Performance of polyurethane-coated concrete in sewer environment

Polyurethane-based coatings are used to protect concrete facilities against corrosive environments. The performances of two commercially available polyurethane coatings were evaluated under sulfuric acid environment (representing sewer condition) for over 5 years. Both dry (representing new construction) and wet (representing rehabilitation) concretes were used in this study. A combination of the full-scale hydrostatic test, bonding test, and chemical resistance tests were performed to evaluate the coatings to protect concrete structures below ground water. The full-scale hydrostatic test was used to evaluate the application and performance of coatings under hydrostatic pressure to simulate underground concrete structures below ground water. Visual inspections and in situ bonding tests were performed on coated concrete under a hydrostatic pressure of 105 kPa. Test results showed that bonding strength of one coating was affected by the moisture condition and hydrostatic water pressure in the full-scale test. Coated cement concrete specimens with pinholes were used to study the chemical resistance of the coated concrete in sulfuric acid to represent the worst sewer condition. Change in weight of coated concrete specimens was measured at regular intervals. Types of failures in coated concrete under acidic environment have been identified. Test results showed that the performance of the two coatings were noticeably different and one coating with pinholes extended the service life of concrete by 14 times while the other coating extended the service life of concrete by 57 times. There was no direct correlation between bonding strength and chemical resistance of the polyurethane-coated concrete. Although both coatings were polyurethane-based, their performances were different under the testing conditions adopted in the study.