Shear and flexural characterization of grid-reinforced asphalt pavements and relation with field distress evolution

The use of geogrids at the interface of asphalt layers is currently adopted to improve pavement performance in terms of rutting, fatigue and reflective cracking. Several test methods have been proposed in order to simulate the complex mechanical behavior of reinforced pavements and assist practitioners in the selection of the appropriate reinforcement product. A particular subject of debate is the evaluation of geogrid effects in terms of both flexural strength and interlayer bonding. In this context, an interlaboratory experiment has been organized as part of the RILEM TC 237-SIB/TG4 with a twofold objective: to compare the predictive effectiveness of different experimental approaches and to analyze the behavior of different geogrid types. For this purpose two experimental reinforced test sections have been realized, the first one to prepare samples for the interlaboratory experiment, the second one to analyze the geogrid field performance under heavy traffic conditions. This paper describes the test results obtained by one participating laboratory on double-layered asphalt samples extracted from the first experimental section and compares them with the periodic visual observation of the reflective cracking evolution occurred in the second test section. The laboratory tests were performed following a specific testing protocol that combines interlayer shear tests, repeated loading tests in a four-point bending configuration and quasi-static three-point bending tests, in order to investigate the overall performance of double-layered asphalt systems. Results have shown that geogrid reinforcement does not noticeably influence the flexural stiffness and strength in the pre-cracking phase, whereas the crack propagation speed can be significantly reduced and the failure behavior may change from quasibrittle to ductile, depending on the interlayer shear resistance. Laboratory results were confirmed by periodic visual observation of field performance in terms of reflective cracking evolution.