Determination of the stiffness of ecological asphalt mixtures with non-destructive impact resonance tests

The objective of this study is to characterize the linear viscoelastic behavior of ecological asphalt mixtures with non-destructive impact resonance testing. Two specimens of each of the four investigated mixtures were produced and tested in laboratory: a reference mixture (REFMIX), a mixture containing a modified binder with 30% of Kraft lignin in mass of total binder (LIGNIN), a mixture with 20% of reclaimed asphalt pavement (RAP) in mass of total aggregates (RAP20), and a mixture with 50% of RAP (RAP50). The specimens were tested at five temperatures (-20 °C, 0 °C, 10 °C, 20 °C, and 30 °C) with an impact resonance equipment to obtain experimental Frequency Response Functions (FRF’s). Subsequently, a back-calculation procedure was used to determine two linear viscoelastic properties (absolute value and phase angle of the complex modulus) from FRF’s measurements using finite element method (FEM) simulations. The results indicated a good repeatability of the test, with results from all specimens presenting the same trend, a decrease of the modulus and an increase of the phase angle with increasing temperature. Results also showed that the modified mixtures are stiffer than the reference mixture at each temperature. Kraft lignin has the greatest influence in increasing the stiffness in comparison with the reference mixture, followed by the addition of 50% and 20% of RAP. It was concluded that the addition of ecological materials, such as lignin and RAP, directly affects the viscoelastic behavior of bituminous materials, which can be beneficial for many applications.