CAIT project no.: 80 RU908
Fiscal Year: 1999/2000
Rutgers-CAIT Author(s): Thomas Bennert, Ali Maher, Nenad Gucunski
External Author(s): Anthony Chmiel
Sponsor(s): NJDOT, FHWA-USDOT
The report pertains to the laboratory evaluation of hot mix asphalt modifiers (HMA-M). These modifiers are defined as materials that are added to hot mix asphalt (HMA) to improve its working capacity, whether for permanent deformation, fatigue/low temperature cracking, or both. The HMA-M is not a standard, approved material for the NJDOT. They are typically materials that customers bring to the NJDOT, with the understanding that the HMA-M would improve the working capacity of the HMA. However, the extent of the improvement is unknown. Therefore, a methodology to evaluate the extent of the improvement was necessary. And since the additives involved in this study claimed to aid in the rut resistance of the HMA, the performance testing focused on the mixes resistance to permanent deformation.
A total of six binders were evaluated in the study. Three of the binders were NJDOT approved materials and were used as baseline comparisons. They were a PG64-22 from Citgo, and a PG76-22 from both Citgo and Koch Materials. The three HMA-M evaluated in the study were; 1) Eastman’s EE-2 polymer additive, 2) Creanova’s Vestoplast polymer additive, and 3) Hydrocarbon Technology’s Carbon Black. The HMA-M were added to the PG64-22 baseline sample by using the manufacturer’s recommended procedures. This allowed for the direct comparison between the initial mix (PG64-22) and the modified mix. The two PG76-22 mixes were used as a high end comparison. All additives and binders were mixed to make a 12.5mm Coarse Superpave mix designed for heavy traffic (3 to 30 million ESAL’s).
The compacted samples were tested in the APA (Asphalt Pavement Analyzer), Superpave Shear Tester (SST) under the Repeated Shear (RSCH), Frequency Sweep (FSCH), and Simple Shear (SSCH) test modes. The results showed that the SST test was extremely useful at evaluating the HMA-M for stiffness, creep, and permanent deformation. RSCH and APA results compared favorably, as did the FSCH and binder test results. The Creanova Vestoplast HMA-M ranked as the best HMA-M tested, however, the Vestoplast did not perform as well as the either of the PG76-22 mixes. An evaluation procedure and test parameters are recommended for future the use of evaluating HMA-M.