Capillary imbibition of water in discrete planar cracks

Knowledge of capillary imbibition of water in distributed microcracks within building materials plays a critical role in assessing and predicting the durability of reinforced concrete structures. This paper focuses on a comprehensive investigation of capillary imbibition of water in discrete planar cracks, involving both theoretical and experimental aspects. In view of dynamic capillary flow of liquid in discrete cracks, which is usually described by Lucas-Washburn (L-W) equation, the correlation between capillary rise height and crack width is theoretically established. A benchmark study to investigate capillary flow in a series of discrete granite cracks, artificially fabricated by means of ultrathin steel disc with various thicknesses, is reported, and this provides data to validate the theoretical model developed in the paper. The experimental results give out the measurement of discrete crack width with different sizes (23.64-240.38 μm) as well as the mass of absorbed water obtained by the traditional gravimetric method. The average cumulative water mass of specimen generally increases with an increase of crack width for the ranges studied. Moreover, the cumulative water mass rapidly increases at the initial stage of water absorption test while at later stage the variation of absorbed water mass is relatively less. The analysis shows that the influence of gravity on the variation of capillary rise height is remarkable when crack width is beyond a critical range. Finally, the comparison between experimental and theoretical results indicates that the L-W capillary imbibition model of porous capillary tube after taking into account the gravity effect can be applied to the case of discrete crack with a certain range of width.