Development of a Profile-Based Smoothness Specification for Asphalt Concrete Overlays (1378-S)

The Texas Department of Transportation (TxDOT) is implementing smoothness specifications based on profilograph testing as part of its construction quality control/quality assurance (QC/QA) program. To improve upon the existing test method, TxDOT sponsored a research project with the Texas Transportation Institute (TTI) to develop a smoothness specification for asphalt concrete overlays based on the current generation of profiling equipment which offer better accuracy and repeatability than the profilograph. To develop this specification, researchers evaluated the relationship between pavement profile and predicted overlay life assuming reflection cracking as the primary failure mechanism. This relationship is evaluated in two steps. First, the effect of surface profile on predicted dynamic loads is determined by vehicle simulation. Then, the effect of dynamic load variability on predicted pavement life is analyzed. This work led to the development of a relationship between the predicted change in pavement life associated with the placement of the overlay, dynamic load variability, and the fracture parameter, n, of the asphalt overlay mixture. Using this relationship, the study developed two categories of evaluation procedures that are applicable for the range of overlay thicknesses and treatments generally used in Texas. Test methods falling under Group A evaluate the contractor's performance based on the change in profile before and after the overlay. These methods are intended for thin overlays (< 63 mm) where no surface preparations are planned or where only spot level-ups are specified. Under these conditions and where a reasonable doubt exists that smoothness requirements based on final profile may be achieved, the Group A test methods can be used as options in lieu of dropping the smoothness specification or using the straightedge to check the surface smoothness on these projects. Test methods falling under Group B evaluate the contractor's performance based on the final surface profile. This report documents the development work conducted during the study.