 |
|
 |
 |
 |
 |
 |
 |
 |
||||||
|
||||||||||||
Corrosion Management: Selecting a Corrosion Mitigation Strategy for Existing Concrete Structures Many engineers and owners, facing rising maintenance costs, recognize the significant incentive to protect existing structures from future corrosion damage by considering the use of corrosion mitigation systems. Selecting the appropriate system is based on many factors, including the amount and level of existing chloride contamination or carbonation, amount of concrete damage, level and location of corrosion activity (localized or widespread), environmental exposure conditions, expected service life of the structure, and the cost and design life of the corrosion protection system. Active corrosion mitigation systems (defined here as systems that supply protective current to reinforcing steel) generally fall into three performance categories: corrosion prevention, corrosion control, and cathodic protection. These systems are similar in that they all provide a protective current to the reinforcing steel to mitigate corrosion activity. However, they differ in terms of the intended application and the intensity of the protective current required to achieve the mitigation objective. Corrosion Prevention Corrosion prevention is defined as preventing corrosion from initiating even though the concrete may be contaminated. Preventing corrosion from initiating is useful in the case of patch repair of chloride-contaminated concrete. If good quality concrete repairs are completed, removing and replacing the spalled or delaminated concrete will address the existing areas of active corrosion. The problem is the surrounding chloride contaminated concrete, which remains. These sections were prevented from corroding by the beneficial side effects of the corrosion activity, which had been occurring within the repair areas. Although the repairs themselves will perform well if they are properly completed, the beneficial protection of the adjacent areas will no longer exist after the repairs are completed and new corrosion activity is likely to initiate next to the repairs. This phenomenon is commonly referred to as patch accelerated corrosion or the halo effect. For corrosion prevention applications, puck-shaped embedded galvanic anodes are tied onto the reinforcing steel at the interface between new and existing contaminated concrete. Once the new concrete is placed, the anodes begin to provide sacrificial corrosion protection to prevent the initiation of future corrosion sites in the adjacent chloride-contaminated concrete. Corrosion Control Corrosion control is characterized by a significant reduction in the corrosion rate of actively corroding steel in concrete. Corrosion control may or may not completely stop on-going corrosion, but the reduction in corrosion activity will significantly extend the service life of existing corroding structures. In corrosion control applications the conditions for corrosion (such as chlorides) already exist and corrosion may have already initiated in some areas, but has not progressed to the point of concrete damage. There are many situations where the corrosion conditions are moderate or are not uniformly widespread such that corrosion control is an appropriate approach since cathodic protection may not be justifiable from a cost point of view. Examples of this would be localized areas beneath leaking expansion joints or decks with isolated areas of high corrosion potentials. In these cases, targeting the protection to address the specific contaminated zone (rather than the entire structure) makes good sense. Cylindrical-shaped embedded galvanic anodes provide targeted corrosion control. The anodes are placed into drilled holes on a grid pattern to address the area of active corrosion and result in an increased service life of the rehabilitated structure at a moderate incremental cost. Cathodic Protection Cathodic protection is intended to provide complete or virtually complete corrosion protection to the cathodically protected elements. It is not always necessary nor is it cost effective to provide the highest level of corrosion protection when it is not economically justified. At the same time, there are many cases where severe corrosion conditions exist which must be addressed, or the condition of the structure will be compromised, and the cost to perform repairs in the future will be excessive. In these cases, a cathodic protection strategy should be considered. There are two broad categories of cathodic protection available: impressed current (ICCP) and galvanic systems. Impressed current systems utilize an outside power source to deliver the required level of current. For long term performance, ICCP systems should be regularly monitored and maintained. Galvanic systems are self-powered though the use of sacrificial anodes and generally require a lower level of maintenance. Since the galvanic anodes are consumed over time, these systems should be designed with sufficient capacity to provide the desired service life. For additional information on products and services for corrosion mitigation of concrete and masonry structures, please contact Vector Corrosion Technologies. |
 |
ARCHIVE
Cylindrical-shaped embedded galvanic anodes provide targeted corrosion control. The anodes are placed into drilled holes on a grid pattern to address the area of active corrosion and result in an increased service life of the rehabilitated structure at a moderate incremental cost. |
©2005 Vector Corrosion Technologies. All rights reserved.
To report technical problems when attempting to use this website please contact the webmaster.
No part of this web site may be reproduced without the express written consent of Vector Corrosion Technologies.