Rheological Characteristics of Selected Polymer-Modified Asphalts Through Their Dynamic Compliances

In past decades polymer-modified asphalts have become commonly used materials for the construction of high-quality flexible pavement. Regardless of the commercial importance of these “modified asphalts,” little is known about the mechanisms of polymer-asphalt interaction, and polymer-asphalt production is purely empirically based. A better understanding of the molecular processes in polymer asphalts is necessary, not only to satisfy scientific curiosity, but also for economic reasons. An attempt is made to investigate the changes in molecular mechanisms after the addition of polymer into asphalt. To see these changes, the contribution of viscous flow to the rheological behavior of paving asphalts has to be mathematically eliminated because this phenomenon masks the more subtle behavior of asphalt materials. It is quite common to present viscoelastic data as components of the complex modulus, G*(ω) In linear viscoelastic theory these material functions, and the stress relaxation modulus, G(t), can generate a complete set of viscoelastic functions that are all mathematically equivalent. The experimental experience, however, does not support such equivalence. It was shown that what is sometimes identified as a plateau or shoulder by the dynamic storage modulus G′(ω) or the stress relaxation modulus G(t) is an artifact of the viscous deformation, which can be subtracted from some compliance functions but not from the modulus functions. Thus, compliance functions can show more attributes of the actual structural dynamics of the studied materials than the dynamic functions. Several polymer-modified asphalts are studied in the terminal and at the beginning of the transition regions. The advantage of using the dynamic compliance functions for modified asphalts is discussed.