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27 CHAPTER FOUR CONCLUSIONS AND RESEARCH NEEDS Information obtained from the survey and additional contact with several agencies that have used multiple sys- tems revealed little unbiased literature and data about the performance of different systems. Although there were reports about products failing to work properly on individ- ual 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 preference for using rubberized asphalt membranes. Waterproofing systems consisting of either constructed- in-place membrane systems or preformed membrane systems are addressed in the AASHTO LRFD Bridge Construc- tion Specifications. The individual materials used in both systems are required to conform to various ASTM speci- fications. State specifications are similar to the AASHTO specifications, with some states providing more details and others providing fewer. Three major differences were noted between the U.S. state and Canadian province specifications: 1. Canadian specifications generally require the use of hot-applied rubberized asphalt, whereas the U.S. specifications permit other types of membranes. 2. Some Canadian specifications required rubber mem- branes or reinforcing fabric over cracks or joints before applying the membrane. 3. Most Canadian specifications require the use of pro- tection board, whereas U.S. specifications do not. The survey conducted for this synthesis identified the fol- lowing findings: â¢ Agencies have a broad range of criteria for using mem- branes, ranging from standard practice to temporary fixes. â¢ The three primary reasons for selecting a particular membrane are track record of previous installations, cost, and desired service life. â¢ Approximately 50% of the agencies that use water- proofing membranes do not have standard details relat- ing to their installation. In many cases, the installation has to conform to the manufacturerâs procedures. â¢ Approximately 60% of the agencies that use water- proofing membranes on new bridge decks have specifi- CONCLUSIONS A waterproofing membrane is defined as a thin imperme- able membrane that is used in conjunction with a hot-mix asphalt wearing surface to protect the deck concrete from the penetration of moisture and deicing salts. Most Canadian provinces and many European countries require the use of waterproofing membrane on new bridge decks. In contrast, about 60% of the U.S. state agencies use them, with greater usage on existing bridge decks than new bridges. The number of states and provinces using waterproof- ing membranes on concrete bridge decks has not changed significantly since NCHRP Synthesis 220 was published in 1995. Most of the states and provinces that did not use them in 1994 are still not using them today. Reasons these agen- cies do not use them include the 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. The survey identified 23 different proprietary products that have been used in the past 16 years. Most are still available today. The systems can be classified as preformed sheet systems or liquid systems. Preformed sheet systems are often rolled into place and bonded to the concrete deck using a pressure-sensitive adhesive on the sheet or through the use of heat. Liquid systems are applied either hot or cold using spray equipment or by hand using rollers and squeegees. Liquid systems may include a layer of reinforc- ing fabric. Both systems use a tack coat between the mem- brane and the asphalt overlay to enhance the bond between the materials. Waterproofing membranes are not expected to last longer than the asphalt wearing surface, including one resurfac- ing of the asphalt overlay. To achieve this, the initial asphalt thickness has to be sufficient to allow the top surface to be milled without damaging the membrane. The expected ser- vice life of waterproofing membranes is generally 16 to 20 years when installed on new bridge decks and anywhere between 6 and 20 years when installed on existing bridge decks. From the information provided in the survey, it could not be determined whether preformed sheet systems or liq- uid systems have a longer service life.
28 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. 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. â¢ Stagger membrane overlaps in the transverse direction. â¢ Repair any blisters that appear in the membrane before the overlay is placed. â¢ Prohibit or minimize traffic on the membrane and allow only rubber-tired vehicles until the overlay is placed. â¢ Specify a minimum and maximum time between membrane application and the first layer of overlay placement. â¢ Use a tack coat to enhance the bond between the membrane and the overlay. 4. Quality Control â¢ Conduct adhesion bond testing for spray-applied membranes. â¢ Perform leak testing after the overlay is placed. No standard tests exist to evaluate the overall perfor- mance of waterproofing membrane systems, no reliable methods exist to assess the quality of the installed systems, and no proven techniques exist to determine any deteriora- tion of the membrane system during its service life. Conse- quently, it is not surprising that agencies with no experience in installing membranes are reluctant to start using them. On the other hand, agencies with experience believe they provide a reliable bridge deck protection strategy. Most Canadian provinces and many European and Asian countries that utilize waterproofing membranes believe that they are essential for the protection of bridge decks. FUTURE RESEARCH The information collected for this synthesis suggests a need to conduct a more in-depth investigation of systems used in the United States and Canada. This investigation would include site visits and meetings with owners who have installed membranes successfully and believe in their use as a deck protection strategy. It could be conducted as a state pooled fund research project by those states interested in enhancing their use of waterproofing membranes. Standard test methods should also be developed to evalu- ate the overall performance of proprietary waterproofing cations for the surface preparation. The corresponding number for existing bridge decks is 80%. â¢ The two major products used in conjunction with waterproofing membranes are primers applied to the concrete deck and tack coats applied to the membrane before placing the protective surface layer of asphalt. â¢ Although several types of defects have been observed with waterproofing systems, the three predominant ones are lack of adhesion between the waterproofing membrane and the concrete deck, lack of adhesion between the waterproofing membrane and the asphalt surface, and moisture penetration through the mem- brane. All types of defects were more prominent with membranes applied to existing bridge decks than with membranes applied to new bridge decks. â¢ Unit costs showed a wide range of values for mem- branes installed on either new or existing bridge decks. The literature review found that only a few articles about research and use of waterproofing membranes have been published since NCHRP Synthesis 220 in 1995. In addi- tion, the methods reported in 1994 to evaluate waterproof- ing membrane systems in the field still exist today, but no method has emerged as being universally acceptable. The review of state and provincial specifications identi- fied the following installation practices for waterproofing membranes: 1. Pre-installation â¢ Require a manufacturerâs representative to be pres- ent when work is performed. â¢ Require that all work be performed by the manu- facturerâs certified personnel. 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 any pre- vious membrane. â¢ Do not use water to clean the deck. â¢ Clean surface with brooms, vacuum, or compressed air to remove all loose material before applying the membrane system. 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. â¢ Specify a dry deck and application only in dry weather.
29 membrane systems, assess the quality of installed systems, and identify deterioration of the membrane system during its service life. Waterproofing membrane systems could then be included in the AASHTO National Transportation Product Evaluation Program. A TRB Maintenance Research Master Planning Work- shop was held in January 2000 to develop a 3-, 5-, and 10-year phased master plan of maintenance research needs (Transportation Research Circular E-C022 2000). Before the meeting, the TRB Highway Maintenance Committees prepared 60 research needs problem statements. The end result of the workshop was a series of recommended research projects and synthesis topics. TRB Committee A3C15â Corrosion developed and submitted the following research problem statement to the workshop: Performance Specification for Bridge Deck Water- proofing Membrane Systems Problem: Waterproofing membranes can be an effective method of protecting both the concrete and embedded reinforcement in new and exist- ing bridge decks. Except for a few states, membranes are used only sporadically in the United States, often to pro- vide only a short extension of service life on existing decks. NCHRP Synthesis Report 220, Waterproofing Membranes for Concrete Bridge Decks, noted that North American prac- tice has changed little in the past 20 years. The vast majority of membranes installed in the United States are preformed products, and the market is dominated by three products introduced in the 1970s. A 1995 FHWA scanning tour of bridge technology in Europe observed the broad range of materials and widespread use of waterproofing systems in protecting bridge decks in aggressive environments. The waterproofing membrane is only one component of waterproofing systems that may include primers, adhesives, protection board, tack coat, and bituminous concrete layers. The performance of the system is determined by the com- plex interaction of material factors, design details, and quality of construction. Research is required to define performance requirements for waterproofing systems, to be followed by development of a suite of quantitative prequalification tests and quality assurance procedures, the findings to be embod- ied in a performance specification. The specification should cover the material requirements for the membrane, adhesives, and protection board (if used), together with requirements for installation. The performance specification could also include provisions for life-cycle costing so that systems that offer superior performance can compete on an equitable basis with systems that have low initial cost but a short service life. Objectives: Develop a performance specification for bridge deck waterproofing membrane systems based on a quantitative definition of performance requirements, objec- tive prequalification tests, and a life-cycle cost analysis. The objective is to encourage competition between a wide range of products and processes, all of which will perform satis- factorily in the field. Cost: $350,000. Duration: 36 months. The statement was not selected by the workshop partici- pants for the master plan. However, based on the information provided in this synthesis, the need for a performance specifi- cation for bridge deck waterproofing systems still exists today.