Wetting and drying cycles with NaCl solution in model microchannels to understand chloride ion transport in concrete

Microchannels were used to study how chloride ions move under cyclic wetting and drying. Each channel was 500 mu m wide, 200 mu m deep and 180 mm long with an inlet and outlet. Sodium chloride (NaCl) solution was introduced to the channels and allowed to dry. Crystals precipitated at the inlets and outlets. Some channels were plugged by the precipitated crystals, thereby preventing evaporation. To investigate if plugging occurs in porous materials, pumices and hardened cement pastes (HCPs) were immersed in NaCl solution and dried. When the concentration of the solution is more than 16%, the mass increase of the pumice after drying was more than that of the precipitated NaCl. The HCP immersed in NaCl solution showed less mass change after immersion and drying compared to the HCP immersed in tap water, indicating that plugging likely occurred from the precipitation of NaCl.