The styrene-butadiene-styrene ͑SBS͒ triblock copolymer was used to modify the asphalt binder. The morphology and engineering properties of the binders were investigated using transmission electron microscopy ͑TEM͒, rotational viscometer, and dynamic shear rheometer. The morphology of polymer-modified asphalt was described by the SBS concentration and the presence of microstructure of the copolymer. When the SBS concentration increased, the copolymer gradually became the dominant phase, and the transition was followed by a change in engineering properties of SBS-modified asphalt. Results from TEM showed that depending on the asphalt and copolymer source, a variety of morphology can be found. The SBS-modified binders might show a continuous asphalt phase with dispersed SBS particles, a continuous polymer phase with dispersed asphalt globules, or two interlocked continuous phases. The optimum SBS content was determined based on the formation of the critical network between asphalt and polymer. Because of this network formation, the binders showed a large increase in the complex modulus that indicates resistance to rutting. At low SBS concentrations, the Kerner model was found to be appropriate to estimate the rheological properties of SBS-modified asphalt. An adapted Kerner equation was proposed in this study to predict the complex modulus of modified asphalt at high SBS concentrations.
Porous asphalt concrete (PAC) has an open-graded aggregate mixture to yield high air voids; PAC is mainly applied to the surface drainage layer on high-speed trafficked highway pavements. The objective of the study was to investigate the effect of binder types on the engineering properties and field performance of PAC mixtures. Three binder types were selected for a 19-mm nominal maximum aggregate size gradation: conventional asphalt AR-80, polymer-modified asphalt, and high-viscosity asphalt. A series of laboratory tests were conducted to evaluate the engineering properties of the PAC mixture, including permeability, resistance to draindown, resistance to disintegration, resistance to rutting, and resistance to indirect traction. A 3-km in-service test road was constructed to monitor the performance of PAC pavements using these three binders. Polymer-modified binder was shown to minimize abrasion loss and enhance the durability of the PAC mixture. Test results indicated that the use of polymer-modified binder, instead of unmodified binder, reduced rutting and raveling. When the mixture contained high-viscosity binder, it showed the best performance in the field. Field measurements indicated improved drainage as a result of replacement of the conventional asphalt AR-80 binder with the polymer-modified and high-viscosity binders. PAC pavement surfaces provided good frictional characteristics once the asphalt binder film was worn from the aggregate.
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