## Abstract

A report is presented of the morphology and composition of the corrosion products formed on galvanized corrugated steel reinforcing bars immersed in ${\displaystyle 0\cdot 05-1\cdot 5M~~KOH}$ solutions designed to simulate concrete pore environments. The morphology was studied by SEM of the in situ corrosion products and optical examination of transverse sections of the bar; phase identification was performed by X-ray diffraction and IR absorption analyses. Passivation events on the corrosion potential and corrosion intensity curves can be related to precipitation of prismatic ${\displaystyle Zn~~(OH)_{2}}$ crystals which form a compact layer on the surface. Active corrosion is associated with formation of porous ${\displaystyle ZnO}$ layers or precipitation of ${\displaystyle Zn~~(OH)_{2}}$ in the solution rather than on the galvanized surface. A solution-precipitation mechanism involving ${\displaystyle ZnO}$ and ${\displaystyle Zn~~(OH)_{4}^{2-}}$ intermediate species is proposed for formation of the passivating ${\displaystyle Zn~~(OH)^{2}}$ coating, although this scheme must be complemented to take account of the localized corrosion observed at ${\displaystyle pH<12}$ in the first part of this study.

### Document information

Published on 01/01/1987

DOI: 10.1179/000705987798271749