Experimental Investigation of Rutting in the Different Phases of Asphalt Mixtures

Rutting is one of the most severe failure mechanisms for asphalt pavements. This phenomenon is due to the accumulation of permanent deformation in consequence of traffic loading. The behavior of asphalt mixture is highly affected by the properties of the asphalt binder used in the mix design. For this reason, the Multiple Stress Creep and Recovery (MSCR) test procedure was recently introduced with the objective of better evaluating the rutting resistance while replacing the conventional Superpave parameter, G*/sin delta. Good understanding of the rutting mechanism within the asphalt binder component is essential for correctly studying the mutual interactions of the asphalt mixture components: binder, fine aggregate and large particles. This paper presents the results of an experimental campaign consisting of MSCR tests performed on asphalt binder, mastic and fine aggregate mixture which compose a typical mixture for asphalt binder layer. All the tests were conducted using a Dynamic Shear Rheometer (DSR). The classical plate-plate configuration having 25 mm diameter and 1 mm gap was selected for asphalt binder and mastic tests. The cylindrical geometry was used for torsional tests on fine aggregate mixture presenting aggregate as large as 1.16 mm. A single testing temperature of 60 degrees C and three different stress levels, 100, 1600, 3200 Pa, were imposed. The results indicate that creep and recovery are functions of filler concentration and stress level.