Rutting Performance of Modified Binders Based on Laboratory Tests and Structural Simulations

The performance of modified binders and mixtures has been assessed through different tests performed in the laboratory. Scarcely, any study has compared it with the performance of the bituminous mix depending on its placement, i.e., whether it is placed in the wearing course or in the binder course. To evaluate the same, four binders, namely, unmodified binder (VG30), Styrelf modified binder, crumb rubber modified binder and hybrid modified binder were considered. To characterize the performance, performance grade and multiple stress creep and recovery tests were performed on the binders; dynamic modulus, flow time, flow number and dry rut wheel tests were performed on the mixtures. The ranking towards rutting performance varied depending on the test method as well as on whether it is a binder or mixture. To evaluate the rutting performance of the pavement, structural simulations were carried out using AASHTOWare software. The rut depth varied between 22.4 and 25.9 mm when VG30 was used in any one of the layers, and between 20.1 and 21.3 mm when modified binders were used in both the layers. No appreciable difference in the rutting performance of pavement was observed when different combinations of unmodified and modified mixes or modified mixes in both layers were used.