Decalcification of calcium silicate hydrate (C-S-H) under aggressive solution attack

Concrete is usually subjected to the environment with aggressive solutions where calcium leaching happens continuously threatening the durability of concrete. A comprehensive understanding of decalcification behaviors of C-S-H, a properties-determining phase in hardened cementitious materials, caused by aggressive ions has not been reached. In this paper, the calcium leaching behavior induced by chloride ions, sulfate ions, and the coupling of these two was systematically investigated by pH measurements, ICP, XRD, SEM-EDS together with XPS. It is concluded that the decalcification of C-S-H is strongly dependent on pH, the type of anions and the initial Ca/Si of C-S-H samples. High pH of the aggressive solution presents higher resistance to decalcification. Sulfate ions exaggerate the leaching of calcium to a larger extent than chloride ions, which may be attributed to their much higher binding energy with calcium ions. It appears that saline water has a more severe effect on the decalcification of C-S-H with low Ca/Si.

Automated summary

This paper systematically investigates the calcium leaching behavior induced by chloride ions, sulfate ions, and the coupling of these two in C-S-H. It is found that the decalcification of C-S-H is strongly dependent on pH, the type of anions, and the initial Ca/Si of C-S-H samples. Sulfate ions exaggerate the leaching of calcium to a larger extent than chloride ions, while high pH of the aggressive solution presents higher resistance to decalcification. Saline water has a more severe effect on the decalcification of C-S-H with low Ca/Si.