Rheological Analysis of Performance Grade Rutting and Fatigue Cracking Criteria in Asphalt Binders

This study critically examines the utility of the rheological parameters, such as phase angle δ, sinδ, complex modulus (|G*|), rutting criterion (|G*|/sinδ), fatigue criterion (|G*|sinδ), etc., in the performance grading (PG) rutting and fatigue criteria. The results show that for unmodified asphalt binders at true PG upper limiting temperature, the PG rutting criterion ‘|G*|/sinδ’ can be equated to the viscosity of the binder. The equivalence of |G*|/sinδ and viscosity is valid over a wide range of testing conditions in oscillatory and rotation shear. Consequently, the correlation of |G*|/sinδ and viscosity with rutting in asphalt pavements was similar. The PG fatigue cracking criterion is based on the energy dissipating capacity (loss modulus G″ = |G*|sinδ ≤ 5000 kPa) of ‘RTFO + PAV’ aged binders. At true PG intermediate temperature, the loss modulus and storage modulus values of ‘RTFO + PAV’ aged binders were similar since the δ values were close to 45°. Therefore, G″ as the fatigue criterion will not provide any particular benefit in predicting the fatigue performance of ‘RTFO + PAV’ aged binders. Furthermore, using δ to forecast fatigue performance may lead to inaccuracies, as fatigue cracking and δ show opposite trends after aging in asphalt binders. The rheological properties of polymer modified binders (PMBs) are better quantified at frequencies ≤ 0.1 rad/s due to the sluggish dynamics of the polymer molecules, and the correlation between the PMBs rheological properties and rutting in asphalt mixes improves at lower frequencies. Hence, analysis at lower frequencies is critical for better grading and performance evaluation in PMBs.