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27 CHAPTER FOUR CONCLUSIONS AND RESEARCH NEEDS CONCLUSIONS Information obtained from the survey and additional contact with several agencies that have used multiple sys- A waterproofing membrane is defined as a thin imperme- tems revealed little unbiased literature and data about the able membrane that is used in conjunction with a hot-mix performance of different systems. Although there were asphalt wearing surface to protect the deck concrete from reports about products failing to work properly on individ- the penetration of moisture and deicing salts. Most Canadian ual bridges, there does not appear to be a general consensus provinces and many European countries require the use of across North America about the best materials to use. The waterproofing membrane on new bridge decks. In contrast, Canadian provinces, however, appear to have a preference about 60% of the U.S. state agencies use them, with greater for using rubberized asphalt membranes. usage on existing bridge decks than new bridges. Waterproofing systems consisting of either constructed- The number of states and provinces using waterproof- in-place membrane systems or preformed membrane systems ing membranes on concrete bridge decks has not changed are addressed in the AASHTO LRFD Bridge Construc- significantly since NCHRP Synthesis 220 was published in tion Specifications. The individual materials used in both 1995. Most of the states and provinces that did not use them systems are required to conform to various ASTM speci- in 1994 are still not using them today. Reasons these agen- fications. State specifications are similar to the AASHTO cies do not use them include the nonuse of deicing salts, poor specifications, with some states providing more details and performance of membranes in the past, the use of alternative others providing fewer. Three major differences were noted deck protection strategies, and the preference for having an between the U.S. state and Canadian province specifications: exposed concrete deck to observe any deterioration. 1. Canadian specifications generally require the use The survey identified 23 different proprietary products of hot-applied rubberized asphalt, whereas the U.S. that have been used in the past 16 years. Most are still specifications permit other types of membranes. available today. The systems can be classified as preformed sheet systems or liquid systems. Preformed sheet systems 2. Some Canadian specifications required rubber mem- are often rolled into place and bonded to the concrete deck branes or reinforcing fabric over cracks or joints using a pressure-sensitive adhesive on the sheet or through before applying the membrane. the use of heat. Liquid systems are applied either hot or cold using spray equipment or by hand using rollers and 3. Most Canadian specifications require the use of pro- squeegees. Liquid systems may include a layer of reinforc- tection board, whereas U.S. specifications do not. ing fabric. Both systems use a tack coat between the mem- brane and the asphalt overlay to enhance the bond between The survey conducted for this synthesis identified the fol- the materials. lowing findings: Waterproofing membranes are not expected to last longer Agencies have a broad range of criteria for using mem- than the asphalt wearing surface, including one resurfac- branes, ranging from standard practice to temporary fixes. ing of the asphalt overlay. To achieve this, the initial asphalt The three primary reasons for selecting a particular thickness has to be sufficient to allow the top surface to be membrane are track record of previous installations, milled without damaging the membrane. The expected ser- cost, and desired service life. vice life of waterproofing membranes is generally 16 to 20 Approximately 50% of the agencies that use water- years when installed on new bridge decks and anywhere proofing membranes do not have standard details relat- between 6 and 20 years when installed on existing bridge ing to their installation. In many cases, the installation decks. From the information provided in the survey, it could has to conform to the manufacturer's procedures. not be determined whether preformed sheet systems or liq- Approximately 60% of the agencies that use water- uid systems have a longer service life. proofing membranes on new bridge decks have specifi-