Influence of foaming on tribological and rheological characteristics of foamed asphalt

Abstract The frictional characteristics of asphalt binder as a lubricant film in an asphalt-aggregate interaction play a major role in workability of warm-mix asphalt (WMA). However, no WMA research considered the frictional characteristics of asphalt to demonstrate the workability of WMA, rather most of the previous studies are limited to foaming and some of the rheological properties. Frictional evaluation can be conducted on asphalt binder through the tribological experimentation with a ball-on-three-plates apparatus assembled inside a dynamic shear rheometer (DSR). This study aims to evaluate the effect of foaming on tribological and rheological characteristics of foamed asphalt binder. The tribological and rheological tests were conducted on six foamed asphalts with varying foaming water contents (FWCs) and on a controlled un-foamed asphalt binder at different temperatures. These binders were also characterized by foaming and chemical properties. Test results show that the foaming process alters the frictional resistance of the foamed asphalt binders, specifically the foaming process reduces the coefficient of friction in the elasto-hydrodynamic and hydrodynamic lubrication regimes. The tribological characteristics are more relevant to the improved workability of foamed WMA over rheological characteristics.