Critical Evaluation of Use of the Procedure of Superpave Volumetric Mixture Design Procedure for Modified Binders (05-2315)**
Dong-Woo Cho, University of Wisconsin, Madison
Hussain U. Bahia, University of Wisconsin, Madison
Nabil Kamel, Asphalt Research and Technical Services, Inc., Canada

This study was conducted to examine the possible interference of modified binders with the standard procedure for volumetric mixture design used in the Superpave system. Sensitivity of volumetric properties and moisture damage performance was evaluated using four binders modified with two different technologies (Polymer and no-additive modifications). The study included three tasks to evaluate effects of compaction temperatures (in the range of 72¡ÆC to 148¡ÆC), effects of vertical pressure (in the range of 200 kPa to 600kPa), and moisture damage according to the AASHTO T283 procedure. The Zero Shear Viscosity concepts were used to estimate mixing and compaction temperatures, compaction energy index was used to study changes in compaction effort, and cohesion and adhesion of binders were measured. The results indicate that temperature effects, within a reasonable range, are somewhat marginal and that unless temperatures are reduced to below 80¡ÆC, the effects on volumetric properties are rather small. It was also found that using a target viscosity of 1.5 Pa¡¤s for mixing and 3.0 Pa¡¤s for compaction can provide very reasonable compaction temperatures, particularly if Zero Shear Viscosity is used. These criteria for temperatures worked well for the grades and type of modification used in the study. The vertical stress used in the gyratory compactor showed very significant effects on volumetric properties. Changing pressure from 600 kPa to 300 kPa resulted in 3.0 to 4.0 % increase in air voids, which is more significant than changing viscosity by more than 10 times. It is therefore postulated that the focus on keeping temperature high during compaction in the lab and in the field could be un-founded. With increasing pressure during compaction in the lab or weight of roller in the field, significant changes in density could be achieved. Moisture damage does not appear to be affected significantly by the variation in binder viscosity profiles for the binders and aggregates used in this study. Because of the limited sample size, more work is needed in this area to study effect of mixing and compaction temperatures on moisture damage.