Geomaterials are porous, discrete and heterogeneous media exposed to environmental interactions. These materials host multiple fluids with which they establish physico-chemical feedbacks. During the last decades, major shifts in climate and the continued exploration of remote environments encouraged the study of phase transitions within the pores of soils and rocks, which include salt crystallization, mineral precipitation, freeze/thaw dynamics, and methane hydrate dissociation, among others. Phase transitions are a key source of weathering, as they cause unprecedented alterations in the strength and deformation properties of natural deposits. Two major sources of weathering process will be envisioned within this project: haloclasty and freezing/melting cycling.
Many materials found in nature are comprised of relatively weak materials, yet they still exhibit superior mechanical performance. This performance originates within elegant hierarchical structures. Nacre exhibits remarkable strength and toughness despite its composition of greater than 95% aragonite, a brittle ceramic. By incorporating just 5% soft biopolymer into a hierarchical structure with the brittle ceramic, nacre is ~1000 times tougher than pure aragonite. This significant increase in toughness stems from toughening mechanisms that act at multiple length scales within the hierarchical structure. A better knowledge of these mechanisms is at sake in material science because they can be directly translated to synthetic materials - biomimicry approach - or we can also directly incorporate these natural materials into synthetic materials to create hybrid biomaterials.
Following the IUPAC recommendation, the pore space in porous materials is divided into three groups according to the pore size diameters: macropores of widths greater than 50 nm, mesopores of widths between 2 and 50 nm and micropores of widths less than 2 nm. Zeolites, activated carbon, tight rocks, cement paste or construction materials are among these materials. In recent years, a major attention has been paid on these microporous materials because the surface-to-volume ratio (i.e., the specific pore surface) increases with decreasing characteristic pore size. These materials can trap an important quantity of fluid molecules as an adsorbed phase. This is important for applications in gas storage, gas separation, petroleum and oil recovery, catalysis or drug delivery.
For these microporous materials, a deviation from standard poromechanics is expected. In very small pores, the molecules of fluid are confined. Fluid-fluid and fluid-solid interactions of molecules are modified and this effect may have significant consequences at the macroscale, such as instantaneous swelling deformations. In different contexts, these deformations may be critical. Generally, natural and synthesized porous media are composed of a double porosity: the microporosity where the fluid is trapped as an adsorbed phase and a meso or a macro porosity required to ensure the transport of fluids to and from the smaller pores. If adsorption in nanopores induces instantaneous deformations at a higher scale, the matrix swelling may close the transport porosity, reducing the global permeability of the porous system or annihilating the functionality of synthesized materials.
Tight quasi-brittle materials are micro and meso-porous materials characterized by a very low permeability (less than a tenth of a millidarcy). Failure of such quasi-brittle materials is characterized by the presence of a fracture process zone (FPZ) where micro-cracks appear, evolve and interact in the course of damage. When the distribution of cracks and the distribution of pore size evolve in such tight quasi-brittle materials, the influence on the permeability in the case of a single or a multiphase fluid flow needs some in depth investigation.