Electrochemical behaviour of steel in low carbon cement mixtures: Insights into corrosion and passivation dynamics

The development of alternative compositions as solutions to the environmental challenges posed by standard Portland (PTL) cement has heightened interest in their corrosion properties. Since cement is primarily used in reinforced concrete, understanding corrosion is crucial for ensuring the structural integrity of constructions. However, current studies remain insufficient to fully characterize early-age passive film behaviour. Data are still missing regarding passive-film composition in alternative cements, early-age corrosion responses, and metal exposure to pore solutions representative of real cement mixtures. This study investigates the electrochemical behaviour of carbon steel reinforcement bars in various cement environments. The analyses include a mixture of PTL cement with calcium sulfoaluminate (CSA) and CEMIII/B cement, a low-clinker cement, both compared to standard PTL cement. Electrochemical tests were conducted using two main setups: a cement extract solution and a 24-hour curing environment. Electrochemical and surface-analysis techniques were combined to assess early-age corrosion behaviour and passive-film composition. The alternative cements created different environments in terms of pH and pore solution chemistry. In the cement extract solution, the least protective passive layer was the one generated in PTLCSA, followed by the CEMIII/B and the PTL. The drop in pH in PTLCSA had a marked impact in the passive layer properties. In the curing setup, the least protective was the CEMIII/B followed by PTLCSA and PTL. In this case, the accelerated hydration properties of the PTLCSA reduced pore solution availability and corrosion activity. In conclusion, the alternative cements generate a less protective passive layer than the PTL cement and have different corrosion responses. PTLCSA could have a corrosion resistance closer to PTL for the first 24 h, but in the long run, the most similar of the alternative cements it is the CEMIII/B the one behaving similar to PTL. • Different cements produce different passive layer compositions • Conditions of steel more similar to the one in industry show a correlation with the more controlled setup. • Curing conditions of different mixtures produced different evolution of the corrosion process during the first 24 h. • Passive layer composition was correlated with electrochemical response.