Fibre Reinforced Plastic (FRP) materials for concrete reinforcement in highway structures - Accelerated tests and durability evaluation

Corrosion induced damage of steel reinforced concrete structures is a serious concern to highway authorities. Fibre Reinforced Plastic (FRP) materials are being considered as one of the non-corrosive alternatives to conventional reinforcing steel. Accelerated Laboratory tests were performed in simulated concrete pore solutions of pH 12 and 13.5 to evaluate the long term durability characteristics of FRP. Experimentally produced basalt fibre reinforced plastic (BFRP) grid and commercially available carbon fibre reinforced platstic (CFRP) grid and glass fibre reinforced plastic (GFRP) in grid and rebar forms were used in this investigation. Retention of tensile properties, morphological and compositional changes in FRP, glass, basalt and carbon fibres were studied. Core samples retrieved from a bridge deck slab and barrier wall reinforced with CFRP and CFRP were also examined for any changes due to service exposure of nearly 20 months. Semi-quantitative analysis of the mineral residue from the composites and the glass and basalt fibres was also performed with a view to correlate the durability characteristics to the composition. The results show that the resistance to alkaline exposure of the experimentally produced BFRP composite was poor. The results of some of the GFRP rebar samples based on vinyl ester resin system were promising when the accelerated test/treatment was performed on unstressed samples. Pretensioned GFRP specimens showed 3 - 4 fold increase in deterioration rate compared to the unstressed samples in the accelerated tests. Pretensionig of FRP prior to alkaline treatment may be necessary, for the selection of FRP materials for use in load bearing bridge components. SEM and EDX studies revealed that the GFRP and CFRP grid specimens obtained from the bridge deck and barrier wall have voids and exposed fibres which could be potential sites for the onset of deterioration on prolonged exposure to service conditions.