Durability of CFRP-wrapped concrete in cold regions: A laboratory evaluation of montmorillonite nanoclay-modified siloxane epoxy adhesive

Externally bonded fiber-reinforced polymer (FRP) is a promising tool to use for either preserving the integrity of new concrete infrastructure or mitigating the deteriorations of aged concrete infrastructure. This laboratory study evaluates the durability performance of carbon FRP-wrapped concrete with a 1.5 wt% montmorillonite nanoclay (NC) modified siloxane epoxy adhesive, under a simulated cold and chloride-laden environment. Five types of concrete samples were fabricated and tested, i.e., reference concrete, FRP-wrapped concrete, NC-modified FRP-wrapped concrete, FRP/pre-aged concrete, and NC-modified FRP/pre-aged concrete, respectively. Both before and after the salt scaling test in 3 wt% NaCl, the NC-modified FRP-wrapped concrete samples exhibited notably better mechanical properties (higher compression strength and elastic modulus) and significantly better transport properties at the interface (reduced water absorption and gas permeability), related to their unmodified FRP-wrapped counterparts. These benefits of nano-modification, along with better resistance to salt scaling, are attributable to the improved microstructure and reduced hydrophilicity of the adhesive, as revealed by microscopic investigations using a high-resolution optical microscope and a water contact angle tester. The Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis revealed that the admixed NC chemically reacted with the adhesive and increased its crosslinking density and thermal stability.