Hydromechanical effects: (I) on the Na-smectite microtexture

Changes in particle organization and pore-spaces with applied mechanical an d hydraulic stresses were followed using TEM, SAXS mercury porosimetry and gas adsorption for two Na-smectites, Laponite and hectorite, with similar s tructural formulae but different particle sizes. The TEM images show that h ectorite has particles larger and more anisotropic than those of Laponite. The particles order perpendicularly to the direction of axial mechanical st ress and become disoriented under hydraulic stress. According to the SAXS r esults, Laponite is composed of 1-3 small layers and hectorite of more comp act (10-80 layers) particles. In Laponite, mechanical stress strongly reduc es the amount of macropores but does not affect micropores and mesopores; h ydraulic stress increases the macropores. In hectorite, the pore-volume is lower than in Laponite. The different techniques used yield complementary r esults and show the considerable effect of layer dimension on the behaviour and microtexture parameters of smectite submitted to hydromechanical stres ses.