Investigation of moisture transport in cement-based materials using low-field nuclear magnetic resonance imaging

Moisture transport has a great impact on concrete durability. In this study, a hard-pulse one-dimensional frequency coding sequence of low-field nuclear magnetic resonance (LF-NMR) imaging was applied to investigate moisture transport in cement-based materials (CBMs) considering the influences of the water/binder (w/b) ratio, sand/cement (s/c) ratio and contents of silica fume (SF) and super-absorbent polymer (SAP). A weighing method was also applied and the results were compared with the LF-NMR imaging measurements. The results showed that the moisture distribution curves can be divided into three stages by height. In addition, it was found that the moisture absorption height (h) increased with time and the growth rate of water absorption proceeded from fast to slow. Additionally, as the w/b ratio of the sample was increased, h increased. The value of h decreased with increasing s/c ratio and increased with an increase in SF content. When SAP was mixed into the CBMs, the values of h increased with 0·15% SAP addition but decreased with the addition of 0·30% SAP. The LF-NMR imaging measurements were in agreement with the results of the weighing method.