CAPÍTULO III -DIFRAÇÃO DE RAIOS-X E O MÉTODO DE RIETVELD AbstractThe project has focused on the application of X-ray diffraction and Rietveld method (XRDRietveld) on the characterization and quantification of Portland cement, and represents a pioneer scientific contribution on the theme in Brazil.Natural and artificial pozzolans, and also industrial byproducts that are highly available in the Brazilian industry were studied, as the blast furnace slags from steel works and fly ash from power stations. Furthermore components of laboratorial cements were studied, as clinker, limestone, gypsum, and finally the Portland cement with additions, prepared in laboratory.Hydration studies to follow the reactions in a cement paste were also performed using XRDRietveld.The Portland cement is composed by clinker, gypsum and fillers, as limestone, pozzolan and slags. Portland cement clinker is the sintered and pelletized product from calcination of an adequate mix of limestone and clay and minor corrective materials.The Rietveld method was introduced by Hugo Rietveld in 1969 and is based on the simulation of the whole diffraction spectrum from the components structural data, allowing for refining instrumental and crystallographic parameters. Quantitative values are obtained by comparing the calculated and actual diffractograms and minimizing differences mathematically through a least squares method. To develop the project several analytical traditional techniques were used with XRD: optical microscopy, electronic microscopic (SEM), X-ray fluorescence (XRF) and calorimeter.XRD-Rietveld presented as a high reproducibility technique with technical and logistics advantages. The evaluation of the instrumental conditions showed that to obtain a good quantitative result in reduced time were with a scan with 20s/step, a 10 minutes scan, possible with position sensitive detectors. Automatic (ADS) and fixed divergent slits (FDS) were tested, validating the technique in both conditions. The reduction in the time of analysis is very important to follow the cement industry interests on quality control. Para desenvolvimento do projeto foram utilizadas técnicas analíticas tradicionais como apoio, tais como a microscopia óptica de luz transmitida, microscopia eletrônica de varredura (MEV-EDS) e fluorescência de raios-X (FRX). Histórico do Cimento Portland CompostoA primeira referência a pozolanas é encontrada em Da Architetura, uma das mais antigas edições existentes do tratado de arquitetura escrito pelo romano Marcus "Vitruvius" Pollio (séc. As escórias de alto-forno foram aplicadas pela primeira vez na Alemanha em 1853. Na maioria dos países do mundo, elas são incorporadas como ingrediente dos cimentos Portland de altoforno contendo entre 25 e 70% em massa de escória. Percebeu-se que a cinza volante enriquecida em cálcio, produzida pela combustão de carvão sub-betuminoso e lignítico é mineralogicamente similar à escória granulada de alto-forno (Malhotra e Mehta, 1996). Um constituinte predominante de ambos é um vidro alumino-silicático enr...

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The tricalcium aluminate (C3A) and sulfate content in cement influence the hydration chemistry, setting time and rheology of cement paste, mortar and concrete. Here, in situ experiments are performed to better understand the effect of gypsum on the early hydration of cubic (cub-)C3A and Na-doped orthorhombic (orth-)C3A. The isothermal calorimetry data show that the solid-phase assemblage produced by the hydration of C3A is greatly modified as a function of its crystal structure type and gypsum content, the latter of which induces non-linear changes in the heat release rate. These data are consistent with the in situ X-ray diffraction results, which show that a higher gypsum content accelerates the consumption of orth-C3A and the subsequent precipitation of ettringite, which is contrary to the cub-C3A system where gypsum retarded the hydration rate. These in situ results provide new insight into the relationship between the chemistry and early-age properties of cub- and orth-C3A hydration and corroborate the reported ex situ findings of these systems.