Subject matter

The ideal implementation of a circular economy involves transforming products that have reached the end of their useful life into resources for the same or different applications [1]. As the awareness and focus on the sustainability of road infrastructure have grown over time, exploring the potential for utilizing recycled, marginal, and secondary materials in pavement has emerged as a crucial challenge in road engineering. This large amount of unused, un-recycled, and often disposed materials derived from a diverse spectrum of activities and industries and their valuable potential when incorporated into pavement materials was the basis for the RILEM technical committee TC 279-WMR on Valorisation of Waste and Secondary Materials for Roads. TC 279-WMR explored several aspects of marginal materials for pavement applications. These include the type of materials that could be used as additives, modifiers, and aggregates and their suitability for use by evaluating their rheological behavior, mechanical response, and environmental sustainability. Such a committee obtained remarkable participation with more than 100 members. It generated solid interest in relevant research topics, as demonstrated by five journal publications, such as Wang et al. [2], several conference presentations, and the recently published State-of-the-Art Report (STAR) [1].

Starting from this seminal work, the proposed technical committee Alternative Paving Materials - Design and Performance (APD), in parallel with the proposed TC Alternative Paving Materials – Sustainability (APS), will continue on the legacy of TC 279-WMR. Specifically, TC APD will work to advance research in design and performance aspects that were only initially explored in the former TC effort while shifting toward a more inclusive vision of waste and secondary materials to a broader concept of alternative paving materials (APMs) as originally part of the native design of road composites. While APMs might include diverse materials, the new TC will identify a limited number of targeted APMs with particular attention to bio-binders, recycled tire rubber, and recycled plastic as a replacement for conventional petroleum-based binders, natural aggregate, and polymeric additives. This choice is also strictly connected to the latter two materials investigated in the previous TC 279-WMR, leaving bio-binders as a new frontier within RILEM technical committees aside from the single effort of Task Group 3 of TC 264-RAP - Asphalt Pavement Recycling [3] that evaluated a bio-based asphalt recycling agent. While the former TC 279-WMR attempted to address the use of different materials globally, its nature was broad and exploratory, which could not provide recommendations on the design and performance at an advanced and robust level. Therefore, the new TC APD will concentrate on three key areas corresponding to three task groups to develop advanced solutions to this urgent research need (Figure 1):

Figure 1 – Graphical Concept of TC APD

• Prepare a Literature Review: The current information on the design and performance of the APMs and paving composites containing APMs is fragmented. Therefore, a comprehensive review to support the activity of other task groups is needed. This work will serve as a basis for the conclusive publication of the TC effort either as a STAR or as a topical collection in Materials and Structures (M&S).
• Address the Design and Performance of paving composites containing APMs, using a multi-scale approach looking at binders, intermediate scale (i.e., mastic/mortar/fine matrix), and with a target focus on mixtures. Hence, the main goal of this task group is to explore the best approach for adapting existing procedures currently used by technologists, such as blend design, performance-engineered mix design, manufacturing, testing, and modeling.
• Evaluate the Field Performance of paving composites containing APMs. To the applicants' knowledge, such an aspect was never addressed in RILEM TCs from cluster F despite the strategic importance of verifying the behavior of paving materials in the field. In this sense, the reference national road authority and the access to existing testing sections and accelerated pavement testing facilities of the chair and co-chair of the proposed TC, respectively, offer a unique opportunity for exploring this essential aspect.

TC APD will work to impress a transformative shift in the culture prevailing within the road pavement sector. Identifying an urgent imperative to advance and extensively demonstrate solutions that transcend conventional bituminous materials, along with the promotion of widespread adoption, is of paramount importance. Realizing these objectives necessitates the integration of a global vision with pragmatic initial steps that embrace interdisciplinarity, thereby leading to solid recommendation outputs. For such a purpose, the coordinated work of the proposed new TCs APD and APS offers a unique opportunity to maximize research and practical, valuable outputs for engineers, practitioners, and authorities in this unfamiliar area of investigation. Therefore, TC APD represents an optimal international collaborative arena that can take a substantial and recognizable stride toward addressing critical aspects associated with an advanced performance-engineered design of paving composites natively conceived with alternative paving materials. Consequently, the new TC will embrace members beyond the traditional domains of civil engineering and materials science, as shown by the interdisciplinary roster of interested parties toward the end of this proposal.

Essential References                                                                                                              

1. Cannone Falchetto A., Poulikakos L., Pasquini E., Wang D. Editors. Valorisation of Waste and Secondary Materials for Roads, State-of-the-Art Report of the RILEM TC 279-WMR. RILEM State of the Art Reports, volume 38, 2023.
2. Wang D., Baliello A., Poulikakos L. D., Vasconcelos K., Kakar M. R., Giancontieri G., Pasquini E., Porot L., Tušar M., Riccardi C., Pasetto M., Lo Presti D., Cannone Falchetto A. (2022). Rheological properties of asphalt binder modified with waste polyethylene: An interlaboratory research from the RILEM TC WMR. Resour Conserv Recycl 186: 106564. https://doi.org/10.1016/j.resconrec.2022.106564
3. Hugener M., Wang D., Cannone Falchetto A. et al. Recommendation of RILEM TC 264 RAP on the evaluation of asphalt recycling agents for hot mix asphalt. Mater Struct 55, 31 (2022). https://doi.org/10.1617/s11527-021-01837-0

Terms of reference

The TC will be active for 5 years (2024-2028) and is planned to be implemented with 3 work packages, as presented in Figure 2:

Figure 2 – Flow Chart on the organization of TC APD

• WP1 – Coordination involves overseeing daily project management activities and engaging with partners, members, and industry stakeholders to foster constructive dialogues among participants. This WP encompasses tasks such as acquiring and managing materials, establishing a shared material database, organizing periodic meetings, and ensuring timely reporting. Particular attention will be devoted to the coordination and collaboration with the work of TC APS, proposed in parallel with TC APD and other ongoing TCs within RILEM Cluster F and other clusters beyond if an opportunity arises.
• WP2 – The research encompasses the activity of the three Task Groups (TG) listed below and described in Section 4:

TG1 – Literature review and STAR

TG2 – Design and performance of paving composites containing APMs

TG3 – Field evaluation of paving composites containing APMs

• WP3 – Communication focuses on establishing virtual platforms (i.e., Microsoft Teams) to facilitate internal collaborations among team members and fostering scientific dissemination through journal papers and technical conferences. Moreover, extensive public engagement will be conducted by creating an online information page (i.e., Google Sites) and/or social media pages (i.e., LinkedIn).

The leadership structure of the proposed Technical Committee (TC) comprises a Chair and Deputy Chair, who will oversee WP1 and WP3, respectively. WP2 will be executed with the support of the Task Groups (TGs) leaders. The selection of themes for each TG serves as a foundational step towards achieving the global vision outlined in Section 2 while also building upon activities initiated in the previous RILEM TC 279-WMR.

It is essential to highlight that although the TG structure draws from the previous TC's activity, the scope, objectives, and aims of the proposed TC APD markedly differ from the existing and most recent TCs in the domain of asphalt materials (e.g., TC 272-PIM, 278-CHA, 264-PAR, 280-CBE, and TC 295-FBB) as moving toward a more comprehensive vision of alternative paving materials. TG1 will mainly focus on bibliographical research; TG2 will be heavily based on interlaboratory activity (ILA) as the core TG of the TC APD; TG3 will combine bibliographical research, data mining, and, toward the end, possibly prepare a limited number of testing cells for short term field evaluation in selected countries and locations (U.S. and Finland as a start). The principal applicant of this proposal has successfully implemented ILA in TC 279-WMR [1] and TC 264-RAP [3]. Therefore, based on previous experience with TC 279-WMR and its large membership and participation, an estimated active involvement of 15 to 20 laboratories in the ILA is expected. Furthermore, participant laboratories are anticipated to represent diverse geographical locations, spanning all continents worldwide, as reported later in the proposal in the list of interested participants. They encompass more senior members, young (doctoral students and researchers), and new members, as in the case of the proposed deputy chairs, TG leaders, and the industry. Concerning the latter, the activity of TG2 and TG3 will be of high interest to the industry as they directly connect to the use of materials from diverse production processes at the source and with the performance of novel paving composites containing APMs at the end. These are highly relevant for materials and paving mixture producers and for the road authorities and departments of transportation for their performance. Substantial cooperation with the proposed parallel TC APS will be sought to maximize the ILA activates concerning material and possibly apply the design procedure to be developed in TC APD TG2 into the corresponding TG2 Recyclability of TC APS.

The proposed timeline of the TC activities is listed hereafter:

• September 2023: Approval of the new TC by TAC
• November 2023: Presentation of the new TC at the annual Cluster F meeting in Lyon, France

• Spring 2024: Kick-off meeting, work program approval, and assignment of group leaders at NCAT, U.S.

• Fall 2024: Annual meeting, discussion, and approval of work plan
• Spring 2025: TG meetings, update of deliverables, and work plan
• Fall 2025: Annual meeting, discussion of results, presentation of achievements
• Spring 2026: TG meetings, data evaluation, presentations, papers
• Fall 2026: Annual meeting, discussion of results, presentation of achievements
• Spring 2027: TG meetings, data evaluation, presentations, papers
• Fall 2027: Annual meeting, discussion of results, presentation of achievements
• Spring 2028: TG meetings, data evaluation, presentations, papers
• Fall 2028: Annual meeting, concluding remarks, final report, presentations of final results
• Spring-Summer 2028: Final TCAPD Symposium in conjunction with TC APS and other RILEM TCs

Increased attendance and engagement will be supported through hybrid meetings (in-person and online). Along with the work schedule mentioned above, TC and TG leaders will actively promote and disseminate TC activities and output in various venues such as the European Asphalt Technology Association and Eurobitume, the Transportation Research Board – TRB and the Association of Asphalt Paving Technologists - AAPT meetings, and the ASCE Engineering Mechanics Institute – EMI, NRRA, in the United States, the Conference on Pavements in Southern Africa, the Ibero Latin American Asphalt Congress, and the Australian Flexible Pavement Association events.

Detailed working programme

Brief descriptions of each task group of the "Research" work package and their related activity are provided next. 

TG1: Literature Review and STAR

The objectives of this TG are to 1) prepare an up-to-date knowledge basis on the use of APMs internationally and 2) coordinate the preparation of the final summary document of the research effort either in the form of a traditional STAR manuscript or a topical collection of papers in M&S at the end of the activities of the proposed TC. For this purpose, TG1 will work on two main activities: a) preparing a comprehensive literature review addressing design techniques, blend, preparation and manufacturing, performance evaluation methods, and testing solutions for paving composites with and without APMs that could be considered in the development of TG2; b) together with this activity, TG1 will lead the preparation of the STAR / topical collection of papers, coordinating the contribution of TG2 and TG3. The decision on which publication means to select (STAR or papers collection) will be agreed upon among the participants to the TC.

Proposed Chair: Dr. Maria Chiara Cavalli – KTH, Sweden.

TG2: Design and performance of paving composites containing APMs

The objective of TG2 is to define a performance-engineered design method for paving composites containing APMs. The activity of this TG will benefit from the literature review of TG1 and the work conducted in TC 279-WMR from TG1 and TG2 on bituminous blends characterization and especially by TG3 on mixtures. As anticipated, selected candidate APMs of interest to this investigation are bio-binders, recycled tire rubber, and recycled plastic, where bio-binders represent an element of novelty compared to the previous TC 279-WMR. Therefore, aspects such as thermomechanical properties of the blends and composites, developing new approaches and methodologies for design, manufacturing, and testing the incorporation of APMs with a multi-scale approach are part of the present TG with an ultimate focus on the mixture level. The research activity of TG2 is expected to be beneficial for the corresponding work conducted in the TG2 Recyclability of TC APS, where the design aspect will be essential. Therefore, robust cooperation across the two proposed TCs is envisioned.

Proposed Chair: Dr. Salvatore Mangiafico, ENTPE – University of Lyon, France. 

TG3: Field evaluation of paving composites containing APMs

The objective of TG3 is to summarize the field performance of paving composites containing APMs already tested or in existing testing sites while possibly preparing a limited number of field cells with new paving composites containing APMs that will be designed using the method proposed by TG2.

The activity of this TG will be initially devoted to the literature review and data mining from different international sources such as past research, road authorities, and departments of transportation to generate more structured information on the currently available field performance of this family of materials. Artificial intelligence will be considered to determine macro trends if a large amount of data can be collected. In addition, by leveraging the available field data from roads already designed with APMs in the Nordics with short (3-4 years) repaving cycles and experimental test sections at well-established accelerated pavement testing facilities in the United States, TG3 will attempt to prepare a limited number of field-testing cells paved with composites containing APMs for short term monitoring with the opportunity for longer-term evaluation for follow-up TC RILEM activities.

Proposed Chair: Dr. Krishna Prapoorna, IIT Tirupati, India.

A co-chair for each Task Group was also identified. The co-leaders agreed to support the coordination effort and activities of the corresponding TG leaders and guarantee the continuity of the research work over the entire duration of the TC.