A Study of the sand patch outflow meter methods of pavement surface texture measurement

A study of the sand-patch and outflow meter methods of pavement surface texture measurement was completed. Included in this study was repeatability testing and testing to determine the degree to which pavement surface texture, as measured by these procedures, correlates with pavement coefficient of friction, skid number, and skid number speed gradient. Test locations were selected on open-graded and dense-graded asphalt concrete, chip-sealed and fog-sealed asphalt concrete, and new, polished, and grooved PCC pavements. The results of the testing indicated that the repeatability of the sand patch test procedures studied was poor to fair and that the outflow meter test results were independent of water temperature. A general trend toward higher skid numbers and coefficients of friction was evident with increasing texture depth, as measured with both the modified sand patch and the outflow-meter procedures. However, neither relationship was considered definitive enough to use as a basis for a minimum texture depth construction specification requirement for pavement surfaces. Also, neither method provided a definitive measure of skid number speed gradient