Corrosion products of low-alloy steel bars and their induction of cracking in seawater sea-sand concrete cover

Abstract

The integration of low-alloy steel reinforcement (LS) with seawater sea-sand concrete (SSC) offers an opportunity for marine infrastructure construction that utilizes local resources, such as seawater and sea-sand, while ensuring exceptional durability of structures in challenging environments. However, the cracking of the concrete cover resulting from rebar corrosion remains the primary factor contributing to the deterioration of reinforced-concrete structures exposed to marine environments. In this study, an external current was applied to accelerate the corrosion process of both LS and ordinary steel bars (OS), which were embedded in SSC that was shallowly buried in a wet-salt sand environment. To accurately determine the timing and location of SSC cover cracking, Digital Image Correlation (DIC) technology was utilized. Microscopic analysis was conducted to examine the morphology, phase composition, and content of each component of the corrosion products. Then, the expansion coefficients of the corrosion products of the rebars embedded in SSC with different water–binder ratios were determined. The results indicated that the primary corrosion products formed on OS are α-FeOOH, β-FeOOH, γ-FeOOH, Fe2O3, and Fe3O4, which form a porous structure. In comparison, corrosion products of LS are fundamentally similar to those of OS but include Cr2O3, producing a compact rust layer for better steel protection. Furthermore, the corrosion products of LS exhibit a lower expansion coefficient compared to those of OS in SSC with an identical water–binder ratio. Finally, the cracking time of the SSC cover, as determined through DIC, was validated through the use of a conventional prediction model.