This study, which presents the results of numerous tests on the sensitivity of mortar permeability under conventional triaxial loading, represents tests carried out over more than a year at various confining pressures under monotonic loading or with loading-unloading cycles. Permeability is measured on a sample, dried prior to the test, by injecting argon -a neutral gas. A description of the experimental method based on applying a permanent flow is given as well as the technique of test study used. In this work, we chose to measure permeability under loading at different levels ofdeviatoric stress and strain since this corresponds more closely to the real conditions under which the works are used. Preliminary tests showed that the permeability under load was susceptible to early appearance of microcracks and began to increase noticeably towards 75/80% of the stress peak. Further tests were then carried out with loading-unloading cycles for stress levels beyond the stress peak. The authors have shown that permeability increases very rapidly, starting from this peak. This is irreversible as the measurements taken after unloading the sample prove. The different tests also prove that the damage level is insufficient to allow for a description of variation in permeability, as it clearly depends on the degree to which the microcracks have opened. Such a claim is supported by results where this variation is presented in relation to lateral strain. R I~S U M I 5
Argon permeability of a mortar, made with a water/cement ratio of 0 . 4, was measured cyclically as a function of confining pressure up to ó 3 ¼ À57 MPa. An original low-transient method was used, in which the time required to observe a slight gas pressure decay is measured. The mechanical behaviour and hydraulic response were both studied. The mortar seems crack-free and isotropic. It behaves elastically, even if a significant hysteresis, ascribed here to some microsliding between the C-S-H sheets and the movement of interlayer water acting as a lubricant, was observed. Similarly, the hydraulic response was shown to be, despite a slight delaying effect, entirely reversible. Surprisingly, permeability versus porosity changes is strongly nonlinear, which is not consistent with the predictions of random shrinkage modelling in which a power law relationship k / ö AE with AE ¼ 3 is obtained between permeability and porosity. The mortar permeability is decreased by 50% when the confining pressure is increased from ó 3 ¼ À3 MPa to ó 3 ¼ À57 MPa, while the overall porosity is only decreased by 2 . 5%. This high sensitivity is thought to be the result of some percolative effects within the interfacial transition zones owing to closure of slitlike pores.
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