Abstract: The water flow behavior in cracks of cementitious materials is investigated experimentally through a permeation device designed by the authors. Fracture surfaces with different roughness are fabricated firstly and then permeation tests are performed on these surfaces with different crack opening widths. On the basis of the recorded flow rates the influence of surface roughness and crack opening width on the flow behavior of water is discussed. Furthermore, repetitive flow tests are performed for one fracture surface with one opening width and the transient flow behavior is studied by the experimental results.