A Study on Deformation Behavior of a Subbase Layer Mixed with Reclaimed Asphalt Pavement under Repetitive Wheel Loads

This study deals with the behavior of the aggregate subbase mixed with reclaimed asphalt pavement (RAP) material. A comprehensive investigation of a standardized well-graded unbound subbase laid over a subgrade of California bearing ratio (CBR) 6% was conducted. The basic compressive and shear behavior of subbase mixes with different RAP content were evaluated by compaction tests, relative density tests, CBR tests, and large-box direct shear tests. The bearing capacity and permanent deformation (PD) of an unpaved subbase layer laid over a subgrade of CBR 6% were evaluated by the model plate load test and repeated wheel load test. It was observed that the partial replacement of RAP with virgin aggregate (VA) resulted in a decrease in the density and CBR by 6.8% and 63% at 59.33% RAP content partial replacement in the VA mix. The friction angle of the mixes was found to range between 52.9° and 48.6°. Similarly, a model plate load test of the subbase layer laid over a subgrade of 6% CBR resulted in a decreased bearing capacity with an increase in the RAP content. When placed over a good-quality subgrade, the static and dynamic failure was observed to be limited to the subbase layer. The PD behavior of the subbase layer with increasing RAP content was evaluated using a unique repeated wheel load arrangement at a load of 560 kPa. The PD was found to increase with an increase in RAP content. The PD increased by 28% at the 20,000th load cycle for RAP content of 44.50%. The regression analysis of PD behavior for unbound granular materials was performed to fit the multiple existing models relating permanent strain to a number of load repetitions. Based on the models, the predicted numbers of cycles at failure were estimated.