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Inspection FAQs


If you have have questions about concrete pipe or box culverts, you're in the right spot.  If you can't find what you are looking for, though, don't hesitate to reach out and someone from the ACPA will reach out and help find you a solution.



What is an acceptable crack width in a concrete pipe?

For a full explanation on inspection see the ACPA “Post Installation Evaluation and Repair of Installed Reinforced Concrete Pipe.”  Longitudinal Cracks–Concrete is strong in compression but weak in tension. Reinforced steel is provided to handle the tensile stresses. Hairline longitudinal crack in the crown or invert indicate that the steel has accepted part of the load. Cracks less than 0.01 inches in width are minor and only need to be noted in the inspection report. Cracks greater than hairline cracks, or those more than 0.01 inch in width but less than 0.1 inches, should be described in the inspection report and noted as possible candidates for maintenance. Longitudinal cracking in excess of 0.1 inch in width may indicate overloading or poor bedding.

What is Autogenous Healing and its relationship to pipe design?

A phenomenon, known as autogenous healing often occurs between two surfaces of cracks in buried concrete pipe. Autogenous healing is the ability of concrete to heal itself in the presence of moisture and air. This explains why the healing occurs in concrete pipe where moist conditions are higher than those of other concrete structures. During this process, calcium carbonate, (a hard white substance), forms when moisture reacts with un-hydrated cement powder and regenerates the curing process. This self-healing process creates a monolithic structure. In Ohio, the Department of Transportation developed a post construction inspection standard for installed pipe that requires nothing be done to a pipe with a crack width up to 0.06-inch, due to the autogenous healing that is expected to occur.