Investigation on sorptivity and capillarity coefficient of mortar and their relationship based on microstructure

Abstract Durability is one of the key properties of the cement-based materials (CBMs) and is affected significantly by water migration in CBMs. Sorptivity S and capillarity coefficient k are two of the vital parameters to evaluate the water migration behavior of CBMs and are related closely to its microstructure. In this study, the low-field nuclear magnetic resonance (LF-NMR) was used to measure the pore size distribution and porosity of mortars. Additionally, according to the authors’ previous experimental results using the LF-NMR imaging and gravimetric method, the S and k were calculated, respectively. The results showed that the equivalent pore radius rm of mortar, determined by the pore size distribution, increased with water to binder (w/b) ratio and sand to binder (s/b) ratio, and decreased with silica fume (SF) and super-absorbent polymer (SAP) content. However, the porosity of mortar increased with w/b ratio and SF content, decreased with s/b ratio, while first increased and then decreased with SAP content. Meanwhile, the S was improved with the increasing w/b ratio and SF content, deteriorated with the increase in s/b ratio, while first improved and deteriorated with SAP content. The trend of the k of mortar was similar to that of S. The analytical models for predicting S and k of mortars were proposed, which were based on their microstructure and considered the effects of tortuosity and roundness, and were successfully verified by the test results with the present investigation and the existing literatures. Besides, the relationship between S and k was given and the ratio k/S was approximately between 5.0 and 10.0.