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Two methods of texture measurement are described: the outflow meter and profile analysis. The outflow meter measures the time for a fixed quantity of water to escape between a rubber seal and the pavement. Its development from a simple gravity flow instrument to a high-pressure device is described. The single number outflow parameter is not sufficient to provide adequate prediction of the pavement friction-speed relationship, but it is a parameter sensitive to pavement porosity in addition to surface texture. The profile tracer produces an electrical signal analogous to profile height as a stylus traverses the pavement. This signal is recorded and reduced to a meaningful set of parameters describing the root mean square values of the surface height and its derivatives. The profile spectral density is also obtained. Results for five test pavements are presented and compared with locked wheel skid data.
surface properties, texture, pavements, skid resistance, test equipment
Assistant professor, Mechanical Engineering, Pennsylvania Transportation Institute, The Pennsylvania State University, University Park, Pa.
Research mechanical engineer, Federal Highway Administration, Washington, D.C.