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<p>The proportion of original RAP bitumen activated during the dry mixing stage of recycled mix production (DoA<sub>total</sub>) significantly affects the extent of RAP bitumen blending with virgin bitumen. Hence, understanding and estimating DoA<sub>total</sub> is important. DoA<sub>total</sub> constitutes two components: the active RAP bitumen that coats virgin aggregates, represented by degree of RAP bitumen activity (DoA), and the active RAP bitumen that coats RAP aggregates. While DoA can be determined through coating experiments or numerical methods using distinct RAP and virgin aggregate size fractions, estimating the amount coating RAP aggregate is more complex. Existing methods based on 100% RAP material do not replicate the practical dry mixing scenario and give an indirect and relative measure of active RAP bitumen within RAP material. There are no experimental or numerical procedures available to provide an absolute quantity of the active RAP bitumen within RAP material, leaving a gap in the ability to estimate DoA<sub>total</sub>. This study addresses the gap by developing an analytical approach to estimate DoA<sub>total</sub> using liquid bridge theory coupled with a practical apportioning of the liquid in the bridge between the contacting particles. The experimental data obtained by carrying out coating studies on thirty-seven combinations, from a previous study, were considered. The liquid bridge theory-based approach was first used to estimate DoA. The estimated DoA was compared against the DoA measured using coating studies to obtain shift factors necessary to address the limitations of liquid bridge theory. The shift factors were further used to estimate DoA<sub>total</sub>. The influence of mix and process variables on DoA<sub>total</sub> was also studied. DoA<sub>total</sub> increased with increase in mixing time and mixing temperature and decreased with the stiffness of RAP bitumen. DoA<sub>total</sub> remained constant with RAP content. The approach proposed in the study can be used to obtain practical estimates of DoA and DoA<sub>total</sub> for a selected aggregate gradation, source of RAP material, and mixing conditions within the range of variables considered in the study. Regression models based on penetration and softening point of RAP bitumen (adjusted R<sup>2</sup> &gt; 0.84) were also proposed to obtain DoA with reasonable accuracy.</p>

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An analytical approach to estimate the total quantity of reclaimed asphalt pavement (RAP) bitumen activated during dry mixing

  • 期刊论文

  • 发表日期：

    2026年6月2日

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  • Tejaswini Lakshmi Tavva,
  • Kusam Sudhakar Reddy

摘要

The proportion of original RAP bitumen activated during the dry mixing stage of recycled mix production (DoAtotal) significantly affects the extent of RAP bitumen blending with virgin bitumen. Hence, understanding and estimating DoAtotal is important. DoAtotal constitutes two components: the active RAP bitumen that coats virgin aggregates, represented by degree of RAP bitumen activity (DoA), and the active RAP bitumen that coats RAP aggregates. While DoA can be determined through coating experiments or numerical methods using distinct RAP and virgin aggregate size fractions, estimating the amount coating RAP aggregate is more complex. Existing methods based on 100% RAP material do not replicate the practical dry mixing scenario and give an indirect and relative measure of active RAP bitumen within RAP material. There are no experimental or numerical procedures available to provide an absolute quantity of the active RAP bitumen within RAP material, leaving a gap in the ability to estimate DoAtotal. This study addresses the gap by developing an analytical approach to estimate DoAtotal using liquid bridge theory coupled with a practical apportioning of the liquid in the bridge between the contacting particles. The experimental data obtained by carrying out coating studies on thirty-seven combinations, from a previous study, were considered. The liquid bridge theory-based approach was first used to estimate DoA. The estimated DoA was compared against the DoA measured using coating studies to obtain shift factors necessary to address the limitations of liquid bridge theory. The shift factors were further used to estimate DoAtotal. The influence of mix and process variables on DoAtotal was also studied. DoAtotal increased with increase in mixing time and mixing temperature and decreased with the stiffness of RAP bitumen. DoAtotal remained constant with RAP content. The approach proposed in the study can be used to obtain practical estimates of DoA and DoAtotal for a selected aggregate gradation, source of RAP material, and mixing conditions within the range of variables considered in the study. Regression models based on penetration and softening point of RAP bitumen (adjusted R2 > 0.84) were also proposed to obtain DoA with reasonable accuracy.