Determination of Optimum Tack Coat Application Rate for Geocomposite Membrane Use in Roads and Overlaid Bridge Decks
Donovan, Erin Patricia
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Two critical components of the United States civil infrastructure, bridges and roads, have deteriorated in the past two decades at an accelerated rate and are 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 roads and bridges. When installed properly, some geosynthetics can act as both a moisture barrier and stress absorption layer. However, the tack coat application rate is critical as an excessive amount can cause eventual slippage, while too little may result in debonding. A new geocomposite membrane, which is comprised of a low modulus PVC layer sandwiched between two layers of nonwoven geotextile, has recently been introduced for use in highway systems for water impermeability and strain energy absorption. A laboratory testing program was conducted to determine the optimum asphalt binder tack coat 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 one of two situations: a concrete bridge deck overlaid with the geocomposite membrane, and an HMA overlay or a flexible pavement with the geocomposite membrane sandwiched between an HMA base layer and an HMA wearing surface. The research concluded that 1.40 kg/m2 of tack coat should be used when the geocomposite surface is in contact with an HMA base mix, 1.5 kg/m2 should be used when it is in contact with an HMA surface mix, and 1.75 kg/m2 should be used when it is in contact with concrete surfaces. However, these tack coat application rates are a function of the structural material type and the tack coat material type (binder performance grade). In addition, an analysis of the simulated bridge deck specimens with geocomposite membrane and the control samples, containing no membrane, shows distinct evidence that the membrane acts as a stress-absorbing material.
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