Optimization of Tack Coat Application Rate for Geocomposite Membrane on Bridge Decks

One of the critical components of the U.S. civil infrastructure, bridges, has rapidly deteriorated in the past two decades and is in need of maintenance and rehabilitation. Geosynthetics may have the potential to provide a long-term solution to some of the problems that are present in these bridges, mainly, chloride intrusion into bridge decks. When installed properly, geosynthetics can act as both a moisture barrier and a stress absorption layer. However, the tack coat application rate is critical, as an excessive amount can cause eventual slippage, whereas too little may result in debonding. A new geocomposite membrane that comprises a low-modulus polyvinyl chloride layer sandwiched between two layers of nonwoven geotextile has recently been introduced for use in highway systems for water impermeation and strain energy absorption. A laboratory testing program was conducted to determine the optimum asphalt binder tack coat application rate that needs to be applied in the field. To accomplish this, a fixture was designed to allow the application of cyclic shear loading at the geocomposite membrane interface when used as an interlayer simulating a concrete bridge deck overlaid with the geocomposite membrane and a hot-mix asphalt (HMA) overlay. The study concluded that 1.75 kg of PG 64-22 binder per m² is an optimum value to achieve excellent bonding and minimum slippage potential. For the upper surface in contact with a wearing surface mix, a tack coat application rate of 1.5 kg/m² may be used. When the geocomposite membrane was included between concrete and HMA, failure occurred after a much larger number of applied loading cycles than the number of loading cycles to failure when the geocomposite was absent. In addition, the slope of shear stress versus the number of loading cycles at failure was much greater when the geocomposite was absent.