Feasibility study on corrosion protection of steel bar in a self-immunity system based on increasing OH− content

In this paper, a kind of novel ethyl cellulose (EC)/calcium hydroxide microcapsule to establish a self-immunity system based on increasing hydroxyl content for the reinforced concrete is proposed. The capacity for lifting the threshold value of [Cl−]/[OH−] in this system is feasibly evaluated. Different dosages of microcapsules are placed in the sodium chloride solution with a concentration of 3.5 wt% to characterize the corrosion protection by means of linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The working mechanism of this system consists of the chemical triggering (capsule shell) and releasing (capsule core) processes when a microcapsule is exposed a decreasing pH condition, and the release of core materials in turn restores the alkaline environment against steel bar depassivation. The test results of environmental scanning electron microscopy (ESEM) equipped with texture element analysis microscopy (TEAM) reveal that the capsule shell sensible to the [Cl−]/[OH−] ratio forms an excellent low-pH trigger mechanism. In addition, the electrochemical experiment indicates the chloride-induced corrosion intensity of a steel bar can be monitored with the decreasing Icorr and more negative Ecorr, which is further observed by the pitting characteristics of steel bars.