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International audience; In 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.

International audience; Reactive Powder Concrete (RPC) is well known for having ultra-high mechanical performances and a very good durability. The goal of our study is to find an extrudable RPC for concrete pipes manufacturing. Five RPC concrete mixtures (W/C = 0.16) were synthesized with variable amounts of polycarboxylate superplasticizer, silica fume and crushed quartz. The first three compositions do not contain any crushed quartz and vary only by their increasing amount of superplasticizer. In the last two compositions, crushed quartz replaces a part of silica fume. Four of the formulations are extrudable. In this paper, we discuss the microstructure of the five samples before extrusion. A systematic study by scanning electron microscopy has been performed on polished sections and fractures. As expected for RPC, all the samples show a high amount of residual anhydrous clinker. The three compositions without crushed quartz are rather similar, whereas two effects of the addition of superplasticizer and quartz on hydration are observed for the two last compositions.

Le comportement de cinq bétons de poudres réactives (BPR), dont quatre présentaient des propriétés d’extrudabilité, a été étudié depuis les premières minutes après leur fabrication jusqu’à plus de 90 jours de maturation. La pression d’extrusion, la cinétique d’hydratation, le développement des retraits chimique, endogène libre et empêché au jeune âge, les résistances mécaniques en compression et en flexion, le module d’élasticité dynamique et les paramètres de durabilité ont été mesurés. L’analyse des résultats a montré l’intérêt d’une substitution partielle de la fumée de silice par du quartz broyé sur les propriétés des BPR. L’analyse coût/performance a mis en évidence que le principal avantage de l’utilisation des BPR se situe au niveau de leur potentiel de durabilité, 10 à 100 plus élevé que celui de bétons ordinaire ou à hautes performances, selon le paramètre considéré. 29ème rencontre de l’AUGC Tlemcen (29-31 Mai 2011).

International audience; The results of an experimental study on the mix design and the characterization of extrudable reactive powder concrete (ERPC) are presented. Five concrete mixes were prepared with variable amounts of polycarboxylate superplasticizer (SP), silica fume (SF) and crushed quartz (CQ). The extrudability of the ERPC was first demonstrated through extrusion tests performed with a ram extruder at different compression speeds. Then, the influence of the dosages in SP, SF and CQ on early-age hydration rate, autogenous shrinkage, 28-days mechanical performances, gas permeability, total porosity and chloride penetration rate was quantified. The increase in SP dosage caused a retardation of hydration and an increase of early-age autogenous shrinkage. Moreover, the partial substitution of silica fume with crushed quartz had a positive effect on hydration rate, autogenous shrinkage and mechanical properties. This result was mainly attributed to a higher amount of water available for cement hydration, induced by the coarser particle size distribution of crushed quartz as compared with silica fume.

International audience; This 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.

International audience; A 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.