Chemo-mechanical coupling at the one-pore scale: fracturing quartz hostby increasing tension in water inclusion

International audienceWater-bearing porous media allow the infilling liquid to become superheated much easily than anyother system. Superheating liquids make them prone to develop a tensile state, that is to say an internalnegative liquid pressure or tension. In this sense, superheated liquid is a close analogue to capillarywater retained in many not-saturated porous media (unsaturated zone of soils, gas/oil-depletedaquifers, CO2-storing aquifers). In granular physics, the role of capillary water tension to rigidify thegranular assemblage is studied for long (sand–castles physics) but little attention has been turned tothe same effect in compacted/continuous systems (rock fissures, fluid inclusions, intra-mineralcavities, etc.).Using synthetic fluid inclusions trapped in quartz, we were able to put the occluded liquid (aqueoussolution, CsCl 12m) at very high tension by isochoric cooling of the samples. Starting with aliquid-vapour assemblage, we heat the sample up to a special temperature at which the vapour bubbledisappears (temperature of homogeneization, Th), and then turn to a cooling procedure that decreasesthe internal pressure of the occluded liquid at constant volume, as long as the bubble does notre-appear again (relaxing the tensile state of the liquid). At a given tension state, we mapped theRaman spectra at the two quartz bands frequencies, in the quartz matrix all around the inclusion undertension. Using frequency-pressure calibration of the literature, it turned out that the quartz host wassubmitted to a small compressive stress in response to the perpendicular traction from the liquid.In a second step, one sample was submitted during one month to repetitive cycles ofsuperheating-relaxation processes, after which the volume of the inclusion changed brutally. This wasrecorded by a change of the liquid density measured through a significant Th shift. In the meantime,another sample was submitted to a constant tension which, after a while, provoked the visiblefracturation of the quartz matrix.These observations and measurements demonstrate that the tension of water occluded in pores, orchannels, or any type of cavities in solids, organics or living cells, is able to exert a stress onto the hostsolid, quantitatively weak. However, it appears that the recurrence of such effect and/or itspreservation through time, create a fatigue in the host that is ultimately able to break out its cohesion,certainly owing to pre-existing matrix defaults. Consequences in terms of chemo-mechanical couplingin hydrosystems or materials submitted to wetting-drying cycles will be eventually highlighted