Influence of concrete cover thickness on steel corrosion in reinforced concrete: Insights from advanced imaging and material analysis

Abstract

This research manuscript presents a comprehensive analysis of the effects of cover thickness on the corrosion dynamics in reinforced concrete structures. Two distinct concrete cover thicknesses were studies namely: the small cover (SC) and the large cover (LC). Employing advanced 3D imaging techniques, X-ray Computed Tomography (CT), and material analysis methodologies, Scanning Electron Microscopy (SEM) equipped with Energy-Dispersive X-ray Spectroscopy (EDS) and Raman spectroscopy. This study delves into the corrosion process under accelerated conditions. The examination of point corrosion in both specimens highlights distinctive patterns influenced by the concrete cover thickness. The SC experiences point corrosion in larger pits within the corrosion zone of the steel reinforcement, resulting in interconnected 'wormholes' pathways that amplify localized corrosion effects. The LC displays a more dispersed pattern of point corrosion initiation within the corrosion zone of the steel reinforcement, with the resulting corrosion products remaining confined to their original locations. Analysis of crack formation reveals that SC exhibits an increase in cracks with branching, but their origins do not align with areas of maximum corrosion pit formation in the steel reinforcement. In contrast, LC displays a unique pattern of crack initiation, originating near pores and within the corrosion pits in the steel reinforcement, with smaller openings and limited branching, primarily guided by pore presence. The Raman spectroscopy analysis reveals that the predominant compounds in SC are iron hydroxides, primarily ferrihydrite with reduced crystallinity, indicating an ongoing corrosion process within the steel reinforcement. In contrast, the corrosion products in LC consist of iron oxides and iron hydroxides, reflecting a more complex corrosion process within the steel reinforcement.