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Carbonation of model cement pastes: The mineralogical origin of microstructural changes and shrinkage

Abstract : This study explored the reactive processes of atmospheric carbonation and the consequences with respect to cementitious materials. Two model pastes were used: hydrated C 3 S (including C-S-H and portlandite) and a paste prepared by hydrating a blend of C 3 S and nanosilica (including C-S-H only). The two pastes were carbonated under accelerated conditions in the laboratory. The resulting mineralogical assemblage was examined using Xray diffraction, thermogravimetric analysis and nuclear magnetic resonance. The microstructural changes were studied by X-ray tomography and porosimetry, and their macroscopic impacts were evaluated through gas diffusion and shrinkage measurements. The use of model pastes allowed for the evaluation of the change in solid volume induced by the carbonation of C-S-H. C-S-H decalcification and subsequent silica chain polymerisation were found responsible for carbonation shrinkage (and potentially cracking). Finally, the results highlight the protective role of portlandite: portlandite helped in limiting C-S-H decalcification and then reducing carbonation shrinkage and cracking.
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Submitted on : Friday, April 9, 2021 - 6:49:27 PM
Last modification on : Friday, August 5, 2022 - 3:03:56 PM
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E. Kangni-Foli, Stéphane Poyet, P. Le Bescop, T. Charpentier, F. Bernachy-Barbé, et al.. Carbonation of model cement pastes: The mineralogical origin of microstructural changes and shrinkage. Cement and Concrete Research, Elsevier, 2021, 144, pp.106446. ⟨10.1016/j.cemconres.2021.106446⟩. ⟨hal-03194818⟩



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