| Summary: | Mineral additions can eliminate the conversion in calcium aluminate hydrates and thus inhibit the future strength retraction of calcium aluminate cement (CAC). However, the impacts of these additions on the protection capacity of CAC concrete in relation to the corrosion of embedded steel reinforcement remains unclear. This paper focused on the corrosion behavior of steel reinforcement in slag, limestone powder, or calcium nitrate-modified CAC mortars via XRD and electrochemical methods (corrosion potential, electrochemical impedance, and linear polarization evaluation). The results indicate that strätlingite (C<sub>2</sub>ASH<sub>8</sub>), which is formed in slag-modified CAC, has poor chloride-binding ability, leading to decline in corrosion resistance of the steel reinforcement. The electrochemical parameters of specimens immersed in NaCl solution suddenly drop at 14 days, which is 28 days earlier than that of the references. In contrast, the Ca<sub>2</sub>[Al(OH)<sub>6</sub>]<sub>2</sub>0.5CO<sub>3</sub>OH·H<sub>2</sub>O (CaAl·CO<sub>3</sub><sup>2−</sup>-LDH) and 3CaO·Al<sub>2</sub>O<sub>3</sub>·Ca(NO<sub>3</sub>)<sub>2</sub>·12H<sub>2</sub>O (NO<sub>3</sub>-AFm) in limestone powder and calcium nitrate-modified CAC mortar show great chloride-binding ability, thereby improving the corrosion resistance of the steel reinforcement. The electrochemical parameters of specimens modified with calcium nitrate maintain a slow decreasing trend within 90 days.
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