Backcalculation of Swollen Crumb Rubber Modulus in Asphalt Rubber Binder and Its Relation to Performance

Abstract

A method is presented to estimate the engineering properties of swollen rubber particles within crumb rubber–modified (CRM) asphalt binders. It was observed that the backcalculated modulus of swollen rubber within the CRM asphalt binder was related to performance. Thus improper mixing temperatures as well as interaction times could lead to the insufficient swelling of rubber and to a performance worse than anticipated in CRM asphalt mixtures. The backcalculated modulus of the rubber within the CRM asphalt could be used as a quality control tool, which could be measured during construction. An experimental approach was taken to investigate the mechanisms of interaction between the asphalt binders and crumb rubber and their effect on the modulus of the rubber within the CRM asphalt binder. The experimental program included dynamic shear modulus (| G*|) as well as linear amplitude sweep tests. These tests were performed on neat binder, CRM binders mixed at three temperatures, neat binder mixed at these three temperatures (without the rubber), and the residual binder obtained through the drainage of the CRM binders (i.e., by filtering out the rubber particles). In addition to the experimental approach, a three-dimensional finite element (FE) based micromechanical model of the | G*| test was developed with ABAQUS software. The FE model provided insight into the relationship between the microscale and macroscale material behavior (i.e., the stiffening and softening effects of rubber in CRM asphalt binders).