A novel approach for chloride control in sea sand cement composites utilizing graphene oxide

Abstract

The scarcity of river sand has resulted in the inappropriate use of sea sand in numerous countries, particularly in coastal regions. Without effective desalination techniques and sufficient monitoring, the presence of chloride ions in sea sand leads to rapid reinforcement corrosion and frequent structural failures every year. In this paper, a novel pre-treatment method utilizing graphene oxide (GO) coating on amino-functionalized sea sand (GO-CAFSS), and the effects of GO-CAFSS on suppressing internal chloride leaching and performance of sea sand cement-based composites were investigated. Due to strong covalent bonds between GO and amino-functionalized sea sand, agglomeration of GO in the cement matrix is restrained, which leads to enhanced cement hydration and densified ITZs proved by combined microstructure tests. The chloride leaching test shows that the mass percentage of chloride ions leached from the surface of GO-CAFSS are effectively inhibited, from 0.082% (untreated sea sand) to 0.042%. The chloride binding experiment reveals that the treatment of sea sand cement-based composites with GO-CAFSS can enhance their chloride binding capacity by up to 39.5% after 14 days of exposure to NaCl solution. XRD/TGA test results indicate that GO can enhance the chloride binding capacity by promoting calcium silicate hydrate (C-S-H) and Friedel’s salts (FS) formation, further increasing the physical adsorption and chemical substitution of remaining free chloride ions in the pore solution. It is also found that GO can contribute to the conversion of Ettringite (AFt) into FS with Cl− substituting SO42− to a certain extent, especially with additional intermixed SO42− brought by sea sand. Overall, GO-CAFSS is investigated to be a promising way for making high performance sea sand cement composites with harmful chloride ions effectively controlled.