The effect of loading on the residual gas permeability of concrete

Permeability is related to the interconnectivity of the pores in the concrete, which measures how fast the gases or liquids will flow through it due to a pressure gradient. Knowledge of permeability will allow us to better understand the fluid transport behaviour in concrete, which could influence its fire spalling behaviour by directly influencing the build-up of pore pressure during heating. Three different gas permeability tests were carried out in SIAME and CSTB on 2 concretes B40-II (3% of slag) and B40-III (43% of slag). They are as follows: i) Residual axial permeability tests under radial confining pressure after unloaded preheating, ii) Residual axial permeability tests under radial confining pressure after preheating under uniaxial loading and iii) Residual radial permeability tests under uniaxial loading. The experimental test results have clearly shown that the presence of loading and their levels have a significant influence on the permeability of concrete. The permeability increase or decrease depends on the orientation and opening of cracking and these two parameters are influenced by compressive loading. The permeability of B40-III (much higher amount of slags) is more sensitive than B40-II in all heating and loading conditions.