Rheological properties of road bitumens modified by natural asphalt

The paper presents comprehensive results of the performance and non-standard rheological tests of chosen paving-grade bitumens modified by adding natural asphalt. It has been demonstrated that standard performance tests give the same classification rating to bitumens that have considerably different rheological properties. In such situations it is indispensable to test visco-elastic properties (complex shear modulus test) and visco-elastic-plastic properties (using tests with repeated stress pulse, such as MSCR). Additionally, a test used for indirect determination of so-called distinct phase transitions was carried out as part of this research. Although phase transitions are not distinct in the case of bitumen binders, the temperature corresponding to the maximum value of the imaginary part of the complex stiffness modulus can be treated as an important parameter from the point of view of thermodynamics and rheology. The benefits of modification of binders by addition of natural asphalts are clearly evident in the standard binder/aggregate bond strength test. Conversely, the respective non-standard tests failed to demonstrate the advantages of paving-grade bitumens modified with natural asphalt until MSCR and phase transition tests were carried out to this effect.