Corrosion Inhibition Mechanism Of Galvanized Steel In Concrete With Supplementary Cementitious Materials

As a cost-effective corrosion prevention method,galvanized steel could be used in the marine concrete structures.While more and more supplementary cementitious materials?SCMs?have been used in the concrete and the hydration process of the cement will be different from that of ordinary portland cement.The pH value and the ionic composition of the pore solution will be changed,which are the two main factors affecting the passivation of the galvanized steel bars in concrete.Therefore,the passivation of the galvanized steel in concrete with SCMs was studied in present work.In order to provide a theoretical basis,the test in the concrete pore solution was firstly conducted.Various solutions were designed to simulate different pore environment of concrete with SCMs.Traditional electrochemical methods were deployed to study the influence of the ion composition at two different pH value on the passivation of the galvanized steel.Secondly,two typical SCMs?fly ash and nanosilica?were selected for addition into mortar.The hydration process,the pH value and the Ca²⁺concentration were monitored.Then the passivation process was monitored using electrochemical methods.Finally,the depassivation mechanism of the passive film on the galvanized steel in the presence of the chloride ions was studied.According to the results,the existence of Ca²⁺accelerated the passivation of the galvanized steel in concrete pore solution.The reaction between the galvanized coating and the solution became less vigorous with the reduction of the Ca²⁺concentration.The passive film was not integrated when the Ca²⁺concentration was low.In the mortar with the addition of the nanosilica,the hydration of the cement was accelerated.The pH value and the Ca²⁺concentration were increased at the early age.The passivation process of the galvanized steel was accelerated during the early age of the cement hydration and the properties of the passive film were improved.In the mortar with fly ash,the hydration of cement at the early age was also accelerated.Though the Ca²⁺was increased,the pH value was significantly reduced.The passivation was inhibited and the passive film was not integrated when the fly ash was added.The chloride threshold value was defined in the concrete pore solution.The depassivation mechanism could be interpreted by point defect model?PDM?.When the pitting corrosion occurred,the corrosion products could cover the pits and inhibit the ingress of the aggressive ions,and thus mitigate the corrosion of the galvanized coating during the protective stage of the corrosion model.