Synergistic Effect of Nano-TiO ₂ and Organic Montmorillonite Modification of Epoxy Resin on the Characteristics of the CFRP–Concrete Interface

This study investigates the influence of a composite material comprising nano-titanium dioxide (TiO2), nanosized organic montmorillonite (OMMT), and epoxy resin on the bond–slip performance of the interface between carbon fiber–reinforced polymer (CFRP) and concrete. Mechanical and microstructural evaluations were carried out on three adhesive types: pure epoxy, OMMT-modified epoxy (ME), and nano-TiO2/OMMT-modified epoxy (TME). For the double-lap shear test, the influence of resin nano-modification on the bonding behavior of the CFRP–concrete interface was examined by analyzing the failure mode, ultimate bearing capacity, stress and strain distributions, bond stress–slip curves, and scanning electron microscopy images. The combined modification of adhesive by nano-TiO2 and OMMT enhanced the peak shear stress of the CFRP–concrete interface and increased the effective bond length. Microscopic analysis revealed that incorporating 1% by weight zero-dimensional nano-TiO2 in the ME resin substantially enhanced the exfoliation of 1% by weight OMMT platelets. In the CFRP–concrete system, the TME adhesive greatly improved the adhesion at the fiber–concrete interface, and the interfacial bond strength and load transfer length were increased by 30% and 22%, respectively. The predicted strength model values exhibited good agreement with the experimental results, effectively reflecting the influence of adhesive nano-modification on the interfacial bond strength.