Chemo-Mechanical Analysis of Bitumen

Abstract

Bitumen is a visco-elastic, organic material, which primarily consists of hydrocarbons and small amounts of oxygen, nitrogen and sulfur. It is used as a binder in asphalt mixtures and as a sealing material in the roofing industry. Over the course of its life-span bitumen is susceptible to aging due to contact with oxygen and other environmental factors, which results in the stiffening of the material. To ensure the quality and durability of the material accurate and comprehensive analysis methods have to be applied. For the characterization of the visco-elastic behaviour of bitumen the dynamic shear rheometer (DSR) can be used, whereby the complex shear modulus represents the stiffness and the phase angle gives information about the degree of viscous response to stress. For the analysis of the chemical composition Fourier-Transformation Infrared (FTIR) spectroscopy is applied, whereby certain spectroscopic bands can be assigned to chemical structures formed during the aging process. The combination of mechanical and chemical information is a crucial step in understanding the properties and the aging behavior of the material. Therefore, the chemo-mechanical correlation was developed, which illustrates the link between the mechanical properties and the chemical composition of the respective bitumen sample. The FTIR aging index, which represents the formation of carbonyls and sulfoxides, is plotted on the X-axis and the norm of the complex modulus |G*| or the phase angle δ is plotted on the Y-axis. This gives visual and graphical information about how an increase in stiffness is correlated to an increase in incorporated oxygen and vice versa.