Open Access BASE2012

Changes on the nanostructure of cementitius calcium silicate hydrates (C–S–H) induced by aqueous carbonation

Abstract

8 páginas; 8 figuras; 3 tablas ; The nanostructure of the main binding phase of the hydrated cements, the calcium silicate hydrates (C–S–H), and their structural changes due to aqueous carbonation have been characterized using TEM, nitrogen physisorption, and SAXS. Synthetic C–S–H has been used for this purpose. Two different morphologies were identified, similar to the high density and low density C–S–H types. When submitting the sample to a CO2 flux, the low density phase was completely carbonated. The carbonation by-products, calcium carbonate, and silica gel were also identified and characterized. The precipitation of the silica gel increased the specific surface area from 95 to 132 m2/g, and its structure, formed by particles of ~5 nm typical radius, was observed by small angle X-ray scattering. In addition, the resistance of the high density C–S–H to carbonation is reported, and the passivating effect of the precipitated calcium carbonate is also discussed. Finally, the results have been compared with carbonation features observed in Portland cement carbonated experimentally at downhole conditions. ; We acknowledge the ESRF for provision of the synchrotron radiation facilities, and would like to especially thank Dr. F. Fauth for his assistance in using the beamline BM16. We also acknowledge the technical services of the Instituto de Ciencia de Materiales de Sevilla (CSIC-US) for its help with characterization measurements. This study was funded by the European Union through a Marie Curie grant within the GRASP project MRTN-CT-2006-035868. Finally, we would like to thank Dr. J. N. Rouzaud for his help with the TEM micrographies, Mr. Yves Pinquier with his help with the teflon reactor, and Dr. Nicolas de la Rosa-Fox for discussion and his wise ideas. ; Peer reviewed

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