Influence of partial cover thickness and mortar quality on steel corrosion in a chloride environment

Abstract

AbstractThe concrete cover is an important factor that influences the corrosion of rebar in concrete. When the specified cover depth is not achieved due to improper placement of formwork or sagging of rebars at the construction stage of RC structures, it results in a partial cover thickness. This partial cover thickness would create an electrochemical imbalance enhancing the macrocell current. This study investigated the influence of partial cover thickness, water-cement (W/C) ratio, and chloride ions on the corrosion of rebar in mortar. A special divided bar was used to make cylindrical specimens with a full cover thickness of 20 mm and partial cover thickness (20 mm and 7.5 mm) with W/C ratios of 0.30 and 0.70. Electrochemical methods such as macrocell, microcell, electric resistivity, and polarization curves were used for measurement. The corrosion current density for a partial cover thickness of 7.5 mm with a W/C of 0.30 was 3.46 μA/cm2, and for 20 mm, it was 1.85 μA/cm2. This study concludes that for a low W/C of 0.30; decreasing the cover thickness partially by 62.5% (7.5 mm) will increase the magnitude of total corrosion current density by 47%. However, for a W/C of 0.70, a partial cover thickness had no influence on the corrosion rate.

Keywords

• Chloride attack
• macrocell corrosion
• partial cover thickness
• quality control
• reinforced concrete (RC)
• water-cement ratio