Volume changes in solids induced by chemical alteration

It is a fundamental issue in material science to understand the mechanical effects of chemical alterations. Often the replacement of one chemical component by another in a solid induces local volume changes. Experiments on chemical alteration in “model” materials reveal an intricate dynamics of elastic stress build-up, fracturing and creation of porosity. In that way permeability is increased and provides a positive feedback on the process rate. Important examples from geology are presented

Experimental pressure solution compaction of synthetic halite/calcite aggregates.

Experimental observations are reported of weakening of sediment-like aggregates by addition of hard particles. Sieved mixtures of calcite and halite grains are experimentally compacted in drained pressure cells in the presence of a saturated aqueous solution. The individual halite grains deform easily by pressure solution creep whereas calcite grains act as hard objects and resist compaction. The fastest rate of compaction of the mixed aggregate is not obtained for a 100% halite aggregate but for a content of halite grains between 45% and 75%. We propose that this unusual compaction behavior reflects the competition between two mechanisms at the grain scale: intergranular pressure solution at grain contacts and grain boundary healing between halite grains that prevent further compaction

Structure of plastically compacting granular packings

The developing structure in systems of compacting ductile grains were studied experimentally in two and three dimensions. In both dimensions, the peaks of the radial distribution function were reduced, broadened, and shifted compared with those observed in hard disk- and sphere systems. The geometrical three--grain configurations contributing to the second peak in the radial distribution function showed few but interesting differences between the initial and final stages of the two dimensional compaction. The evolution of the average coordination number as function of packing fraction is compared with other experimental and numerical results from the literature. We conclude that compaction history is important for the evolution of the structure of compacting granular systems.Comment: 12 pages, 12 figure

Evaporation et cristallisation de sels solubles dans un réseau poreux modèle

L’objectif de ce travail expérimental est d’observer à l’échelle du pore la cristallisation de sels dans un réseau poreux au cours de l’évaporation. Des tests effectués en laboratoire sur un réseau poreux modèle avec de l’eau pure puis de la saumure montrent que le sulfate de sodium a peu d'effet sur la vitesse d'évaporation, que le chlorure de sodium la ralentit fortement après quelques heures alors que la sulfate de magnésium l'inhibe presque entièrement dès le début

The Role of Pressure Solution Creep in the Ductility of the Earth’s Upper Crust

The aim of this review is to characterize the role of pressure solution creep in the ductility of the Earth's upper crust and to describe how this creep mechanism competes and interacts with other deformation mechanisms. Pressure solution creep is a major mechanism of ductile deformation of the upper crust, accommodating basin compaction, folding, shear zone development, and fault creep and interseismic healing. However, its kinetics is strongly dependent on the composition of the rocks (mainly the presence of phyllosilicates minerals that activate pressure solution) and on its interaction with fracturing and healing processes (that activate and slow down pressure solution, respectively). The present review combines three approaches: natural observations, theoretical developments, and laboratory experiments. Natural observations can be used to identify the pressure solution markers necessary to evaluate creep law parameters, such as the nature of the material, the temperature and stress conditions, or the geometry of mass transfer domains. Theoretical developments help to investigate the thermodynamics and kinetics of the processes and to build theoretical creep laws. Laboratory experiments are implemented in order to test the models and to measure creep law parameters such as driving forces and kinetic coefficients. Finally, applications are discussed for the modeling of sedimentary basin compaction and fault creep. The sensitivity of the models to time is given particular attention: viscous versus plastic rheology during sediment compaction; steady state versus non-steady state behavior of fault and shear zones. The conclusions discuss recent advances for modeling pressure solution creep and the main questions that remain to be solved