A Study of Life Extension of Two Prestressed Concrete Cylinder Pipelines

The paper presents the results of an analytical and experimental study performed to predict the impact of current and future expected degradations of the inner-core concrete, resulting from biochemical degradation due to exposure to lake water, on the structural performance and remaining service life of the Cedar Creek (CC) and Richland Chambers (RC) pipelines for Tarrant Regional Water District. Compression tests and petrographic examinations of the concrete inner core are performed to evaluate and quantify the extent of current degradation, strength, permeability, and quality of the inner core and the mortar coating. The biochemical degradation of the inner core is simulated in the STADIUM program and is used to predict the extent of future degradation in 50 to 100 years of additional service. The results are then used to evaluate the performance of the pipes under service load accounting for current and future degradation states. The remaining service life of the pipeline is found to depend on the mode of degradation and failure, including biochemical degradation of the inner core, degradation of mortar coating, and hydrogen embrittlement breaks of the wires. Each mode of failure is discussed, and mitigation measures needed for life extension are identified and discussed for each pipeline.