The dynamic rheometer consists of an external tube rigidly joined to an internal cylindrical rod. The tube is fixed at one end and free of loading along its lateral surface. The other end of the tube where it joins the internal rod is solidly closed. With an electromagnetic transducer fixed at the free end of the internal rod, the system is forced to perform high frequency vibrations of very low amplitude at one of its torsional eigenmodes. The frequency is stabilized with the help of a phase-locked loop fixing the phase between the applied torque and the measured angle of rotation. The damping is obtained from the frequency difference at two values of the phase angle in the vicinity of resonance. The resonance frequency corresponds to a phase angle of 90°. When the free and closed end of the external tube is placed on the surface of a viscoelastic medium, only a boundary layer of the medium in the immediate vicinity of the contact surface participates in the motion, provided that the frequency is sufficiently high. Nonetheless, the measured resonance frequency and the damping will change in comparison to similar measurements taken in air. Through the accurate measurements (the frequency is stabilized down to 0.005 Hz) and use of a realistic model of the vibrating system, the real and imaginary parts of the complex viscosity can be determined.

The rheometer is currently installed on a highway plug joint near Basel, Switzerland. The results obtained so far confirm that the subject rheometer can be used as a relatively fast and cost effective non-destructive tool in the field. The goal of the on-going experiment is to evaluate the status of such binder materials as a function of temperature and climate and to improve on the basis of the measured data the quality, safety and durability of bituminous binders.

[1]: Goodbread, J., Sayir, M., Häusler, K., Dual, J., Method and Device for Measuring the Characteristics of an Oscillating System; US Patent No. 5,837,885, (1998), European Patent No. 0749570 (1998).

[2]: Sayir, M.B., Hochuli, A., Partl, M.N., Measuring the Complex Viscosity of Bitumen in the KHz Range with a New Resonance Rheometer, Workshop Briefing, Eurobitume Workshop 99 on Performance Related Properties for Bituminous Binders, 3-6 May Luxemburg, Paper No. 106.