Effect of Gradient of Soil Aeration on Corrosion Rate at Different Depths from Ground Surface

Soil corrosion around a ground surface was experimentally examined by measuring macrocell current, spontaneous potential, and corrosion weight loss at different depths in soil. An experiment was carried out by placing small electrodes and small test pieces in the depth direction. The results showed that mainly anodic current flowed in the electrode around the ground surface. In addition, the corrosion rate estimated based on weight loss was the highest. Therefore, it is considered that macrocell current influences soil corrosion around the ground surface. However, it appears that the spontaneous potential difference and macrocell current due to the gradient of soil aeration do not contribute significantly to soil corrosion around the ground surface.

Macrocell corrosion between crossed steel rebars embedded in concrete under chloride environments

Steel reinforcement corrosion is found to be more severe at stirrups or some intersection zones of steel rebar mesh in concrete structures subjected to chloride penetration. This can be caused by macrocell corrosion formed between steel rebars with different potentials. Such potential differences are usually contributed by 1) chloride concentration gradients during the penetration process and 2) material differences between crossed steel rebars. With the forming of macrocell corrosion, the anodic current of steel with more negative potential will increase. The present study aims to deal with the macrocell corrosion between crossed steel macro-couples by dividing the steel rebar into intersected zone (IZ) and non-intersected zone (NIZ). The distribution of macrocell current on the surfaces of NIZ was obtained by means of a transmission line model. Based on the calculated macrocell current, the influence of the macrocell corrosion on the service life of reinforced concrete (RC) structures was analyzed. The results showed that the coupled micro- and macro-cell corrosion of stirrups could accelerate the change of the failure mode of a beam from bending to shear failure when the macrocell corrosion rate was no less than the microcell corrosion rate.

Macrocell Corrosion Formation in Concrete Patch Repairs - A Laboratory Study

Corrosion of reinforcement steel bars is a major threat to the durability of concrete structures exposed to chloride contaminated environment. Patch repairing is widely practiced in affected structures to avoid further damage due to corrosion. Macrocell formation within the patch repair is identified as one main reason for the failure of patch repairs. In the present study, a group of patch repairing materials is tested for their potential to form macrocell corrosion after repaired in a chloride contaminated environment. The influence of parameters such as level of chloride contamination, type of repair materials and the area of steel bar receiving repair are presented based on macrocell current measurements. The selected repair materials for study were cement based, GGBS based and polymer based in its composition. It is found that the severity of macrocell depends on the driving potential existing between the repair and substrate concrete. The quality of substrate concrete and repair material influences the macrocell formation. The surface area of the steel bar that receives the repair also affects the macrocell current. The study will be used for the evaluation of repair materials for macrocell corrosion formation potential before their field application in a chloride contaminated environment.

Effect of Nitrite Inhibitor on the Macrocell Corrosion Behavior of Reinforcing Steel

The effect of nitrite ions on the macrocell corrosion behavior of reinforcing steel embedded in cement mortar was investigated by comparing and analyzing the macrocell corrosion current, macrocell polarization ratios, and slopes of anodic and cathodic steels. Based on the experimental results, the relationship between macrocell potential difference and macrocell current density was analyzed, and the mechanism of macrocell corrosion affected by nitrite ions was proposed. The results indicated that nitrite ions had significant impact on the macrocell polarization ratios of cathode and anode. The presence of nitrite could reduce the macrocell current by decreasing the macrocell potential difference and increasing the macrocell polarization resistance of the anode.

Effect of Water-Cement Ratio on the Macrocell Polarization Behavior of Reinforcing Steel

The effect of water-cement ratio on the macrocell polarization behavior of reinforcing steel embedded in cement mortars was investigated by comparing and analyzing the macrocell polarization ratios and slopes of anodic and cathodic steels. Based on the experimental results, the relationship between macrocell potential difference and macrocell current density was also analyzed, and the mechanism of macrocell polarization affected by water-cement ratio was proposed. The results indicated that the water-cement ratios had little impact on the macrocell polarization ratios of cathode and anode. The lower water-cement ratio could reduce the macrocell current by decreasing the macrocell potential difference and increasing the macrocell polarization resistance of the cathode and anode.