Fatigue Tolerance of Aged Asphalt Binders Modified with Softeners

Abstract

Fatigue cracking caused by repeated heavy traffic loading is a critical distress in asphalt concrete pavements and is significantly affected by the selected binder. In recent years, the growing use of recycled asphalt materials has increased the need for the production of softer asphalt binder. Various modifiers/additives are marketed to adjust the grade and/or enhance the binder performance at high and low temperatures. The modifiers are expected to alter the rheological and chemical characteristics of binders and, therefore, their performance. In this study, the damage characteristics of modified and unmodified binders, at standard long-term and extended aging conditions, were tested using the linear amplitude sweep (LAS) test. Current data-interpretation methods for LAS measurements (including AASHTO TP 101-12, T 391-20, and recent literature) showed inconsistent results for modified binders. An alternative method to interpret LAS results was developed in this study. The method considers the data until peak shear-stress is reached because complex stress states and failure patterns are observed in the specimens after that point. The proposed parameter (Δ| G*|peak τ) quantifies the reduction in complex shear modulus measured at the peak shear-stress. The parameter successfully captures the effect of aging and modification of binders.

Impacts of Field and Laboratory Long-Term Aging on Asphalt Binders

“…Consistent with the methodology in García Mainieri et al ( 24 ), the shifting was done by fitting an n th order polynomial to the reference isotherm and the isotherm to be shifted. Z [x, y] (frequency, modulus) points were sampled with equal intervals in the y-axis; where Z was the number of data points measured.…”

“…The following frequency-sweep parameters were calculated following the approach presented by García Mainieri et al ( 24 ).…”

“…The phase angle was found to be related to chemical composition and capable of identifying phase-incompatible asphalt binders ( 27 ). The black angle was interpolated from measured phase angle ( δ ) data for a | G* | of 8,967 kPa using fourth-order polynomial fit ( 24 ).…”

“…The coefficients C1 and C2 are the constants determined by Williams et al ( 28 ) to develop master curves. The detailed procedure for determining these parameters is explained in García Mainieri et al ( 24 ).…”

“…Material ejection occurred while testing the aged asphalt binders and challenges were encountered in interpreting the LAS results. Therefore, a new practical parameter, Δ|G*| peakτ , from LAS test ( 29 ) was used in this study. Δ|G*| peakτ is defined as the reduction in complex shear modulus ( G *), as measured from the start of the LAS test until peak shear stress is achieved.…”