A field study was conducted at the Pennsylvania Transportation Institute's Pavement Durability Research Facility at Pennsylvania State University to determine the effects of specific construction, traffic, and material variables on the performance of bituminous seal coats. As part of the study, the adequacy of existing seal-coat design procedures, quality control procedures, and seal-coat performance measuring techniques was evaluated. The focus of this paper is on the latter evaluation; the effects of the other variables are reported elsewhere. The evaluations were based on actual field measurements and led to numerous recommendations for improvements in seal-coat design methods, equipment calibration, measurement and evaluation of seal-coat performance, prediction of seal-coat life, and the appropriate use of seal coats as a maintenance technique. The recommendations are reported herein. Finally, a definitive pattern of seal-coat macrotexture degradation was identified under this closely monitored field experiment. This finding was used to develop a prediction model for seal-coat life. Aggregate wear rates and embedment rates were measured on two surfaces under closely monitored traffic loading conditions. The wear and embedment rates were used to illustrate the potential of the seal-coat-life prediction model to evaluate the effects of different variables on expected seal-coat life. On the basis of the deficiencies observed in the existing design procedures, updated design charts that use more objective methods of evaluating the existing pavement surface are proposed, as are potential methods for rating the surface.
Abstract