The possibility to monitor aging of pavements and bituminous binders directly on the operative field, under their typical environmental conditions, can contribute to better understand the factors influencing the aging process, can be used for material optimization and to improve the performance behavior of bituminous binders. The high frequency torsional rheometer (HFTR) described in this paper is a useful device to study the time evolution of the theological properties of bituminous binders during field tests. In comparison with prevailing rheometers, the HFTR is inexpensive and, due to its portability and operative frequency (5 kHz) that allows measurements to be unaffected by traffic induced low frequencies, is a useful tool for continuous monitoring of field tests. The HFTR device and the measurement technique are described in this paper. The extraction of the theological parameters from the experiments is made through analytical and finite element models that reproduce the particular conditions of the field tests. In this study, the long-term aging of an asphaltic plug joint of a highway bridge is investigated with an HFTR over three consecutive years of exposure to environmental conditions. The evolution of the theological properties of the plug joint material, containing styrene-butadiene-styrene polymer modified bitumen, is quantified in terms of the complex shear modulus G*, showing a progressive material hardening and an increase in the temperature susceptibility of the binder. (c) 2006 Elsevier Ltd. All rights reserved.