Thermorheological Properties Of Styrene-Butadiene-Styrene (SBS) Copolymer Modified Road Bitumen

The purpose of the research work was to assess the rheological properties of SBS copolymer modified bitumens (PMB), which are mainly used in hot mix asphalt laid in the top layers of road and airfield pavements. Modified bitumens containing 0-9% of SBS copolymer were the objects of the tests. They were obtained by mixing highly modified bitumen containing 9% of SBS copolymer with Venezuelan and Russian road bitumens. The analysis includes the effect of temperature on the properties of the modified asphalt binders investigated in the range from -40°C to +80°C. Tests of modified bitumen samples were performed using dynamic shear rheometer (DSR) with oscillatory torsional kinematic force. The use of oscillatory force allowed to determine the rheological parameters of the tested binders, i.e. the complex shear modulus G⁎, the phase angle δ as well as the real (elastic) and imaginary (viscous) parts of the complex shear modulus. On the basis of the results of the study, rheograms showing a significant variation in the rheological properties of the tested binders were prepared. The following relationships were taken into account: shear modulus and damping factor vs. temperature, shear modulus vs. phase angle (Black diagram) as well as the relationship between loss and storage moduli (Cole-Cole diagram). In order to compare the influence of temperature on the stiffness of the tested binders, the SMI (Shear Modulus Index) was calculated using the Walther equation, covering a wide range of pavement operation temperatures (from -30°C to +60°C). Analysis of the SMI values showed a significant effect of the SBS copolymer content on reducing the temperature susceptibility of asphalt binders.