Influence of laboratory aging and asphaltene content of asphalt on frictional coefficient by tribological analysis − a case study

• After short-term aging the behavior of the asphalt binders changed as a function of the initial colloidal structure. • Long-term aging generates an increase of the CoF at higher sliding velocities. • The asphaltene content of asphalt has an important effect on lubricant properties. • Asphalt viscosity appears to be related to the CoF in hydrodynamic domain. An increase in use of reclaimed asphalt pavement (RAP) materials was observed for the last few years. These materials are composed of aged asphalt which can cause implementation issues due to its high viscosity. This work suggests a new way to explain a part of this problematic by tribological analysis and to assess the lubricating ability of aged asphalt. The influence of asphalt aging is investigated on the frictional properties using two 35/50 asphalt penetration graded specimens and a third one extracted from RAP. Short and long-term as well as natural effects of aging are examined on penetration grade, ring and ball temperature, infrared indices, and asphaltene content to demonstrate a physical hardening of the studied asphalts. The influence of natural or thermal aging are also studied by tribological measurements on lubricating properties. A ball on a three-plate equipment are used to evaluate the coefficient of friction (CoF) as a function of sliding velocity (Stribeck Curve) from 120 °C to 80 °C. The increase in asphaltene content after oxidation increases the frictional coefficient in the hydrodynamic regime. These observations were confirmed by tribological analysis performed on asphalts with controlled asphaltene contents (0, 15, 20 wt%). In addition of the physical hardening, asphalt oxidation causes a decrease of the lubricant properties. The evaluation of frictional coefficient can be added to the other well-known parameters to explain workability issues in presence of aged materials.