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6 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. in the previous 20 years. It now appears that the decline has Membranes for Concrete Bridge Decks (5). Consequently, bottomed out for both new and existing bridge decks, as the it mainly includes information that has been published percentages for 2011 and 1994 are almost identical. It is also since 1994. The synthesis documents information related evident that more states continue to use waterproofing mem- to materials, specification requirements, design details, branes on existing bridge decks than new bridge decks. application methods, construction inspection, system per- formance, and costs of waterproofing membranes for both One observation from the survey is that waterproofing new and existing bridge decks. In particular, it identifies membranes are used proportionately more in Canada than domestically available materials, processes, specifications, in the United States. Nine of 10 respondents from Canada and installation practices that have been reported. It is reported their use on either new or existing bridge decks, com- intended to help practitioners and bridge owners determine pared with 25 of 43 respondents (58%) in the United States. the appropriate use of membranes as an alternative to other A similar observation was made in NCHRP Synthesis 220. bridge deck protection strategies. Agencies that do not use or have discontinued their use The information in the synthesis was gathered from of waterproofing membranes provided numerous reasons for literature reviews and surveys of highway agencies in the their decision, including the following: United States through the AASHTO Highway Subcommit- tee on Bridges and Structures and in the Canadian provinces · Do not use deicing salts on bridge decks or experience through the Transportation Association of Canada. Some only a few freeze-thaw cycles and, therefore, see no information about European and Asian systems and prac- benefit to using a waterproofing membrane. tices is included. · Have experienced poor performance of waterproofing membranes in the past. The remaining text of this synthesis is organized as · Have adopted the use of alternative deck protection follows. strategies such as concrete overlays or full-depth low permeability concrete. Chapter two identifies and discusses items related to the · Prefer to have an exposed concrete deck for easy visual use of waterproofing membrane systems with new construc- inspection of any deterioration. With a waterproof- tion and existing bridge decks. These include materials used ing membrane, the concrete deck surface cannot be in membrane systems, materials and construction specifica- inspected. tions, design issues, construction and inspection details and practices, observed performance, and costs. Some agencies responded that they limit the use of water- proofing membranes to certain types of superstructures such as Chapter three describes laboratory testing methods, field voided slabs or deck bulb-tees or only use waterproofing mem- evaluation methods, and recent research. branes to extend the life of an existing bridge for a few years. Chapter four summarizes the findings from the informa- tion collected for this synthesis. It includes a list of the prac- SCOPE tices that are used with waterproofing membrane systems for concrete bridge decks. Important knowledge gaps that are For the purpose of this synthesis, a waterproofing mem- worthy of research are identified. brane is defined as a thin impermeable layer that is used in conjunction with a hot mix asphalt wearing surface. Appendix A provides the survey questionnaire, and This study updates NCHRP Synthesis 220: Waterproofing Appendix B summarizes the responses to the questionnaire.