Understanding migration between old and new bitumen Benoît Dubergé Esso SAF

Understanding diffusion between recycled and virgin bitumen Benoît Dubergé Esso SAF

High RAP use: a unique challenge to paving industry Quality & Quantity of RAP binder & aggregates Virgin binder & mix design selection Blending between RAP & virgin binders - Extent of binder blending critical to mix rheology Pa.s 60 1, Bi-layered sample viscosity lower than ideal homogenous blend Virgin bitumen acts as a ‘lubricant shear

Study to understand extent of blending Objectives Understand binder blending in hot / warm mix asphalt during typical production & paving operation Approach Test RAP-virgin blends in rheological tests Understand diffusion kinetics & impact on rheology Translate findings to production & paving conditions

Diffusion Rate Measured in DSR Diffusion rate depends on molecular mobility  temperature & molecular structure Extent of diffusion is time dependent Diffusion in mixTest in RheometerResults Oxidation Evaporation

Diffusion rates under realistic conditions Diffusion coefficient decreases with mix cooling

Rapid diffusion between thin layers Binder film thickness is critical parameter In hot mix asphalt blending is achieved before placement In warm mix asphalt blending may not be achieved for thicker film thicknesses Good blending Poor blending

Study outcomes Extent of RAP and virgin blending is critical to effective binder viscosity in asphalt mix Binder film thickness significantly impacts time to complete blending Under favorable conditions diffusion can blend RAP & virgin binders prior to mix placement on the road In warm mix application there is a potential for incomplete blending of thicker binder layers RAP pre-heating to ensure good re-coating is encouraged when binder blending is considered