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3 and only 11% selected membranes as one of the first three options for deck repair (5). NCHRP Report 297: Evaluation of Bridge Deck Protec- tive Strategies (6) reported the results of an investigation of five strategies for preventing corrosion in bridge decks. Waterproofing membranes with asphalt overlays were found to be effective in preventing salt intrusion into the underlying deck. Nevertheless, after 10 to 15 years of ser- vice, membranes had deteriorated as a result of aging and traffic. The report concluded that such membranes, when properly constructed, can prevent salt infiltration indefi- nitely, but their service life depended on the rate at which the membrane deteriorated. Babaie and Hawkins (6) explained that the accumulation of water above the membrane in the bottom portion of the asphaltic concrete was the primary cause of deterioration. This phenomenon, combined with freezing and thawing and repeated hydraulic pressure from traffic, weakens both the bottom layer of the asphalt and the bond between the asphal- tic concrete and the membrane. NCHRP Synthesis of Highway Practice 220: Waterproof- ing Membranes for Concrete Bridge Decks (5) stated that 25% of state highway agencies reported using membranes on new bridge decks. The synthesis also reported that agencies are sharply divided on the merits of waterproof- ing bridge decks. Reasons given for not using membranes included the inability to inspect the top surface of the deck, poor performance of experimental installations, and short service life of asphalt overlays. Other agencies reported that membranes were cost-effective in new construction, and especially so in rehabilitation. In a survey for NCHRP Synthesis 333: Concrete Bridge Deck Performance (7), respondents were asked to identify which waterproofing membrane systems they had used in the past and which they were using in 2004. The infor- mation identified that the only major change in the use of membranes had been a reduction in the number of agencies using preformed systems with asphalt-impregnated fab- ric, asphalt-laminated board, and polymers. The number of agencies using elastomer preformed systems and liquid systems remained about the same. In a rating of 1 to 5 for CHAPTER ONE INTRODUCTION BACKGROUND AND HISTORY Concrete bridge deck deterioration is one of the most extensive maintenance problems affecting the service life of bridges. Moisture and chloride intrusion can accelerate concrete bridge deck distress through corrosion of the steel reinforcement. A 2009 International Scan, Assuring Bridge Safety and Serviceability in Europe (1), found that European agencies consistently reported success incorporating water- proofing membranes into concrete bridge deck construction to both extend service life and delay the need to rehabilitate or replace bridge decks. In contrast, their general use in the United States remains limited. The first NCHRP synthesis report on bridge deck dura- bility, NCHRP Synthesis of Highway Practice 4: Concrete Bridge Durability (2), reported that bridge deck deteriora- tion was a major maintenance item, with the most commonly reported conditions being cracking, scaling, and spalling. Spalling was considered to be the most serious defect, with the cause attributed to corrosion of the reinforcing steel. The same report stated that the use of an impermeable inter- layer membrane had won favor throughout the country, with Maine, Massachusetts, New Hampshire, and Rhode Island specifying it for all important bridges. California, Illinois, Michigan, Ohio, and Tennessee were specifying membranes on selected bridges. In 1976, the FHWA published a policy requiring all fed- eral-aid system structures that might be damaged by deicing salts to apply a deck protective system (3). One option was to use a waterproofing membrane. The market for waterproof- ing systems expanded as new products were introduced and put to use. A second NCHRP synthesis dealing with durability of concrete bridges, NCHRP Synthesis of Highway Practice 57: Durability of Concrete Bridge Decks (4), reported that concrete bridge deck durability continued to be a problem because of corrosion of steel reinforcement. Membranes were reported to be available in a variety of systems; however, field experience had been highly variable, lead- ing to doubt about their long-term performance. In a 1977 survey, only 19% of the respondents indicated that mem- branes were the preferred protective system on new decks,
4 laminated board systems (5). A 2003 survey indicated that the most frequently used materials were bituminous for con- structed-in-place systems and asphalt-impregnated fabric for preformed systems. RECENT USAGE In the survey for this synthesis, 34 of the 53 respondents reported that they have installed waterproofing membranes on concrete bridge decks since 1994. Of the 34, 3 respon- dents have discontinued their use, 4 continue to specify them only for new concrete bridge decks, 11 specify them for only existing bridge decks, and 16 specify them for both. Overall, more respondents use them on existing bridge decks than new bridge decks. Most respondents indicated that the use of waterproofing membranes is about the same as in previous years. Based on the survey, the reported use on new decks only, existing decks only, or both types in the United States is illustrated in Figure 1. Figure 2 shows similar data from NCHRP Synthesis 220. systems performance, where 1 = excellent and 5 = poor, all membranes received an average rating between 2.6 and 3.3. MEMBRANE SYSTEMS A membrane is a barrier placed on top of the concrete and then protected by another material that functions as the riding sur- face. As such, the waterproofing membrane is only one com- ponent in a waterproofing system (5). Other components are used to improve adhesion of the membrane to the deck and to the protective riding surface. Inadequate performance by any component can result in poor performance of the system, which adds to the complexity of the system and its specifications. In general, waterproofing membrane systems can be divided into constructed-in-place systems or preformed membrane systems. Constructed-in-place systems can be subdivided into bituminous and resinous liquid-sprayed sys- tems. Preformed membrane systems can be subdivided into asphalt-impregnated fabric, polymer, elastomer, and asphalt- FIGURE 1 Current usage of waterproofing membranes in the United States.
5 The three states that have discontinued the use of water- proofing membranes provided various reasons. New Jersey indicated that it has discontinued the use of waterproofing membranes in favor of an impervious bridge deck water- proofing surface course. The specification does not permit the use of dynamic rollers to compact the hot mix asphalt overlay on bridge decks, which has created some issues about the porosity of the overlay. The use of a bridge deck waterproofing surface course avoids the issue because it can be compacted using a static roller. New Mexico reported that membranes have not worked well, resulting in water and salt being trapped between the asphalt and the deck. With subsequent freeze-thaw cycles, the asphalt spalls off and the deck deteriorates. When used on adjacent box beam bridges, the membranes cracked at the interface between the box beams, allowing water and salt to penetrate. New Mexico now prefers to use a concrete deck with reinforcement on these types of structures. Texas reported that it does not recommend placing asphalt on bridge decks and does not use proprietary waterproofing systems. Its waterproofing system consists of an asphalt oil followed by the application of two courses of rock. In Canada, New Brunswick reported that it discontin- ued the use of two self-adhesive preformed systems after concerns were raised about a number of debonding fail- ures. Quebec reported that it discontinued the use of cer- tain spray-applied liquid systems because of the difficulty of maintaining the required thickness. Both provinces continue to use other types of membranes. NCHRP Synthesis 220 contained a table showing the results of four surveys between 1974 and 1994 about the use of waterproofing membranes on new or existing bridge decks. Table 1 reproduces a portion of this table, along with data obtained from the synthesis survey. In 1994, it was con- cluded that the use of waterproofing membranes had declined FIGURE 2 Usage of waterproofing membranes in the United States, 1992 [Source: Adapted from Manning 1995 (5)].
6 in the previous 20 years. It now appears that the decline has bottomed out for both new and existing bridge decks, as the percentages for 2011 and 1994 are almost identical. It is also evident that more states continue to use waterproofing mem- branes on existing bridge decks than new bridge decks. One observation from the survey is that waterproofing membranes are used proportionately more in Canada than in the United States. Nine of 10 respondents from Canada reported their use on either new or existing bridge decks, com- pared with 25 of 43 respondents (58%) in the United States. A similar observation was made in NCHRP Synthesis 220. Agencies that do not use or have discontinued their use of waterproofing membranes provided numerous reasons for their decision, including the following: â¢ Do not use deicing salts on bridge decks or experience only a few freeze-thaw cycles and, therefore, see no benefit to using a waterproofing membrane. â¢ Have experienced poor performance of waterproofing membranes in the past. â¢ Have adopted the use of alternative deck protection strategies such as concrete overlays or full-depth low permeability concrete. â¢ Prefer to have an exposed concrete deck for easy visual inspection of any deterioration. With a waterproof- ing membrane, the concrete deck surface cannot be inspected. Some agencies responded that they limit the use of water- proofing membranes to certain types of superstructures such as voided slabs or deck bulb-tees or only use waterproofing mem- branes to extend the life of an existing bridge for a few years. SCOPE For the purpose of this synthesis, a waterproofing mem- brane is defined as a thin impermeable layer that is used in conjunction with a hot mix asphalt wearing surface. This study updates NCHRP Synthesis 220: Waterproofing Membranes for Concrete Bridge Decks (5). Consequently, it mainly includes information that has been published since 1994. The synthesis documents information related to materials, specification requirements, design details, application methods, construction inspection, system per- formance, and costs of waterproofing membranes for both new and existing bridge decks. In particular, it identifies domestically available materials, processes, specifications, and installation practices that have been reported. It is intended to help practitioners and bridge owners determine the appropriate use of membranes as an alternative to other bridge deck protection strategies. The information in the synthesis was gathered from literature reviews and surveys of highway agencies in the United States through the AASHTO Highway Subcommit- tee on Bridges and Structures and in the Canadian provinces through the Transportation Association of Canada. Some information about European and Asian systems and prac- tices is included. The remaining text of this synthesis is organized as follows. Chapter two identifies and discusses items related to the use of waterproofing membrane systems with new construc- tion and existing bridge decks. These include materials used in membrane systems, materials and construction specifica- tions, design issues, construction and inspection details and practices, observed performance, and costs. Chapter three describes laboratory testing methods, field evaluation methods, and recent research. Chapter four summarizes the findings from the informa- tion collected for this synthesis. It includes a list of the prac- tices that are used with waterproofing membrane systems for concrete bridge decks. Important knowledge gaps that are worthy of research are identified. Appendix A provides the survey questionnaire, and Appendix B summarizes the responses to the questionnaire. TABLE 1 STATE AGENCY RESPONSE TO VARIOUS SURVEYS ON THE USE OF MEMBRANES New Construction Existing Bridge Decks 19741 19771 19861 19941 20112 19771 19891 19941 20112 Membrane use % 74 69 53 25 26 58 51 46 47 No. of Responses 42 48 45 48 43 48 47 48 43 1 From NCHRP Synthesis 220 (Manning 1995). 2 From survey for this synthesis.