METHOD OF EVALUATION OF STRESS RELAXATION PROPERTIES IN ROAD BITUMENS

ABSTRACT

One of the most important properties of bitumen is - among others – its ability to stress relaxation. This ability affects the energy absorption from the vehicles’ wheels by asphalt pavement. It has also influence on deformation, damages and durability of road surface. The problem of the destruction of asphalt layers is common and current. In order to determine the physicomechanical characteristic of bitumen, in the article, a method of evaluation of stress relaxation properties in road bitumens is presented.
In this method, direct shear apparatus was used. With it, the shear force of bitumen placed between two polished stone tiles was determined. Vertical force was not applied to the device. Therefore, as an analogy to soil tests and knowing the dimensions of the tiles, asphalt cohesion could be determined. The tests were performed for two shear speeds and five bitumen temperatures. Dividing the value of asphalt cohesion at higher shear rate by its value at a lower speed, stress relaxation coefficient was determined. Five different types of road bitumen, including clean and modified, were tested. Stress relaxation coefficient specified by this method, may be helpful in selecting the type of bitumen for pavement constructions.

Keywords: stress relaxation, road bitumen, asphalt cohesion, direct shear apparatus, Coulomb’s law