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7 CHAPTER TWO WATERPROOFING MEMBRANE SYSTEMS As depicted in Figure 4, liquid systems generally consist of application of a primer followed by application of the membrane. The membrane may be placed using either spray equipment or rollers and squeegees. The membranes are applied either hot or cold depending on the manufacturerâs requirements. Liquid systems may or may not contain a reinforcing fabric. If a reinforcing fabric is used, one layer of liquid is sprayed. The fabric is then placed on the liquid and a second layer of liquid placed on top. A tack coat is generally used with liquid systems before placement of the asphalt overlay. Various manufacturers describe the materials used for the liquid systems as rubberized asphalt, two-component poly- mer, polyurethane, methyl methacrylate, rubber polymer, polymer-modified asphalt, or rubberized bitumen. Twelve states reported information on the products they have used. Six states have used only preformed systems, two have used only liquid systems, and four have used both systems. In Canada, two provinces reported using only preformed systems, two used only liquid systems, and three used both systems. According to Kepler et al. (8), three types of waterproof- ing membranes were used in North America in 2000: pre- formed sheets, liquid membranes, and built-up systems. Preformed sheets were most often used in the United States, while a liquid membrane of hot applied rubberized asphalt was used exclusively in Canada. It was also the most com- mon liquid membrane used in North America. MATERIALS As part of the survey for this synthesis, respondents were asked to identify what waterproofing products they had used since 1994. At least 23 different proprietary products from 19 companies have been used as waterproofing membrane systems on bridge decks in the United States and Canada since 1994. In the 1992 survey for NCHRP Synthesis 220, 22 different proprietary products were identified (5). In general, the systems can be classified as either preformed sheet sys- tems or liquid systems, with approximately an equal number of products of each type. As depicted in Figure 3, preformed sheet systems involve the application of a primer to the clean concrete deck to improve the adhesion of the membrane to the deck. This is followed by installation of the membrane. Most preformed systems identified in the survey included a self-adhesive backing on the membrane sheet. These sheets can be rolled into place and then bonded to the deck primer using a roller. In other systems, the membrane is bonded to the deck by heating the membrane using either a hand torch or a machine. After the membrane is installed, a tack coat is applied to the top surface to increase bond with the asphalt overlay. Materials used to form the sheet membranes are described by the various manufacturers as rubberized asphalt, bitumi- nous membrane, polymer-modified asphalt, modified bitu- men, polymeric membrane, or bitumen and polymers. FIGURE 3 Schematic of possible components of preformed systems.
8 SPECIFICATIONS AND STANDARDS AASHTO Specifications Waterproofing of concrete bridge decks is addressed as part of Section 21 of the AASHTO LRFD Bridge Construction Specifications (9). Waterproofing is defined as either a con- structed-in-place asphalt membrane system or a preformed membrane system, both of which include appropriate prim- ing materials and, when required, protective coverings. An asphalt membrane system consists of a coat of primer applied to the prepared surface, a firmly bonded membrane composed of two layers of saturated fabric, and three mop- pings of waterproofing asphalt with a protective cover when required. Materials listed for use with asphalt membrane systems are required to conform to one or more of the fol- lowing ASTM specifications published by ASTM Interna- tional, West Conshohocken, Pennsylvania: â¢ D41 Standard Specification for Asphalt Primer Used in Roofing, Dampproofing, and Waterproofing (used for the primer) â¢ D173 Standard Specification for Bitumen-Saturated Cotton Fabrics Used in Roofing Waterproofing (used for the reinforcing fabric) â¢ D449 Standard Specification for Asphalt Used in Dampproofing and Waterproofing (used for the asphalt) â¢ D3515 Standard Specifications for Woven Glass Fabric Treated with Asphalt (used for the reinforcing fabric). According to the AASHTO specifications, a pre- formed membrane system consists of a primer applied to the prepared surface, a single layer of adhering preformed membrane sheet, and a protective cover when required. Pre- formed membrane sheets consist of either the rubberized asphalt system or the modified bitumen type. Both types are required by the specifications to conform to minimum val- ues for the following properties: â¢ Tensile strength in machine direction per ASTM D882 Method A of 50 lb/in. for rubberized asphalt and 40 lb/ in. for modified bitumen. â¢ Percentage elongation at breach in machine direction per ASTM D882 Method A of 15% for rubberized asphalt and 10% for bitumen at 73.4Â°F. â¢ Pliability per ASTM D146 based on 180-degree bend over a 4-in. diameter mandrel at 10Â°F with no cracks. â¢ Minimum thickness of 65 mils for rubberized asphalt and 70 mils for modified bitumen. â¢ Softening point per ASTM D36 of 165Â°F for rubber- ized asphalt bitumen and 210Â°F for modified bitumen. All materials are required to be tested before shipment. For roadway surfaces of bridge decks, the protective cover to the waterproofing system is required to consist of a layer of special asphalt concrete as specified in the contract documents. The AASHTO specifications require that all concrete sur- faces to be waterproofed shall be reasonably smooth and free of foreign matter, projections, or holes. The surface shall be dry and have a temperature not less than 35Â°F or that recom- mended by the manufacturer, unless otherwise approved by the engineer. The specifications contain specific detailed instruc- tions for the installation of asphalt membrane waterproofing systems and preformed membrane waterproofing systems. State Specifications State specifications for waterproofing membranes are simi- lar to the AASHTO specifications. Table 2 reviews the dif- ferences identified in the state specifications. Some states specify more details than the AASHTO speci- fications; others specify fewer. Some of the states with fewer details rely heavily on the manufacturerâs recommended instal- lation procedures and the stateâs approved products list. Some state specifications are very specific about the generic type of FIGURE 4 Schematic of possible components of liquid systems.
9 materials that may be used. For example, the Massachusetts specifications allow the use of three types of membranes: 1. Coal tar emulsion reinforced with two plies of coated glass fabric 2. Hot applied rubberized asphalt membrane 3. Preformed sheet systems, either reinforced rubber- ized asphalt or reinforced tar and resin. System 2 is not used on grades steeper than 3%, and Sys- tem 3 is the only system acceptable for butted deck beams and adjacent box beams. For the two plies of coated glass fabric, the first ply is laid transverse to the center line of the bridge and the second layer parallel to the center line. The bituminous concrete protective course is to be applied within 24 hours after the membrane is installed. Virginia DOT specifications permit five systems: 1. System AâA primer and prefabricated membrane consisting of a laminate formed with suitably plasti- cized coal tar and reinforced with nonwoven synthetic fibers or glass fibers. 2. System BâA primer, mastic, and prefabricated mem- brane consisting of a laminate formed with rubberized asphalt and reinforced with synthetic fibers or mesh. 3. System CâA primer and prefabricated membrane consisting of a laminate formed with suitably plasti- cized asphalt, reinforced with open-weave fiberglass mesh and having a thin polyester top surface film. 4. System DâA hot-poured liquid elastomeric mem- brane with protective covering. 5. System EâA surface conditioner and a hot-applied rubberized asphalt membrane with protective covering. Based on the results of the survey and review of state specifications, the following is a summary of practices that are followed: 1. Pre-installation â¢ Require a manufacturerâs representative to be pres- ent when work is performed. One stateâs specifi- cations require that the representative be readily identified with a photo ID badge. â¢ Require that all work be performed by the manu- facturerâs certified personnel. It is important that the certified personnel and the manufacturerâs rep- resentative not be the same person. 2. Surface Preparation â¢ Ensure that the concrete surface is free of protru- sions and rough edges. â¢ Use abrasive blasting to remove all contamination from the deck, including all material from the pre- vious membrane. â¢ Do not use water to clean the deck, as the surface must be dry before the primer is applied. â¢ Clean surface with brooms, vacuum, or compressed air to remove all loose material before applying the membrane system. Some specifications require inspection and approval by the engineer before priming. Other states delegate the responsibility to the manufacturerâs representative. â¢ Reinforce or repair cracks before placing the membrane. 3. Installation of Waterproofing System â¢ Specify a minimum deck and/or air temperature before applying the membrane. Specified values range from 35Â°F to 50Â°F. For heat-welded mem- branes, one state requires the substrate temperature to be at least 5Â°F above the dew point. â¢ Specify a dry deck and application only in dry weather. One state specifies a surface moisture con- tent of less than 6% and requires the contractor to have a calibrated electronic surface moisture meter. â¢ Use a primer to enhance the bond between the con- crete deck and the membrane, where required by the specifications or the manufacturer. â¢ Install reinforcing membrane over cold joints and cracks in the concrete deck. â¢ Make a complete seal with the curb up to the depth of the asphaltic concrete overlay. â¢ Begin placement of preformed membranes on the low point of the deck and provide adequate lap between adjacent strips. This permits water to drain without accumulating against the seams. The TABLE 2 SUMMARY OF STATE SPECIFICATION REQUIREMENTS Property AASHTO States Minimum thickness for rubberized asphalt, mil. 65 50 and 60 Minimum thickness for modified bitu- men, mil. 70 50 and 60 Minimum deck or air temperature, Â°F 35 40, 45, and 50 Puncture resistance, lb â 40 and 200 Maximum permeance, perms â 0.10 Minimum longitudinal overlap, in. 2.0 2.0, 2.5, 3.0, 4.0, and 6.0 â = Not specified.
10 4. Quality Control â¢ Conduct adhesion bond testing for spray-applied membranes. â¢ Perform leak testing after the overlay is placed. The easiest time to do this is during a rainstorm. However, the United States does not have a stan- dard test procedure for leak testing. ASTM Standards The AASHTO and state specifications reference numerous ASTM standards for material specifications and test meth- ods. Table 3 lists the relevant standards identified from the survey and review of state specifications during the develop- ment of this synthesis. ASTM D4071 covers liquid applied, preformed, and built- up membrane systems and their application, including the bituminous wearing course. The practice provides a guide for the factors to be considered prior to waterproofing bridge decks with a membrane system. Guidance for the specifi- specified minimum overlap for longitudinal seams ranges from 2 to 6 in. â¢ Stagger membrane overlaps in the transverse direc- tion so that transverse seams do not line up. One state requires that end laps be in the direction of the paving operation. â¢ Repair any blisters that appear in the membrane before the overlay is placed, per the manufacturerâs recommendations. â¢ Prohibit or minimize traffic on the membrane and allow only rubber-tired vehicles until the overlay is placed, or use protection boards. â¢ Specify a minimum and maximum time between membrane application and the first layer of over- lay placement. The minimum time allows for the membrane to cure properly and depends on the manufacturerâs recommendations. The maximum time reduces the length of time that the membrane is exposed to potential damage. Specified values range from 1 to 5 days. â¢ Use a tack coat to enhance the bond between the membrane and the overlay. TABLE 3 ASTM STANDARDS RELATED TO WATERPROOFING MEMBRANES ASTM Designation Title D5 Standard Test Method for Penetration of Bituminous Materials D36/D36M Standard Test Method for Softening Point of Bitumen (Ring-and-Ball Apparatus) D41/D41M Standard Specification for Asphalt Primer Used in Roofing, Dampproofing, and Waterproofing D146 Standard Test Methods for Sampling and Testing Bitumen-Saturated Felts and Woven Fabrics for Roofing and Waterproofing D173 Standard Specification for Bitumen-Saturated Cotton Fabrics Used in Roofing and Waterproofing D449 Standard Specification for Asphalt Used in Dampproofing and Waterproofing D517 Standard Specification for Asphalt Plank D882 Standard Test Method for Tensile Properties of Thin Plastic Sheeting D1228 Withdrawn Standard Methods of Testing Asphalt Insulating Siding Surfaced with Mineral Granules (Withdrawn 1982) D1668 Standard Specification for Glass Fabrics (Woven and Treated) for Roofing and Waterproofing D1777 Standard Test Method for Thickness of Textile Materials D3236 Standard Test Method for Apparent Viscosity of Hot Melt Adhesives and Coating Materials D3515 Historical Standard Standard Specification for Hot-Mixed, Hot-Laid Bituminous Paving Mixtures D4071 Standard Practice for Use of Portland Cement Concrete Bridge Deck Water Barrier Membrane System D4541 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers D4632 Standard Test Method for Grab Breaking Load and Elongation of Geotextiles D4787 Standard Practice for Continuity Verification of Liquid or Sheet Linings Applied to Concrete Substrates D6153 Standard Specification for Materials for Bridge Deck Waterproofing Membrane Systems D6690 Standard Specification for Joint and Crack Sealants, Hot Applied, for Concrete and Asphalt Pavements E96/E96M Standard Test Methods for Water Vapor Transmission of Materials E154 Standard Test Method for Water Vapor Retarders Used in Contact with Earth Under Concrete Slabs, on Walls, or as Ground Cover
11 â¢ Canadian specifications generally require the use of hot applied rubberized asphalt for waterproofing mem- branes, whereas U.S. specifications permit other types of membranes. â¢ Some Canadian specifications require rubber mem- branes or reinforcing fabric to be installed over cracks and joints before the asphalt membrane is applied, as shown in Figure 5. â¢ Most Canadian specifications require the use of protec- tion board on top of the waterproofing membrane. United Kingdom Practices In 1999, the United Kingdom Department for Transport (UKDOT) formally issued BD47/99, Waterproofing and Surfacing of Concrete Bridge Decks (11). This standard gives the requirements for the design, materials, and work- manship for the waterproofing and surfacing of concrete decks for highway bridges. It specifies that decks of high- cation of materials, application of membrane systems, and placement of the bituminous wearing surface is provided. The standard is more of a checklist of items to address than a standard specification that spells out all the details. Canadian Specifications The specifications from six Canadian provinces were reviewed for this synthesis. In general, the different speci- fications contain similar provisions although the degree of detail varies. The Ontario provincial specification OPSS 914, Construction Specifications for Waterproofing Bridge Decks with Hot Applied Asphalt Membranes (10) provides the most details, including separate specifications for the hot applied rubberized asphalt membrane and the protec- tion board. The U.S. and Canadian specifications have three major differences. FIGURE 5 Waterproofing over joints and cracks (150 mm = 6 in.) [Source: Alberta Transportation].
12 â¢ Whenever an asphalt overlay is used. â¢ When replacing an asphalt overlay on an existing bridge at a location with freeze-thaw cycles. â¢ Not allowed on bridges with average daily traffic more than 10,000 vehicles or interstate bridges. â¢ Temporary overlay on existing bridge deck until funds are available to replace the deck. â¢ Only for new construction using adjacent box beams or cored slabs and average daily traffic less than 1,000 vehicles. â¢ When bridge deck condition rating is less than 6, chloride content is minimal, and an asphalt overlay is practical. â¢ Standard practice for all new bridge decks. â¢ Standard practice for rehabilitating existing bridge decks. In summary, the criteria range from standard practice for all new or existing bridge decks to temporary fixes for exist- ing bridge decks. Agencies were asked in the survey if they had specific reasons for selecting a particular membrane system. Twenty- two of 31 agencies (71%) replied that they did. Figure 6 sum- marizes their reasons. The predominant reasons for selecting a particular mem- brane were track record of previous installations, cost, and desired service life. In response to the survey, New Hampshire reported that from the 1970s until about 2000, it used peel-and-stick bar- rier systems. Since then, heat-applied membranes have been used on essentially every bridge deck built or rehabilitated. Spray-applied membranes were used from 1997 to 2005, but contractors now use heat-applied membranes. For bridges longer than about 100 ft, the machine method of applying the membrane is used. Otherwise, the membrane is manu- ally rolled out and heated with a torch to apply enough heat to develop adequate bond. DESIGN DETAILS North America In the survey for this synthesis, agencies were asked what standard details they have relating to the installa- tion of waterproofing membranes. Figure 7 presents their responses. Fourteen of the 25 U.S. state agencies (56%) that responded to this question indicated that they had no standard details for the items listed. In contrast, only two of nine Canadian provinces (Prince Edward Island and Saskatchewan) reported not having any. Several provinces have details available as part of their standard drawings, as illustrated in Figure 8. way bridges be protected to prevent surface water from coming into direct contact with the structural deck. This is achieved by providing adequate drainage and by water- proofing the upper surface of the deck. The waterproofing has to be sufficiently robust to resist transient vehicle load- ing, maintain good adhesion to the deck and the surfacing, be resistant to deicing salts, and possess long-term durabil- ity. Waterproofing systems are required to have a British Board of AgrÃ©ment Roads and Bridges AgrÃ©ment Certifi- cate or European equivalent before they may be installed on concrete bridge decks. The required tests for certifica- tion include tests on unbonded sheets, boards, and the film of liquid-applied membranes and tests on waterproofing membranes or systems bonded to concrete. In addition, a site trial is required after all laboratory tests have been suc- cessfully completed. BD47/99 (11) gives details of the tests and site trials. The standard does not permit the use of ventilating layers, partial bonding, or bond breakers with the waterproofing system. All systems are to be terminated in a chase. Where a prefabricated system is terminated in a chase, the rebate (return) is to be filled with a compatible sealant. Where a liq- uid-applied membrane is used, the membrane is to be taken into the chase but a sealant is not required. The membrane is to be protected from subsequent construction operations with a 20-mm (0.8-in.) nominal thickness of additional pro- tective layer consisting of bituminous material. The stan- dard also requires that new bridge decks be protected by a designed total minimum thickness of 100 mm (4 in.) of asphalt, excluding the thickness of the waterproofing system and the additional protective layer. According to the United Kingdom Waterproofing Asso- ciation website (12), the use of sheet membrane systems has been superseded by more modern liquid sprayed systems. It reports that the liquid systems consist of three elements: â¢ Primer used to penetrate and seal the concrete surface and enhance the bond of the membrane; â¢ Membrane applied in one or two coats; and â¢ Tack or bond coat to enhance the bond to the riding surface material. The association states that systems based on methyl meth- acrylate and polyurethane resins have proved successful. SELECTION CRITERIA In the survey for this synthesis, 17 of 32 agencies (53%) that use membranes reported that they have criteria for when waterproofing membranes are used on new bridge decks. The corresponding response for existing bridge decks was 20 of 33 (61%). The range of criteria was broad, and included the following:
13 Agencies were also asked what products were used in conjunction with waterproofing membranes. Figure 9 pres- ents their responses. More than 60% of the respondents use primers applied to the concrete and a tack coat before appli- cation of the asphalt. The products included under âOtherâ in Figure 9 were manufacturerâs recommendations, bleeder pipes, wick drains, and membrane reinforcing fabric. No respondents used venting layers, and only a few used separate adhesive to bond the membranes. Only one respon- dent reported the use of seepage layers to allow water that penetrates through the asphalt to drain more easily. Although 29% of the respondents indicate the use of protection board, 25% were Canadian provinces. Only one U.S. state (New Hampshire) reported its use, indicating a major difference between U.S. and Canadian practices. Europe and Asia A 1995 scanning review of European bridge structures iden- tified the use of bridge deck waterproofing systems as a sig- nificant observation (13). The following system from top to bottom was reported to be used in Denmark: â¢ 40-mm (1.6-in.) thick wearing course of asphalt con- crete or stone mastic asphalt, â¢ 40-mm (1.6-in.) thick binder course of modified asphalt concrete, â¢ 15- to 20-mm (0.6- to 0.8-in.) thick drainage layer of open-graded asphalt concrete, â¢ Two polymer-modified bitumen sheets fully bonded to the concrete, and Pe rc en ta ge R es po ns e 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
14 appropriate maintenance. The contractor is required to war- rant the deck protection system for 5 years. In France, the scanning review reported that all bridges received waterproofing consisting of mastic asphalt, either epoxy or polyurethane resins, a proprietary system of prefab- ricated sheets, or a proprietary system (13). Two types of mas- â¢ Epoxy-with-sand prime coat applied to the concrete deck after cleaning with abrasives. The prefabricated bitumen sheets are heated with an open flame, partially melting them, to bond them to the epoxy- primed concrete bridge deck and to other overlapping sheets. The system is expected to provide a 30-year service life with Pe rc en ta ge R es po ns e 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
15 (c) (d) 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]. (e) (a) (b)
16 in Japan and the use of liquid membranes and preformed sheet membranes in South Korea (14). This report did not provide details of these systems. A 2003 scanning study recommended a research project to study the success of waterproofing measures for protect- ing reinforced concrete members (15). A 2004 scanning study identified the use of a multiple- level corrosion protection system in Germany (16). The sys- tem shown in Figure 10 consists of the following layers of material from top to bottom: â¢ Asphalt wearing surface: 35- to 40-mm (1.4- to 1.6-in.), â¢ Asphalt protective layer: 35- to 40-mm (1.4- to 1.6-in.), â¢ Bituminous fabric sheet material welded to the concrete deck by heat and pressure: 4.5-to 8-mm (0.18- to 0.31-in.), â¢ Epoxy-coating primer, and â¢ Concrete cover to the steel reinforcement: 40-mm (1.6-in.). tic asphalt were used. One type consisted of an 8-mm (0.3-in.) thick layer of naturally occurring bituminous limestone mixed with refined bitumen applied over a dry surface primed with a 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 layer of 4-mm (0.2-in.) thick polymer asphalt mastic followed by a 26-mm (1-in.) thick layer of asphalt and gravel. The sheets were similar to those used in Denmark and consisted of poly- mer-modified bitumen reinforced with nonwoven polyester. The scanning review also reported on a proprietary sys- tem that consisted of the following from top to bottom (13): â¢ Layer of slate flakes to protect the membrane, â¢ 2-mm (0.1-in.) thick membrane of asphalt, â¢ 15- to 30-mm (0.6 to 1.5-in.) thick layer of bitumen, and â¢ Elastomer-modified emulsion. A 1997 scanning review of Asian bridge structures iden- tified the use of a waterproofing membrane below the asphalt Pe rc en ta ge R es po ns e 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
17 The system was reported to have been in use since the mid-1980s. Previously, a system of asphalt overlay on a sheet of mastic or glass fleece had been used, but it did not provide the necessary protection against the ingress of water con- taining deicing salts. A 2009 scanning study reported that the use of water- proofing membranes on concrete decks for corrosion pro- tection with epoxy underneath to seal cracking in the young concrete is standard practice throughout Europe (1). The use of waterproofing membranes on integral and continuous bridges is mandatory in the United Kingdom. Its engineers were reported to be highly confident of the enhanced per- formance that waterproofing membranes can provide and do not believe that other deck protection strategies can pre- clude the use of membranes. The standard deck design in the United Kingdom consists of 8- to 10-in. thick decks with a waterproofing membrane overlaid with asphalt. European practice, however, is not to use bare concrete decks or decks reinforced with epoxy-coated, stainless steel clad, or solid stainless steel bars. The 1995, 2004, and 2009 scanning studies recom- mended that further consideration be given to implementing the use of European waterproofing membrane systems in the United States (1, 13, 16). CONSTRUCTION AND INSPECTION According to the specifications reviewed for this synthesis, bridge deck waterproofing generally consists of the follow- ing steps: 1. Deck surface preparation, 2. Application of a primer to the concrete, 3. Installation of the waterproofing membrane, 4. Installation of protection board if used, 5. Repair of unacceptable areas resulting from mem- brane thickness inadequacies, and 6. Installation of asphaltic concrete riding surface. Figures 11 and 12 show various steps in the installation process. Results from the survey for this synthesis showed that 19 of 31 agencies (31%) have specifications for the surface preparation of new concrete bridge decks prior to applica- tion of the waterproofing membrane system, and 26 of 32 (81%) have them for existing bridge decks. These numbers reflect that more agencies use waterproofing membranes for existing bridge decks than for new bridge decks. In general, the specifications require that the concrete surface be free of protrusions or rough edges, all contamination be removed, and the surface be cleaned of all loose material without the use of water. Most specifications do not go into the means and methods to achieve the desired concrete surface. However, the New Hampshire specifications for surface preparation for use with heat-welded and liquid-spray barrier membranes provide more details. The specifications require that the deck be shot-blasted FIGURE 10 Bridge deck multiple-level protection system (16).
18 (b) (d) (e) (a) (c) FIGURE 11 Steps in the installation of a preformed sheet membrane: (a) Application of primer to the concrete deck, (b) Laying out the sheet membrane, (c) Heating the sheet membrane with a torch, (d) Sealing the overlap seams with a hand roller, (e) Completed membrane, (f) Compacting the hot mix asphalt [Source: Photos courtesy of Soprema for a, b, c, and e; New York State DOT for d and f]. (f)
19 (a) FIGURE 12 Application of a liquid membrane: (a) Hand spraying, (b) Machine spraying [Source: Photos courtesy of Stirling Lloyd for a; New York State DOT for b]. (b)
20 using self-contained, self-propelled equipment to achieve a con- sistent anchor profile that is free of sharp protrusions. The abra- sive media must consist of shot and grit sufficient to provide an angular surface profile that satisfies the requirements published by the International Concrete Repair Institute (17). Areas that are not accessible to self-propelled shot-blasting equipment are to be blasted with mineral grit or steel grit and air pressure sufficient to achieve the specified surface profile. The use of todayâs machinery for deck preparation and the availability of guidelines are improvements in both productivity and technol- ogy since NCHRP Synthesis 220 was published in 1995. The Saskatchewan specifications for surface preparation require that the concrete deck have spray-painted reference marks. Surface preparation is considered acceptable when the shot-blasting effort removes the painted reference marks completely from the concrete surface. Thirteen of 32 agencies (41%) have special inspection practices during installation of waterproofing membranes. Reported practices included monitoring, inspecting, or measuring surface preparation, membrane temperature, installation of protection boards if used, and conformity to standard drawings and specifications. PERFORMANCE Sohanghpurwala (18) described the advantages of mem- branes as follows: â¢ Membranes can be applied relatively rapidly, including application of the asphalt wearing surface. â¢ Membranes can bridge and prevent reflection of most moving cracks. â¢ The asphalt wearing surface can provide a good riding surface. â¢ Membranes can be applied to almost any deck geometry. He also described their limitations: â¢ The service life of the membranes may be limited by the wearing surface life. â¢ The system is not suitable for grades greater than 4% because bond capacity is limited for some systems and shoving and debonding can occur. The ideal waterproofing system should satisfy the follow- ing criteria: â¢ Impermeable to water, â¢ Good adhesion to the deck, â¢ Good adhesion to the protective riding surface, â¢ Tolerant of deck surface roughness, â¢ Resistant to traffic before application of the riding surface, â¢ Capable of bridging cracks in the concrete deck or opening of joints between adjacent precast members, â¢ Safe to apply and with low volatile emissions, â¢ Able to withstand high and low temperatures, â¢ Can be applied over a wide range of temperatures, and â¢ Extended service life of 50 to 100 years. He also listed the following performance criteria for waterproofing membranes: â¢ Chloride ion permeability: Protection of concrete from chloride ion intrusion is a major requirement for mem- branes. The report suggests that concrete that is water- proofed with a membrane be tested for permeability in accordance with the modified version of AASHTO T-277, Rapid Chloride Permeability Test, and the charge passed should not exceed 100 coulombs. â¢ Low-temperature flexibility: Membranes need to possess adequate flexibility to withstand the stresses caused by deck movements at low temperatures. No visible damage should occur when wrapping a sample of membrane around a 1-in. diameter mandrel at 9Â°F. â¢ Crack bridging: Cracks already in existence on the bridge deck will grow with temperature and load changes; the membrane must have elastic properties to be able to accommodate changes in width. The report suggests that membranes be able to bridge a crack width of 0.06 in. at 32Â°F. â¢ Bond strength: A strong adhesive bond between the membrane and wearing surface reduces deformation of the hot mix asphalt wearing surface layer by heavy wheel loading. The adequacy of the bond should be evaluated in both tension and shear, with minimum allowable values of 690 kPa (100 psi) and 172 kPa (25 psi), respectively. â¢ Resistance to indentation: Because of the thermoplastic nature of some membranes, indentation and puncture by aggregates may occur during application and roll- ing of the hot mix asphalt wearing surface. Testing for resistance to indentation should result in no penetra- tion at the expected maximum placement temperature. In the survey conducted for this synthesis, agencies were asked to identify the expected service lives of the water- proofing membranes they have used. Figure 13 presents the results. Most agencies expected 16 to 20 years for new bridge decks and 6 to 20 years for existing bridge decks. Based on the information supplied, it was not possible to determine whether prefabricated systems or liquids systems last longer. From the survey, the basis for the expected service lives can be summarized as follows: â¢ Expected life of the asphalt overlay, â¢ Past performance experience, â¢ Deck condition at time of installation, and â¢ One or two paving cycles with partial depth replace- ment of the asphalt.
21 bridge deck or beams when adjacent members are used. Defects listed as âOtherâ in Figure 14 included spalling and deterioration of the concrete deck below the membrane and insufficient thickness of membrane material. Xi et al. (19) reported on the inspection and evaluation of 16 bridges in Colorado that used a variety of corrosion protection methods, including 6 with asphalt membrane overlay. These bridges were constructed between 1958 and 1985. It is not reported when the asphalt membranes were placed. On one bridge that was repaired in 1978, the authors observed severe delamination and cracking of the membrane with significant reinforcement corrosion. Another bridge constructed in 1983 was reported to be in excellent condi- tion. Other bridges had corrosion of the bridge deck rein- forcement. On the basis of the inspection of all bridges, the authors found that the results were inconclusive for deter- mining whether epoxy-coated reinforcement, corrosion inhibitors, or membranes were the best solution. In 1985, two bridge decks in Kansas were restored using a nonwoven polypropylene membrane over an asphalt cement tack coat and topped with a 2-in.-thick wearing surface of hot mix asphalt (20). Annual surveys of these bridges con- sisted of visual inspection, chain drags to check for delami- Many agencies reported that the life of the membrane sys- tem is limited by the life of the asphalt. Sohanghpurwala (18) reported that the service life of hot mix asphalt with a pre- formed membrane would be less than 10 years if the overlay failed when used to extend the service life of existing bridge decks. Otherwise, the service life would be 25 years. Many types of defects may occur with waterproofing membrane systems used on new or existing concrete bridge decks. Figure 14 summarizes the defects that agencies reported in the survey. From the data shown in Figure 14, defects are more likely to occur when membranes are used on existing bridge decks than on new bridge decks. The defects most agen- cies reported were lack of adhesion between the membrane and the deck and between the membrane and the asphalt. In addition, about half of the agencies that use membrane sys- tems reported moisture penetration through the membrane without knowing the cause. Debonding of the membrane from either the concrete or asphalt is almost impossible to detect until it becomes evident through some defect on the asphalt surface. In contrast, water penetrating through the membrane and appearing on the underside of a bridge deck can be observed readily by deposits on the underside of the Pe rc en ta ge R es po ns e FIGURE 13 Expected service life of waterproofing membranes.
22 nations, resistivity readings, and crack measurements. The bridge decks were 14 and 15 years old at the time of their res- toration. Fourteen years after installation, both decks receive ratings of âgoodâ from the Kansas Department of Transpor- tation (KDOT) bridge management inspectors. These results are consistent with an earlier report (21) that looked at the condition of six bridge decks with asphalt interlayer membrane overlays installed between 1967 and 1971 after 20 to 25 years in service. Three different types of membranes were used: a preformed coal tar and polypro- pylene sheeting, a coal tar modified polyurethane elastomer membrane covered with an asphalt roofing sheet, and a non- woven polypropylene fabric. All three types of membranes were overlaid with hot-mix asphalt. The system using the nonwoven polypropylene membrane was the most effective. According to Distlehorst (20), Kansas currently uses asphalt membrane overlays only as a rehabilitation measure on existing bridge decks in very bad condition to extend the service life by 3 to 5 years. This was confirmed by the KDOT response to the survey for this synthesis. KDOT also uses asphalt membrane overlays to reduce the added dead load when deck rehabilitation is needed on bridges with total load limitations (20). COSTS Kepler et al. (8) compared the life cycle costs of 33 differ- ent corrosion protection systems and concluded that the use of hot rubberized asphalt membrane was the second-lowest- cost strategy, with assumed discount rates of 2% and 4%. At Pe rc en ta ge R es po ns e FIGURE 14 Observed types of defects in waterproofing membrane systems. a. Lack of adhesion between the waterproofing membrane and the concrete deck b. Lack of adhesion between the waterproofing membrane and the asphalt surface c. Punctured waterproofing membranes d. Membrane blistering e. Horizontal shear failure at the membrane f. Cracks in the waterproofing membrane g. Voids under the waterproofing membrane h. Reinforcement corrosion i. Moisture penetration through the membrane but cause unknown j. Other
23 a 6% discount rate, hot rubberized asphalt membrane was the sixth-lowest-cost strategy. The analysis was based on a service life of 75 years and assumed that the top 40 mm (1.6 in.) of the asphalt overlay was replaced at 20 and 60 years and the membrane and asphalt overlay replaced at 40 years. Hearn and Xi (22) evaluated the relative costs of the follow- ing four types of protection of reinforcement in bridge decks: â¢ Uncoated reinforcing bars with rigid overlay, â¢ Epoxy-coated reinforcing bars and a concrete surface sealer, â¢ Uncoated reinforcing bars protected with a waterproof- ing membrane and bituminous overlay, and â¢ Epoxy-coated reinforcing bars protected with a water- proofing membrane and bituminous overlay. The history of 82 bridge decks built between 1969 and 1991 was used to estimate the service life and to generate population models of service life. Costs were computed as present value, discounted annualized cost, and annual- ized cost without discount factors. Discount factors rang- ing from 2% to 10% were used. By all present value and annualized cost measures, decks with waterproofing mem- branes were the least expensive. This conclusion was not sensitive to the value of the discount factor but was influ- enced in part by the longer service life predicted for bridge decks with membranes. Distlehorst (20) provided estimates of relative annual costs of bridge deck overlays used in Kansas. She compared the cost of retrofit epoxy-coated reinforcement, Iowa system overlays, Kansas system overlays, and membrane overlays. She concluded that the membrane overlays, with an average cost of $0.12/ft2/year of service life based on 1979 dollars, were the most cost-effective rehabilitation technique. Liang et al. (23) reported that preformed sheet membranes with asphalt overlays have been used in Colorado. Hot rub- berized asphalt membranes and spray-applied liquid mem- branes are less expensive than preformed sheet membranes. In the survey for this synthesis, agencies were asked to provide unit costs for labor, equipment, and materials for waterproofing membranes systems used on new and existing bridge decks. The reported data showed a wide variation of costs within each state and between states. In the United States, reported bid prices ranged for $0.56 to $42.80/ft2. In Canada, reported costs ranged from C$1.69 to C$8.55/ft2. REPAIRS In the survey for this synthesis, agencies were asked if they had requirements or specifications for repair of membrane systems. Most respondents who answered this question indi- cated that they do not repair damaged membranes but would replace a part or all of the system depending on the sever- ity of the damage. Any damage caused before the asphalt overlay was placed would be repaired per the manufacturerâs recommendations.