Corrosion Mitigation - the Real Problem in Concrete Repair and Restoration
Corrosion Mitigation - Addressing the Real Problem
The application of Value-Engineering to the repair of reinforced concrete structures can significantly affect the cost-effectiveness and quality of the final construction product. This approach typically requires addressing the corrosion problems that are the cause of spalled and delaminated concrete. “ If the cause of the problem is not addressed, you have not created a solution.” Effective solutions must include measures to reduce the occurrence or re-occurrence of corrosion-induced spalling in reinforced concrete structures, especially in concrete contaminated with chlorides. At a minimum, these mitigation measures address the Ring Anode Effect, the phenomenon whereby corrosion is accelerated in areas adjacent to recently repaired steel-reinforced concrete. Samples from representative areas of the structure should be obtained and sent to a laboratory for analysis of the level of chloride contamination in the concrete. This procedure is an integral part of condition surveys essential in assessing structural deterioration and compiling an appropriate repair specification that will extend the service life of reinforced concrete structures.
Galvanic corrosion mitigation systems installed in the repair areas are a cost-effective means of providing state-of-the-art corrosion mitigation technology. Typically, these systems are installed during the repair process and will stop the corrosion of steel reinforcing in areas adjacent to the repairs. In addition to traditional steel (rebar) reinforcing, there are systems that provide protection for post-tensioned structures such as parking decks, and for cantilevered slabs such as walkway and lanais. Other systems are specifically designed for high-exposure and sensitive oceanfront environments such as piers and docks. Stopping the expansive forces created by rusting and corroding steel also stops the corresponding spalling of surounding concrete. As opposed to more costly Cathodic Protection systems, galvanic systems rely on the differences in the electrochemical potential of dissimilar metals to generate the necessary current flow to protect steel reinforcing. These galvanic systems avoid the wiring necessary to energize the complex cathodic protection systems commonly used to protect industrial pipelines and storage tanks.
It is important to note that even after concrete is properly repaired in accordance with industry guidelines, these repairs only address areas with the highest level of corrosion activity, areas where the spalling can be readily observed. Chloride contaminated concrete in unrepaired areas is not remediated. New corrosion sites will form in unrepaired areas that were passive prior to the repairs to the damaged concrete as a result of the Ring Anode Effect. Systems can be designed to provide sufficient galvanic current flow effective at preventing the initiation of corrosion even in concrete with significant chloride concentrations. Most galvanic systems are also self-regulating and current flow will decrease as the electrochemical reaction increases the alkalinity of the concrete and the concentration of chloride ions decreases at the steel/concrete interface.
A wide range of corrosion mitigation resources is available today to contractors specializing in concrete repair. One tool not mentioned above is the use of migrating corrosion inhibitors. Specialty contractors can improve the efficacy of their concrete repair projects by selecting the appropriate corrosion mitigation system to either prevent or stop the corrosion of steel in reinforce concrete structurs. Waterproofing systems and extended warranties to accompany long-term inspection and maintenance programs are also offered by “upper tier” concrete repair firms.
-by Joe Enright, President of Structural Systems.