Ductility in FRP rods for concrete reinforcement by interfacial shearing.

Non-corrosive reinforcement of concrete provides great potential for reducing life cycle costs (LCC) of highway infrastructure (bridge decks and columns, light-standards, dividers) and concrete structures near water (piers, retaining walls, platforms). This is especially important in areas where salts are common (cold weather road salting, coastal regions) and is achieved by extending the life of structures and the period between major repairs. Costs of infrastructure rehabilitation due to corrosion of reinforcement are estimated to be $1.2 billion dollars in Ontario in the next few years, and up to 40% of all annual infrastructure costs in the province of Quebec. Efforts to reduce the frequency of repair and replacement of ageing structures include using epoxy coating of the reinforcing bar (rebar), cathodic protection, alternate types of steel and fibre reinforced polymer (FRP) rebar. Of these, FRP rebar appears to be the most promising. The limitation of FRP rebar is the low maximum strain and linear behaviour up to failure. Prior attempts at increasing the ductility and producing non-linear behaviour have had limited success. Maximum strain remains limited to that of the highest strain fibres available. Pseudo-ductility has been achieved by combining multiple fibre types having different material properties. The work described in this thesis focussed on non-traditional methods for achieving ductility in FRP rebars by taking advantage of the frictional interface of two materials. Two methods were tested. The first employed a solid inner-core with an over-wrap cut at regular intervals and relied on the rebar pulling out of the concrete at sustained load. Rods were tested in concrete beams under bending loads. Sustained load was achieved for significant pull-out. The second method combined continuous fibres with discontinuous meso-rods wherein the continuous fibres provide initial stiffness and maximum strength and the discontinuous meso-rods provide high-ductility via fibre pull-out. A concept model using aligned short steel fibres was manufactured and tested. Load-displacement behaviour showed substantial local elongation. Prototype models using carbon fibres were manufactured and tested. Specimens showed evidence of fibre pull-out. Future specimens should employ an intermediate material with a controlled and repeatable shear strength for the interface