Interruption of the Aggregate Matrix by Geogrid Reinforcement in Resilient Modulus Testing

Inclusion of geogrid in aggregate base materials is an increasingly popular practice in pavement construction. Geogrid reinforcement can improve the performance of pavements by stiffening the base material and decreasing pavement deformations. The objectives of this research were to establish a possible explanation for why laboratory resilient modulus testing is ineffective for assessing improvements in the stiffness of geogrid-reinforced aggregate base specimens and to recommend possible testing solutions. The scope of the research included one aggregate base material and one type of geogrid. Cyclic loading data were used to calculate the resilient modulus on 200-cycle intervals up to 10,000 cycles, and quick shear data were used to calculate the modulus at 2 percent strain after the conditioning period. Specimens with and without geogrid reinforcement were assessed in the testing. As with other studies, the results do not show a significant benefit of geogrid reinforcement on resilient modulus of the tested material. Indeed, specimens reinforced with geogrid had significantly lower dry densities than specimens without geogrid, which suggests that the geogrid interrupted the aggregate matrix. However, the results do show a significant benefit of geogrid reinforcement on modulus at 2 percent strain of the tested material. Because the modulus at 2 percent strain appears to have promise for evaluating the benefits of geogrid reinforcement in aggregate base materials, further research is recommended to correlate this property with typical pavement design inputs.