Experimental analysis on the relationship between pore structure and capillary water absorption characteristics of cement-based materials

Capillary absorption capacity has an important influence on the durability of concrete and is closely related to pore structure. In this study, the pore structure and capillary water absorption of samples were determined by low-field nuclear magnetic resonance spectroscopy and the gravimetric method, respectively. The test results show that the most probable pore diameter and equivalent pore diameter of cement-based materials increase with increasing water to cement ratio (w/c) and fly ash (FA) content and decrease with increasing curing age and cement to sand ratio (c/s). The porosity of cement-based materials increases with increasing w/c and c/s, decreases with increasing curing age, and first decreases and then increases with increasing FA content. The curves for the amount of capillary water absorption per unit area in specimens with the square root of time for cement-based material under different influence factors are similar and show obvious linear and stable stages. The capillary absorption coefficient is nearly linearly related to w/c or c/s, and nonlinearly related to curing age or FA content, observation that are well correlated with the porosity and square root of the equivalent pore radius. A modified model is proposed for the capillary absorption coefficient with consideration of the pore structure, and the theoretical results of the model are in good agreement with the test results.