EVALUATION OF OPEN-GRADED PLANT-MIX SEAL SURFACES FOR CORRECTION OF SLIPPERY PAVEMENTS

This paper presents an extended evaluation of skid characteristics of various experimental plant-mix seal (PMS) and dense-graded hot-mix surfaces. The evaluation was performed on 1,000-ft (304.8-m) duplicate sections on US-190 in the Baton Rouge area. The sections consisted of a dense-graded gravel hot-mix surface of approximately 1-in. (25-mm) thickness and 3 PMS surfaces (crushed gravel, slag, and expanded clay) of 5/8-in. (16-mm) thickness. Evaluation of these surfaces consisted of skid measurements according to ASTM E274. Four-year data on the frictional performance of these surfaces have indicated that, in general, the PMS surfaces seem to possess the most desirable features with respect to constructability, skid resistance, texture, and drainage; specifically, the expanded clay and slag PMS surfaces show higher initial skid numbers and are able to maintain these numbers over an extended period of time under light and heavy traffic conditions; in addition to providing high skid resistance these PMS surfaces tend to reduce the potential for hydroplaning and ice glaze; and, in general, PMS surfaces provide flatter friction-speed gradients than does the corresponding hot-mix surface. The paper also provides information on the factors to be considered during the design and construction of these PMS surfaces and supplementary specifications for their design, construction, and acceptance.