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Reinforced Concrete Pipe Cracks - Acceptance Criteria

E. Busba / A. Sagues / G. Mullins

Inspection of recently placed reinforced concrete pipes often reveals cracks. Florida DOT was in need of in-lace crack acceptance criteria. The project was intended to determine the influential parameters responsible for crack healing in in-place Reinforced Concrete Pipes (RCP), determine what maximum crack width was amendable to autogenous healing and sufficient to mitigate reinforcement corrosion, and formulate guideline models for pipe crack acceptance criteria during construction. A literature survey indicated a reasonable expectation for autogenous healing to eventually occur for cracks narrower than about 0.020 inch. The prognosis was less favorable for wider cracks, and there was little assurance that autogenous healing would reliably take place for crack widths exceeding about 0.100 inch. Laboratory experiments did not produce significant autogenous healing of 0.100-inch or 0.020-inch-wide cracks in reinforced concrete pipe specimens over an approximately 2-month-long period. Corrosion tests showed that significant reinforcement wire corrosion could take place in a short time in reinforced concrete pipe with 0.100-inch-wide cracks, and that corrosion damage as considerably slower when the crack were 0.020 inch wide. Corrosion was aggravated by the presence of moderate chloride ion contamination (500 ppm), but active steel corrosion occurred even without it. A predictive model for corrosion development in cracked reinforced concrete showed for 500 ppm chloride very short durability projections for the 0.200-inch-wide crack condition, and moderately strong to little limitation in durability for the 0.020-inch-wide crack cases. Acceptable crack width guideline models proposed for discussion included a restrictive alternative, with 0.020 inch width allowable only for environmental chloride no greater than 500 ppm; a less restricted alternative allowing 0.020 inch up to 2000 ppm chloride; and a sliding option for up to 2000 ppm chloride where pipe service life was progressively derated to zero for crack widths increasing from 0.020 inch to 0.100 inch. In all models the acceptable width defaulted to 0.010 inch if the other conditions were not met.