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4 systems performance, where 1 = excellent and 5 = poor, all laminated board systems (5). A 2003 survey indicated that membranes received an average rating between 2.6 and 3.3. the most frequently used materials were bituminous for con- structed-in-place systems and asphalt-impregnated fabric for preformed systems. MEMBRANE SYSTEMS A membrane is a barrier placed on top of the concrete and then RECENT USAGE protected by another material that functions as the riding sur- face. As such, the waterproofing membrane is only one com- In the survey for this synthesis, 34 of the 53 respondents ponent in a waterproofing system (5). Other components are reported that they have installed waterproofing membranes used to improve adhesion of the membrane to the deck and to on concrete bridge decks since 1994. Of the 34, 3 respon- the protective riding surface. Inadequate performance by any dents have discontinued their use, 4 continue to specify them component can result in poor performance of the system, which only for new concrete bridge decks, 11 specify them for only adds to the complexity of the system and its specifications. existing bridge decks, and 16 specify them for both. Overall, more respondents use them on existing bridge decks than In general, waterproofing membrane systems can be new bridge decks. Most respondents indicated that the use of divided into constructed-in-place systems or preformed waterproofing membranes is about the same as in previous membrane systems. Constructed-in-place systems can be years. Based on the survey, the reported use on new decks subdivided into bituminous and resinous liquid-sprayed sys- only, existing decks only, or both types in the United States tems. Preformed membrane systems can be subdivided into is illustrated in Figure 1. Figure 2 shows similar data from asphalt-impregnated fabric, polymer, elastomer, and asphalt- NCHRP Synthesis 220. FIGURE 1 Current usage of waterproofing membranes in the United States.
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5 FIGURE 2 Usage of waterproofing membranes in the United States, 1992 [Source: Adapted from Manning 1995 (5 )]. The three states that have discontinued the use of water- Texas reported that it does not recommend placing asphalt proofing membranes provided various reasons. New Jersey on bridge decks and does not use proprietary waterproofing indicated that it has discontinued the use of waterproofing systems. Its waterproofing system consists of an asphalt oil membranes in favor of an impervious bridge deck water- followed by the application of two courses of rock. proofing surface course. The specification does not permit the use of dynamic rollers to compact the hot mix asphalt In Canada, New Brunswick reported that it discontin- overlay on bridge decks, which has created some issues ued the use of two self-adhesive preformed systems after about the porosity of the overlay. The use of a bridge deck concerns were raised about a number of debonding fail- waterproofing surface course avoids the issue because it can ures. Quebec reported that it discontinued the use of cer- be compacted using a static roller. tain spray-applied liquid systems because of the difficulty of maintaining the required thickness. Both provinces continue New Mexico reported that membranes have not worked to use other types of membranes. well, resulting in water and salt being trapped between the asphalt and the deck. With subsequent freeze-thaw cycles, NCHRP Synthesis 220 contained a table showing the the asphalt spalls off and the deck deteriorates. When used results of four surveys between 1974 and 1994 about the on adjacent box beam bridges, the membranes cracked at the use of waterproofing membranes on new or existing bridge interface between the box beams, allowing water and salt to decks. Table 1 reproduces a portion of this table, along with penetrate. New Mexico now prefers to use a concrete deck data obtained from the synthesis survey. In 1994, it was con- with reinforcement on these types of structures. cluded that the use of waterproofing membranes had declined