51313-02726-Service Life Modeling: An Assessment Tool for Existing Concrete Structures

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Product Number: 51313-02726-SG

ISBN: 02726 2013 CP

Author: Jonah Kurth

Publication Date: 2013

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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 in Arizona 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. Non-destructive 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 chloride content testing to obtain concentration profiles and rapid chloride permeability testing. 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 columns 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 columns) would be expected. Based on the results of the model strategies for corrosion control and durable repairs were developed for each element. Combination barrier system and cathodic protection “life jackets” were recommended for the columns to control future corrosion. In contrast the service life of the beams and girders could be reasonably assured without cathodic protection or other major repair resulting in an efficient solution providing significant cost savings to the owner.