1. Viscoelastic Properties

This chapter is introductory and discusses aspects related to viscoelastic behavior of bitumen and asphalt mixture. This chapter highlights the viscoelastic properties applicable to asphalt and asphalt concrete which are to facilitate further reading. Some fundamental concepts of linear viscoelasticity are reviewed in order to understand the behavior of bitumen and asphalt concrete. Included in that discussion are the stiffness modulus as introduced by Van der Poel in asphalt technology; the concept of viscoelastic material that was first introduced by Maxwell on the example of bitumen; the concepts of viscosity and relaxation time. This chapter explains how the Boltzmann superposition principle can be applied to predict the evolution of either the deformation or the stress for continuous and discontinuous mechanical histories in linear viscoelasticity. Mathematical relationships between transient compliance functions and transient relaxation moduli are obtained, and interrelations between viscoelastic functions in the time domain are given. Experimental methods to measure the viscoelastic functions in the time and frequency domain are described as applied to asphalt concrete relaxation testing under axial tension and bitumen shear testing under cyclic loading. The first chapter discussed various rheological characteristics of viscoelastic properties of asphalt: creep compliance, relaxation modulus, complex modulus as well as the stiffness modulus, and it was shown that they were interrelated. Last paragraph outlines the time-temperature correspondence principle and gives an example of shift factors obtained based on the test data on asphalt concrete stiffness modulus in the uniaxial tensile testing at different temperatures.