Corrosion mechanism of recycled mortar prepared from CO2-treated hardened cement paste powder

Abstract

CO2-treated recycled powder improves the mechanical properties of concrete. However, its corrosion mechanisms are not thoroughly understood. This study focused on the carbonation-induced corrosion mechanism of recycled mortar prepared from CO2-treated hardened cement paste powder (CCPP). First, the corrosion behavior of the steel reinforcement in a CCPP mortar (CCPPM) was evaluated using electrochemical and corrosion mass loss tests. Furthermore, the carbonation resistance of the CCPPM was quantified by testing the carbonation coefficient, and a corrosion model was established to predict corrosion. Finally, the microproperties of CCPPM and CCPP were investigated to reveal the corrosion mechanism. The results show that the corrosion rate of the steel reinforcement in the CCPPM is controlled by the combined effect of the concentration of OH– ions around the steel reinforcement and mortar porosity; the former plays a more critical role than the latter. Moreover, the variation in the w/c ratio of the CCPP base material had a slight effect on the compressive strength and carbonation resistance of the CCPPM and the corrosion rate of the steel reinforcement. The low concentration of OH– ions in the CCPPM increases the corrosion current density of the steel reinforcement by 15.91%–26.79%, consistent with the 10.96%–18.67% higher corrosion mass loss of the steel reinforcement embedded in the CCPPM cured for 540 days relative to that of the hardened cement paste powder mortar. Although incorporating CCPP increases the steel corrosion risk, the corrosion model developed herein demonstrates that CCPP can be used to guarantee a service life of 50 years for mortars when its replacement ratio is less than 20%.