Carbonatation atmosphérique des systèmes cimentaires à faible teneur en portlandite

Abstract : Reaction of gaseous atmospheric CO2 with calcium-bearing phases in concrete infrastructure components is known to cause a lowering of alkalinity, leading to depassivation and corrosion of rebars. Carbonation mechanism is quite well understood from a physico-chemical point of view, especially in the case of materials made of OPC. Nonetheless the impact of supplementary cementitious materials (SCM), such as fly-ash, on carbonation is still an active research field. The pozzolanic reaction between CH and fly ash implies a lower portlandite content and a higher CSH content. Whilst CH is buffering the pH, its lower content in these materials may lead to a lower resistance to carbonation and to a higher contribution of CSH in terms of microstructural changes. Thus, this PhD thesis aims at understanding the effect of cement substitution by high contents of fly ash and develop a numerical model describing the carbonation of these cementitious materials. Accelerated carbonation tests (10% CO2, 25°C and 63% RH) were performed on various cement pastes containing fly ash (0%, 30% and 60% of volumic substitution and water-to-cement ratio before substitution of 0.45 and 0.6). Carbonation profiles were assessed by destructive and non-destructive methods such as thermogravimetric analysis and mercury intrusion porosimetry (destructive), as well as gamma-ray attenuation (non-destructive). Carbonation penetration was studied at different ages of CO2 exposure. By correlating microstructure changes with the degree of carbonation of each hydration product related to the formation of calcium carbonate, we are able to propose analytical relationships linking the decrease in porosity and the amount of released water to the carbonation level of CH and CSH. The modeling platform Bil (GPL) developed at Ifsttar was used to develop a reactive transport modeling of atmospheric carbonation, using a finite volume method. We introduced in the model the constitutive equations we highlighted using the experimental data. Microstructure evolution was quantified, taking into account the effect of the progressive decalcification of CSH linked to their molar volume, as well as the quantity of water released by carbonation. Combined with a kinetic formulation of CH dissolution, CSH decalcification was described by an original thermodynamic approach. In the end, many chemical species were introduced in the model, such as alkalis which strongly affect pH.
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Submitted on : Wednesday, January 22, 2014 - 9:09:45 PM
Last modification on : Wednesday, December 19, 2018 - 3:02:08 PM
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Antoine Morandeau. Carbonatation atmosphérique des systèmes cimentaires à faible teneur en portlandite. Génie civil. Université Paris-Est, 2013. Français. ⟨tel-00932816v2⟩

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