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Repairs with self-consolidating concrete and galvanic anodes to extend bridge life.
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2017-08-01
[PDF-2.23 MB]
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Abstract:Historically, repairs of substructure elements that contain vertical and overhead sections have used either shotcrete or a conventional Virginia Department of Transportation (VDOT) Class A3 (3,000 psi) or Class A4 (4,000 psi) concrete. This study investigated the use of self-consolidating concrete (SCC), which has high flow rates, bonds well, has low permeability, and provides smooth surfaces, as another option. SCC can be placed in narrow areas and fit the existing geometry of the element. This study also explored the use of galvanic anodes in SCC repairs at various locations. VDOT has been evaluating galvanic anodes in substructure repairs as a means to prevent corrosion deterioration in the area around a repair, as corrosion is the main source of damage in reinforced-concrete structures. In VDOT’s Lynchburg and Staunton districts, SCC repairs were made using galvanic anodes in select locations. Several locations in these structures were repaired with the same SCC mixture but did not include anodes so as to provide a means for determining the benefit of embedding galvanic anodes. Based on the field results, repairs of substructure elements should be performed using SCC mixtures when possible. These repairs can be aesthetically pleasing if the formwork is carefully installed, as the finished SCC surface will strongly replicate the form surfaces and edges when the forms are removed. In addition, the use of SCC mixtures ensures that the repair concrete is of known quality and will flow through restrictive areas and fill the entire repair volume when the repair is properly performed. Although small vertical cracks were evident in the patched areas, they did not appear to reduce durability. This was based on the observation that after 7 years of service, the repairs and areas around the repairs did not exhibit corrosion activity. In patch areas with anodes, the anodes did provide protection to the steel immediately adjacent to the repair area. However, chloride-contaminated concrete areas in contact with reinforcement steel not removed and located away from the repairs were not protected. Unfortunately, corrosion is progressing in these areas where the concrete was considered acceptable based on sounding of the concrete during repairs, but now these areas require repair. This is due to the fact that concrete sounding is not a reliable way of locating chloride-contaminated concrete since it requires the concrete to be delaminated. A more reliable method would be the use of half-cell potential measurements to identify the areas in which concrete should be repaired. Progression of corrosion demonstrates the necessity of removing all chloride-contaminated concrete adjacent to the reinforcement as anodes in the patch will provide protection only in a narrow area around the patch.
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