Fatigue characterisation of modified asphalt binders containing warm mix asphalt additives

Fatigue is one of the major distresses in asphalt pavements and is strongly influenced by the properties of asphalt binder. Use of warm mix asphalt (WMA) additives allows production of asphalt mixes at lower temperatures than conventional hot mix asphalt. Lower production temperatures reduce the oxidative ageing of binders and thus addition of WMA additives may significantly impact fatigue performance of the binders and the mixes. The existing Superpave specifications prescribe the parameter G*sin delta as an indicator for fatigue behaviour of asphalt binder. In view of critical weaknesses associated with G*sin delta, several test procedures have been proposed for evaluating the fatigue performance of asphalt binder. The current study investigated fatigue characteristics of two modified binders (polymer- and crumb rubber-modified, PMB and CRMB) containing different dosages of two WMA additives: an organic additive, and a chemical additive. A total of twelve binders including ten warm asphalt binders and two control binders were studied. Five binder fatigue test procedures were employed in the study: Superpave fatigue parameter G*sin delta, linear amplitude sweep (LAS) test, DSR-based elastic recovery (DSR-ER) test, elastic recovery from MSCR (MSCR-ER) test, and binder yield energy test (BYET). Additionally, mixes were prepared and evaluated for fatigue using indirect tensile fatigue test. Results of the study showed that PMB and CRMB binders containing the chemical additive performed better in fatigue than the control binders and the binders containing the organic additive. The trends of mix fatigue life corroborated the binder fatigue results. Further, the results showed that monotonic test procedures (DSR-ER and BYET) produced the best correlations with mix fatigue results.