Tribological Approach to Demonstrate Workability of Foamed Warm-Mix Asphalt

Asphalt binder acts as a lubricant film between two aggregates during mixing and compaction. The frictional phenomena in an asphalt–aggregate interaction play an important role in mixing and compaction of warm-mix asphalt (WMA). This study evaluates the frictional behavior of WMA with foamed asphalt through tribological characterization. A ball-on-three-plates apparatus assembled inside a dynamic shear rheometer (DSR) is utilized for tribological experimentation. Six foamed asphalts with varying foaming water content (FWC) and a controlled unfoamed asphalt have been tested at various temperatures: 25°C, 60°C, 100°C, and 135°C. These binders were also characterized for rheological properties. Test results show that the foaming process alters the frictional resistance of the foamed asphalt; specifically, the foaming process reduces the coefficient of friction in elastohydrodynamic and hydrodynamic lubrication regimes. Reduced frictional resistance helps in the formation of better coating during mixing and improves the sliding ability between aggregates during compaction at reduced temperature.