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Poromechanical behavior of cement-based materials subjected to freeze-thaw actions with salts : modeling and experiments

Abstract : When subject to freezing/thawing cycles with or without deicing salt, cement-based materials can suffer severe damage, which raises the long term sustainability problem of concrete/mortar in cold regions. Leaving aside the precise fracture mechanics and damage processes in this kind of problem, this PhD deals with the physical and thermomechanical phenomena undergone by cohesive porous solids under freezing, with particular attention to the material properties arising from cement hydration and microstructure development. The present work revisits the poromechanics of freezing porous materials developed by Olivier Coussy. This gives the opportunity to add the effect of the bulk supercooling and of salt in the liquid saturating the porous space.We measured the relation between depressed temperature at the end of bulk supercooling and salt concentration. We then obtained that the contact angle between ice and pore wall by heterogeneous nucleation decreases as salt concentration increases. We showed that the instantaneous dilation at the end of bulk supercooling is related to the pore structure because the latter determines the in-pore ice content. Using the pore size distribution measured by mercury intrusion porosimetry, we estimated the ice saturation degree with temperature and NaCl solution at different concentration through the Gibbs-Thomson equation. We measured the deformation of saturated cement pastes. The poromechanical analyses show that the strains depend on the initial salt concentration and pore structure of our cement pastes. By the same experimental approach on dried cement pastes, we concluded that the porosity (with or without air voids) has significant influence on the thermal expansion coefficient of our cement pastes. We also performed measurements on the deformation of saturated air entrained cement pastes. The results obtained by both experiments and poromechanical analyses under drained and undrained conditions showed that the initial saturation degree in air-voids has significant influence on the deformation curves with temperature
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Qiang Zeng. Poromechanical behavior of cement-based materials subjected to freeze-thaw actions with salts : modeling and experiments. Materials. Université Paris-Est, 2011. English. ⟨NNT : 2011PEST1131⟩. ⟨pastel-00666725⟩

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