Unsteady-State Creep of an Asphalt Concrete

This paper reports the experimental investigation of the unsteady-state creep process for road hot fine-grained asphalt concrete within the variation for a stress (from 0.0081 to 3 MPa) and a temperature (from +60 to -24 degrees C) at uniaxial tension. It is found out that unsteady-state creep for the asphalt concrete is approximated with a high accuracy at all the considered temperatures and stresses by the power function (with 3 parameters: epsilon(0), alpha, delta) obtained from the Rabotnov's fraction-exponential function; at temperatures from -12 to +12 degrees C the parameter alpha has the mean value of 0.5; unsteady-state creep duration for the asphalt concrete depends strongly on the stress and the temperature. It is satisfactorily described by the mathematical expression in the form of multiplication of the exponential and the power functions. Mathematical expressions have been obtained which describe the unsteady-state creep and the steady-state creep rates for the asphalt concrete. It was found that the strain rate is varied sharply in the initial time moments from t approximate to 0 to 500-600 s (theoretically from infinity at t = 0 to approximate to 1 - 2 x 10(-3)%/s at t = 500-600 s); then it decreases monotonously in the following time moments, approximately according to a straight-line dependence. An asphalt concrete creep as a physical process can be similar to the viscous liquid flow: it is proposed to call the sites of the unsteady-state and the steady-state creeps as the sites of the transient and the constant viscosities respectively; a mechanical (rheological) model is represented which describes the sites of the transient and the constant viscosities for the creep curve of the asphalt concrete through Trouton and Newton viscosities respectively. Meanwhile, it has been stated that the viscosity of the asphalt concrete can reach 26,000 and 45,000 MPa at the temperatures of +24 and +36 degrees C respectively at the end of the unsteady-state creep.