Effects of SCMs on chloride binding capacity of ultra-low water-to-binder ratio cement paste with internally introduced chloride

Chloride binding is a critical factor affecting the chloride-induced corrosion of concrete with embedded steel reinforcement. The supplementary cementitious materials (SCMs) play an important role in chloride binding including chemical binding and physical adsorption. However, limited knowledge is available on effects of SCMs and their chemical components on chloride binding of cement systems with ultra-low water-to-binder ratio (w/ b). This study investigated the chloride binding mechanisms of cement paste with ultra-low w/b ratio incorporating three types of SCMs with different chemical compositions. The chloride was introduced internally through the mixing water. The free chloride content was measured using pore solution expression and titration. The characterization techniques, including XRD and TGA, Zeta potential, SEM/EDS, and FTIR were conducted to evaluate the physically and chemically bound chlorides. The results showed that the content of total bound chloride was a function of the content of chemical bound chloride and physical adsorbed chloride that were governed by CaO and Al2O3 in SCMs. The CaO had an instrumental effect on the physical chloride binding capacity, while Al2O3 was the main factor in the chemical chloride binding.