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Near surface mounted reinforcement

The technique of near-surface mounted reinforcement for strengthening concrete structures is currently being developed as an alternative to externally bonded fibre composite materials. The process involves cutting a series of shallow grooves in the concrete surface in the required direction. (The depth of the groove must obviously be less than the cover so that the existing reinforcement is not damaged.) The grooves are partially filled with epoxy mortar into which pultruded carbon fibre composite rods or strips are pressed. The remainder of the groove is then filled with epoxy mortar and the surface levelled. The approach can be used to increase the flexural (bending) of beams and slabs, or the shear capacity of beams. It can also be used for strengthening concrete masonry walls.

As the fibre composite material is embedded in the concrete, it is less susceptible to damage, for example by fire or vandalism, than material bonded to the surface. It is obviously very appropriate for strengthening the top surfaces of slabs, where externally bonded fibre composites would require a protective layer; damage may be caused to the composite if it is necessary to remove the protective layer at a later date. A further potential advantage of the technique over the use of externally bonded fibre composite is that no preparation of the concrete surface is required. Clearly one limitation on the technique is the need to have sufficient cover to the existing reinforcement to allow the grooves to be cut without the risk of damaging the steel.

Acknowledgement: The Concrete Society

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TR55 Design guidance for strengthening concrete structures using fibre composite materials