is observed.But contrary to earlier statements, a net difference of reactivity between them is highlighted as a result of the present X-ray powder diffraction study: i) a significant dilatation is observed along the c - axis, more significant in brucite than in portlandite as already reported during thermal decomposition studies, ii) but a contraction is here revealed in the basal plane of brucite, along the a – axis, while a slight dilatation is still being observed in portlandite. Contraction in the basal plane seems a specific feature of electron irradiation only once previously observed by TEM in brucite. Moreover for brucite, the decreasing intensities of Bragg lines together with the appearance of a diffuse scattering over the whole angular range is compatible with the appearance of some static structural disorder induced by electron irradiation. Finally electron irradiation leads to a significant reduction in crystallite size with increasing dose, by a factor of 2 at the intermediate dose of 310 MGy in brucite, while for a comparable effect to occur an absorbed dose of 3.5 GGy should be attained in portlandite

Early-age volume changes of Extrudable Reactive Powder Concrete

International audienceThis article presents a study on the early-age autogenous deformations of Extrudable Reactive Powder Concretes (ERPCs), especially designed for the making of concrete pipes by extrusion. Different ERPC mixtures, with variable amounts of polycarboxylate superplasticizer (SP), have been investigated. Results on 28-day mechanical properties, early-age hydration rate, autogenous shrinkage and premature cracking risk are analyzed and discussed in relation with the ERPC mix parameters