Bonding Strength of Epoxy Coatings Used to Protect Concrete in Wastewater Facilities and 3-D FEM Analysis

In this study, three commercially available epoxy-based coatings were selected to determine the changes in bonding strengths to concrete with curing time. The CIGMAT CT-2 (modified ASTM D 4541) test was used to determine the bonding strengths of the coatings to dry and wet concrete surfaces. The tests were conducted over a period of two years. A total of 33 CIGMAT CT-2 tests (laboratory and in-situ tests) were performed on the three epoxy coatings. Five failure types were identified. Test results showed that although all of the coatings were epoxy based, the bonding strength of the coatings to the dry and wet concrete surfaces were different. Epoxy-A (pure epoxy) and Epoxy-B (glass fiber reinforced epoxy) had good bonding strength (>1.4 MPa, 200 psi) on both dry and wet concrete surfaces; Epoxy-C (cementitous based epoxy coating) had poor cohesive bonding strength (<0.7 MPa, 100 psi) between the topcoat (epoxy) and the base material. A 3-D FEM analysis was performed to determine the effects of coating modulus and thickness on the stress distribution in the coating, coating to concrete interface and concrete.