CFRP Repair of Complex Structures in Wastewater Applications

Carbon-fiber-reinforced polymer (CFRP) has been utilized for repairing degrading or failed water and sewer pipelines for decades. For a circular pressure pipeline, CFRP rehabilitation technology designed based on AWWA C305 standard is one of the few trenchless repair technologies available. However, when the question comes to degrading access structures and vaults of non-circular geometry, CFRP repairs are underutilized due to the lack of existing examples and explicit design guidance. This paper presents a case study where CFRP rehabilitation was used to fill the "non-circular gaps" between other lining technologies in various circular sections of a sewer gravity pipeline. The project consisted of 16 access structures wherein both circular and non-circular sections of the structures and the circular sewer in between the structures were lined using a combination of Cured-In-Place Piping (CIPP) and Geopolymer. CFRP was utilized to provide watertightness and structural continuity between the new pipe lining systems across the rectangular or oval sections or circular sections with hindrances. The paper provides insight into the owner's perspective in selecting such repairs and discusses the design methodology, which consists of a mix of AWWA C305, ACI 440.2R, and ACI 318 approaches. The paper also presents various construction challenges encountered and overcome. The paper concludes by showing a successful rehabilitation project with enhanced service life.