External bonding of composite strips to the components of concrete construction is an effective technique in rehabilitation and upgrading of concrete construction. This thesis reports a study regarding the effects of adhesive properties on mechanical and structural performance of reinforced concrete beams strengthened with carbon fibre reinforced plastic (CFRP) strips....[ Read more ]

External bonding of composite strips to the components of concrete construction is an effective technique in rehabilitation and upgrading of concrete construction. This thesis reports a study regarding the effects of adhesive properties on mechanical and structural performance of reinforced concrete beams strengthened with carbon fibre reinforced plastic (CFRP) strips.

The concrete beam was subjected to four point bending test to examine the effect of adhesive properties. It is found that the rubber modifier increased the maximum bending force, the corresponding displacement and flexural ductility, compared with those bonded with a neat epoxy resin, for all concrete beams tested with different number of FRP layers. There was a transition of major failure mechanism from 'delamination of CFRP strip' along the CFRP-concrete interface with relatively clean fracture surface to 'peel-off of concrete' with cracks propagating irregularly through the inside of concrete, when the number of CRRP strips was increased from two to four layers.

The interlaminar fracture toughness of FRP strips-concrete interfaces was measured using the asymmetric double cantilever beam specimens. The mixed-mode interlaminar fracture toughness increased with the rubber content for both the epoxy or vinyl ester resin, the improvement being as large as about 13% with 20% rubber content. Apart from the higher interlaminar fracture toughness, the rubber modifier gave rise to higher stability during delamination, suggesting a beneficial effect of mitigation catastrophic failure in practical applications. A series of micro-hardness test on polished cross-sections of adhesive-concrete interface indicates that the rubber promoted the penetration of adhesive into the concrete, which may further improved strengthening of concrete beams using FRP strips.

The finite element analysis method was carried out to study the stress profiles along the interface between CFRP strip and concrete. The numerical study indicates that both the shear and normal stress concentrations within about 15mm from the strip ends were reduced with increasing the rubber modifier content, while the stress profiles remain much the same for the rest of interface. Also, the thicker the CFRP strip used, the higher the stress concentrations.