In situ visualization of water transport in cement mortar with an ultra-low w/b ratio under the coupling conditions of osmotic pressure, confining pressure, and temperature

The deep underground environment has complex geological conditions, which result in cement-based materials under the coupling conditions of high crustal stress, high pressure, and high temperature for the long-term. Thus, the mechanism of water transport is more complicated and often accelerates the deterioration of cement-based materials. In this study, the rules of water transport in mortar with an ultra-low w/b ratio under the coupling conditions of osmotic pressure, confining pressure, and temperature were systemically investigated based on a novel experimental device and low-field NMR technology. Experimental results showed that the saturation of the pore structure and penetration depth of mortar increased rapidly in the early stage (the first 10 min), and the water was mainly filled in nano-scale pores. Low-field NMR imaging technology could be applied to the visualization study of water transport in WPC mortar. With the increase of osmotic pressure and ambient temperature, the penetration rate of water in mortar was significantly increased, and the water was preferentially filled in nano-scale pores with pore sizes less than approximately 200 nm. The increase of confining pressure could improve the permeability of mortar to a certain extent due to the decrease in the penetration rate of water. For water transport in mortar with an ultra-low w/b ratio, the descending order of influence degree of different factors was osmotic pressure, confining pressure, and temperature.