Browsing by Subject "Asphalt reinforcement"

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A study on geosynthetic-reinforced asphalt systems
(2018-10-04) Yang, Luming; Zornberg, Jorge G.
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.
Field evaluation of reinforced asphalt overlays using strain measurements
(2018-01-25) Phillips, James Ryan; Zornberg, Jorge G.; Roodi, Gholam Hossein
The design of paved surfaces under different geological, environmental, and inclement scenarios is a topic of major relevance within the geotechnical and transportation engineering discipline. Roads and other paved surfaces should be adequately maintained for both civilian and commercial operations to thrive. Pavement deterioration is inevitable as are the associated maintenance costs. Techniques to prevent and mitigate pavement deterioration typically become more expensive as the expected service life is increased. This research focuses on the inclusion and evaluation of geosynthetic-reinforced asphalt overlays. Specifically, polyester (PET) and polyvinyl (PVA) geogrid reinforcement was installed and evaluated using strain measurements from subsurface asphalt layers to further understand the associated structural benefits and mitigation of reflective cracking. The presence of interlayer reinforcements is expected to increase the service life of constructed overlays and eventually lead to less overall costs in road maintenance. A field monitoring site located along US77 in Lee County, Texas is the focus of this research. This road is a four-lane highway that has shown significant reflective cracking through multiple overlays. PET and PVA geosynthetic-reinforcements were installed in 500 ft. sections followed by an unreinforced control section. Each of these sections was instrumented with asphalt strain gages placed at two inches below the surface of the overlay. The strain gages were arranged in the longitudinal and transverse directions located in the right wheel path as well as between the wheel paths. Two sensors in each section were placed on a preexisting crack. A testing campaign was conducted one year after installation that included vehicle passes by a heavy dump truck and a pickup truck. The passes were conducted directly over the sensors in the wheel path as well as offset towards the shoulder. Static testing was also performed by the heavy truck, in which the truck stopped directly on each sensor for a period of time. Falling weight deflectometer (FWD) tests were also conducted on each sensor to assess the development of the strains from each drop. The sensor configuration allowed the comparison of measured strains between the two types of reinforcement as well as between the reinforced sections and the unreinforced section. The PET reinforced section was found to consistently develop lower strains under traffic loads than the control section, both in terms of longitudinal strain in the wheel paths and over preexisting crack locations. The PVA reinforcement also showed the development of lower strains over preexisting cracks than the control section. Both reinforced sections showed development of higher strains than the control section in the area between the wheel paths, indicating the load was distributed over a comparatively greater area, which is expected to ultimately lead to comparatively low rutting.