Optimization of the Mixing Conditions of Waste Materials for the Modification of Base Bitumen Using Integrated Variance Optimal Mixture Design

Various industries’ waste, including polymer and waste sludge, can be released into the environment and cause irreparable damage. Therefore, their reuse in different fields is very important. This study focuses on the simultaneous use of waste polyethylene (PE), oily waste sludge (WS) resulting from the oil refining process, and micronized styrene-butadiene-styrene to improve the quality of base bitumen (PG58-22). Using the integrated variance optimal mixture design (I-OMD) method, which is used for the first time to optimize bitumen modification conditions, is the second goal of this project. The percentage composition of independent variables, including PE, SBS, and WS, were optimized based on several responses such as penetration (Pen), softening point (SP), ductility (Duct), retained penetration after short-term ageing (rPen), and change of mass after short term ageing (CM). Under the optimal conditions obtained for the modified bitumen, the rheological properties were studied. In the optimal conditions obtained using this method, the values of the independent factors PE, SBS, and WS were 3, 5, and 4% (wt/wt), respectively. Also, in the above optimal conditions, the response values of Pen, SP, Duct, rPen, and CM were 51 dmm, 64 °C, 27 cm, 83%, and 0.07%, respectively. In addition, under the above conditions, the rheological parameters of modified bitumen obtained from the bending beam rheometer and dynamic shear rheometer showed the characteristics of PG64-22 bitumen.