The effect of bitumen chemical composition, amounts of elastomeric polymer and a kind of warm mix additive on the Dynamic Shear Rheometer, Bending Beam Rheometer, Elastic Recovery and Viscosity responses of the bitumen binders was investigated by using Response Surface Methodology. The individual effects of parameters on response functions were analyzed. Then the optimization was performed by the simultaneous analysis within the desired limits and optimum values of variables were determined as GI: 0.988, SBS: 3.2% and Wax: 3%. The performance grade of neat bitumen was increased from PG70-22 to PG82-16 by modification at optimum conditions. (C) 2019 Elsevier Ltd. All rights reserved.