The Relation Between Absolute Viscosity and Penetration of Asphaltic Bitumens

The relationship between absolute viscosity and penetration for asphaltic bitumens has been reinvestigated. With purely viscous materials in a wide range of penetration figures (5 to 250) a general relation exists. It is found, however, that the depth of penetration depends somewhat upon the conditions under which the measurements are made. Inadequate adhesion of the bitumen to the penetration needle increases the penetration. This effect, however, is not great and is the same for all purely viscous bitumens of the same penetration. Penetration depth determinations were also made with elastic bitumens. Here the final penetration depth is increased by interruptions of the determination as a consequence of the dissipation of the elastic tension during interruption. It is concluded that Traxler, Pittman, and Burns in their experiments have overlooked the elastic behavior of some of their bitumens and that therefore their criticism of the relation deduced by us between penetration and absolute viscosity is not valid.