Catechol-modified epoxy coatings with high adhesive strength on saturated concrete substrate

Abstract

A series of catechol-modified epoxy resin biomimetic coatings (CE-X, X represents the weight fraction of catechol-modified epoxy resin, X = 0, 5%, 10%, 15%, 20%, 25%) with high adhesive strength on saturated concrete substrate were designed and synthesized. The chemical structures of the CE-X were confirmed by proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance spectroscopy (13C NMR), and Fourier transform infrared spectroscopy (FTIR). The thermal property of CE-X was characterized by thermogravimetric analysis (TGA). The adhesive properties were characterized by pull-off tests. Results showed that when the content of catechol–epoxy resin was under 20% by weight, the adhesive strength could be further increased by forming hydrogen bonds and coordination complexes in the interface of coating and saturated concrete of the substrate. When the content of catechol–epoxy resin was above 20% by weight, the pull-off tests showed cohesive failure, and the adhesive strength on saturated concrete substrate reached the maximum value of 4.61 ± 0.8 MPa, which was improved by ~ 3 MPa compared to that of the control sample. The adhesive properties of epoxy coatings on saturated concrete substrate could be improved by adding a proper amount of catechol groups. In addition, when it was immersed in water for 30 and 120 days, its adhesive strength was reduced by about 7.8% and 22%, respectively. This work provides a new method for designing and synthesizing protective coatings with high adhesive strength on the saturated concrete substrate.