Effect of electrochemically reactive rust layers on the corrosion of steel in a Ca(OH)2 solution

Electrochemical and gravimetric measurements are used to study the effect of rust layers on the corrosion of rusted steel in a saturated Ca(OH)2 solution imitating the liquid phase in concrete pores. The results indicate that the reduction of rust is the main cathodic reaction in the first phase of the corrosion process of rusted steel. Subsequently the oxygen reduction reaction becomes the cathodic predominant reaction, in which the rust seems to act as a porous electrode. In this research rust clearly favours the corrosion of rusted steel, and an approximately direct correlation is seen between the rust mass and the mass loss due to steel corrosion. In the electrochemical measurements, attention is paid to the overestimation of the corrosion rate deduced from the polarisation resistance in the case of specimens with the highest rust contents, a problem that is attributed to the inappropriateness of the conventional measuring procedure in the presence of high capacitance values and redox processes.