Effects of Tortuosity, Surface Roughness, and Crack Width on Capillary Water Absorption in Mortar Cracks

Capillary absorption in cracks of cementitious materials is significantly influenced by the surface roughness and tortuosity. To quantify these effects independently, an improved capillary absorption model was developed that incorporates distinct geometric parameters. A fabrication technique combining 3D printing, silicone molding, and mortar assembly was employed to fabricate sinusoidal rough mortar cracks with widths ranging from 120 to 450 μm and four tortuosity levels. Capillary rise was tracked using high-speed photography. Results indicate that surface roughness and tortuosity affect both the absorption rate and quasi-steady rise height, with their effects being crack-width-dependent. Surface roughness enhances absorption in narrow cracks due to flow channel constriction and the surface channeling effect but inhibits it in wide cracks where gravity dominates. Tortuosity consistently impedes absorption by reducing the vertical driving force, extending the flow path, and altering the meniscus shape, with a more pronounced effect in narrower cracks. The proposed model significantly improves prediction accuracy for the quasi-steady rise height by 70-91% and for the entire process by 51-80%. Validations against independent experimental data from previous studies further confirm the physical validity and universality of this model.