Evaluation of Louisiana Friction Rating Table by Field Measurements

This study aims to evaluate the current Louisiana Department of Transportation and Development (LADOTD) friction rating table by field measurements and provide recommendations for the frictional mix design guidelines. The current friction rating table is based on the Polished Stone Value (PSV) of coarse aggregate as the only surface friction guideline in a wearing course mixture design, which is only one of many factors that affect the pavement surface friction. To achieve the objective, the pavement surface friction and texture properties were measured using Lock-Wheel Skid Trailer (LWST), Dynamic Friction Tester (DFT) and Circular Track Meter (CTM). Twenty two different asphalt p avement sections were selected across the Louisiana covering commonly used aggregate sources and four typical mixture types namely 12.5mm and 19mm Superpave, Stone Mastic Asphalt (SMA) and Open Graded Friction Course (OGFC). 1,000-ft. test section was marked to conduct the field tests. Three skid number measurements were taken at the beginning, the mid-point, and the end of each test section using both ribbed and smooth tire. Three DFT and three CTM tests were conducted within each segment that LWST took the skid number. In addition to field testing, multiyear field skid number data were retrieved from LADOTD Project Management System (PMS) database and included in the analysis of this study. Statistical analyses were performed on the collected data to develop correlations among different test devices and frictional properties. Subsequently, the analysis results led to the development of a procedure to predict the surface skid number at the end of design life based on design traffic, aggregate and mixture properties. The developed skid prediction procedure can be used to update the current DOTD friction rating table. An exemplary updated PSV table was also provided under different traffic level through selection of different mixture to achieve end of design life SN40S equals to 20. Similarly, a minimum DFT20 requirement table after 100,000 polishing cycles under Three Wheel Polishing Device (TWPD) was also developed for friction evaluation of new aggregate in mixture by comparing field DFT and CTM measurements with laboratory measurements (obtained from LTRC project 09-2B)