Experimental study on the leakage of gas through cracked concrete walls

In the previous paper (Trans. of A.I.J. No.373), the degree of gas leakage through a single crack in a concrete wall was discussed and the following equation was proposed to estimate the leakage rate: Q=α-bar·Δp·W3/(μ·T) where W=crack width, T=wall thickness, μ=viscosity of gas, Δp=pressure differential across the wall, coefficient α-bar is a function of W (crack width). This paper deals with additional leakage tests and new equations. In order to study the effect of irregularities of crack surfaces, leakage tests were executed using four kinds of concrete. Leakage test of an idealized crack made of two parallel glass plates was also carried out. In this paper, the leakage test results were arranged by taking into account the compressibility effects on the gas flow. Conclusions are as follows. 1) Q (leakage rate) can be estimated by the following equation: f=W3·(P12-P22)/(2·P0·Q2·ρ0·T), f=α(W)/Q+b(W) where P1=pressure at the inflow pressure box, P2=pressure at the outflow pressure box, P0=1.01325 x 105 (Pa), ρ0=density of gas, f=coefficient of friction, α(W) and b(W) are experimental functions. 2) The coefficient of friction f is influenced by the particle diameter of aggregate and the shape of aggregate. 3) To say the least, in the range of 0.8 x 105 (Pa)≤P1, P2≤1.2 x 105 (Pa), Δp≤0.2 x 105 (Pa), Re (apparent Reynolds' number)≤102, the equation presented in the previous paper can be applicable and can be recommendable for practical use. (author)