Passivation behavior of reinforcement in simulated pore solutions of composite cement incorporating ultrafine steel slag and blast furnace slag

The steel slag and ground granulated blast furnace slag with high fineness exhibit synergistic effects on hydration progress and can be introduced into concrete in high volume. In this paper, the simulated pore solution (SPS) of ternary cement incorporating ultrafine steel slag (US) and ultrafine ground granulated blast furnace slag (UG) was prepared to examine the passivation behavior of the HRB400 reinforcing steel under SPS. It is found that the rapid growth of passive films occurs primarily within the initial 2–3 days after immersion in the SPS, while the compaction of passive films takes place mainly at the later stages. The open circuit potential and charge transfer resistance of the passive films initially increase and then decrease with the continuous rise in the US content. The Fe2O3 constitutes a significant portion of the passive films above the steels treated with the SPS irrespective of US dosages, whereas the content of FeO is highly influenced by US dosages. The UG-US-C pore solution could enhance the passivation behavior because of lower Ca2+ and higher Na+. In case of UG/US ratio at 2:3, the passive film exhibits the greatest thickness at 7.5 nm and meanwhile with the highest compaction and the least roughness.