Effect of the prepared barium@hydrogel capsule on chloride ion binding of Portland cement paste

Utilization of sea sand in reinforced concrete is limited, due to the risk of steel corrosion caused by the introduced chloride. The chloride ions can be chemically bound by chloroaluminate salts (i.e., Friedel's salt and Kuzel's salt) in Portland cement, which would be an effective way to reduce the risk. However, SO 4 2− from gypsum in Portland cement could form sulfoaluminate hydrates (e.g., monosulfate and ettringite), which would hinder the generation of chloroaluminates and weaken the chloride binding. In this study, an attempt was made to reduce this negative effect by introducing Ba 2+ which had the effect of precipitating SO 4 2− . A design of barium@hydrogel capsule with core-shell structure was proposed to control the release rate of Ba 2+ to avoid the disturbance to the paste setting process. Results showed that the release process of Ba 2+ from the capsule was controlled by the slow swelling behavior of hydrogel in the shell structure. Since most of Ba 2+ was released from the capsule after 8 hours, the negative influence of Ba 2+ on the early setting process of cement paste was avoided. The released Ba 2+ facilitated the transformation of sulfoaluminates to chloroaluminates, thus enhancing the chloride binding capacity of Portland cement system.