Capillary suction in concrete with analytical pipe model - part 1: Numerical study of flow conditions

Absorption of water in concrete is often described by the simple linear water uptake vs square-root-of-time law. However, a deviation from this behavior is frequently seen depending on factors such as initial water content, water/binder ratio and specimen thickness. The increasing deviation at increasing thickness is seen even for very dry specimens with a significant fraction of capillary pores when the specimen thickness increases from around 25 to around 100 mm. In this paper, we have combined Navier-Stokes flow equation with Laplaces law for suction created under a curved meniscus between air and water, and applied it to series of pipes with different lengths and radii, (the analytical model). The analytical model is in good agreement with the numerical models at abrupt reduction or increase of pipe radius, even at very small radii, and our analytical pipe model made with different radii and lengths thus works satisfactorily in terms of flow conditions.