The use of low-clinker concrete is one way to reduce the carbon footprint of the concrete industry. However, a low-clinker content increases carbonation rate, resulting in an early corrosion initiation of embedded steel. Nevertheless, carbonation-induced corrosion in reinforced concrete structures largely depends on interfacial properties such as electrical resistivity (ρ) and moisture state (RH). Hence, the corrosion rate in carbonated low-clinker concrete can be mitigated by optimizing mix design parameters to extend the service life by prolonging the propagation phase. This work involved concretes such as 100% ordinary portland cement (OPC), FA30 (30% fly ash), and LC45 (45% limestone calcined clay) (with w/b from 0.4 to 0.5) were exposed to 3% CO2. The embedded RH sensors and electrochemical techniques were used to characterize the interfacial environment (such as RH, pH, and ρ) and evaluate their impact on the corrosion characteristics. Results showed that the w/b ratio is a decisive factor in controlling both carbonation and corrosion kinetics, which is mainly due to pore structure alteration effects on resistivity and corrosion rate. Carbonated low-clinker concretes with w/b > 0.45 showed high corrosion rate (>1 μA/cm2), while mixes with w/b ≤ 0.45 showed nearly five times lower corrosion rate even after carbonation.
