An Investigation on the Usability of Acceleration Test by Impressed Anodic Current for Evaluating Corrosion Behavior of Hot-Dip Galvanized Rebar in Concrete

Abstract

Hot-dip Galvanized rebar (hereafter, HDG rebar) has an anti-corrosion effect due to the sacrificial anodic reaction of zinc. Additionally, the zinc coating itself provides barrier protection for the steel substrate. Meanwhile, from one of the investigations on the field performance of HDG rebar in concrete, HDG rebar did not protect the substrate when the remaining zinc was under 50 µm. For the evaluation of this property over a short period of time, an acceleration test using impressed anodic current (hereafter, acceleration test) may be useful. This test impresses constant direct current into the rebar and can result in the intended quantitative extent of the anodic reaction. However, in using this test on HDG rebar, it was found that the high rate of applied current density could cause an unintended early end of the anti-corrosion effect of zinc, despite there being more than 50 µm of remaining zinc thickness. In this study, the usability of the acceleration test was investigated to determine if it is a suitable method for evaluating the anti-corrosion behavior of HDG rebar in concrete. As a test variable, a comparatively low rate of applied current density was used in the experiments. As a result, it was clarified that an effective corrosion protection of the substrate was made with an increase of the zinc corrosion amount. This anti-corrosion effect was similar to that known to exist in actual corrosion environments. This behavior was terminated when the concrete cracked, and the substrate became corroded. While the test condition in this study resulted in an early end of the anti-corrosion effect of zinc, a linear correlation was achieved between the applied current density and the remaining zinc thickness at the time that the anti-corrosion effect was terminated. It was found that lowering the applied current density resulted in a more suitable test condition. In conclusion, the acceleration test was found to be useful, although further experimental validation is necessary to confirm this finding.

Corrosion Resistance of Concrete Reinforced by Zinc Phosphate Pretreated Steel Fiber in the Presence of Chloride Ions

“…Recently, researchers found that phosphating was an effective and important process applied to steels which has been successfully used in automotive industries due to easy operation and low cost [22]. The phosphating method (phosphate coats) can improve the corrosion resistance and lubrication properties of steel fibers [23] as well as steel rebars [24,25]. Among phosphate coats, zinc phosphate is the most popular coating, due to its capacity for anodic protection of Zn 2+ and barrier protection of the existing phosphate film, and, therefore, phosphate coatings have attracted more attention in recent years.…”