Evaluation of tests on water-jet equipment

In Sweden, water-jetting, or hydrodemolition, has been used in concrete repair since the mid eighties. Properly used, water-jetting results in a sound, rough, and clean concrete surface providing beneficial circumstances for a bonded overlay or other repairs. The water-jet technique is considered to be selective, since it removes deteriorated concrete, but leaves sound concrete. In order to guarantee the excellent result that can be obtained by a properly conducted water-jet repair, the Swedish National Road Administration has demanded that water-jetting companies must carry out a specific test before removing concrete from Swedish bridges. The tests consist of two identical reinforced concrete slabs composed of concrete of two qualities. The low quality concrete is superposing the high quality concrete. The proportion between the qualities varies stepwise over the slab in the shape of two staircases. The aim of the test is to remove all low quality concrete without removing any high quality concrete. This defines the selectivity. Other test criteria are intact slab edges, limited number of pits, limited shadows below rebars, limited ridges below rebars, and sufficient surface roughness. The full paper describes the test procedure in detail, summarises the evaluation of the test results, identifies limitations in the test procedure, and suggests improvements.