ON THE DYNAMIC CHARACTERISTICS OF ASPHALT MIXTURES

Abstract

Dynamical properties of asphalt mixtures were studied by vibrating the cantilever beams of the mixtures. We found that the properties of actual mixture are so complicated that we cannot approximate by the simple linear viscoelastic models such as Voigt type and Maxwell type. When the vector locus of complex elastic modulus E* (iω) for asphalt mixtures was plotted with the dynamic elastic modulus as abscissa and loss modulus as ordinate, it forms a wing shape locus and is not so simple as the semicircle (Maxwell) or straight half line (Voigt).We proposed a new index which shows the mechanical properties of mixtures. It was defined by the length between the intersection of two asymptotes and frequency characteristic curve of mixture on E* (iω) and frequency plane at which the phase difference between stress and strain was 45°. From the vertical location of both ends of the line, we can estimate the resistance to deformation of mixtures as a function of frequency, since the top end shows the elastic characteristic at infinitive frequency and the bottom end shows the actual stiffness of the mixture. The horizontal location of the line shows the frequency at which the phase difference between stress and strain is 45°, when the viscous and elastic resistance is equal at this frequency. The length of the line shows the rate of change from viscous to elastic state when frequency increases, for example, the longer the length, the more gradual the change will be.Some of the test results are discussed, applying the characteristic line concept, and we found that the thin asphalt film with less than about 5 micron thickness has different properties from thicker ones. And also the mixing effect of mineral particles to asphalt are discussed.