The use of fractional calculus to model the experimental creep-recovery behavior of modified bituminous binders

Fitting of experimental creep-recovery curves obtained from rheological tests carried out on viscoelastic materials can reveal difficulties when handled by classical rheological theories, which generally provide exponential-type functions requiring a great number of parameters to be determined. Fractional calculus may represent a natural framework to develop more synthetic and efficient methods, overcoming most of the problems encountered with the classical approach. In this paper, a fractional model consisting of a dashpot in series with a springpot is proposed to describe the viscoelastic behavior of modified bituminous binders used in road pavements. The purpose is twofold: (i) to evaluate the adequacy of a rheological model involving a limited number of parameters, each of which with a precise physical meaning; (ii) to improve the accuracy of other fractional approaches proposed in literature. The investigation was validated by means of experimental data gathered from shear creep-recovery tests carried out at various temperatures on two modified bituminous binders containing a styrene–butadiene–styrene polymer and crumb rubber from end-of-life tires.