Study on Cover Depth for Prestressed Concrete Bridges in Airborne-Chloride Environments

摘要

style="text-align: left;">In Japan, prestressed/reinforced concrete bridges often suffer deterioration from steel corrosion in the chloride-laden air of marine environments with high concentrations of airborne chloride particles.  Only a few decades after erection, several prestressed concrete bridges have already been replaced due to significant corrosion in the main girders. To develop a reasonable design policy for building  more durable concrete bridges that require less maintenance, the performance of conventional concrete cover as corrosion protection in coastal environments needs to be properly evaluated. In this paper,  the authors address the effectiveness of conventional concrete cover with a water-cement ratio  of 0.36 and 0.43 in airborne-chloride environments and propose a realistic evaluation method based on Japanese surveys of airborne chloride distribution and  deterioration in existing concrete highway bridges. The proposed evaluation method uses the chloride diffusion coefficient for uncracked concrete exposed to the chloride atmosphere and the boundary chloride level based on its relationship to airborne chloride  levels. The results of this research provide the basis for a cogent policy for corrosion protection in coastal areas for concrete bridges with 100-year design lives. >References style="text-align: left;">1. Public Works Research Institute, March 2001, Investigation on Life Cycle Cost of Concrete Bridgesa€”Deterioration and Maintenance Cost of Concrete Bridge, Technical Memorandum of PWRI No.  3811, Tsukuba, Japan. (in Japanese) style="text-align: left;">2. Virmani, Y. P. and Clemena, G. G., September 1998, a€?Corrosion Protection-Concrete Bridges,a€? Report No. FHWA-RD-98- 088, Federal Highway Administration, Washington, D.C. style="text-align: left;">3. Kessler, R. J. and Powers, R. G., September 1987, a€?Corrosion evaluation of substructure Long Key Bridge,a€? Interim Report, Florida Department of Transportation. style="text-align: left;">4. Kessler, R. J. and Powers, R. G., August 1988, a€?Corrosion of Epoxy Coated Rebar Keys Segmental Bridges Monroe County,a€? Report No. 88-8A, Florida Department of Transportation. style="text-align: left;">5. Pfeifer, D. W., 2000, target="_blank" title="a€?High Performance Concrete and Reinforcing Steel with a 100-Year Service Life,a€?" href="http://dx.doi.org/10.15554/pcij.05012000.46.54 ">a€?High Performance Concrete and Reinforcing Steel with a 100-Year Service Life,a€? PCI Journal, V. 45, No. 3, May-June 2000, pp. 46-54. style="text-align: left;">6. McDonald, D. B.; Pfeifer, D. W.; and Sherman, M. R., December 1998, a€?Corrosion Evaluation of Epoxy-Coated, Metallic Reinforcing Bars in Concrete,a€? Report No. FHWA-RD-98-153, Federal   Highway Administration, Washington, D.C., 137 pp. style="text-align: left;">7. McDonald, D. B.; Sherman, M. R.; Pfeifer, D. W.; and Virmani, Y. P., 1995, a€?Stainless Steel Reinforcing as Corrosion Protection,a€? Concrete International, V. 17, No. 5, May 1995, pp. 65-70. style="text-align: left;">8. Poston, R. W.; Carrasquillo, R. L.; and Breen, J. E., 1987, target="_blank" title="a€?Durability of Post-tensioned Bridge Decks,a€?" href="http://dx.doi.org/10.14359/1622 ">a€?Durability of Post-tensioned Bridge Decks,a€? ACI Materials Journal, July-August 1987, pp. 315-326. style="text-align: left;">9. Smith, J. L. and Virmani, Y. P., August 1996, a€?Performance of Epoxy Coated Rebars in Bridge Decks,a€? Report No. FHWARD- 96-092, Federal Highway Administration, Washington, D.C. style="text-align: left;">10. Sagues, A. A., et al., May 1994, a€?Corrosion of Epoxy Coated Rebar in Florida Bridges,a€? Final Report, Florida Department of Transportation. style="text-align: left;">11. Public Works Research Institute, December 2000, a€?Study on Prestressed Concrete Bridges Minimizing Maintenance