Modification and Validation of Linear Amplitude Sweep Test for Binder Fatigue Specification

TLDR

Current asphalt binder specifications cannot adequately characterize fatigue damage resistance, prompting investigation of accelerated tests such as the widely accepted linear amplitude sweep (LAS) test, though its promising results are hampered by time‑consuming and complex numerical analysis. The study aims to simplify LAS analysis and assess whether extended strain levels improve damage accumulation for accurate binder fatigue law estimation. The modified LAS procedure employs viscoelastic continuum damage mechanics with cyclic loading of increasing amplitudes, simplified analysis, and extended strain levels, and its effectiveness was validated against Long‑Term Pavement Performance data. The modified LAS test produced sufficient damage accumulation in polymer‑modified binders and showed fair correlations with Long‑Term Pavement Performance data, indicating its potential for binder specification.

Abstract

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.