Tribological characterization of bituminous binders with Warm Mix Asphalt additives

Warm Mix Asphalt (WMA) technologies allow reducing production, laying and compaction temperatures of bituminous mixtures, leading to relevant environmental and technical benefits. According to recent studies, some WMA additives lead to this temperature reduction by potentially improving the lubricating properties (i.e. the tribological behaviour) of the bituminous binder. In this study, the effect of a chemical and a wax additive on the tribological behaviour of two base bituminous binders was investigated, by considering different percentages of additive. All the binders were preliminarily characterized with Fourier Transform Infrared Spectroscopy (FTIR) and viscosity analysis. After optimizing the test procedure, tribological tests were carried out with a ball-on-three-plates fixture at 85 °C and 120 °C. A statistical analysis was also performed on the tribological results to evaluate the statistical significance of the differences between the binders. Results showed that the additives might alter the oxidative state of the binder, the chemical additive is able to modify the tribological behaviour of the binder, the wax additive acts solely on the viscosity and the effect of the additive depends on the chemical composition of the base binder. Moreover, a correlation between the minimum friction and the viscosity was found.