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7 CHAPTER TWO WATERPROOFING MEMBRANE SYSTEMS MATERIALS As depicted in Figure 4, liquid systems generally consist of application of a primer followed by application of the membrane. As part of the survey for this synthesis, respondents were The membrane may be placed using either spray equipment or asked to identify what waterproofing products they had used rollers and squeegees. The membranes are applied either hot since 1994. At least 23 different proprietary products from or cold depending on the manufacturer's requirements. Liquid 19 companies have been used as waterproofing membrane systems may or may not contain a reinforcing fabric. systems on bridge decks in the United States and Canada since 1994. In the 1992 survey for NCHRP Synthesis 220, 22 If a reinforcing fabric is used, one layer of liquid is different proprietary products were identified (5). In general, sprayed. The fabric is then placed on the liquid and a second the systems can be classified as either preformed sheet sys- layer of liquid placed on top. A tack coat is generally used tems or liquid systems, with approximately an equal number with liquid systems before placement of the asphalt overlay. of products of each type. Various manufacturers describe the materials used for the liquid systems as rubberized asphalt, two-component poly- As depicted in Figure 3, preformed sheet systems involve mer, polyurethane, methyl methacrylate, rubber polymer, the application of a primer to the clean concrete deck to polymer-modified asphalt, or rubberized bitumen. improve the adhesion of the membrane to the deck. This is followed by installation of the membrane. Most preformed Twelve states reported information on the products they have systems identified in the survey included a self-adhesive used. Six states have used only preformed systems, two have backing on the membrane sheet. These sheets can be rolled used only liquid systems, and four have used both systems. In into place and then bonded to the deck primer using a roller. Canada, two provinces reported using only preformed systems, In other systems, the membrane is bonded to the deck by two used only liquid systems, and three used both systems. heating the membrane using either a hand torch or a machine. After the membrane is installed, a tack coat is applied to the According to Kepler et al. (8), three types of waterproof- top surface to increase bond with the asphalt overlay. ing membranes were used in North America in 2000: pre- formed sheets, liquid membranes, and built-up systems. Materials used to form the sheet membranes are described Preformed sheets were most often used in the United States, by the various manufacturers as rubberized asphalt, bitumi- while a liquid membrane of hot applied rubberized asphalt nous membrane, polymer-modified asphalt, modified bitu- was used exclusively in Canada. It was also the most com- men, polymeric membrane, or bitumen and polymers. mon liquid membrane used in North America. FIGURE 3 Schematic of possible components of preformed systems.