Destruction and Recovery of Internal Structure in Polymer-Modified Asphalts

Abstract

Nowadays, asphalt cement is frequently modified by blending it with various polymers in order to obtain a material with improved engineering properties. In number of studies it has been shown that ethylene-vinyl-acetate (EVA) and styrene-butadiene-styrene (SBS) copolymers can enhance the rheological properties of conventional asphalt at relatively wide range of temperatures. It is believed that when polymer is added to the base asphalt it absorbs low molecular weight oil fraction of asphalt and swells, thus forming a three-dimensional network structure. The properties of this structure determine the rheological behavior of polymer-modified asphalt. Asphalt modified by SBS and EVA copolymers (concentrations from 2 to 8% by weight) was investigated in dynamic mechanical analysis and interrupted shear flow tests. The interrupted shear test involves two phases of shearing (stress growth and flow relaxation in between) with varying rest periods between the two shear phases. All the tests were performed at 60°C in strain control rotational viscometer. The destruction and reformation of the internal network structure of polymer-modified asphalts can be demonstrated in this test.