Corrosion resistance of several metallic materials in contact with mortar

摘要

In structural engineering, different metals such as carbon steel, stainless steel, aluminium, copper, zinc and lead get into contact with different mineral building materials, and those produced with cement, play an important role. Besides, several formulations made with cements are frequently used in the immobilisation of Intermediate Level Radioactive Waste containing some of these metals. The aim of the present work is to compare the corrosion susceptibility of several metallic materials: copper, lead, aluminium, zinc, AISI 304 stainless steel and SAE 1040 carbon steel, when they are in contact with mortar, under different relative humidity conditions and chloride contents. The electrochemical parameters normally used to characterize the corrosion behaviour of reinforcing steel in concrete were monitored periodically for 3.3 years. These parameters are the corrosion potential, the polarization resistance and the electrical resistivity of mortar. After the exposure time, weight loss determinations were performed to compare the real corrosion rate of the metals with the electrochemical results in order to obtain the constant “B” of the Stern-Geary equation. It was possible to establish a ranking of materials in terms of their corrosion resistance in mortar. The results indicate that aluminium shows the major corrosion attack in all the systems studied and that stainless steel exhibits the best performance in all conditions tested. It was found that the instantaneous corrosion rate determined from the measurement of the polarization resistance by the galvanostatic pulse technique, provided results that are consistent with the gravimetric technique in most systems. The present work shows that, even though it has been used so far only in various types of steels, the measurement of the polarization resistance is a valid non-destructive tool to determine instantaneous corrosion rates of most metals which are embedded in mortar.