Crumb rubber and bitumen interaction as a function of crude source and bitumen viscosity

This paper describes the interaction between crumb rubber and various penetration grade bitumens in terms of the absorption of the light fractions of the bitumen by the rubber and the chemical composition and rheological properties of the residual binder. Eight bitumens from two crude oil sources and four penetration grades ranging from 200 pen to 35 pen have been mixed with 2 mm to 8 mm sized crumb rubber at three rubber to binder ratios of 1:8, 1:6 and 1:4 by mass. The increased mass of the crumb rubber was used to determine the loss of volatiles and light fractions that have been absorbed from the different bitumens under constant temperature and equiviscous temperature conditions. The residual binders were then subjected to dynamic mechanical analysis using a dynamic shear rheometer to determine their rheological properties following the interaction with crumb rubber. The results show that the rate of adsorption as well as the total amount of absorption is directly related to the penetration grade (viscosity) of the binders, although the threshold (maximum) amount of absorption is also a function of the nature of the crumb rubber. In terms of the rheological properties of the residual bitumen, all the binders showed an increase in stiffness (complex modulus) as well as elastic response with these changes being consistent for both crude sources and all four penetration grades.