Enhancing accuracy of predictive fatigue life model in rejuvenated RAP binders through LAS test and complex modulus test at multiple temperatures

The linear amplitude sweep (LAS) test is widely accepted as a valuable tool for assessing binder fatigue. However, due to the binder's viscoelastic nature, the fatigue life varies with temperature, leading to a challenge in determining the LAS testing temperature. This research primarily addressed inaccurate assumptions of a linear relationship between the logarithms of the storage modulus (logG′(ω)) and angular frequency (log (ω)), as well as intermediate testing temperature. Then, by performing the LAS test at four different temperatures on rejuvenated RAP binders, a method for determining the rejuvenated RAP binder's fatigue behavior was introduced. The results demonstrated that LAS parameters, including A and B, correlated linearly at various temperatures with the rejuvenated RAP binder's complex modulus (|G*|) calculated at corresponding temperatures. Therefore, a fatigue life model, considering strain level and temperature effects, was developed using a power function of |G*|. It was found that the residual analysis exhibited a lack of fit, indicating that the linear model was inadequate throughout the whole range of experimental frequencies at multiple temperatures. Moreover, the newly introduced model predicted fatigue life more accurately at various temperatures utilizing the maximum stress failure criterion and the 35% damage level. This model will allow the LAS procedure to be used in a wider range of temperatures and strain levels for which rejuvenated RAP binders are used in the flexible pavement.