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Effectiveness of geogrids in flexible pavement reinforcement was investigated throughout laboratory testing and finite-element analysis (FEA). The laboratory testing involved routine material characterization, resilient modulus testing, and five pavement prototype sections. These sections consisted of a 5 cm asphalt concrete (AC) layer, 15 cm granular base layer, and a 30 cm clay subgrade. The base layer was reinforced with a single layer of uniaxial geogrid placed at four different positions within the base layer. The pavement sections were loaded with a static plate-loading equipment and the results were compared with the control section (CS), which had no reinforcement. Results from this study showed that geogrids can be used to reduce tensile stresses in flexible pavement systems. The optimum position of the geogrid reinforcement to reduce tensile strains was found to be directly underneath the AC layer then within 33-50% of the granular base layer height as measured from the bottom of the base layer.

International roughness index (IRI) is the mathematical measurement of pavement smoothness. In this study, a regression model for IRI prediction for jointed plain concrete pavements (JPCP) was developed based on data from the Long Term Pavement Performance (LTPP) Project. A total of 327data points from 81pavement sections distributed all over the U.S. was used for the model development. The model predicts IRI as a function of pavement age, initial IRI, faulting, number of spelled joints, and number of transverse cracks, precipitation, and freezing index. The goodness of fit statistics of the model show excellent improvement over the previous model implemented in the Mechanistic-Empirical Pavement Design Guide (MEPDG). The model has a high coefficient of determination (R 2) of 0.80.In addition the bias in the predicted values of IRI was significantly lower compared to the previous MEPDG regression model.

Effectiveness of geogrids as a reinforcement of the cross section of flexible pavement system was investigated. The study involved conducting of routine as well as advanced laboratory testing for comprehensive material characterization. It also included testing five large-scale pavement sections in the laboratory. These sections consists of a 5 cm asphalt layer (AC), 15 cm granular base layer, and a 30 cm clay subgrade. Five pavement sections were tested. The large-scale pavement sections were instrumented with strain gauges at different depth within the base layer. The base layer was reinforced with a single layer of RE540 uniaxial Tensar geogrid placed at four different positions within the base layer, one position at a time. These positions were 1) at the interface between the base and subgrade (B0), 2) 5 cm from the bottom of the base layer (B1/3h), 3) the middle of the base layer height (B1/2h), 4) and finally at the interface between the AC and base (Bh). These pavement sections were loaded with a static plate loading equipment until failure and the results were compared with the control section (CS) which had no reinforcement. Results from this study showed that geogrid can be used to improve the performance of flexible pavement systems. The position of the geogrid in the pavement system affects the performance significantly. The optimum position of the geogrid reinforcement to improve the pavement fatigue life was found to be directly underneath the AC layer then within 33 to 50% of the granular base layer height measured from the bottom of the base layer.