Tensile bonding strength of epoxy coatings to concrete substrate

Abstract

In this study, four commercially available epoxy coatings were selected to investigate their tensile bonding characteristics to dry and wet concrete with and without 105-kPa backwater pressure. The CIGMAT CT-2 (modified ASTM D4541-95e1) and CIGMAT CT-3 (modified ASTM C321-00) tests were used to determine the tensile bonding strength of the coatings with curing time. The tests were conducted over a period of 2 years. Fifty-three CIGMAT CT-2 tests and 26 CT-3 tests were performed for the four epoxy coatings. Five failure types were identified for both the test methods based on the failure mechanisms observed during the tests. In situ bonding tests (CIGMAT CT-2, full-scale test with back pressure on) were also performed on coatings that were tested under a hydrostatic (back) pressure of 105 kPa (simulating 10 m of groundwater) for at least 6 months (full-scale test). All the coatings investigated were epoxy based, but their bonding strength and failure modes to dry and wet concrete surfaces were different. For all the coatings investigated, in situ bonding strength with dry concrete was higher than wet concrete. Epoxy-A and Epoxy-D (fiber-mat-reinforced epoxy) had good bonding strength (>1.3 MPa, 190 psi) to both dry and wet concrete surfaces during the 2 years of testing period. The bonding strength of Epoxy-B and Epoxy-C varied with time for both dry and wet concrete surfaces. Although for coatings with higher bonding strength, better correlations between the two test methods were observed, in general, the bonding strength from CIGMAT CT-3 test was higher than that from CIGMAT CT-2 test for the coatings tested.