Corrosion resistance of steel reinforcement in carbonated reactive magnesia cement-based mixes with different Portland cement contents

Carbonated reactive magnesia cement (RMC)-based mixes raise questions about the corrosion resistance of reinforcement. This study investigated steel reinforcement behaviour in RMC-based mixtures containing 2 % (M98) and 20 % (M80) Portland cement (PC), compared to 100 % PC (M0). Response to carbonation curing through electrochemical measurements, changes in OH⁻ content, chemical composition and microstructure within carbonated pastes were reported. Reduced porosity with increased PC content before carbonation was attributed to distinct pore structures of hydrated RMC/PC mixes. Calcite was the primary carbonation product in all, with nesquehonite and hydromagnesite detected in M98 and M80. Steel reinforcement in M98 exhibited corrosion, while that in M80 displayed corrosion resistance comparable to M0, which remained passivated even under carbonation conditions. Microstructure densification via the formation of carbonation products proved insufficient in preventing further carbonation in M98 due to its high porosity. Corrosion of reinforcement in M98 was ascribed to its relatively high porosity and low OH⁻ content. Valuable insights for optimizing carbonated RMC-based mixtures for structural applications were provided.