Investigation of a new mixing method in production of hot mix asphalt

A two-phase mixing method was developed in this thesis as a new mixing method in production of hot mix asphalt (HMA). Course aggregate was mixed with 20 percent of optimum binder content and kept at 135-160 oC for 1 hour in the first phase. Fine aggregate and filler were mixed with 80 percent of optimum binder content and then course aggregate was added to mix and mixed together in the second phase. Marshall stability, indirect tensile strength and moisture susceptibility, stiffness modulus and fatigue tests were applied to Marshall samples prepared with both the new method and traditional method in order to evaluate the two phase mixing method. At first characteristics of the materials and their appropriateness to the specifications were determined in the study. AC 100-150, AC 75-100, AC 60-70 penetration asphalt cements and 5 percent stryrene butadiene stryrene (SBS, Kraton D1011) modified AC 75-100 penetration asphalt cement were used as binder in the experiments. Basalt was used as aggregate. It was determined that the mechanical properties of samples prepared with two-phase mixing system were higher than the ones prepared with traditional method and the binder used in first phase have a significant effect on stiffness of mixtures. It was determined that the specimens prepared with modified asphalt gave the better results at all experiments and among the unmodified binders the best results were obtained with the specimens prepared with AC 75-100. Furthermore it was determined that the effect of two-phase mixing system on mixtures prepared with SBS modified binder was higher than those of the conventional mixtures. Moreover, an asphalt plant was designed to enable producing hot mix asphalt according to two-phase mixing method. Keywords: Hot mix asphalt, Mixing method, Mechanical properties. I