Field validation of Wisconsin modified binder selection guidelines

Abstract

In June 2005, a report with Modified Binder Selection Guidelines for Wisconsin was finished under the sponsorship of the Wisconsin Highway Research Program. The report name is Development of Guidelines for PG Binder Selection in Wisconsin (SPR# 0092-01-01). In that report five areas were covered for the guidelines: binder storage and stability; mixing and compaction temperatures of binders; fatigue characterization; low temperature cracking and rutting characterization. The results of the project included the development of new specification guidelines. The new specifications included some new parameters: Zero Shear Viscosity (ZSV) mixing and compaction temperatures limits; a critical cracking temperature obtained using BBR, DTT and Tg testing for low temperature characterization; a fatigue parameter called Np20 obtained by time sweep testing in the Dynamic Shear Rheometer (DSR); and a rutting parameter called Gv obtained by repeated creep and recovery using DSR. The present report deals with the field validation of these new parameters. It is divided into four chapters, each one dealing with one of the topics. The first chapter is Mixing and Compaction Temperatures. Eight different projects were surveyed and sampled for this section. The study concluded that compaction in the field happens at temperatures ranging from 120 degrees C to 70 degrees C. The compaction temperatures from ZSV are too high and not realistic. The temperature at which the binder has a low shear viscosity of 50 Pa.s is recommended as a lower limit for compaction in the field. The mixing temperatures using ZSV are lower and more appropriate than the ones recommended by the Superpave Criteria. The current procedure for determining ZSV temperatures, however, includes significant extrapolations that make the results inaccurate. A better procedure should be developed before implementing this method. Eight projects were considered for the fatigue validation. The fatigue parameter Np20 showed good correlation with the longitudinal cracking in the field. A new surrogate test using stress sweep was also compared with field data and no good correlation was found. The results of the low temperature study indicated that the current Superpave criteria of S(60) = 300 MPa, from BBR data, shows good correlation with field transverse cracking. It seems that there is no need to use the DTT or Tg for low temperature characterization. No conclusive results could be obtained from the rutting study. None of the six projects followed for this section showed any rutting during the duration of this study. The research team, however, maintains the validity of the new parameter Gv. The prediction of allowable ESALs for each project, based on Gv, are higher than the accumulated traffic until now. This agrees with the field performance that shows no rutting damage up to date.