264-RAP : Asphalt Pavement Recycling

Technical Committee 264-RAP

General Information

Chair: Dr. Gabriele TEBALDI
Deputy Chair: Dr. Eshan V. DAVE
Activity starting in: 2015
Activity ending in: 2021
Cluster F

Subject matter

The proposed RILEM technical committee with conduct scholarly research and knowledge dissemination with focus on the asphalt material recycling. The main contribution of the committee will be enhancement of the fundamental understanding on the interactions between recycled asphalt (RA) materials and new virgin materials in asphalt paving mixtures. 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. 

With the dwindling sources for new aggregates and increased costs and environmental impacts of using asphalt, which is a by-product of petroleum refining, the recycling of asphalt materials for highway construction has become a necessity. While use of RA in new production of bituminous mixtures is wide-spread and routine, the present mix design methods to include RA are empirical in nature. Several mix design methods treat RA as another source of aggregate and binder (as separate contributions in new mix) rather than a conglomerate material with multiple phases (binder, aggregate, mastic and mixture). In order to maximize use of RA in an engineered manner, the fundamental understanding of the role of RA in new mix and its interaction with other constituents is urgently needed. Furthermore, there is need for exploring the life-cycle analysis (LCA) tools that provide comprehensive evaluation of the economical, energy and environmental impacts of RA usage. These types of tools can provide practitioners with an optimization tool to help maximize the use of RA materials without affecting the performance of infrastructure system. The LCA can also provide support to agencies in decision making process.

The proposed committee will spend significant effort on development of standards and work protocols to be adopted by practitioners. The level of investigation will be at the laboratory evaluation and field assessment scales. The committee scope will be limited to asphalt layers of pavement structure (that is, it will not include unbounded layers or subgrade). This TC will aid in bringing the cutting edge research solutions from academia to the practitioners (road transportation administration and pavement materials industry). Some of the examples of proposed committee activities include standardization of mix designs for RA, performance of mixtures with RA materials and LCA tools to compare various RA materials and construction methods.

The two primary approaches for asphalt recycling can be classified by the temperature associated with the recycling process.  Thus the research and implementation focus can be on either cold recycling or non-cold (warm and hot) recycling. Also, often times additive are needed to be added to binders to enhance the properties of mixes with RA and to be able to conduct recycling at lower temperatures. Since asphalt binder properties also have tremendous effects on the final performance of asphalt mixtures, there is need to have evaluation of binders and additives that are used in recycled mixtures. As discusses earlier, LCA is necessary to evaluate the suitability of recycling and to make comprehensive comparisons between various material alternatives. Keeping all of these factors in mind, four task groups are proposed for this committee. It should be noted that while there will be four TGs, they will work very closely with each other and will have continuous interactions between them.

Terms of reference

The activities of the new TC are proposed to be conducted over a 5-year time period. In order to achieve the intended goals, the new TC will perform its activities within four task groups (TG): TG1 – Cold Recycling; TG2 – Non-cold (Hot and warm) Recycling; TG3 – Asphalt Binders and Additives for RA, and; TG4 – Life Cycle Assessment for Optimal RA Usage. These topics have been chosen as extension of the activities that were initiated in the previous RILEM TCs. Primarily from the TG5 and TG6 of the TC-237 SIB. Please note that while the TG structure is on basis of the previous TC activities, the scope, aim and objectives of the proposed TC are significantly different that the current TCs in the field of asphalt materials (i.e. TC-237 SIB, TC-241 MCD and TC CMB). 

  • March 2015 – April 2015

Submission of new TC for approval. Pending approval, work plan refinement, revision and formation of TGs will ensue.

  • June 2015:

Workshop between TC leadership and industry to finalize TC goals. Meeting is planned to be held at EMPA in Zurich and the purpose is to gain industry interest in the TC activities and use the industry feedback in finalizing goals of the proposed TC.

  • Summer 2015

Web based meetings between TC leadership to prepare for the kick-off meeting and to formalize the preliminary list of active members in the TC.

  • November 2015 (Annual Cluster F Joint Meetings, Barcelona Spain):

TC Kickoff Meeting; presentation of first draft of work-plan for each TG; discussion of first set of TG goals and activities;  planning of workshops; potential for concurrent meeting of the scientific committee.

  • Spring 2016 (Web based meeting):

Report from each TG on their activities (expected to develop comprehensive database of existing laboratory methods and analysis to evaluate interactions between RA materials and new virgin materials as well as on the available LCA tools and their suitability for evaluation of materials with high RA contents). 

  • Summer 2016:

Workshop for highway agencies on basis of initial literature reviews by the TGs and the demonstration of RA equipment and LCA tools.

  • Fall 2016 (Annual Cluster F Joint Meeting): 

2nd Annual meeting of the TC: Annual review of TC activities. Revaluation of TG work plans to ensure that they are realistic and on target. Discussion of laboratory campaigns to meet TC goals. 

  • Spring 2017 (Web based meeting): 

Presentation of draft standardized procedures and manuals by each TG. The standardized procedures focus on design of cold and non-cold RA mixes. The design standards will be accompanied with best practices manuals. Selection of laboratories to deploy the draft standards to evaluate the feasibility and repeatability of the procedure.

  • Fall 2017 (Annual Cluster F Joint Meeting):

3rd Annual meeting of the TC: Annual review of TC activities. Discussion of field trials to demonstrate use of the standardized procedures. Presentation of initial results from use of standardized procedures and best practices manual. 

  • Spring 2018 (Web based meeting):

Presentation of the results from various laboratories using the draft standardized test procedures and design manuals. Proposal for revised and final version of the standardized methods and best practices manuals. Presentation of data from field trials.

  • Summer 2018: 

Workshops and webinars on the proposed standardized test methods and manuals. The targeted audience will be highway agencies and industry.

  • Fall 2018 (Annual Cluster F Joint Meeting):

Formalization of the technical outcomes from this TC (Standardized procedures for asphalt recycling and guidelines for proper use of life cycle assessment). Proposal of the layout of the final report for the TC and assignment of final report tasks for various TGs.

  • Spring 2019 (Web based meeting):

Finalize the organization of the final report of the TC. Announcement of the technical committee, location and preliminary program for the RAP2020 workshop and conference.

  • Fall 2019 (Annual Cluster F Joint Meeting)

Final report preparation that include proposed standards and work protocols. Report on the RAP2020 conference organization.

  • Spring/Summer 2020 (Final meeting and conference)

RAP2020 Conference

Detailed working programme

The main objective of the proposed TC is to gain fundamental understanding of the interaction between various constituents in recycled asphalt (RA) mixtures to aid in development of standardized methods for design of such mixtures. For example, the understanding of interactions between bitumen from RA and new virgin materials can help standardize the procedures for determining the required new bitumen content.  There is an urgent need for this type of research and development to establish standardized mix design methodology that can help produce recycled asphalt mixtures with improved in-service performance and greater life cycle resiliency. In order to achieve this goal the TC will be organized in the form of three task groups. TG1 and 2 will spend efforts on the aspects of laboratory tests to aid in understanding of interactions between RA and new mix components and to standardize the laboratory mix design procedures. The TG3 will focus on the topic of asphalt binder and additives. When designing asphalt mixtures with high RA contents, it is necessary to modify the type of asphalt binder, specifically in the case of warm and cold recycling technologies, other additives are also needed to be evaluated in order to optimize the emulsified and foamed asphalt products. Preliminary working program of each of the TG is described next.

  • TG1: Cold Recycling (TG Leader: Daniel Perraton, ÉTS Montreal Canada)

A round robin test (RRT) performed by the RILEM TC 237-SIB TG6, allowed to point out that new test methods could be used to quickly characterize different sources of recycled asphalt pavement (RA) materials. Two tests were proposed: fragmentation test and indirect tensile strength (ITS) test. Results of the RRT program show the capability of both tests to characterize RA material and to be used to possibly classify them in accordance to the source. In continuation to the TG6 work has achieved so far, we need a more scientifically driven approach to ensure superior performances of the mixtures. In this context, the material characterization, the mix design and the curing process are the key steps that still need research to adapt and/or modify our practices. Team works of the future TG1 of the new TC-RAP will focus on some of those aspects. First step of the global action of the TG1 will be to report on mix design and curing processes currently used in the laboratory in countries of participated members. Exchanges and a literature review will focus particularly on the curing process to apply for laboratory investigation. Also, in purpose to evaluate the ability of the fragmentation and ITS tests to show differences in the properties of mixes prepared with different RA sources, a new RRT program will be proposed to the TG1 members. Basically, 2 or 3 distinctive RA materials will be supply at each participated laboratories with a specific formulation for foam and/or emulsion processes. One of the RA materials to supply will be sampled from a real job site conducted or on process by one of the TG1 member. Based on the specific characteristic of that reference RA material, one or two other RA sources will be selected to cover a wide range of characteristic in accordance to the fragmentation and ITS tests. In accordance to their own procedures, compacted samples of RA source materials will be characterized by each laboratory following a common curing process as established in a consensual manner by the TG1 members. Also, TG members will try to get cored samples (or slabs) of the cold mix put in place on the project to compare lab and in-site properties.

  • TG2: Non-Cold (Warm and Hot) Recycling (TG Leader: Paul Marsac, IFSTTAR France)

Environmental concerns are fostering the Half Warm Mix Asphalt (HWMA) processes in road construction and the international trend is for a generalization of these processes. However, the current recycling procedures were almost exclusively gained from emulation of the Hot Mix Asphalt (HMA) process.  There are several aspect of warm mix processes which are not properly understood, for example the blending potential between new bitumen and that from RA as well as effect of storage time on the extent of blending. These type of topics warrant more close investigation on the topic of non-cold RA mixtures. In this framework, the TG2 intends to evaluate different lab mixing processes (across the world) and their representativeness in actual HWMA recycling plant processes. Furthermore, the TG will delve into investigation of the predictive ability of the different water sensitivity and low-temperature sensitivity tests for HWMA with RA. This latter objective will be satisfied through interlaboratory studies. 
The former TC ATB and the current TC-237 SIB TG6 on hot/warm asphalt recycling concentrated on the ageing of RA binder and its characterization through Fourier transform infra-red (FTIR) methods without connection with a real on-site experimentation. A collaborative French project (http://www.pnmure.fr/en/) on recycling combined with low-temperature processes (foam and additive) has recently became active. The first on site experimentation is planned for spring 2015. This project will provide researchers with a unique opportunity to get access to material for RRT with availability of on-site performance evaluation.

  • TG3: Asphalt Binder for Recycled Asphalt Mixtures (TG Leader: Martin Hugener, EMPA Switzerland)

The binder is the component in the asphalt mixture, which is affected most by the aging during service life, which results in considerable stiffening. To reactivate the binder in the RAP, fresh binder is added which, in the case of hot recycling, is general softer than the target binder viscosity, depending on the degree of mixing which is assumed. For high recycling amounts above 50%, very often rejuvenating agents have to added, as there are no conventional binders available with the required low viscosity. In parallel, the political and economic pressure to increase the amount of RAP will lead an increased use of rejuvenators. However, they can be of very different chemistry depending on the base product used, which are not only petroleum based, but come from very different sources like cashew nut waste, vegetable oils, etc.. Still, in general only the viscosity criterion is required to characterize a rejuvenator. The use of rejuvenators in pavement construction is discussed very controversially and the quality of pavements containing rejuvenators are varying strongly, reflecting certainly the different type of rejuvenators used. Based on this the following topics will be studied by this TG to aid in increased used of RA:

(a) Defining methods and parameters apart from rheological values to better characterize rejuvenators (Simple chemical analysis (FTIR, UV etc.), methods to characterize aging of rejuvenators and bitumen rejuvenator mixes, testing the compatibility between RAP binder and rejuvenator. A special emphasis will be on the topic of quality control. This is important as typically a physical parameter (such as viscosity) is specified as quality control measure, while this was not an issue with traditional manufacture of asphalt mixtures, in case of RA mixtures rejuvenators the chemical changes in the formulation can result in very differing final products. Thus, use of traditional quality control measures may no longer be effective. The chemical changes in the formulation of the rejuvenator can affect the binder properties in terms of compatibility and aging, but maybe the water sensitivity (adhesion) as well. Use of fingerprint methods could help solve this problem.

(b) A major concern is the aging property of bitumen-rejuvenator mixes. Especially, if the chemistry of the rejuvenator is much different, the aging will be not the same as for conventional bitumen. Various aging simulation methods (RTFOT, RFT (rotating flask) and PAV) are used in general to simulate the aging behaviour of binders. But already for standard bitumen they are in dispute, for bitumen-rejuvenator mixes the conventional and other methods need to be evaluated. 

(c) A step further for RA mixtures is the topic of repeated recycling, which is especially interesting but complex for modified binders. Independent of the modification, whether these are polymers, rejuvenators or other agents added, they can make the new binder formulation difficult, especially at high RAP content. The simple mixing equations and tables do not take this into account, even less after short term aging. However, the binder properties after construction are actually the target values.

The final outcome of this TG will to evaluate and standardize tools to properly validate a rejuvenator for the use in asphalt pavements.

  • TG4: Life Cycle Assessment for Pavements with RA Mixtures (TG Leaders: Gordon Airey and Alex Apeagyei, University of Nottingham UK)

It is generally agreed that Life Cycle Assessment (LCA) provides an adequate instrument for environmental decision support. The United Nations Environment Program defines LCA as a tool for the systematic evaluation of the environmental aspects of a product or service system through all stages of its life cycle. In the pavement sector, engineers have adopted LCA techniques to evaluate different aspects of pavement construction, maintenance and rehabilitation. Examples include using LCA for sustainable procurement of materials, considering the benefits of asphalt modification, comparing different pavement types (i.e. flexible vs rigid), LCA of warm-mix asphalt and using LCA to optimize pavement design. Very few studies have focused on the use of LCA to directly assess the sustainable use of RA in asphalt pavement construction and performance. Significant assumptions need to be made in applying LCA to RAP, including end-of-life options and allocation of environmental burdens between new and recycled material. Furthermore, there is a lack of reliable data that can be used to validate some of the existing LCA methods which hinders the widespread incorporation of the technique in routine design. Previous studies show service life assumptions used in existing LCA tools have a large influence on calculated environmental impact. The aim of this TG is to develop an appropriate LCA framework that could be used to assess the environmental sustainability of asphalt pavements that contain RAP. This will be linked to the current development of product category rules for asphalt LCA and the development of environmental product declarations that meet ISO and EU standards. The following include the activities proposed by TG4 to enhance the life cycle of RA mixtures:

(a) Identify and evaluate existing LCA methods and recommend the most promising for assessing environmental sustainability of pavements containing RAP.

(b) Quantify the sensitivity of LCA results associated with using RAP, including effects of RAP usage percentage on pavement performance. 

(c) Quantify the influence of RA on the service life of pavements containing RAP.

(d) Develop guidelines on LCA use for pavements that incorporate RAP, extending current product category rules for asphalt.

Technical environment

The proposed TC has direct links to previous TC ATB and current TC237 SIB (TC237 SIB will end later in this year). Both of these TCs included TG on the topic of asphalt recycling (2 in case of TC237 SIB). In each case the activities of the TGs on asphalt recycling have led to tremendous progress in identifying the relevant lacking areas and making progress on them. One of the major lacking area is the availability of standards on the topic of asphalt recycling. Especially, the standards that are actually based on the fundamental understanding of interactions between RA and new mixture constituents as well as the once that utilize newly developed test methods for quantifying the role of RA in the new mixture (such as cohesiveness and fragmentation tests from the TG6 of TC237 SIB). Most of the current standards are based on extension of hot-mix asphalt or traditional asphalt mixture procedures. 

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.

Expected achievements

Direct benefits of the TC:

  • Fundamental understanding on the issues related to characteristics of recycled asphalt mixtures
  • Development of standardized procedures for quality control and performance achievement from recycled asphalt mixtures
  • Development of material selection and mix design procedures in context of recycled asphalt mixtures using life-cycle assessment
  • 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:

  • State of the art reports on the TC focus area
  • 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
  • Each TG will be strongly encouraged to develop special issues of journals as well as journal and peer-reviewed conference articles from the activities of the committee

Organization of Events:

  • RAP2020 conference
  • Focussed sessions at various asphalt conferences (RILEM events)
  • 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 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, majority of these methods are based on the empirical information and the approaches for mixtures with RA have been developed for relatively lower RA contents (typically up to 30%). With rise in use of cold as well non-cold recycled asphalt, there is an urgent need to gain fundamental understanding of interactions between various asphalt mixture constituents, specifically the interaction of RA and new constituents (including additives such as rejuvenators). The work of previous RILEM TCs have paved 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 the area of mix design standardization, best practices manuals and life-cycle assessment tools to aid in correct selection of materials, methodology and proportioning of RA mixtures.

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 tools (such as, FTIR) to understand chemical interactions between rejuvenating agents and aged binder RA materials, experimental techniques to quantify the availability of binding material in cold recycled asphalt mixtures, laboratory tests and models to predict moisture damage susceptibility and performance of roadways with RA materials, 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 standardized 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 GreenRoads initiative that has been ongoing in both Europe and United States. 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.