“Effect of concrete quality and cover depth on the efficiency of impressed anodic current to induce corrosion of steel in concrete”

Abstract

Accelerated corrosion tests have been used by various researchers to study the effects of corrosion of reinforcement steel embedded in concrete, within a reduced time frame. Currently there is a paucity of literature on the relationship between accelerated corrosion tests and durability parameters of concrete, even though the results from accelerated corrosion tests are used in predicting the durability and service life models of reinforced concrete. In this study, the galvanostatic method, from the impressed anodic current technique was used to induce corrosion in eighteen 100 x 100 x 500 mm beams containing a single Y12 ribbed, high yield tensile strength bar. The study focused on chloride-induced corrosion, as such a 5% NaCl solution reservoir was placed on top of the beams so as to introduce chloride ions into the concrete. In this study, the effect of varying the concrete quality by using three different binder types, and varying the cover depth on the efficiency of impressed anodic current to induce corrosion in reinforcing steel was also be investigated. Concrete quality was varied by using three different binder types namely, 100% PC (CEM 1), 50/50 PC/SL (CEM III A-S) and 70/30 PC/FA (CEM IV-V/W). The different concrete cover depths to reinforcing steel were 20 mm, 35 mm and 50 mm. The efficiency of the impressed anodic current technique was determined as a percentage of the theoretical mass loss, determined by using Faraday’s Law over the actual mass loss. The actual mass loss was determined by conducting gravimetric tests on the steel at the end of the corrosion experiments. The results showed a general overestimation of Faraday’s mass loss for both binder types and cover depths. For the different cover depths, a closer approximation to 100% efficiency was observed in the order 20 > 35 > 50 mm. With regards to the different binder types, closer approximation to 100% efficiency was observed in the order SL > FA > PC. In general, an overestimation of theoretical mass loss was achieved due to the effect of the concrete’s resistivity. A modified equation of Faraday’s law was developed, taking into account the resistivity of the concrete so as to get a better estimate of theoretical mass loss.