Microstructural Analysis of Corrosion Products of Steel Rebar in Coral Aggregate Seawater Concrete

To explore the formation of corrosion products of steel bars in coral aggregate seawater concrete (CASC), this study used X-ray powder diffraction (XRD) to examine the ingredients of corrosion products of CASC steel bar, and scanning electron microscopy (SEM) to scan the surface structure of the steel rust layer to understand the difference between the steel corrosion products under different test environments. In addition, this paper analyzes the steel corrosion in CASC and seawater sea-sand concrete (SSC) at the micro level. The results demonstrate that the CASC in the marine environment undergoes electrochemical reactions to produce insoluble Fe(OH)2. Under the immersion environment, the large amount of alpha-FeO(OH) contained in the rust layer of the steel bars can accelerate the corrosion process. There are more free chloride ions (Cl-) in the dry and wet cycle environment, which leads to the corrosion products of the steel bar containing more beta-FeO(OH). Furthermore, it was noticed that the presence of small openings in the needle-shaped crystals can cause water molecules to become trapped, making the pitting corrosion of the steel bar worse. This situation provides an ideal setting for the occurrence of severe corrosion. The corrosion process in a dry-wet cycle environment is less than the corrosion products of the steel bar under the full immersion environment; the structure of steel corrosion products of CASC are less than that of SSC.