Performance of Coated Concrete in Wastewater Environment

Abstract

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 for over five years. Both a dry application (representing new construction) and a wet application (representing rehabilitation) concrete were used in this study. It was necessary to use a combination of full-scale, bonding and chemical resistance tests for evaluating coatings to protect concrete structures below groundwater. Full-scale test facilities were used to evaluate the performance of coatings under hydrostatic pressure and to simulate underground concrete structures below groundwater. Visual inspections and in-situ bonding tests were performed. 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 under acidic environment 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 performances of the two coatings were noticeably different and one coating with pinholes extended the service life by 14 times while the other by 57 times. There was no direct correlation between bonding strength and chemical resistance of coated materials. Although both coatings were polyurethane based, their performances were different under the testing conditions adopted in the study.