Development of test protocols for the analysis of magneto-rheological properties of field-responsive bituminous binders

Magneto-rheological fluids are materials that exhibit a significant change in their rheological properties in the presence of a magnetic field. Because of such a field-dependent behavior, they can act as smart materials in applications in which changeable performances are desired. In road pavement engineering, the use of bitumen-based magneto-rheological fluids may open innovative scenarios related to the construction of smart pavement sections and to the investigation of damage mechanisms in binders and mixtures. The research work presented in this paper explored magneto-rheological properties of several field-responsive bituminous binders obtained from two different base bitumens combined with multi-wall carbon nanotubes and powder iron. The experimental program included oscillatory shear loading tests at different temperatures, performed in the strain controlled mode by means of a dynamic shear rheometer equipped with a magneto-rheological device. The investigation was carried out with the specific goal of identifying critical issues which should be taken into account in materials preparation, testing procedures and data analysis. Undesired overheating of specimens during testing was identified and taken into account for a correct inter-pretation of experimental data. Thus, while the field-sensitivity of carbon nanotubes was found to be negli-gible as a result of the magnetic shielding action of bitumen, it was shown that powder iron can significantly affect the magneto-rheological properties of bituminous binders when employed in sufficiently high amounts. Moreover, obtained results indicated that selection of base bitumen is a key factor in designing bituminous-based smart materials. Practical implications which derive from the study are mainly relative to the fine-tuning of laboratory char-acterization procedures which should necessarily overcome current limitations in temperature regulation and magnetic field generation. Experimental data presented in this paper also suggest that future development of pavement magnetic sensing techniques should consider the combined effects of temperature and field intensity.