Click for next page ( 31

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 30
20 using self-contained, self-propelled equipment to achieve a con- Safe to apply and with low volatile emissions, sistent anchor profile that is free of sharp protrusions. The abra- Able to withstand high and low temperatures, sive media must consist of shot and grit sufficient to provide an Can be applied over a wide range of temperatures, and angular surface profile that satisfies the requirements published Extended service life of 50 to 100 years. by the International Concrete Repair Institute (17). Areas that are not accessible to self-propelled shot-blasting equipment He also listed the following performance criteria for are to be blasted with mineral grit or steel grit and air pressure waterproofing membranes: sufficient to achieve the specified surface profile. The use of today's machinery for deck preparation and the availability of Chloride ion permeability: Protection of concrete from guidelines are improvements in both productivity and technol- chloride ion intrusion is a major requirement for mem- ogy since NCHRP Synthesis 220 was published in 1995. branes. The report suggests that concrete that is water- proofed with a membrane be tested for permeability The Saskatchewan specifications for surface preparation in accordance with the modified version of AASHTO require that the concrete deck have spray-painted reference T-277, Rapid Chloride Permeability Test, and the marks. Surface preparation is considered acceptable when charge passed should not exceed 100 coulombs. the shot-blasting effort removes the painted reference marks Low-temperature flexibility: Membranes need to completely from the concrete surface. possess adequate flexibility to withstand the stresses caused by deck movements at low temperatures. No Thirteen of 32 agencies (41%) have special inspection visible damage should occur when wrapping a sample practices during installation of waterproofing membranes. of membrane around a 1-in. diameter mandrel at 9F. Reported practices included monitoring, inspecting, or Crack bridging: Cracks already in existence on the measuring surface preparation, membrane temperature, bridge deck will grow with temperature and load installation of protection boards if used, and conformity to changes; the membrane must have elastic properties to standard drawings and specifications. be able to accommodate changes in width. The report suggests that membranes be able to bridge a crack PERFORMANCE width of 0.06 in. at 32F. Bond strength: A strong adhesive bond between the Sohanghpurwala (18 ) described the advantages of mem- membrane and wearing surface reduces deformation branes as follows: of the hot mix asphalt wearing surface layer by heavy wheel loading. The adequacy of the bond should be Membranes can be applied relatively rapidly, including evaluated in both tension and shear, with minimum application of the asphalt wearing surface. allowable values of 690 kPa (100 psi) and 172 kPa (25 Membranes can bridge and prevent reflection of most psi), respectively. moving cracks. Resistance to indentation: Because of the thermoplastic The asphalt wearing surface can provide a good riding nature of some membranes, indentation and puncture surface. by aggregates may occur during application and roll- Membranes can be applied to almost any deck geometry. ing of the hot mix asphalt wearing surface. Testing for resistance to indentation should result in no penetra- He also described their limitations: tion at the expected maximum placement temperature. The service life of the membranes may be limited by In the survey conducted for this synthesis, agencies were the wearing surface life. asked to identify the expected service lives of the water- The system is not suitable for grades greater than 4% proofing membranes they have used. Figure 13 presents the because bond capacity is limited for some systems and results. Most agencies expected 16 to 20 years for new bridge shoving and debonding can occur. decks and 6 to 20 years for existing bridge decks. Based on the information supplied, it was not possible to determine The ideal waterproofing system should satisfy the follow- whether prefabricated systems or liquids systems last longer. ing criteria: From the survey, the basis for the expected service lives Impermeable to water, can be summarized as follows: Good adhesion to the deck, Good adhesion to the protective riding surface, Expected life of the asphalt overlay, Tolerant of deck surface roughness, Past performance experience, Resistant to traffic before application of the riding surface, Deck condition at time of installation, and Capable of bridging cracks in the concrete deck or One or two paving cycles with partial depth replace- opening of joints between adjacent precast members, ment of the asphalt.

OCR for page 30
21 Percentage Response FIGURE 13 Expected service life of waterproofing membranes. Many agencies reported that the life of the membrane sys- bridge deck or beams when adjacent members are used. tem is limited by the life of the asphalt. Sohanghpurwala (18) Defects listed as "Other" in Figure 14 included spalling and reported that the service life of hot mix asphalt with a pre- deterioration of the concrete deck below the membrane and formed membrane would be less than 10 years if the overlay insufficient thickness of membrane material. failed when used to extend the service life of existing bridge decks. Otherwise, the service life would be 25 years. Xi et al. (19) reported on the inspection and evaluation of 16 bridges in Colorado that used a variety of corrosion Many types of defects may occur with waterproofing protection methods, including 6 with asphalt membrane membrane systems used on new or existing concrete bridge overlay. These bridges were constructed between 1958 and decks. Figure 14 summarizes the defects that agencies 1985. It is not reported when the asphalt membranes were reported in the survey. placed. On one bridge that was repaired in 1978, the authors observed severe delamination and cracking of the membrane From the data shown in Figure 14, defects are more with significant reinforcement corrosion. Another bridge likely to occur when membranes are used on existing bridge constructed in 1983 was reported to be in excellent condi- decks than on new bridge decks. The defects most agen- tion. Other bridges had corrosion of the bridge deck rein- cies reported were lack of adhesion between the membrane forcement. On the basis of the inspection of all bridges, the and the deck and between the membrane and the asphalt. In authors found that the results were inconclusive for deter- addition, about half of the agencies that use membrane sys- mining whether epoxy-coated reinforcement, corrosion tems reported moisture penetration through the membrane inhibitors, or membranes were the best solution. without knowing the cause. Debonding of the membrane from either the concrete or asphalt is almost impossible to In 1985, two bridge decks in Kansas were restored using a detect until it becomes evident through some defect on the nonwoven polypropylene membrane over an asphalt cement asphalt surface. In contrast, water penetrating through the tack coat and topped with a 2-in.-thick wearing surface of membrane and appearing on the underside of a bridge deck hot mix asphalt (20 ). Annual surveys of these bridges con- can be observed readily by deposits on the underside of the sisted of visual inspection, chain drags to check for delami-