International audienceThis study examined the effects of traversing cracks of concrete on chloride diffusion. Three different concretes were tested: one ordinary concrete (OC) and two high performance concretes with two different mix designs (HPC and HPCSF, with silica fume) to show the influence of the water/cement ratio and silica fume addition. Cracks with average widths ranging from 30 to 250 mu m, were induced using a splitting tensile test. Chloride diffusion coefficients of concrete were evaluated using a steady-state migration test. The results showed that the diffusion coefficient of uncracked HPCSF was less than HPC and OC, but the cracking changed the material behavior in terms of chloride diffusion. The diffusion coefficient increased with the increasing crack width, and this trend was present for all three concretes. The diffusion coefficient through the crack D-cr was not dependent of material parameters and becomes constant when the crack width is higher than similar to 80 mu m, where the value obtained was the diffusion coefficient in free solution

Gas permeability is commonly used to evaluate durability characteristics of concrete. However, these values are often achieved using never stressed or damaged specimens. The objective of this study is to examine experimentally the effect of axial compressive loading on the permeability of three different types of concrete: ordinary concrete (OC), high-performance concrete (HPC), and high-performance steel fiber-reinforced concrete (HPFC). Monotonic and cyclic loads are applied on 220 Â 110-mm diameter specimens. Stress levels vary between 60% and 90% of the ultimate strength. At the end of the loading phase, a disc is extracted from the middle part of the cylinders and is dried in a ventilated oven. Four different gas permeability tests are conducted during the drying procedure. The results show that, for each drying stage, the gas permeability of the discs increases with the load-induced strain. A correlation is worked out between the increase in permeability and the applied-strain/yield-strain ratio. Finally, a relationship between mechanical damage indicators and the increase in permeability is also discussed.

International audienceThe objective of this study is to investigate damage-temperature-stress level-permeability interactions in structural concrete. The tests are performed on hollow cylindrical concrete specimens, subjected to compressive loading and temperature up to 150 °C. The results emphasize that at stress levels lower than 80% of the peak stress, the variation of permeability is small and it is slightly influenced by the stress. As a matter of fact, the permeability under load is smaller than the permeability measured after unloading. As the load exceeds 80% of the peak stress, micro-cracking increases rapidly, causing an increase of the permeability and a greater sensitivity to the applied load, i.e. a noticeable difference between the permeability measured under load and after unloading, the first becoming greater than the latter. In the post-peak phase the increase of permeability is much larger due to significant crack width growth. The increase of permeability with the applied load seems to be greater with temperature, inducing further alterations of concrete and dilation of the porous structure of the material. Finally, the experimental results seem to agree with the format of coupled evolution of the permeability due to damage and temperature assumed by Gawin et al. [D. Gawin, C.E. Majorana, B.A. Schrefler, Numerical analysis of hygro-thermal behaviour and damage of concrete at high temperature, Mechanics of Cohesive-Frictional Materials 4 (1999) 37–74.]