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Publication Number: FHWA-SA-96-013
Date: February 1996
As part of the long-term pavement performance (LTPP) studies, the Federal Highway Administration (FHWA) is monitoring approximately 30 bridges in the United States and Canada that have been treated with corrosion inhibitors, are outfitted with cathodic protection systems, or have undergone electrochemical chloride extraction (ECE). The project is a continuation of a Strategic Highway Research Program (SHRP) study, which examined these different protection and rehabilitation strategies on concrete bridges and structures.
The monitoring is being conducted by Concorr, Inc., under a 5-year contract with FHWA. The project, which is now in its second year, involves examining concrete bridge protection and rehabilitation methods to gauge their effectiveness and to determine how long they retain their protective qualities. The project will also help to identify the most appropriate laboratory and field tests for evaluating the effectiveness of the various treatments.
At the conclusion of the project, Concorr will prepare a report describing how well the techniques worked and recommending the most appropriate tests for determining the effectiveness of the treatments. A manual of practice will also be prepared, covering the design, placement, quality control, finishing, and other factors that affect the effectiveness of these systems.
Before visiting a site, the inspector contacts the regional LTPP coordination office to arrange for traffic control at the site. Sites will be examined periodically over the next 4 years.
The majority of the sites have cathodic protection systems installed. Others have been treated with the ECE process or with corrosion inhibitors. Cathodic protection systems and the ECE process are similar, except that cathodic protection systems are permanent installations and require 50 to 500 times lower current density.
The type of system installed at a particular site determines the performance-related criteria that are evaluated. For example, for cathodic protection systems, Concorr engineers assess whether the system is working properly and providing adequate protection. If problems are found, Concorr recommends remedial actions to be taken.
"For the ECE process there remain critical unanswered questions, such as the extent of chloride ion remigration," says Concorr's Ali Sohanghpurwala. "We check existing chloride concentration profiles and compare them to previous results." They also assess whether corrosion is reoccurring within the structure and how effective the treatment has been in stopping long-term corrosion.
For corrosion inhibitor sites, Concorr compares the level of corrosion activity in both treated and untreated areas and then evaluates the effectiveness of the corrosion inhibitor.
During each visit, a number of tests appropriate for the method of treatment are conducted. Besides visual inspection, tests include delamination surveys, chloride concentration profiles, cores for petrographic analysis, half-cell surveys, corrosion rate estimates, depolarization testing, and hardware evaluation.
Many of the systems studied in this project were initially set up with FHWA funding during SHRP, and the results of the study will provide answers to questions about the long-term effects of these treatments. "At the end of the 5-year period," says Concorr's William Scannell, "we will have looked down the road 7 to 16 years after the treatments were first applied and gained additional experience on the long-term effects of cathodic protection systems, electrochemical chloride extraction, and corrosion inhibitors."
For more information about the concrete bridge and rehabilitation project, contact William Bellinger, FHWA's project manager (telephone: 703-285-2530; fax: 703-285-2767).
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