Influence of hindered phenol additives on the rheology of aged polymer-modified bitumen

Oxidation (aging) in polymer-modified bitumen occurs due to exposure in air at high temperatures. The aging mechanism tends to alter the physical and chemical properties of bitumen as reflected by the change in their rheological properties. In this study, a blend of SBR and hindered phenols (HPs) was used to improve the rheological characteristics of base (unmodified) and polymer-modified bitumen. Rheological properties were measured using a Rotational Viscometer, a Dynamic Shear Rheometer and a Bending Beam Rheometer. Stiffening indices and complex modulus indices were used to assess the effectiveness of the additives in the bitumen and its thermal stability, respectively. It was found that the additives were capable of increasing the stiffness at high temperature and reducing the hardening propensity of aged bitumen at intermediate and low temperatures. Bitumen morphology suggests that the degree of polymer network chain break-down was less severe when the HP was used in the bitumen. Performance testing of bituminous mixtures indicated that the HP additives enhanced the stripping resistance, improved rutting performance and extended the mixture service life.