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26 psi with failure in the concrete. Testing is performed using stick barrier membranes was discontinued and replaced samples of the membrane before installation of the com- with welded-by-torch and spray-applied liquid membrane plete membrane. Testing of the installed membrane is not systems because of the latter's higher adhesion strengths. specified. Illinois requires and New Hampshire may require According to the survey for this synthesis, NHDOT has holiday testing of the liquid membrane in accordance with used heat-applied barrier membranes on essentially every ASTM D4787, Standard Practice for Continuity Verification bridge deck since 2000. Although spray-applied barrier of Liquid or Sheet Linings Applied to Concrete Substrates. membranes are still permitted, contractors provide the heat-applied systems because of their lower initial cost. The New York State DOT special specification for spray- Various installation methods were also studied, with the applied waterproofing membranes also requires testing of the following conclusions: substrate after the primer has been applied and after the mem- brane has been installed. A minimum adhesion of 1 MPa (145 Air blast versus abrasive blast surface preparation psi) is specified for portland cement concrete decks. showed no effect on bond. Rolling versus brooming of preformed membranes New Jersey requires testing of the adhesion between the showed no substantial benefit of either method. primer and the substrate in accordance with ASTM D4541, Standard Test Method for Pull-Off Strength of Coatings Alaska DOT performed field evaluations of selected Using Portable Adhesion Testers, at a frequency of at least bridges to determine whether the waterproofing membrane three tests for areas less than 5,000 ft2 and one test for every was bonded to the concrete bridge deck and the asphalt over- 3,000 ft2 for areas more than 5,000 ft2 and at locations where lay (32). The project was initiated because some of the pre- deficient adhesion is suspected. formed membranes, generally on high-traffic volume roads, had failed to bond adequately to either the asphalt overlay Infrared Thermography or the concrete bridge deck. Five proprietary products were included in the evaluation. Infrared thermography senses the emission of thermal radia- tion and produces a visual image from the thermal signal. It Concrete cores were taken from three bridge decks to has the potential to identify defects in waterproofing mem- inspect for bonding. Bonding between the membrane and branes because it permits large areas to be surveyed in a short the concrete or the asphalt overlay was observed in all but time. Its disadvantage is the requirement for the appropriate one core, although no measurements of bond strength were environmental conditions to achieve the heat flow conditions reported. Separate pull-out tests using similar procedures to to detect the presence of anomalies. Thermography has the ASTM C900, Standard Test Method for Pullout Strength of ability to detect blisters in waterproofing membranes (28), Hardened Concrete, were used to determine the tensile bond delaminations in bridge decks (29), and defects after the strength between the asphalt overlay and the membrane. installation of waterproofing membranes (30 ). Based on the reported loads, the bond stresses ranged from 22 to 112 psi, with higher asphalt temperatures giving higher bond strengths. RECENT RESEARCH One recommendation from the research was to require In 1996 and 1997, the New Hampshire Department of Trans- a 4-in. thickness of pavement over the membrane to allow portation (NHDOT) evaluated various membrane materials, for future pavement surface rehabilitation without damaging primers, and application methods to determine the effects the existing membrane (33). of materials and methods on the adhesion strength of com- mercially available membranes (31). Concrete pads simulat- Research about tack coats for use with asphalt is being ing dry and wet substrates as typically encountered on New performed under NCHRP Project 09-40, "Optimization Hampshire bridge decks were constructed at two locations. of Tack Coat for HMA Placement." The objectives of this The test program included 11 preformed membranes, 5 liquid study are to determine optimum application methods, equip- membranes, and 14 primers in various combinations. The pri- ment type and calibration procedures, application rates, and mary method of evaluating the systems was adhesion testing. asphalt binder materials for the various uses of tack coats and to recommend revisions to relevant AASHTO methods The study findings resulted in a change in NHDOT spec- and practices related to tack coats. Bond tests are expected ifications in 1998. The use of standard preformed peel-and- to be recommended.