Evaluation of intermediate temperature cracking performance of warm mix additive modified asphalt binders

In the present study, intermediate temperature cracking performance of different types of asphalt binders containing warm mix asphalt (WMA) additives was evaluated using three test methods namely, Superpave fatigue parameter, linear amplitude sweep (LAS) and double edge notch test (DENT). The Superpave fatigue, LAS, and DENT tests are based on dissipated energy, viscoelastic continuum damage (VECD) and work of fracture approaches, respectively, and thus each of the tests may result into different performance ranking of asphalt binders. The outcome of the Superpave fatigue, LAS and DENT tests are G∗sinδ, number of cycles to fatigue failure (Nf), and critical tip opening displacement (CTOD) based on which cracking potential of asphalt binder can be assessed. An asphalt binder having a low Superpave parameter, high Nf and high CTOD values are expected to have better intermediate temperatures cracking performance. The present study selected three control binders namely virgin (AC), styrene-butadienestyrene (SBS) and crumb rubber modified (CRM) binders were modified using three WMA additives namely Fischer-tropsch (FT) wax based, chemical surfactant (CS) based and water based (WB). Control binders were modified with 2%, 6% and 2% (by weight of asphalt binder) of FT, WB and CS, respectively, using a mixer. The results showed that, based on G∗sinδ and CTOD parameters, CS modification reduced stiffness (reduced G∗sinδ) and improved ductile performance (increased CTOD) of control binders. However, WB and FT modification increased stiffness and degraded the ductile performance of control binders, except for SBS with 6%WB binder which showed higher CTOD than control SBS binder. On the other hand, considering performance based on Nf parameter, WMA additive modification improved fatigue life of control binders, except for SBS with 2%CS binder which showed lower Nf as compared to control SBS binder. Control binders with and without WMA additives were ranked based on G∗sinδ, Nf and CTOD parameters. AC and CRM binder with and without WMA additives followed similar performance ranking based on G∗sinδ and CTOD parameters. It is difficult to conclude over the best suitability of intermediate temperature performance parameter as mentioned tests involve different loading conditions and analysis approaches. Hence, further investigation on asphalt mixes is necessary to identify the best suited intermediate temperature performance parameter of asphalt binders, and its possible correlation with mix performance.