Field evaluation of reinforced asphalt overlays using strain measurements

Phillips, James Ryan
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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.