Long-term performance of ZnO as a rebar corrosion inhibitor

This paper compares the action of ZnO with Ca(NO2)2, examines the effect of the w/c ratio on the performance of both inhibitors and how they affect the physical–chemical properties of concrete. To study that effect, 244 probes were prepared with tap water and water from Maracaibo lake (≅3000 ppm Cl), and exposed to saline environment for more than two years. Water/cement ratios were 0.45, 0.5 and 0.6, with inhibitor concentrations of 2%, 3% and 4% and a mixture of both at 2%, all by cement weight. The results indicate that ZnO and its mixture with Ca(NO2)2 show better performance than Ca(NO2)2. In spite of the higher corrosion rates of the ZnO probes (w/c=0.45), the potentials values (E>−200 mV vs. Cu/CuSO4) and the cyclic polarization curves show passivation of the steel after more than two years' exposure to the aggressive environment.