Abstract

In the marine environment,the concrete in the tidal zone is subject to the periodic drying and wetting,where chloride-induced steel corrosion is the most severe.During the wetting period,the chloride penetrates into concrete quickly along with capillary absorption.During the drying period,the water moves towards the exposed surface and the diffusion process of chloride ions became dominant.The wetting and drying cycles accelerate the chloride penetration into concrete.In this study,the coupled effects of moisture and chloride transport in cement mortar(including two mixing ratios,the water-cement ratio is 0.5,and one group is mixed with 15% fly ash)during wetting-drying cycles were investigated.Three different tests,i.e.the water vapor sorption,capillary absorption and cyclic drying-wetting tests,were conducted for cement mortar specimens.The water retention of cement mortar with dif ferent chloride concentrations was measured by water vapor adsorption tests[1].The hysteretic behavior of the adsorption isotherms was also studied[2].Under an ambient environment with constant temperature and relative humidity,the drying rates of the mortar containing different amount of chlorides were measured.In the capillary absorption tests,the water penetration depths were measured for the mortars exposed to 0%,1%,3% and 5% NaCl solution.The chloride penetration depths were measured by Ag NO3 colorimetry,potentiometric titration and Electron Microprobe(EPMA),respectively[3,4].The comparison of the measured depths by different methods indicated that the Ag NO3 colorimetry was reliable for the chloride penetration depth.The water penetration depths were also analyzed by Photo colorimetry and Nuclear magnetic resonance and the two methods were compared.The results also showed that the water penetration depth of mortar specimens was significantly greater than the chloride penetration depth the same exposure time[4].Finally,the chloride transport tests were conducted under cyclic drying-wetting conditions[5].The effects of dry-wet ratio on chloride ion and water transport in mortar were analyzed.The interaction between the chloride and water transport during the cycles was discussed based on the measured results.