A study on geosynthetic-reinforced asphalt systems

Inclusion of geosynthetics within hot-mix asphalt (HMA) layers has been reported to be an effective technique to enhance the performance of pavements. The main benefits expected from geosynthetic reinforcement of HMA layers include enhanced structural capacity as well as mitigation of reflective cracking. This research presents a study on various aspects relevant to geosynthetic-reinforced asphalts. Specifically, this thesis has been organized in three stand-alone sections: 1) Literature Review; 2) Overlay Testing; 3) Shear Fatigue Testing. The main objective of the first section is to provide a comprehensive overview of the previous studies on the asphalt reinforcement and their major findings. This literature review identifies various aspects relevant to research and implantation of geosynthetic-reinforced asphalt and highlights important features of previous research as well as unsolved problems that needs additional research. Findings from this literature review provided direction for the experimental research presented in Sections II and III of this study and can also be used as a guide for relevant research programs in the future. Section II presents the experimental research that was conducted using overlay testing involving geosynthetic-reinforced asphalt specimens. The standard overlay test has been designed to evaluate crack propagation in asphalt concrete using a fatigue loading mechanism that induces tensile and shear stresses. The experimental study presented in Section II adopted this test to evaluate the effectiveness of the geosynthetics in retarding the reflective cracking from an old asphalt into a new overlay. The asphalt specimens were tested in the standard overlay test along with geosynthetic-reinforced asphalt specimens. In addition, an image acquisition system was used to track propagation of cracks during overlay tests. It was found that the predominant failure mechanism for geosynthetic-reinforced specimens in the overlay test was debonding along the asphalt-geosynthetic interface. Therefore, the conventional form of the overlay test was found not to be suitable to evaluate reflective cracks that may cross the geosynthetic plane. The experimental study presented in Section III introduces a new focus for evaluation of geosynthetic-reinforced asphalt. Specifically, a new test, referred to as the Shear Fatigue Test (SFT), was developed to evaluate the geosynthetic benefits in geosynthetic-reinforced asphalt specimens subjected to pure shearing in the cross-geosynthetic direction. In the Shear Fatigue Test, the cross section of the specimens is subjected to cyclic pure shear loading. The cracks are expected to initiate and propagate along the cross-geosynthetics direction as the number of loading cycles increases. Accordingly, a relevant test procedure was developed at the University of Texas. The test results from the shear fatigue tests confirmed that the geosynthetic reinforcements can effectively enhance the shear resistance of the asphalt. The shear crack energy was dispersed by the geosynthetics at the asphalt interlayer by changing the dominated major shear crack in the unreinforced specimens to multiple shear cracks in the reinforced specimens. In addition, the stiffness of the geosynthetics was found to significantly affect the energy absorption and the toughness of the asphalt specimens. The polymeric reinforcements exhibited clear advantages over glass fiber reinforcements in terms of enhancing the shear fatigue resistance in asphalt concrete.