Composition and rheological characteristics of bitumen in short-term and long-term aging
This paper investigates the impact of sequential short-term and long-term aging of blown bitumen of the grade BND 70/100 on its mechanical characteristics in the temperature interval from 76°С to -36 °С. Group chemical composition of the bitumen has been determined by the method of liquid adsorption chromatography by the chromatograph “Gradient M”. Short-term aging has been performed in the vertical rolling thin film oven (RTFOT) under the standard of AASHTO T 240-08, and the long-term aging - in the pressure aging vessel (PAV) under the standard of ASTM D 6521-08. Mechanical characteristics of the bitumen are complex shear modulus G* and phase angle δ at the mean and high temperatures (from 4 °С to 76 °С) have been measured by dynamic shear rheometer (DSR) under the standard of AASHTO T 315-08. Bitumen stiffness S at low temperatures (from -24 °С to -36 °С) has been measured by bending beam rheometer (BBR) under the standard of AASHTO T 313-08. It has been determined that during short-term aging the content of oils in the bitumen has been decreased for 1.5 %, and the content of asphaltenes has been increased for 2 %. After the long-term aging, performed after the short-term aging, the content of oils in the bitumen has been decreased for 7 %, and the content of asphaltenes has been increased for 6.3 %. The content of resins in the bitumen remains practically constant at both types of aging. At the mean and high temperatures the short-term and long-term aging increase the complex shear modulus up to 2 and 7 200 times respectively and decrease the phase angle at average for 4-6° and 8-10° respectively. At low temperatures the short-term aging and long-term aging increase the bitumen stiffness in 1.5 and 2.5 times respectively.