The objective of this research was to determine the causes of pavement slipperiness in Alabama, develop remedies for eliminating pavement slipperiness, and make recommendations for specifications for future pavements which would ensure satisfactory skid resistance in them during their anticipated service lives.
The skid test data were obtained by the Alabama State Highway Department. The analysis of the data was made by the Engineering Experiment Station of Auburn University, Auburn, Ala.
All skid tests were made using a two-wheel skid trailer meeting the requirements of ASTM Specification E 274-65 T equipped with tires meeting ASTM Specification E 249-66. All data were obtained by locking the left wheel only at a speed of 40 mph.
The results of this research indicate that the use of limestone as a coarse aggregate in asphalt plant mixes and surface treatments produces slippery pavements apparently due to polishing under traffic.
They further indicate that well-graded coarse sands, when used as fine aggregate in asphaltic concretes, make a significant contribution to their skid resistance. The same is true when they are used in hot-sand asphalt hot mixes.
Gravels and granites, when used as coarse aggregates in asphaltic concrete plant mixes, produce pavements that are fairly skid resistant but caution must be exercised by vehicle drivers on these pavements when they are wet.
The most skid resistant pavements in the plant mix and surface treatment groups are those incorporating slag as a coarse aggregate.
Most Portland cement concrete pavements are highly skid resistant until they have been exposed to heavy traffic loads for long periods of time.
The net result of this research is that fairly definite guidelines have been developed for writing specifications for future pavements in Alabama that will ensure skid resistant pavements. As a result there should be a marked reduction in the number of skidding accidents in the state.