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Understanding Blending of RAP and Virgin Binders in Hot and Warm Mix Asphalt

This study investigates the complexities of blending recycled asphalt pavement (RAP) with virgin bitumen in hot and warm mix asphalt. It aims to comprehend the extent of binder blending during production and paving operations, focusing on how diffusion kinetics impact mix rheology. Key findings highlight that binder film thickness and temperature significantly affect diffusion rates and blending quality. The research emphasizes the importance of good blending for achieving optimal binder viscosity and recommends pre-heating RAP to enhance re-coating and ensure effective blending before placement.

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Understanding Blending of RAP and Virgin Binders in Hot and Warm Mix Asphalt

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  1. Understanding migration between old and new bitumen BenoîtDubergé Esso SAF

  2. High RAP use: a unique challenge to paving industry Quality & Quantity of RAP binder & aggregates Virgin binder & mix design selection Blendingbetween RAP & virgin binders - Extent of binder blending critical to mix rheology 60 Bi-layered sample viscositylowerthanidealhomogenousblend 10 5 Vis@100C, Pa.s shear 1,7 Virgin bitumen acts as a ‘lubricant

  3. Study to understand extent of blending • Objectives • Understand binder blending in hot / warm mix asphaltduringtypicalproduction & pavingoperation • Approach • Test RAP-virginblends in rheological tests • Understand diffusionkinetics & impact on rheology • Translate findingstoproduction & pavingconditions

  4. Diffusion Rate Measured in DSR Diffusion rate depends on molecular mobility  temperature & molecular structure Extent of diffusion is time dependent Oxidation Evaporation Diffusion in mix Test in Rheometer Results

  5. Diffusion rates under realistic conditions Diffusion coefficient decreases with mix cooling

  6. 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 Goodblending Poorblending

  7. Studyoutcomes 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

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