Corrosion of steel bars in concrete with various steel surface conditions

A detailed investigation was carried out to clarify the corrosion of steel bars and steel-concrete interface in concrete with various surface conditions of steel bars, such as mill-scaled (M), polished (P), brown-rusted (BR), black-rusted (BL), and pre-passivated (PP). Moreover, to find a possible way to improve steel-concrete interface, three alternatives such as PP, revibration of concrete after casting, and insertion of steel bars in concrete after casting were investigated. Reinforced concrete specimens of 100 mm in diameter and 200 mm in height were made with 13 mm steel bars at a cover depth of 20 mm. The specimens were exposed to an artificially created accelerated marine exposure and tested for the corrosion of steel bars and chloride ingress into concrete at a regular interval. Steel-concrete interfaces were examined by a scanning electron microscope (SEM) to check the nature of the steel-concrete interface with the variation of surface condition and casting method. The chloride threshold level over the steel bars was sequenced as PP > BL > P > BR > M. Application of a cement paste coat over the steel bar created a remarkably dense steel-concrete interface compared to the other cases investigated, and therefore significantly improved the chloride threshold level. M bars produced the most corrosion compared to the other bars investigated. Revibration also resulted in more corrosion over the steel bars.