Effects of Thermoplastic Block Copolymers on Rheology of Asphalt

Abstract

The Dynamic mechanical properties of thermoplastic block copolymer modified asphalt were investigated. A viscosity graded AC-20 asphalt cement and five styrene-butadiene block copolymers with linear and radial structures were mixed at three concentration levels to yield 15 modified blends. The effect of short-term aging on rheological properties was simulated by the rolling thin film oven test (RTFOT) procedure. After establishing the linear viscoelastic range of response through performing stress sweeps, frequency sweeps were carried out at temperatures ranging from 5 to 75°C and frequencies between 0.063 and 188.496 rad/s. Using the time-temperature superposition principle, isothermal response curves were reduced to dynamic master curves of complex modulus and loss tangent. Relaxation spectra were developed by means of an approximate interrelationship between viscoelastic functions. Effects of polymer type and content, and aging condition on viscoelastic response were studied. Addition of polymer was found to substantially broaden the relaxation spectra. With increasing polymer contents, significant changes in the complex modulus and loss tangent at intermediate and low frequencies were observed. At higher frequencies the variations were less apparent and were found to be highly influenced by the aging condition of the modified binders. Evaluation of the measured shift factor data indicated that in all cases a Williams-Landel-Ferry (WLF) equation with universal constants could reasonably represent the temperature dependence of response.