Seasonal variation in skid resistance of bituminous surfaces in Indiana

Results are reported of repetitive testing of 15 individual bituminous sections at speeds of 40, 50, and 60 miles/h by means of a skid-resistance measuring system as described by ASTM E274 to identify the surface types that provide and maintain satisfactory skid resistance independent of speed, seasonal changes, and climatic factors such as rainfall and temperature. The bituminous test sections represent surface types commonly used in Indiana, an experimental open-graded friction course, and conventional mixes modified by the substitution of slag for some or all of the conventional aggregate portion. A complete petrographic analysis that concentrated on the carbonates of the coarsest fraction was performed on individual pieces of aggregate extracted from a series of cores taken from the test sections. The report also briefly describes the calibration and standardization of Indiana's skid-resistance measurement system. The cyclic nature of skid resistance relative to season is very apparent for all of the surface types included in the study. With one exception, the skid resistance was highest in the spring, dropped off noticeably during the summer, and began to recover in late fall. Average skid values at 40 miles/h for all the test sections ranged from a high of 61.8 to a low of 23.8. Speed gradients were calculated and compared to provide an indication of seasonal sensitivity. Information obtained from the petrographic analysis and accelerated wear rates determined by means of the British polish wheel in the laboratory revealed that slag has a greater potential for polishing than the aggregates, which are predominantly limestone. However, skid test results show that the addition of slag improves the frictional characteristics of the pavement. Dolomite appears to be more susceptible to polishing than limestone but is not as susceptible as the slag. (Author)