EPOXY ADHESIVES MODIFIED WITH NANO- AND MICRO-PARTICLES FOR IN-SITU TIMBER BONDING: EFFECT OF MICROSTRUCTURE ON BOND INTEGRITY

The bond integrity of thixotropic, shear-thinning epoxy adhesives for in situ bonding of FRP connections into timber was investigated. The manufacture of such joints requires adhesives which can produce thick bond-line where the bonding environment does not allow any use of pressure and heat. Four adhesives were evaluated based on a standard adhesive to which nano-silica, nano-rubber and ceramic micro-particles were added to modify rheology and improve adhesive bonding. Viscosity and shear stress of the adhesives were measured as a function of shear rate. The rubber-modified formulation was found to possess the highest viscosity and required higher shear stress to reduce its viscosity. The wettability of nano-modified adhesives on timber substrates was assessed by contact angle measurements and the rubber-modified formulation possessed the highest contact angle which was expected from viscosity measurements. The shear strength of timber to adhesive interfaces was measured using block shear tests and pull-out tests on FRP rods bonded into timber. The addition of nano- and micro-filler additions increased the bond strength of the base adhesive by up to 20%. However the measured contact angle negatively correlated with measured bond strength. Overall, the less ductile micro-particle-filled adhesive delivered the highest shear strengths when bonding timber and FRP rods