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

Abstract

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, SO42− 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 Ba2+ which had the effect of precipitating SO42−. A design of barium@hydrogel capsule with core-shell structure was proposed to control the release rate of Ba2+ to avoid the disturbance to the paste setting process. Results showed that the release process of Ba2+ from the capsule was controlled by the slow swelling behavior of hydrogel in the shell structure. Since most of Ba2+ was released from the capsule after 8 h, the negative influence of Ba2+ on the early setting process of cement paste was avoided. The released Ba2+ facilitated the transformation of sulfoaluminates to chloroaluminates, thus enhancing the chloride binding capacity of Portland cement system.