It is currently a requirement that when concrete bridge decks are re-waterproofed, repairs to the surface are needed so that the waterproofing is applied to a finish equivalent to the U4 finish defined in the Specification for Highway Works. A study has been carried out to assess whether lengthy and costly closures to make the repairs can be avoided by applying waterproofing directly to rough or damaged concrete surfaces. The most frequently occurring defects on bridge decks were identified and ranked according to their frequency, severity, difficulty to repair and cause of delays. Some defects must be repaired prior to waterproofing so the study focussed on other types. Finite element analyses determined the effect of increasing the thickness of the waterproofing membrane in large depressions. The maximum principal strains induced in surfacing overlaying a waterproofing system were calculated and fatigue lives were estimated. A laboratory investigation determined the ease of application of two spray-applied systems and a ‘pour and roll’ sheet system to concrete slabs with small depressions, small holes and ridges. The performance of the systems applied to slabs with defects and those with a U4 finish were compared. Tensile adhesion tests were carried out and the thickness of the membrane of the spray-applied systems was measured. The test results demonstrated that satisfactory waterproofing performance can be achieved by applying waterproofing to some defects, although the thickness of the membrane of the spray-applied systems was not easy to control and the defects were filled with bonding bitumen prior to the application of the sheet system. The benefits and costs of waterproofing a non-U4 finish without making repairs was assessed. The overall time savings if concrete repairs are not made before waterproofing a non-U4 finish may not be realised if other bridge works take longer than the time taken for concrete repairs to be made and cure. However, the use of rapid curing repair materials is likely to bring similar if not greater benefits than waterproofing without making repairs. A number of clauses are recommended for inclusion in the Specification for Highway Works.

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