This paper describes the technique of increasing beam strength by means of externally applied reinforcing steel plates, bonded by means of epoxy-resin adhesive. Test methods, application data, and some indication of preferred resin formulation are given. Steel plates are bonded to the beams by means of epoxy-resin paste adhesive. During curing of the resin the plates are held in place by clamps and/or bolts. This provides an inexpensive method of restoring or upgrading the strength of damaged or substrength concrete bridge and similar beams. To date, results have proved entirely satisfactory, but possible dangers of corrosion on the steel-concrete interface are being investigated. Further work is foreseen that will employ new materials and methods of application and enlarge the scope of the process.

The use of epoxy-resin adhesives in bridge construction and repair is well known< 11£). Spall repair compounds, rebar adhesives, new-to-old concrete bonding, and the bonding of precast units have been used for more than 20 years. In 1964, the accidental omission of reinforcing steelwork in an apartment complex in Durban, South Africa, resulted in the first recorded application of malleable steel plates bonded to the basement beams in order to replace the missing bars. Research and control operations were carried out by the University of Natal (}). Many further contracts have been carried out in South Africa, eg, on bridges and in a damaged multistory parking garage. According to current practice in South Africa, typical specifications call for the adhesive to be gray and have the consistency of a thick paste. The maximum vertical wet film is 15 mm, the thickness of the wet film is unlimited, the minimum pot life is 1 h, the curing time at 62 F is several days, and the minimum shelf life is 12 months: application is by trowel. The mechanical properties of the adhesive after full cure are a minimum compressive strength of 80 MPa, a minimum tensile strength of 11 MPa, and a minimum shear strength of 10 MPa. The procedure is as follows: