Skid-Resistant Characteristics of Experimental Bituminous Surfaces in Illinois: Fid-Bau Portal

Skid-Resistant Characteristics of Experimental Bituminous Surfaces in Illinois

P. G. Dierstein / P. F. Ryan / W. C. Purcell

Skid resistance was among several factors used to evaluate bituminous mixtures, which were placed as experimental surfaces at 17 sites in Illinois. Skid tests indicated that surface texture as represented by changes in macroroughness and microroughness substantially controls the skid resistance of a surface. For the same kind of aggregate, dense-graded mixes that have a 1/2-inch top size aggregate provided higher skid numbers than either sand asphalt or binder course mixes. On the other hand, when aggregate gradation was held constant, air-cooled slag or Synopal, which have excellent microroughness, gave higher skid numbers than limestone or other aggregates that have less microroughness. Moreover, adding rubber to bituminous mixes or substituting stone sand for natural sand in a regular Class I surface course mix produced little, if any change in skid resistance. Bituminous surfaces designed for optimum macroroughness and microroughness should continually give adequate skid numbers regardless of wear, and bituminous mixes that produce a smooth surface texture obviously should be avoided.