Numerical determination of pavement mean texture depths at different degrees of traffic polishing-induced wear

All existing digital image-based numerical mean texture depth (MTD) calculation methods are unable to achieve a consistent level of acceptable accuracy for MTD values calculated at different degrees of pavement polishing. To solve this problem, a novel procedure is proposed to determine MTD as a function of degree of polishing represented by a texture statistic 'directional wear index' DWI. First, a relationship is established between DWI and the elevation Heq that defines the equivalent top surface of MTD. Heq is derived from 3-D digital image based on the concept of planation surface. Through studying laboratory specimens and field pavements polished to different degrees, a well-defined relationship between DWI and Heq was established. Knowing Heq from the Heq–DWI relationship, MTD is calculated as the mean depth of the voids between Heq and the test surface. The digital image-based procedure is able to concurrently determine MTD and the surface's degree of polishing.