Harmonization of Texture and Friction Measurements on Florida's Open-Graded and Dense-Graded Pavements

Abstract

A study was initiated to harmonize the dynamic friction tester and a locked-wheel tester on Florida's typical open-graded and dense-graded surfaces under various speed conditions. In addition, two texture measuring devices, the circular track meter and a high-speed 64-kHz laser mounted to the locked-wheel tester, were evaluated. These devices were first harmonized at a standard test speed of 40 mph (65 km/h). Because of the increased level of macrotexture in the open-graded mixtures, the open- and dense-graded surfaces were assumed to show different frictional behavior under different speed conditions. As a consequence, the harmonization equations for the open- and dense-graded surfaces were developed separately. Harmonization of different test speeds was also performed for each given test method to allow for converting the friction measured at a range of speeds—30 mph (50 km/h) to 60 mph (95 km/h)—back to that of the standard speed. The flexibility provided by these harmonization efforts is of great practical use and provides an alternative to the international friction index for Florida's conditions.