Laboratory Characterization of Geogrid-Reinforced Unbound Granular Material for use in Flexible Pavement Structures

Abstract

This thesis documents and summarizes research and background information carried on geogrid reinforced base course in pavement design. Research was experimental carried through Repeated Load Triaxial (RLT) tests at the Louisiana Transportation Research Center. The experimental tests were performed to observe the benefit of the geogrid as well as to differentiate between geogrid location, geometry and tensile modulus of the various geogrid. Experiments were also carried to further describe the Shakedown Theory and its use for characterization of base course materials. The experimental results showed that there was a benefit in placing the geogrid within the aggregate specimen. There were also noticeable differences in performance resulting from the geogrid placement location in the specimen as well as the different tensile strength of the geogrid. The results followed the intuitive expectation the stiffer the geogrid, the lesser the plastic deformation. Geometry had a noticeable effect as well when comparing the bi-axial (BX) geogrid and the tri-axial (TX) geogrid. The experimental results also showed that less deformation was obtained under cyclic loading for geogrid reinforced bases versus unreinforced bases. The results also supported that a change in moisture will yield different permanent strain values in repeated load tests. The same reinforcement trend obtained at optimum moisture content was also transferred for the moisture effect tests. The higher frequency tests with increased number of cycles also produced the same trend. The geogrid with the higher tensile modulus and the new geometry gave the best results.