An experimental, numerical and analytical investigation of gas flow characteristics in concrete

A series of tests are reported which used existing pressure cell apparatus to measure nitrogen gas flow in concrete. A finite difference numerical model is described which is used to investigate the time to reach steady state and the long-term transient response of the experimental system. An analytical solution is derived for the cell-pressure-time function from which a formula is derived for the intrinsic permeability coefficient. The permeabilities calculated from the experimental data have variations consistent with those from other investigations. The analytical solution matches the experimental pressure-time decay curves closely in the range of interest but there is a tendency for the curves to diverge for lower cell pressures. This is attributed to gas slippage and modifications to both the numerical and analytical solutions are described to account for this factor. Revised formulae are derived which give both the intrinsic permeability and Klinkenberg factor. These are then applied to the present experimental data and results compared with those from the literature.