Laboratory apparatus, consisting essentially of a torque generator and a torque meter, in which a rubber annulus is driven against a plane surface of a rock core or pavement specimen, as in an ordinary friction clutch, was used to study variations in the coefficients of friction with respect to texture and material characteristics. Dry friction coefficients were found to be rather high in magnitude. and fairly constant throughout wide variations in surface textures. In contrast, wet friction coefficients were very high for rough textures but very low for polished surfaces. Wet friction values correlated in an approximately hyperbolic manner with 60-degree specular reflectivity. Limestones were found to polish readily whereas sandstones tended to undergo coarse wear during preparation of the surfaces.

Experiences with sand-asphalt mixes, blends of limestone coarse aggregates and silica sands, and sandstone aggregates are briefly described.

Recent experiments in the adaptation of an automobile for monitoring pavement slipperiness are also described.

Report Date


Report Number

No. 132

Digital Object Identifier



Prepared for the First International Skid Prevention Conference, University of Virginia, (September, 1958).