Exploratory Field Study of Aggregate-Skid Resistance Effectiveness: Fid-Bau Portal

Exploratory Field Study of Aggregate-Skid Resistance Effectiveness

H. W. Kummer / D. L. White

Twenty-four test sections (surface treatments) 11 ft. wide and 2800 ft. long were placed on a 5.9 mile long main rural highway, to determine the influence of aggregate type (gravel, limestone and slag) shape (crushed and uncrushed) and size (1B, modified 1B and S.P. -9 grading) on skid resistance. The exposure of the test sections to traffic was determined from a traffic counter installed at the midpoint of the test road and an assumed normal distribution of wheel passes across the wheel track. Minimum and maximum air temperatures and precipitation were recorded by a nearby weather station. The test crew performed air and wet surface temperature measurements prior to running skid tests. The skid resistance data accumulated during the months of October and November indicate that the pavement wear and aggregate polishing process and the resulting decrease of the Skid Number is offset by the increase of the Skid Number due to decreasing air and wet surface temperatures. Pavement wear and aggregate polishing effects on skid resistance can thus be evaluated only when the Skid Number - temperature gradient is known. The latter appears to be about 0.34 SN/F for wet pavement temperature range of 40 to 70F and 0.3 SN/F for the range of 70 to 100F. The general lack of control over variables which affect the polishing process and skid test data in the field and the resultant uncertainties associated with such data strongly emphasizes the need for development of laboratory methods which permit the rapid and realistic evaluation of the polishing resistance of aggregates and aggregate mixtures under controlled conditions and a return to field experiments of this nature at a later date when the influence of principal parameters is understood. (Author)