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SUMMARY WATERPROOFING MEMBRANES FOR CONCRETE BRIDGE DECKS Concrete bridge deck deterioration is one of the most extensive bridge maintenance prob- lems affecting the service life of bridges. One cause of the deterioration is the penetration of moisture and chlorides into the concrete with subsequent corrosion of the steel rein- forcement. The use of waterproofing membranes is one strategy to prevent moisture and chlorides from reaching the concrete by providing a barrier on the top of the concrete deck. The waterproofing membrane is then protected from the traffic by an asphalt overlay. The objective of this synthesis is to update NCHRP Synthesis of Highway Practice 220: Waterproofing Membranes for Concrete Bridge Decks on the same topic published in 1995. This synthesis documents information on materials, specification requirements, design details, application methods, system performance, and costs of waterproofing membranes used on new and existing bridge decks since 1995. The synthesis focuses on North Ameri- can practices with some information provided about systems used in Europe and Asia. Information for the synthesis was gathered from a survey sent to all U.S. state depart- ments of transportation (DOTs) and all Canadian provincial transportation agencies. The DOT survey achieved an 84% response rate (42 responses); the Canadian survey response rate was 83% (10 responses). Several agencies were contacted after the survey for addi- tional details. Information was also obtained from U.S. national specifications, state and provincial specifications, a literature review, and manufacturersâ literature. Key findings are described in the following paragraphs. Based on information collected for this synthesis, waterproofing membrane systems gen- erally consist of either preformed sheet systems or liquid systems. Preformed sheet systems are often rolled into place and bonded to the concrete deck using a pressure-sensitive adhe- sive on the sheet or through the use of heat to bond the membrane to the concrete deck. Liquid systems are applied as either hot or cold liquids and may include a layer of reinforcing fabric. All waterproofing systems use proprietary products; the agencies identified at least 23 differ- ent proprietary products used in the last 16 years. After installation, the membrane is covered with a layer of asphalt to protect the membrane and provide a riding surface. Primers are applied to the concrete deck to increase the bond between the concrete and the waterproofing membrane. A tack coat is used between the membrane and the asphalt overlay to increase the bond between these two materials. This report includes a list of practices that are used for the installation of waterproofing membranes (see chapter two). The survey and literature review found that most Canadian provinces and many Euro- pean countries require the use of waterproofing membranes on all new bridge decks. In contrast, only 60% of U.S. state agencies reported the use of waterproofing membranes. More states reported using them on existing bridge decks to prolong the service life rather than installing them on new bridge decks at the time of construction. The reasons agencies do not use waterproofing membranes include nonuse of deicing salts, poor performance of membranes in the past, the use of alternative deck protection strategies, and the preference for having an exposed concrete deck to observe any deterioration. However, many agencies
2 that do use them believe they provide a reliable protection strategy. The types of membranes used and the states that use them have not changed much since the 1994 survey. The survey identified that agencies have a broad range of criteria for when membranes are used, ranging from standard practices to temporary fixes. Waterproofing membrane types are selected for a variety of reasons, with the primary reasons being track record of previous installations, cost, and desired service life. Yet approximately 50% of the agencies that use waterproofing membranes do not have standard details relating to their installation. In many cases, the installation is required to conform to the manufacturerâs procedures. Agencies that used waterproofing membranes expect them to last 16 to 20 years when installed on new bridge decks and 6 to 20 years when installed on existing bridge decks. This expectation is often dictated by the service life of the asphalt wearing surface, which includes one resurfacing of the asphalt. Information obtained from the survey and additional contact with several agencies that have used multiple systems revealed little unbiased literature and data about the performance of different systems. Although there are reports about products failing to work properly on individual bridges, there does not appear to be a general consensus across North America about the best materials to use. The Canadian provinces, however, appear to have a prefer- ence for using rubberized asphalt membranes. The survey respondents identified several types of defects observed with waterproofing membranes. The predominant ones are a lack of adhesion between the membrane and the concrete deck, lack of adhesion between the membrane and the asphalt surface, and mois- ture penetrating through the membrane. All types of defects were more prominent with membranes applied to existing bridge decks than with membranes applied to new bridge decks. Most manufacturers recommend a primer on the concrete deck and a tack coat on the waterproofing membrane to improve the adhesion between the layers. The literature review identified only a limited number of articles about the use of water- proofing membranes published since NCHRP Synthesis 220 in 1995. Consequently, this synthesis relies heavily on analyses of information obtained from the survey and state and provincial specifications. The literature review and survey also identified that limited research on waterproofing membranes has been performed since 1995. This synthesis indentified gaps in the knowledge base that could be filled with the fol- lowing research: â¢ Conduct a more in-depth investigation of existing systems used in the United States and Canada, including site visits and meetings with owners who have installed mem- branes successfully and believe in their use as a deck protection strategy. â¢ Develop standard test methods to evaluate the overall performance of waterproofing membrane systems, to assess the quality of the installed system, and to determine whether the membrane is deteriorating during its service life.