Dynamic mechanical analysis of crumb rubber modified asphalt binder containing warm mix additives

Crumb rubber modified (CRM) binder has high working temperatures, which may be reduced with addition of warm mix additives (WMA). The dynamic mechanical analysis of CRM binder containing three different WMA additives, namely Fischer–Tropsch wax-based (FT), water-based (WB) and chemical surfactant-based (CS) additive, was undertaken in the present study. The CRM binder was blended with different percentages (by weight of asphalt binder) of WMA additives, i.e. FT (1, 2 and 3%), WB (4, 6 and 8%) and CS (1, 2 and 3%). The viscosity, rutting and fatigue performance of CRM binder with and without WMA additives were evaluated using Brookfield viscosity, multiple stress creep recovery and linear amplitude sweep tests, respectively. The FT modification effectively reduced the viscosity of CRM binder, while the inclusion of CS showed similar viscosity and WB increased the viscosity of CRM binder. The WB modification observed to create foaming effect in asphalt binder. The FT- and WB-modified CRM showed same High Superpave performance grade (PG), however, the addition of CS degraded high PG of CRM binder (from PG88 to PG82). The CRM binder showed reduced J nr value and improved R-value after FT and WB modification, indicating improved rutting resistance. Whereas, CS-modified CRM indicating poor rutting performance (high J nr and low R). Asphalt binder combinations showed significantly different rutting performance parameters (J nr and R-value), whereas they were graded as E. Therefore grading of asphalt binders based on AASHTO MP 19 should be relooked. All WMAs improved the N f i.e. fatigue resistance of CRM binder. The 2% FT dosage observed to be optimum for CRM binder. The study showed that selection of WMA additives should not only be based on viscosity criterion but also rheological performance parameters are to be looked into for making appropriate conclusions about their effectiveness.