Water Vapor Transmission Properties of Autoclaved Aerated Concrete of Four Density Classes—Experimental Determination in Stationary Processes

Moisture in porous building materials significantly affects all their technical parameters. For this reason, it is important to accurately determine coefficients that describe moisture transport inside these materials. The main parameters concerning the hygroscopic range are as follows: water vapor permeability δ, water vapor resistance factor μ, and water vapor diffusion coefficient D. Autoclaved aerated concrete (AAC), one of the most popular materials used for the construction of external walls, was tested. The study focused on the four density classes: 400, 500, 600, and 700. Using a modified cup method, measurements of the corresponding coefficients δ, μ, D were carried out in six ranges of relative air humidity: 11–30, 30–54, 54–60, 60–75, 75–85, 85–98%. The results prove that not only the level of humidity tested, but also the structure within the same material group has a significant impact on all parameters, strongly differentiating their values. In this regard, precise numerical simulations concerning moisture transport processes in autoclaved aerated concrete must take into account both its density class and the moisture range in which these processes occur.