Optimised cathodic protection design for maximum bond performance in reinforced concrete

Abstract

The influence of the long‐term effects of impressed current cathodic protection (ICCP) on the bond strength is investigated. A total of 16 pull‐out specimens were divided into four series and the steel bars pre‐corroded to target degrees of 0% (control), 1, 2 and 5% weight loss. Four levels of ICCP current density ranging from approximately 0 (control) to over 1000 μA/cm2 were applied to each series. These are considerably higher than the levels typically used in practice, which rarely exceed 2 μA/cm2, but were used to replicate long‐term application within a reasonable timescale. Following pull‐out tests, the values of bond load were determined. The analysis accounts for the accelerated ICCP by relating the total charge to the steel reinforcement in coulombs (current x time) to the bond values and migration of chloride ions. The results show that although some loss in bond is evident from the ICCP, an optimised current density can be applied to a real structure without affecting the as‐designed bond strength in the long‐term e.g. ≤0.65 μA/cm2 for an ICCP duration of 70 years. Application of the same current density reduces the chloride concentration from around the steel irrespective of the degree of corrosion.

Influence of accidental over‐polarisation on the mechanical properties of cathodically protected pre‐tensioned tendons

“…[ 9 ] Furthermore, as the degree of corrosion increases, deeper corrosion pits will form, meaning that the loss in the cross‐sectional area to cause over‐stressing will be achieved more easily. It was also determined elsewhere [ 28 ] that the application of CP can lead to a slight reduction in the bond between the steel and concrete. However, in the early stages of corrosion, the bond can actually increase due to the increased roughness of the steel surface.…”

“…However, in the early stages of corrosion, the bond can actually increase due to the increased roughness of the steel surface. [ 28 ] Hence, the application of ICCP versus the impact of corrosion is a trade‐off, but it is likely to yield more positive outcomes as a result of a do‐nothing approach where the formation of an increasing pit could be detrimental if corrosion is present.…”

“…A constant current density of 1 mA/cm 2 was adopted in this investigation, based on previous work carried out by the authors. [9,[26][27][28][29] It is accepted that this current density is much higher than would be present in a real situation, but this was applied to give the appropriate level of corrosion within a reasonable timescale. At 28 days after casting the mortar, the tendon in each specimen was subjected to general corrosion by applying an anodic impressed current provided by a DC power supply and the tendon acting as the anode and MMO Ti mesh as the cathode.…”

Considerations over the Italian road bridge infrastructure safety after the Polcevera viaduct collapse: past errors and future perspectives

“…This strategy cab be implemented by the use of sacrificial anodes (galvanic protection) directly connected to exposed reinforcements ( Fig. 16) [24]. These anodes, usually realized in zinc-based compounds, guarantee local protection to the steel by the higher electronegative power of the sacrificial anode.…”