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12 way bridges be protected to prevent surface water from · Whenever an asphalt overlay is used. coming into direct contact with the structural deck. This · When replacing an asphalt overlay on an existing is achieved by providing adequate drainage and by water- bridge at a location with freeze-thaw cycles. proofing the upper surface of the deck. The waterproofing · Not allowed on bridges with average daily traffic more has to be sufficiently robust to resist transient vehicle load- than 10,000 vehicles or interstate bridges. ing, maintain good adhesion to the deck and the surfacing, · Temporary overlay on existing bridge deck until funds be resistant to deicing salts, and possess long-term durabil- are available to replace the deck. ity. Waterproofing systems are required to have a British · Only for new construction using adjacent box beams Board of Agrément Roads and Bridges Agrément Certifi- or cored slabs and average daily traffic less than 1,000 cate or European equivalent before they may be installed vehicles. on concrete bridge decks. The required tests for certifica- · When bridge deck condition rating is less than 6, tion include tests on unbonded sheets, boards, and the film chloride content is minimal, and an asphalt overlay is of liquid-applied membranes and tests on waterproofing practical. membranes or systems bonded to concrete. In addition, a · Standard practice for all new bridge decks. site trial is required after all laboratory tests have been suc- · Standard practice for rehabilitating existing bridge cessfully completed. BD47/99 (11) gives details of the tests decks. and site trials. In summary, the criteria range from standard practice for The standard does not permit the use of ventilating layers, all new or existing bridge decks to temporary fixes for exist- partial bonding, or bond breakers with the waterproofing ing bridge decks. system. All systems are to be terminated in a chase. Where a prefabricated system is terminated in a chase, the rebate Agencies were asked in the survey if they had specific (return) is to be filled with a compatible sealant. Where a liq- reasons for selecting a particular membrane system. Twenty- uid-applied membrane is used, the membrane is to be taken two of 31 agencies (71%) replied that they did. Figure 6 sum- into the chase but a sealant is not required. The membrane marizes their reasons. is to be protected from subsequent construction operations with a 20-mm (0.8-in.) nominal thickness of additional pro- The predominant reasons for selecting a particular mem- tective layer consisting of bituminous material. The stan- brane were track record of previous installations, cost, and dard also requires that new bridge decks be protected by desired service life. a designed total minimum thickness of 100 mm (4 in.) of asphalt, excluding the thickness of the waterproofing system In response to the survey, New Hampshire reported that and the additional protective layer. from the 1970s until about 2000, it used peel-and-stick bar- rier systems. Since then, heat-applied membranes have been According to the United Kingdom Waterproofing Asso- used on essentially every bridge deck built or rehabilitated. ciation website (12), the use of sheet membrane systems has Spray-applied membranes were used from 1997 to 2005, but been superseded by more modern liquid sprayed systems. contractors now use heat-applied membranes. For bridges It reports that the liquid systems consist of three elements: longer than about 100 ft, the machine method of applying the membrane is used. Otherwise, the membrane is manu- · Primer used to penetrate and seal the concrete surface ally rolled out and heated with a torch to apply enough heat and enhance the bond of the membrane; to develop adequate bond. · Membrane applied in one or two coats; and · Tack or bond coat to enhance the bond to the riding surface material. DESIGN DETAILS The association states that systems based on methyl meth- North America acrylate and polyurethane resins have proved successful. In the survey for this synthesis, agencies were asked what standard details they have relating to the installa- SELECTION CRITERIA tion of waterproofing membranes. Figure 7 presents their responses. Fourteen of the 25 U.S. state agencies (56%) In the survey for this synthesis, 17 of 32 agencies (53%) that that responded to this question indicated that they had no use membranes reported that they have criteria for when standard details for the items listed. In contrast, only two waterproofing membranes are used on new bridge decks. of nine Canadian provinces (Prince Edward Island and The corresponding response for existing bridge decks was Saskatchewan) reported not having any. Several provinces 20 of 33 (61%). The range of criteria was broad, and included have details available as part of their standard drawings, as the following: illustrated in Figure 8.
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13 Percentage Response FIGURE 6 Reasons for selecting a particular membrane system. a.Cost b. Speed of installation c. Staged construction options d. Surface preparation e. Track record of previous installations f. Desired service life g. Availability h. Coordination requirements i. Product support j. Other Agencies were also asked what products were used in Europe and Asia conjunction with waterproofing membranes. Figure 9 pres- ents their responses. More than 60% of the respondents use A 1995 scanning review of European bridge structures iden- primers applied to the concrete and a tack coat before appli- tified the use of bridge deck waterproofing systems as a sig- cation of the asphalt. The products included under "Other" nificant observation (13). The following system from top to in Figure 9 were manufacturer's recommendations, bleeder bottom was reported to be used in Denmark: pipes, wick drains, and membrane reinforcing fabric. · 40-mm (1.6-in.) thick wearing course of asphalt con- No respondents used venting layers, and only a few used crete or stone mastic asphalt, separate adhesive to bond the membranes. Only one respon- · 40-mm (1.6-in.) thick binder course of modified asphalt dent reported the use of seepage layers to allow water that concrete, penetrates through the asphalt to drain more easily. Although · 15- to 20-mm (0.6- to 0.8-in.) thick drainage layer of 29% of the respondents indicate the use of protection board, open-graded asphalt concrete, 25% were Canadian provinces. Only one U.S. state (New · Two polymer-modified bitumen sheets fully bonded to Hampshire) reported its use, indicating a major difference the concrete, and between U.S. and Canadian practices.
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14 · Epoxy-with-sand prime coat applied to the concrete appropriate maintenance. The contractor is required to war- deck after cleaning with abrasives. rant the deck protection system for 5 years. The prefabricated bitumen sheets are heated with an open In France, the scanning review reported that all bridges flame, partially melting them, to bond them to the epoxy- received waterproofing consisting of mastic asphalt, either primed concrete bridge deck and to other overlapping sheets. epoxy or polyurethane resins, a proprietary system of prefab- The system is expected to provide a 30-year service life with ricated sheets, or a proprietary system (13). Two types of mas- Percentage Response FIGURE 7 Standard details available for the installation of waterproofing membranes. a. Installing waterproofing membranes b. Terminating edges of membranes c. Curb details for membranes d.Concrete barrier details for use with membranes e. Over construction joints f. At expansion joints
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15 (a) (b) (c) (d) (e) FIGURE 8 Examples of details provided in standard drawings: (a) Composite deck, (b) Noncomposite deck, (c) Detail A, (d) Legend, (e) Drain pipe detail [Source : Alberta Transportation].
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16 Percentage Response FIGURE 9 Products used in conjunction with waterproofing membranes. a. Primers applied to the concrete b. Venting layers c. Separate adhesives to bond the membrane d. Seepage layers e. Protection board f. Tack coat g.Other tic asphalt were used. One type consisted of an 8-mm (0.3-in.) in Japan and the use of liquid membranes and preformed thick layer of naturally occurring bituminous limestone mixed sheet membranes in South Korea (14). This report did not with refined bitumen applied over a dry surface primed with a provide details of these systems. tack coat. The system was topped with a 22-mm (0.9-in.) thick layer of asphalt mixed with gravel. The other type consisted of A 2003 scanning study recommended a research project a layer of 4-mm (0.2-in.) thick polymer asphalt mastic followed to study the success of waterproofing measures for protect- by a 26-mm (1-in.) thick layer of asphalt and gravel. The sheets ing reinforced concrete members (15). were similar to those used in Denmark and consisted of poly- mer-modified bitumen reinforced with nonwoven polyester. A 2004 scanning study identified the use of a multiple- level corrosion protection system in Germany (16 ). The sys- The scanning review also reported on a proprietary sys- tem shown in Figure 10 consists of the following layers of tem that consisted of the following from top to bottom (13): material from top to bottom: · Layer of slate flakes to protect the membrane, · Asphalt wearing surface: 35- to 40-mm (1.4- to 1.6-in.), · 2-mm (0.1-in.) thick membrane of asphalt, · Asphalt protective layer: 35- to 40-mm (1.4- to 1.6-in.), · 15- to 30-mm (0.6 to 1.5-in.) thick layer of bitumen, and · Bituminous fabric sheet material welded to the concrete · Elastomer-modified emulsion. deck by heat and pressure: 4.5-to 8-mm (0.18- to 0.31-in.), · Epoxy-coating primer, and A 1997 scanning review of Asian bridge structures iden- · Concrete cover to the steel reinforcement: 40-mm tified the use of a waterproofing membrane below the asphalt (1.6-in.).