Waterproofing bridge decks with non-U4 concrete finishes

The UK Highways Agency currently requires old or damaged concrete bridge decks to be repaired to provide a finish equivalent to the U4 finish defined in the Specification for Highway Works before they are re-waterproofed. Normally, cementitious or resinous repair products are used so that waterproofing membranes are fully supported by and firmly bonded to the substrate; and the minimum thickness of liquid-applied membranes is 2mm and they have no pinholes. Significant savings could be made if the waterproofing could be applied to rough or damaged surfaces without them being repaired. A laboratory study of small depressions, rough highly ridged finishes, and holes and voids was carried out. Large depressions were studied using finite element analysis. The investigation was based on concrete slabs cast using natural aggregates and lightweight coarse aggregates combined with CEM 1 cement. The results from slabs with defects were compared with the results from control slabs with a U4 finish. Three waterproofing systems were applied. After waterproofing, the resistance to pinholing and blistering due to out-gassing was determined by overlaying the slabs with hot sand to simulate the temperatures induced by asphalt during surfacing. Satisfactory performance was achieved by applying waterproofing directly over some of the defects but this could result in additional labour costs for the preparation of decks, grit blasting and additional cleaning. Additional labour and material costs are likely because of the additional time involved in extra priming, the application of the membrane over defects and the testing of spray-applied membranes for pin holes. The tensile failure stresses at the defects for both spray-applied systems were generally less than those for the U4 slabs but mostly at least three-fold the minimum requirement specified in the Departmental Standard BD 47/99 (0.3 MPa). The application time for the sheet waterproofing system was less affected by the presence of the defects but the sheet system took longer to apply than the spray-applied systems. It is considered that the decision on whether it is more cost effective to make repairs to an old bridge deck is dependent entirely on the condition of the bridge deck.

  • Authors:
    • CALDER, A J
    • Jordan, R W
    • POWELL, S M
  • Publication Date: 2009

Language

  • English

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 01155363
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Apr 23 2010 11:03AM