Current asphalt binder specifications lack the ability to characterize asphalt binder damage resistance to fatigue loading. Multiple accelerated testing procedures that attempt to efficiently and accurately characterize the contribution of asphalt binders to mixture fatigue are under investigation. One of these tests, which has received significant acceptance by experts and has been submitted as a draft AASHTO standard, is the linear amplitude sweep (LAS) test. This procedure uses viscoelastic continuum damage mechanics to predict binder fatigue life as a function of strain in the pavement. The LAS test uses cyclic loading with systematically increasing load amplitudes to accelerate damage and provides sufficient data for analysis in less than 30 min. Although results of the current LAS testing protocol are promising, the time and the complex numerical procedures required for the analysis have raised concern. In addition, insufficient damage accumulation was observed when the strain amplitudes proposed in the LAS test were used for a set of polymer-modified binders. This paper presents simplifications of the current analysis procedures and evaluates the ability of extended strain levels to cause sufficient damage for better calculation of the binder fatigue law parameters. The effectiveness of the modified procedure was validated by comparison of the results with the fatigue performance recorded by the Long-Term Pavement Performance program with consideration of the pavement structure. The fair correlations showed the potential for effective use of the modified method for binder specifications.

Understanding moisture damage mechanisms in asphalt pavements and evaluating the right combination of materials that are resistant to moisture damage are important. Moisture damage is the loss of strength or stiffness in asphalt mixtures caused by a combination of mechanical loading and moisture. Many test methods have been developed to evaluate loss of adhesion and cohesion in binders. However, a simple procedure to address moisture damage in the asphalt–aggregate interface is not available. The feasibility of the newly developed bitumen bond strength (BBS) test for moisture damage characterization was investigated. An experimental matrix that included various binders, modifications, and aggregates to account for the chemical and physical conditions in the aggregate–asphalt interface was completed. A statistical analysis was performed to verify reproducibility of the BBS test. The results indicated that the bond strength of asphalt–aggregate systems was highly dependent on modification and moisture exposure time. Polymers were found to improve the adhesion between asphalt and aggregate as well as the cohesion within the binder. Results from this study indicated that the BBS test was repeatable and reproducible. To further validate the effectiveness of the BBS test, a comparison of the BBS test results and the modified dynamic shear rheometer strain sweep test was conducted. The comparison showed that the BBS test could rank materials similarly to a more sophisticated and time-consuming test.

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