Viscoelasticity modelling of asphalt mastics under permanent deformation through the use of fractional calculus

Abstract

This study focuses on the mechanical behaviour of asphalt mastic composed of filler particles bonded with an asphalt bitumens. Asphalt mastics are viscoelastic composite materials widely used in the construction of pavement layers. The mechanical properties and the influence of the fillers on the filler/bitumen (f/b) matrix is one of the main areas of current research. In particular, the elastic determination of fillers for mechanical testing in asphalt mastic is relevant to understand permanent deformation caused by temperature variations caused by seasonal changes and vehicular traffic loads. In this sense, this research proposes a new methodology for rheological characterization of the elastic properties of the filler ξ2 and elastic-viscous properties of the asphalt bitumen, ξ1 and η, respectively, complementing the existing designs of asphalt mixture. The proposed methodology allows for identification of the influence of non-conventional fillers in the behavior of the asphalt mastic for the different recovery cycles of the Multiple Stress Creep Recovery (MSCR) and determination of new rheological parameters for the compression of the recovery phenomena and the elastic capacity of the type of filler and weight of the base bitumen. The results obtained show a greater adjustment to the experimental curves in determining the elastic modulus in each cycle for the hydrated lime and fly ash fillers with different filler/bitumen ratios. In particular, the proposed model for bituminous mastics achieves a strong fit with the experimental curves by empirically reducing the quadratic error (R2 = 0.99) and managing to differentiate the elastic capacity ξ2 of each filler and its effect with increasing concentration. For example, it establishes that the Hydrated lime filler (HL) acquires an average Young's modulus of 0.005 MPa, being 99.31% more elastic than Fly ash filler (FA) for a load of 3.2 kPa at a 1.25f/b ratio. In addition, the new model can be used to modify bitumen properties to design optimized and stronger asphalt mixtures.