Strengthening concrete beams using fibre reinforced polymer

In the last decade, the use of fibre reinforced polymers (FRP’s) as a preferred method of retrofitting existing structures has dramatically increased. This has brought about improvements in the mechanical properties of the materials and greater options for engineers and designers. This research has determined the most suitable fibre material to provide a maximum increase in structural performance at the lowest possible cost. Carbon fibre sheet and yarn were used. A unidirectional CFRP sheet and yarn had a cotton sheath attached that was been designed to promote resin impregnation and thus improved bond performance. The test methodology was to statically test concrete beams with surface applied FRP to comparatively examine the flexural strength and toughness. Sixteen beams were manufactured, eight with rebar and eight plain. Carbon fibre sheet and carbon fibre yarn was applied to all beams in equal proportions. The theoretical moment capacity was calculated for the steel reinforced beams using Eurocode 2 and compared against the actual moment capacity derived from the three point loading test. The findings displayed a tendency for higher flexural strength, moment capacity and toughness due to the surface application of FRP composite sheet and yarn. The carbon fibre sheet provided the most suitable form of retrofitted reinforcement. However the loose yarn was 25% cheaper than the sheet and may be a consideration where maximum performance is not an issue. The beam performance was dependant upon the effective epoxy bond between the carbon fibre sheet and the concrete surface and this is a key area for further research.