Abstract
Service life modeling can be a valuable tool to guide corrosion assessment and control strategies in reinforced concrete structures. After 25 years of service, many of the concrete tanks and other structures at a wastewater treatment plant are experiencing corrosion of embedded reinforcing steel. An in-depth assessment of a tower trickling filter was performed to determine the cause and extent of corrosion-related deterioration and develop appropriate repair and corrosion control strategies. Evaluation techniques used for the assessment included half-cell potential, corrosion rate, and concrete cover measurements, as well as thorough visual and sounding surveys. Laboratory evaluation of extracted concrete cores included petrographic analysis and chloride content testing to obtain concentration profiles. The assessment showed steel reinforcing corrosion was driven by residual chloride present in the influent water supplied to this secondary treatment facility. To date, corrosion-related deterioration had occurred on some of the beams, girders, and piers supporting plastic packing on the interior of the structure. Analysis of laboratory data showed elevated chloride content levels near reinforcing steel depths at many locations. A service life model was used to predict the time before significant chloride-induced corrosion damage to each interior element type (beams, girders, and piers) would be expected. Based on the results of the model, strategies for corrosion control and durable repairs were developed specifically for each element providing significant cost savings to the owner.
