Quality Control of Carbon Fiber Composite System Repairs of PCCP from the Inspector's Viewpoint

This paper provides an inspector's view of quality control procedures followed for the repair of the Baltimore Area's Southwestern Transmission Main literally from the "inside out". A 2006 condition assessment of the Southwest Transmission Main which serves Baltimore City, Maryland and several adjoining Counties identified deficiencies that were sufficiently serious that, to avoid a potential catastrophic failure of the main, the engineering consultant recommended that repairs be made before the main was returned to service. A number of reaches of the transmission main which were comprised of 54-, 48- and 36-inch diameter pre-stressed concrete cylinder pipe (PCCP) exhibited significant numbers of pre-stressing wire breaks, longitudinal cracking and delamination of the concrete core. Restoration of service required that three methods of pipe rehabilitation be undertaken: 1) pipe replacement, 2) slip-lining with steel pipe, and 3) lining with a carbon-fiber composite system (CFCS). In Baltimore County, 5,000 feet of 54-inch main was replaced in its entirety with new PCCP, 300 feet of 54-inch was slip-lined and 16 sections of 54-inch pipe were repaired with CFCS. In Baltimore City, 11 sections of 54-inch main were repaired with CFCS. In Howard County 33 sections of 36-inch pipe were repaired with carbon fiber, and in Anne Arundel County, 600 feet of 48-inch pipe was repaired by steel slip-lining, and 8 sections of 36-inch main were repaired using CFCS. This paper provides a perspective from the firsthand viewpoint of two inspectors who were responsible for implementing the quality control procedures that were followed for the repair of 68 sections of 54- and 36-inch PCCP with CFCS. It reviews the methodology employed to conduct quality control inspections of the CFCS repairs, identifies specialized equipment developed for use in the inspections and highlights difficulties that can be encountered depending on the type and size of pipe being repaired. The paper concludes with a review of especially significant inspection procedures, problems and other quality control considerations.