Absorption of Bitumen into Crumb Rubber Using the Basket Drainage Method

This paper describes an evaluation of the absorption of different sources and grades of bitumen into particles of crumb rubber using a basket drainage method. The effect of the rubber–bitumen interaction has been investigated in terms of the absorption of the light fractions of the bitumen into 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 to 35 pen have been mixed with 2–8 mm sized granulated crumb rubber at three rubber to binder ratios of 1:4, 1:6 and 1:8 by mass. The increased mass of the crumb rubber was used to determine the loss of volatiles and light fractions absorbed from the different bitumens. The residual binders were then subjected to asphaltene content tests, high temperature viscosity and dynamic mechanical analysis using a dynamic shear rheometer to determine the chemical composition and rheological properties of the binders following their interaction with crumb rubber. The results show that the rate of adsorption is directly related to the penetration grade (viscosity) of the binders as well as to the chemical composition of the bitumen (crude source) but that the total amount of absorption is controlled by the nature of the crumb rubber. In terms of the rheological properties of the residual bitumen, all the binders showed an increase in viscosity, stiffness (complex modulus) as well as elastic response with these changes being consistent for both crude sources and all four penetration grades.