Ultrasonic shear wave reflectometry applied to the determination of the shear moduli and viscosity of a viscoelastic bitumen

Ultrasonic shear wave reflectometry is widely used in process control to measure the dynamic shear viscosities of Newtonian liquids. We apply the technique to study the temperature dependence of produced bitumen: a non-Newtonian ultra-heavy 6° API hydrocarbon with a room temperature viscosity of ∼103 Pa·s. The experimental apparatus employs a delay line made of polyetheretherketone (PEEK) whose shear impedance more closely matches that of the bitumen allowing for greater sensitivity but at the cost of long equilibration wait times. The temperature dependent values of the complex shear modulus and consequent estimates of the steady flow shear viscosity both follow close to an Arrhenius-like behaviour over the range of 10 °C-50 °C, but there are significant discrepancies between the ultrasonic and more conventional spindle viscosities. These may reflect differences between the particle displacements, the strains, and the strain rates associated with each measurement technique. It is in the nature of bitumen to shear thin at high shear rate using ultrasonic technique. Regardless, these measurements do show that the shear wave reflectometry does provide information on the changes in the viscoelastic bitumen with temperature that may be useful in for purposes of its monitoring during production and processing.