Speaker
Description
Evaporation-driven drying of earthen construction materials is a two-phase (air–water) displacement problem in a heterogeneous porous medium, where capillary forces, evolving connectivity, and (for swelling clays) matrix deformation jointly control the Darcy-scale effective properties. A central missing input for predictive multiphase models is the relative permeability function k_r(S), especially at low saturations where standard hydraulic measurements typically lose sensitivity. This contribution presents an imaging-based upscaling route that links transient saturation fields to Darcy-scale transport parameters.
We determine k_r(S) in earthen mortars using a method derived from Darcy’s law, requiring (i) local liquid flux and (ii) local hydraulic gradient. The liquid flux is obtained non-invasively from time-resolved 1D MRI saturation profiles during controlled convective drying. Cylindrical specimens (diameter 7 cm; height 2–5 cm) are dried under an imposed air flow, while MRI slices (1.25 mm resolution) are acquired every 6 minutes, enabling quantitative water-content fields. In parallel, the capillary pressure–saturation relation is measured over the full saturation domain by combining a tensiometer at intermediate saturations and a dew-point potentiometer at low saturations, yielding a continuous mapping from MRI-derived saturation to matric potential.
By pairing the transient MRI saturation fields with the capillary curve, we compute local pressure gradients and reconstruct k_r(S) throughout drying. This framework captures two regimes typical of evaporation from porous media: a constant-rate period with nearly homogeneous saturation profiles, followed by a falling-rate period characterized by increasing saturation heterogeneity and the emergence of moisture-gradient structures. The resulting k_r(S) curves contain hundreds of datapoints across the full saturation range, including low-water-content stages that are difficult to access with tensiometers alone, thereby bridging a key experimental gap for multiphase constitutive laws.
We further probe the impact of matrix deformability and pore-structure evolution by adding swelling clay (montmorillonite, 5–10%). Drying kinetics remain qualitatively similar, but the inferred relative permeability decreases across the saturation range, consistent with swelling-induced constriction and altered hydraulic connectivity in the partially saturated network.
Beyond earthen materials, the methodology provides a general pathway to infer effective multiphase properties from imaged saturation dynamics, supporting model development where transport transitions, heterogeneity, and evolving microstructure dominate Darcy-scale behavior.
| Country | France |
|---|---|
| Green Housing & Porous Media Focused Abstracts | This abstract is related to Green Housing |
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