308-PAR : Performance-based Asphalt Recycling

Technical Committee 308-PAR

General Information

Chair: Dr. Gabriele TEBALDI
Deputy Chair: Prof. Eshan V. DAVE
Activity starting in: 2022
Cluster F

Subject matter

The proposed RILEM technical committee will follow the previous TC 264-RAP to continue scholarly research and knowledge dissemination on the asphalt material recycling. Need for incorporating and developing performance-based tools (laboratory tests, pavement performance prediction models, life cycle assessment tools) have been recognized in the activities of previous RILEM TCs as well as by both academic and industrial stakeholders. The focus of the proposed committee will be on recycling of asphalt materials. Materials studied will include cold, hot, and warm bituminous mixtures for applications in pavement construction.  The main contribution of the committee activity will be in terms of developing laboratory methods, analysis methods and life-cycle assessment tools that incorporate performance measures and predictions to support recycling decisions. TC activities will enhance of the fundamental understanding on the interactions between recycled asphalt (RA) materials and new virgin materials in asphalt paving mixtures in context of the impacts of RA use on performance of pavements. Performance in for the proposed TC activities will be considered in terms of design service life, capacity to resist primary load related (such as fatigue cracking and rutting) and non-load related (such as moisture damage) distresses, maintenance costs and global warming potentials.

At present, there are significant efforts underway to develop and implement balanced mix design tools for bituminous mixtures that adopt performance related laboratory tests to support proportioning of mixture. There is a lack of consensus on the selection of laboratory tests as well as their thresholds. Further, use preliminary versions of balanced mix designs (BMD) have been developed for bituminous mixtures with lower RA contents and often without consideration of rejuvenating agents that are often used for mixtures with higher RA contents. The outcomes of the technical committee will have balance between fundamental developments and knowledge disseminations to aid in improved mixture design methods and use of life-cycle analysis tools.

The proposed TC will undertake four interlaboratory studies on topics of performance based cold recycled asphalt mixture design procedures, selection and dosage recommendations for asphalt recycling agents (binder additives), quantification of the degree of binder activation and blending between RA binder and new virgin asphalt binder added to mixes, and finally on optimizing the warm mix asphalt designs with RA on the basis of long-term performance. Further, TC will also undertake a comparative analysis of different product category rules (PCR) and environmental product declaration (EPD) development procedures on the basis of life cycle assessment. The outcome of these activities will be to develop a series of RILEM recommendations on new or improved lab procedures and on PCR and EPD development.

Terms of reference

The activities of the proposed TC will be conducted over the period of five years. In order to achieve the intended goals, the new TC will perform its activities within five task groups (TG): TG1 – Performance-based Evaluation of Cold Recycled Asphalt Mixtures; TG2 – Long Term Performance Evaluation of Warm Mixes with Recycling; TG3 – Degree of Binder Availability, TG4 – Mixture Performance-based Dosage Optimization of Asphalt Recycling Agents; and, TG5 – EPD and PCR for Asphalt Mixtures with RA and Recycling Agents. These topics have been chosen as extension of the activities that were initiated in the previous RILEM TC 264-RAP. Please note that while the TG structure is on the basis of the previous TC activity, the scope, aim and objectives of the proposed TC are significantly different than the current TCs in the field of asphalt materials (i.e. TC 272-PIM, 278-CHA, 279-WMR, 280-CBE and TC FBB).

TG1, TG2, TG3 and TG4 will each undertake an interlaboratory study. Materials for these will be overlapping, in other words, multiple labs will be able to use same set of materials for ILS of multiple TGs. This approach was successfully implemented in previous TC 264-RAP by the TC leaders.

A conservative estimate for the active participation in ILS by 15-20 labs is expected, once again on the basis of previous experience with TC 264-RAP. Geographically the participant labs are expected to be coming from all continents of the world (the distribution of proposed TG leaders indicates such geographical diversity).

Proposed timeline of TC activites is presented below:

  • December 2021: Pre-launch meeting to solicit active members and to present the work plan to industrial partners for feedback was already held at the Université Gustave Eiffel in Marné la Vallée. Industrial members were invited to make presentations on research needs from practice perspective. The inputs of this meeting was used to refine the TC proposal workplan.
  • March – April 2022: Official launch (kick-off) of TC (if TC is approved by TAC at RILEM Spring Convention in 2021): Plans for TC objectives and outcomes will be presented along with preliminary version of work plans for each TG. Active members for each TG will be identified and call will be made regarding common materials that will be evaluated by the TC.
  • June 2022: Official Kick-off meeting and industry workshop will be held at the University of New Hampshire in United States
  • September 2022: Workshop will be held in Costa Rica in conjunction with the International Society of Asphalt Pavements (ISAP) Conference. The objective here will be to increase participation from central and South America in TC and RILEM activities.
  • October 2022: TC Annual Meeting in conjunction with the cluster F joint TC meetings. The TC meeting will be scheduled either before or after cluster F meetings that will take place in Palermo, Italy. At this meeting TG workplans will be finalized and materials for ILS will be identified.
  • March or June 2023: Either In conjunction with RILEM spring convention or the European Asphalt Technology Association conference (in Warsaw, Poland), TC meeting will be organized. By this time all ILS materials should be shipped to participating labs.
  • September/October 2023: TC Annual Meeting in conjunction with the cluster F joint TC meetings. Main purpose of this meeting will be getting updates from TGs on testing and analysis. It is expected that 50% of data collection is completed by this time.
  • Summer 2024: TC Annual meeting and an industry workshop on asphalt recycling will be held in conjunction with the 2nd RILEM International Symposium on Bituminous Materials (ISBM) will be held. At this point in time, 75% of the testing activities for the ILS are expected to be completed and the initial analysis on EPD and PCR development methods for TG5 is expected to be completed.
  • September/October 2024: TC Annual Meeting in conjunction with the cluster F joint TC meetings. Main purpose of this meeting will be getting updates from TGs on testing and analysis. It is expected that 90% of data collection is completed by this time.
  • March or June 2025: Either In conjunction with RILEM spring convention or the European Asphalt Technology Association conference (in Ancona, Italy), TC meeting will be organized. All TGs will be requested to present the findings from ILS and plans for developing RILEM recommendations and other TC outcomes.
  • September/October 2025: TC Annual Meeting in conjunction with the cluster F joint TC meetings. Main purpose of this meeting will be to finalize the topics for RILEM recommendation development. An industry workshop will also be organized to present the recommendations from TC activities and to obtain feedback on their practicality.
  • Summer 2026: TC meeting will be held to finalize and vote on various RILEM recommendations developed by various TGs. Also, a workshop will be held on presentation of the EPD and PCR development framework generated by TG5 activities.
  • September/October 2026: Close-out meeting of TC for final approval of all TC outcomes (RILEM recommendations, M&S thematic issue). TC will also propose to make presentations at the 2026 RILEM week.
  • March 2027: Official closure of TC at TAC meeting during RILEM spring convention.

In general, all TC meetings will be held in hybrid (in-person and online) formats to maximize attendance and participation. Further, in addition to above planned work plan, TC leaders will also actively disseminate TC activities and updates at other venues (Transportation Research Board meetings in United States, European Asphalt Technology Association, Eurobitume, Conference on Pavements in Southern Africa, Ibero Latin American Asphalt Congress, and Australian Flexible Pavement Association events).

Detailed working programme

Brief descriptions of each task group and their corresponding activity are provided next.

  • Task Group 1 Performance based evaluation of cold recycled asphalt mixtures (TG leader: Prof. Alan Carter, ETS Montreal; TG Co-Leader: Prof. Jian Ouyang, Dalian University of Technology):: This TG will undertake interlaboratory studies to explore various laboratory performance test methods that can be used to assess in-service performances of cold recycled asphalt mixtures. The main objective of this effort will be to identify laboratory performance tests that are most suited for: (1) materials selection, (2) mix proportioning, and (3) used as input in mechanistic pavement design procedures.
  • Task Group 2 Long Term Performance Evaluation of Warm Mixes with Recycling (TG leader: Prof. Maria Carmen Rubio, University of Granada; TG Co-Leader: Dr. Fernando Moreno, University of Granada): This task group will undertake interlaboratory studies to explore suitable laboratory aging protocols and laboratory testing methods to reliably predict in-service performances of warm-mixed asphalt mixtures with high amount of RA (>35%). Significant thrust for the activity will be assessing cracking performance of the pavements.
  • Task Group 3 Degree of Binder Availability (TG Leader: Dr. Kamilla Vasconcelos, University of Sao Paulo; TG Co-Leader: Dr. Davide Lo Presti, University of Palermo): The main objective of this task group will be to identify or develop a method to quantify or account for binder availability from recycled asphalt materials that can be used to improve mix design procedures and specifications. There is still a need for assessing this property as an additional parameter within improved characterization of the RAP (Degree of Activity - DoA). However, since in any mix design processes, RA materials are blended with additive and/or admixtures, there is also the need to assess the available binder in the presence of recycling agents.
  • Task Group 4 Mixture Performance-based Dosage Optimization of Asphalt Recycling Agents (TG Leader: Dr. Martin Hugener, EMPA; TG Co-Leader: Dr. Augusto Cannone-Falchetto, Aalto University): This TG will undertake interlaboratory-study with focus on identifying practical and reliable asphalt mixture performance testing procedures, preferably those that can be conducting during mix design process, that can be used to optimize the dosage of recycling agents in asphalt mixtures to maximize RA amounts with minimal performance penalties.
  • Task Group 5 EPD and PCR for Asphalt Mixtures with RA and Recycling Agents (TG Leader: Prof. Amlan Mukherjee, Michigan Tech University; TG Co-Leader: Dr. Elisabeth Keijzer, TNO): This TG will involve owners, contractors, producers and researchers to make a direct connection between what information producers and contractors can provide to help owners support meaningful decisions that aid long-term sustainability based on "first cost" environmental impacts as well as long-term performance. Specifically, detailed literature reviews and surveys will be conducted to develop a work plan. Comparative evaluations will be conducted of various current systems for EPD and PCR development in context of asphalt mixtures with RA and recommendations will be developed to fulfil missing links and knowledge gaps in current LCA approaches that are used for PCR and EPD development.

Technical environment

The proposed TC has direct links to previous TC 264-RAP. The previous TC made significant progress on developing laboratory methods and analysis procedures for design and characterization of asphalt mixtures with RA. One of the major lacking areas in previous effort was on consideration of performance based tests and performance parameters in selection of materials, mix design processes and inputs for pavement structural design. The proposed TC will fulfil these missing links and work towards developing RILEM recommendations that can be adopted by research and practitioners in use of recycled apshalt mixtures that have superior or comparable performance to non-recycled asphalt mixtures.

This TC fits well within the mission of RILEM in the sense that it aims to develop and disseminate new standardized methods, conduct round robin and interlabotaory studies, and advance the state of art as well as practice on the topic of material characterization and infrastructure construction. The areas of proposed study are of great interest and relevance to asphalt materials and paving industry. Activities of this TC can help guide the agency and industry by producing standards and best practices manuals on the topic of asphalt recycling. The proposed TC will be most relevant to be under Cluster F of RILEM.

The activities of the proposed TC are well aligned with the current needs of European Asphalt Paving Association (EAPA) and the United States’ National Asphalt Paving Association. Technical directors from both these associations will be active member of the proposed TC.

Expected achievements

  • Direct benefits of the TC:
    • Fundamental understanding on the issues related to characteristics of recycled asphalt mixtures
    • Development of standardized procedures for performance assessment of recycled asphalt mixtures
    • Development of material selection and mix design procedures in context of recycled asphalt mixtures using performance-based specifications
    • Development of LCA tools to support PCR and EPD development for RA and mixtures with RA
    • Provide methods and manuals to state and national transportation agencies that can help develop sustainable pavement solutions by combining material recycling with life cycle assessment
  • Outcomes/products of TC:
    • Thematic issue/paper compilation in Materials and Structures with theme of Performance-based Asphalt Recycling
    • Standardized test procedures for material selection and mix design methods for recycled asphalt mixtures leading to RILEM recommendations on the topic
    • Short courses and web based training modules to be used as educational and implementation tools by academia, industry and highway agencies
  • Organization of Events:
    • Have dedicated sessions at the 2nd RILEM ISBM conference
    • Organize thematic sessions at the RILEM week and RILEM Spring Convention
    • Focussed sessions at various asphalt material conferences
    • Web based education courses

Group of users

  • Academics, road authorities and standardization committees
  • Testing laboratories and test equipment producers
  • Material producers and construction equipment manufacturers
  • Professionals and practitioners
  • Researchers

Specific use of the results

The use of recycled asphalt (RA) in pavement mixtures has been on continuous increase. This is driven by a combination of economic, environmental and social reasons. The sources of new materials for asphalt manufacture are rapidly diminishing, for example fewer and fewer aggregate mining permits are being issued. The currently used asphalt mixture design methods are based on extension of methods that were originally developed for proportioning of new materials. Furthermore, current methods use laboratory tests and parameters that are not directly correlated to pavement performance. The work of previous RILEM TCs has paved the path for the activities of the proposed TC by developing state of the art reviews as well as some very promising laboratory-based RA evaluation methods. The current needs are in identifying suitable lab procedures that can practically evaluate asphalt mixtures with RA (and binder additives, such as rejuvenators) and have direct correlation to in-service performance and longevity of roadways.

Both scientific and economic impacts of the proposed TC are very high. The scientific impacts will be realized through gaining of fundamental understanding in the field of bituminous materials. Some examples of this include: use of sophisticated lab experiments to understand fracture and cyclic degradation processes in asphalt mixtures which are heterogeneous viscoelastic composites, experimental techniques to quantify the availability of asphalt binder from RA, laboratory tests and models to predict performance of roadways with cold recycled asphalt mixtures, and life cycle assessment models as well as model inputs and performance predictors for mixtures with high RA contents. The economic impacts will be realized through availability of the performance-based mix design methods and best practices manuals. These will be readily available to the highway administration agencies as well as industry. Use of these methods will allow practitioners to design asphalt mixtures (both cold and non-cold) with high RA contents that will perform comparably to the new asphalt mixtures but can be manufactured with significantly lower environmental impacts and energy demands. Finally, the proposed TC activities fall closely along the ongoing circular-economy initiatives that has been ongoing globally. This TC differs from such initiatives in the sense that it will bring together research knowledge and researchers from across the world to have feasible and implementable outcome that has not been possible in the past.