Crystalline phases involved in the hydration of calcium silicate-based cements: Semi-quantitative Rietveld X-ray diffraction analysis

Chemical comparisons of powder and hydrated forms of calcium silicate cements (CSCs) and calculation of alterations in tricalcium silicate (Ca3SiO5) calcium hydroxide (Ca(OH)2) are essential for understanding their hydration processes. This study aimed to evaluate and compare these changes in ProRoot MTA, Biodentine and CEM cement. Powder and hydrated forms of tooth coloured ProRoot MTA, Biodentine and CEM cement were subjected to X-ray diffraction (XRD) analysis with Rietveld refinement to semi-quantitatively identify and quantify the main phases involved in their hydration process. Data were reported descriptively. Reduction in Ca3SiO5 and formation of Ca(OH)2 were seen after the hydration of ProRoot MTA and Biodentine; however, in the case of CEM cement, no reduction of Ca3SiO5 and no formation of Ca(OH)2 were detected. The highest percentages of amorphous phases were seen in Biodentine samples. Ettringite was detected in the hydrated forms of ProRoot MTA and CEM cement but not in Biodentine

Combustibles de substitution dans les fours de cimenteries : effet du phosphore sur la phase majoritaire du ciment Portland

Le ciment anhydre Portland est obtenu par broyage du clinker (roche artificielle issue de la cuisson à 1450 °C d'un mélange de calcaire et d'argile) et de gypse. Pour des raisons économiques et environnementales, les cimentiers recyclent de plus en plus de combustibles alternatifs à l'origine d'impuretés supplémentaires dans le clinker, tel le phosphore dans le cas de la combustion des farines animales. Il est donc important de contrôler voire de prédire l'effet de ces impuretés sur les performances du matériau hydraté. Cette étude expérimentale traite de l'effet du phosphore (0 à 0,9 % massique P2O5) sur la phase majoritaire du clinker, le silicate tricalcique, avec une analyse systématique de la localisation du phosphore dans le composé anhydre et de la résistance mécanique du composé hydraté. La seconde partie s'inscrit dans une démarche thermodynamique prédictive, avec la mise au point d'une approche calculatoire des diagrammes de phases majoritaires du clinker

Radioactive waste conditioning: the choice of the cement matrix versus irradiation

International audienceThe aim of this study is to compare the behavior of Portland and Ciment Fondu® cement under irradiation taking into account both real cement pastes and synthetic hydrates. First, γ-irradiations were performed using a 60 Co source (dose rate: 0.17-0.25 Gy.s-1, dose: up to 500×10 3 Gy). Thermogravimetric analysis measurements were performed in order to determine the amount and the type of water involved. H2 gas production was measured by gas chromatography. Regardless of the water to cement ratio (W/C) chosen (0.2, 0.4 and 0.6), it is shown that Ciment Fondu® pastes produce less H2 under irradiation. Moreover, the H2 production of portlandite and gibbsite, constituent hydrates of Portland and Ciment Fondu® cements respectively, shows that the amount of gas produced depends on the hydrate nature. Secondly, portlandite and gibbsite were electron-irradiated up to 300 MGy and 3 GGy using the LSI SIRIUS accelerator platform. X-Ray Diffraction analyses were performed before and after irradiation in order to investigate structural damage. Only limited structural disorder was observed, which confirms the good stability of both hydrates under present irradiation conditions