| Freeze-thaw (F-T) deterioration is one of the most important durability problem-s. Quantitative analysis of the pore pressure when pore solution solidifies, is still anopen question. Within the poromechanical frameworks, the present work studies thecrystallization processes of pore solution confined in cement based materials (CBM)theoretically and experimentally.In the present work, the ice formation processes were first studied according tothermodynamic equilibrium, and the penetration of ice into thinner pores with temper-ature was described by Gibbs-Tomson equation. The impact of solutes was retained tomodify the solidification processes of pore solution. By means of material propertiesand heterogeneous nucleation (HN) theory, the relation between supercooled tempera-ture and the salt concentration of pore solution was established. From the poro-elastictheory, a poromechanical model was established to bridge over the crystallization ofpore solution and the macro behaviors of CBM under freezing. The Darciean and Fick-ian transport in porous medium were considered together in the present poromechan-ical model. The conservation equations for ions, water and energy were establishedon the basic variables: liquid pressure, salt concentration and temperature. The classicproblems of air-entrained CBM and the effect of supercooling were analyzed by theestablished model to verify its robustness.The CBM samples were prepared and the set-up of deformation measurement ofCBM under F-T loadings was designed specially. The pore structure of samples werecharacterized comprehensively by mercury intrusion porosimetry (MIP) and Nitrogenadsorption/desorption (NAD). The porosity, characteristic pore size (CPS), pore sizedistribution (PSD) and specific surface area (SSA) were evaluated and discussed com-bined with the hydration processes. The fractal dimensions and drying effect of freeze-drying (F-drying) were discussed as well. The F-T deformation of dried pastes andmortars, entrained with different dosages of air-voids, were measured to obtain the ther-mal expansion coefficient (TEC). The F-T deformation of samples saturated with salinesolution were measured comprehensively. Poromechanical analysis was performed onthe sealed pastes saturated with saline solution under F-T loading, where the sources for deformation during freezing were specified in detail. The drained and undrainedconditions, corresponding to the empty and saturated air voids respectively, were usedto analyze the freezing deformation of air entrained CBM.The study indicates that: x The contact angle between ice and pore wall decreaseswith salt concentrations; y Continual shrinkage of air-entrained paste (AEP) is dueto the negative liquid pressure and cryo-suction of ice formed on the interface of airvoids, while continual expansion of ordinary paste (OP) is due to the hydraulic pressureinduced by ice formation; z the instantaneous ice formation and the corresponding heatreleasing account for the ice nucleation significant deformation;{The blended cementpastes show the scale related properties;|F-drying only removes capillary water andpartial gel water confined in low density C-S-H;} The TEC of CBM is related to theporosity in form of power law: α=α0(1)C;~The F-T deformation of OP is relatedintimately to the pore structure, while the F-T deformation of AEP highly depends onthe saturation degree of air voids;The deformation of OP under undrained freezingis associated with the amount of ice formation, while the deformation of AEP dependson the boundary conditions charged by the saturation degree of air voids. |
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