Effect of corrosion pit distribution of rebar on pore, and crack characteristics in concrete

Abstract

This research paper delves into the impact of corrosion-induced changes, particularly pit distribution, on pore structures and crack propagation in concrete subjected to galvanostatic accelerated corrosion. Two samples with different pit configurations were investigated—one with larger and spread pits, the other with smaller and localized ones. Various characterizations methods were applied including X-ray Computed Tomography (CT), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and Raman spectroscopy. The 3D CT images reveals dynamic changes in pore volumes, pit expansion, emergence of new pores at cement-aggregate interfaces, and distinctive crack formation patterns. Image analysis accurately quantifies corrosion products, highlighting their dependence on pit presence and characteristic. The sample with larger pit volume experiences exclusive initial formation of iron hydroxides, while small pit volume contains both iron oxides and hydroxides simultaneously. Raman spectroscopy shows the dynamic interplay of iron oxides and hydroxides, marking an evolution from oxides to hydroxides within the cement paste. Crack formation analysis reveals distinct patterns in samples with high pit dispersion, including cracks originating from pores near reinforcing bar pits, larger cracks diffusing corrosion products outward, and zipper cracks emerging from distant interconnected pores. Conversely, low pit content sample exhibits a different crack pattern with varying origins and narrower apertures. The temporal evolution of cracks in this sample appears simultaneous, possibly linked to ongoing corrosion processes. Elemental mapping indicates elevated corrosion product volumes within and around cracks, possibly due to water migration into the concrete matrix. These insights deepen our understanding of concrete deterioration mechanisms, guiding strategies to enhance structural integrity and durability in critical infrastructure.