introduCtion Significance of Cracking The principles of reinforced concrete design are based upon the accepted concept that cracking of the concrete is necessary to permit development of the full tensile strength of the reinforcing steel. With precast reinforced concrete pipe, it became possible to utilize this cracking characteristic as a criteria for nondestructive quality control testing. This led to the development of the three-edge bearing test and the adoption by ASTM in the early 1930’s of the 0.01-inch crack test as a measurable and reproducible method for determining pipe strength. This particular crack width was arbitrarily proposed by Professor W. J. Schlick of Iowa State University because a leaf gage of that dimension was readily available. There is no structural significance to a 0.01-inch crack. It is simply the test criterion assigned by ASTM standards for reinforced concrete pipe, and the 0.01-inch crack has no meaning as a criterion of structural performance in the field. At 0.1 inches (approximately the width of two dimes), the steel reinforcement of the concrete is being tested further, but is still not near to approaching its yield strength. Where principle aggressive factors are present, crack sealing recommendations may vary as described on the following page. For cracks measuring greater than 0.1 inches, there still may not be any structural concern with the pipe, but it is recommended that these cracks be repaired so as to prevent the crack from worsening. One common repair method recommended is the injection of a polyurethane grout. Polyurethane is an expansive material routinely used for in-situ concrete pipe repair. The material will not only fill the cracks to which it is applied, but also fill any voids surrounding the pipe in the vicinity of the cracks, thereby reducing the potential for any infiltration that may be occurring. Certainly, the magnitude of permissible cracks is important from the standpoint of potential exposure to aggressive factors. The 0.01- inch crack came to be widely regarded as a conservative value for the maximum width that should be accepted as nondeleterious in exposed structures. That the criterion is conservative is demonstrated by more than 50 years of experience in the United States and Canada during which there have been no reports of deleterious corrosion of reinforcement in a concrete pipe due to the existence of cracks of 0.01 inch magnitude. For more information regarding the evaluation and repair of concrete pipe as it pertains to cracking, please visit the American Concrete Pipe Association for their document entitled “Post Installation Evaluation and Repair of Installed Reinforced Concrete Pipe”. ConCrete pipe stormwater treatment teChnologies box seCtions manhole and CatCh basin material LAFARGE PIPE eMANUAL PAGE 63