Behavior of Asphalt Overlays with Geogrids and Geocomposite Interlayer Systems

Geosynthetics in the form of geotextiles, geogrids, and geocomposites have been incorporated into pavement systems to enhance the service life of asphalt overlays by retarding reflective cracking. In this study, the performance of asphalt overlays reinforced with geogrids and geocomposite interlayer systems placed on pre-existing asphalt layer was evaluated. Specifically, both unreinforced and geosynthetic-reinforced, two-layered asphalt beam specimens prepared with a pre-existing 25 mm-deep notch (crack) in the bottom layer were tested under repeated four-point bending load conditions. The two-layered asphalt specimen consisted of a 45 mm-thick, old pavement layer collected from an existing highway as a bottom layer, a binder tack coat, the tested interlayer, and a 45 mm-thick hot mix asphalt (HMA) overlay. A glass-geogrid composite (GGC) involving a geotextile backing interlayer and two different types of geogrid interlayers, namely, a polyester geogrid (PET) and a polypropylene geogrid (PP) were used in this study. Repeated loading was applied to all specimens using a four-point bending configuration in a load-controlled mode at a frequency of 1 Hz. The performance of the different geosynthetic-reinforced specimens was compared against that of the control specimen (CS) and the improvement in fatigue life was estimated. Considering the specific products in this study, results indicate that all the geosynthetic-reinforced specimens resulted in extended fatigue life of overlays in relation to the CS, and among them, the best performance was obtained using the GGC

Mechanical response of full-scale geosynthetic-reinforced asphalt overlays subjected to repeated loads

This study aims at evaluating the influence of geosynthetic reinforcements on the structural improvement of asphalt overlays placed on distressed pavement layers using repeated load tests. Full-scale instrumented pavement models were constructed in an indoor steel tank measuring 1000 mm in length, 1000 mm in width and 1000 mm in depth. Full-scale instrumented pavement models consisted of a 650-mm-thick weak subgrade, 250-mm-thick base, 90-mm-thick distressed asphalt layer, binder tack coat, geosynthetic reinforcement (except in control sections), and 50-mm-thick hot mix asphalt overlay. Sensors used in the instrumentation program included earth pressure cells and linear variable displacement transformers installed on the subgrade and surface layers, respectively. Four different geosynthetic types, including woven geo-jute mat (GJ), polypropylene geogrid (PP), polyester geogrid (PET), and fiberglass geogrid composite (FGC) were adopted as asphalt reinforcements. A servo-hydraulic actuator was used to replicate a live traffic wheel load by applying an equivalent single axle contact pressure of 550 kPa at a frequency of 1 Hz. Repeated load tests were terminated after 100,000 load cycles and the behaviour of geosynthetic-reinforced full-scale models was compared with that of unreinforced model. Performance indicators, including Traffic Benefit Ratio (TBR) and Rut Depth Reductions (RDR), were estimated and repeated load test results indicated an increase in the structural performance of geosynthetic-reinforced full-scale models in relation to that of unreinforced model. Among the geosynthetic-reinforced models considered in this study, the FGC-reinforced model showed a comparatively better performance with a maximum TBR of 20 at a permanent deflection of 5 mm and the highest RDR of 56% after 100,000 load cycles, respectively. Maximum reductions of 56% in surface deflection and of 30% in vertical pressure on the subgrade were also observed after 100,000 load cycles in the FGC-reinforced model. © 2021 Elsevier Lt