“…To overcome these limitations, the transient flow method has emerged as a successful alternative to estimate the hydraulic properties of low permeability materials such as rocks, soils (Haskett et al, 1988;Carles et al, 2007;Barral et al, 2009), concrete (Figg, 1973;Claisse et al, 2003), asphalt coating (Li et al, 2004) and bentonite geocomposite (Mendes et al, 2010;Pitanga et al, 2011).This method is essentially founded on monitoring of system's pressure drop as the gas passes through the permeable barrier. Therefore, compared with the conventional method for measuring permeability in a permanent flow regime, the pressure drop method seems to have advantages such as simplicity, economy and quick results.…”