Capturing Durability of High Recycled Binder Ratio (RBR) Asphalt Mixture

Environmental sustainability and economic benefits motivate maximum use of recycled asphalt materials (RAM), including reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS), in asphalt mixtures. However, when stiff, brittle, aged materials are added to virgin asphalt-aggregate mixtures, adequate durability (initially and with time) must be maintained by engineering each unique combination of virgin and recycled materials. To maximize durability, state departments of transportation (DOTs) currently limit the RAP and RAS contents and their overall recycled binder ratio (RBR). Strategies for improving binder rheology and mixture durability include utilizing a softer base binder or adding a recycling agent (rejuvenator), but the durability of mixtures utilizing these strategies is unknown. In addition, these types of high RAM content asphalt mixtures are difficult for agencies to accept because no uniform AASHTO practice for their assessment is available. A comprehensive standard practice is needed that specifically guides the complex task of engineering durable, high RAM content asphalt mixtures within the context of balanced mix design. This practice will promote environmental sustainability of the most recycled product worldwide and realize significant economic benefits. The objectives of this research are to (1) produce a proposed AASHTO standard practice and associated test methods for design and evaluation of durable high RAM content asphalt mixtures and (2) revise the proposed AASHTO Standard Practice for Characterization of Asphalt Mixtures with High Recycled Materials Contents and Recycling Agents produced in NCHRP Project 09-58 (see NCHRP Research Report 927: Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios) to address mixture durability. In this research, durability is defined as the ability of an asphalt mixture to withstand traffic and environmental conditions without deterioration evidenced by raveling, surface cracking, pop outs, and damage attributed to moisture. The research shall comprehensively investigate the interaction of material, traffic, and environmental factors that cause deterioration in pavements containing high RAM contents. Note: High RAM content is defined as yielding an RBR between 0.3 and 0.5. Higher RBRs are not currently considered the industry norm, nor are RAS RBRs greater than 0.25. Task descriptions are intended to provide a framework for conducting the research. The NCHRP is seeking the insights of proposers on how best to achieve the research objectives. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in enough detail to demonstrate their understanding of the problem and the soundness of their approach to accomplishing the project objectives. Accomplishment of the project objectives will require the following tasks: PHASE I Task 1. Critically review the literature on tests and methods for evaluating the durability of asphalt mixtures with high RAM content, to include, but not be limited to, information from: (1) NCHRP Research Report 763: Evaluation of the Moisture Susceptibility of WMA Technologies (2) NCHRP Research Report 817: Validation of Guidelines for Evaluating the Moisture Susceptibility of WMA Technologies (3) NCHRP Project 09-54, Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction (4) NCHRP Research Results Digest 399: Field Validation of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures: An Experimental Design (5) NCHRP Project 09-57A, Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures (6) NCHRP Research Report 927: Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios (7) NCHRP Project 09-60, Addressing Impacts of Changes in Asphalt Binder Formulation and Manufacture on Pavement Performance through Changes in Asphalt Binder Specifications (8) NCHRP Project 09-61, Short- and Long-Term Binder Aging Methods to Accurately Reflect Aging in Asphalt Mixtures (9) NCHRP Project 20-07(406), Development of a Framework for Balanced Asphalt Mixture Design (10) other commercially available mixture durability tests and methods Task 2. Develop a Phase II work plan with a series of experiments to: (1) define practical durability parameters for asphalt mixtures containing high RAM contents and varying RAS to RAP ratios (2) identify practical characterization methods for virgin binder, rejuvenator, RAM, combined virgin/RAM binder, and aggregate, and protocols for mixture sample preparation, conditioning, and testing (3) develop guidelines to adapt the durability testing to specific project conditions selection of factors such as testing rates, testing temperatures, binder and mixture aging, air void contents, RAS/RAP ratio, etc. (4) compare results developed with the testing guidelines to durability performance thresholds developed in, at a minimum, NCHRP Project 09-58, the MnROAD-NCAT cracking Pooled Fund, and NCHRP Project 09-60 Task 3. Submit an interim report that presents (a) the Task 1 findings and (b) the Phase II work plan developed in Task 2. PHASE II Task 4. Conduct the work plan approved by NCHRP in Task 3. Analyze the results to: (1) define practical durability parameters for high RAM content asphalt mixtures (2) identify tests and methods for characterizing the durability of high RAM content asphalt mixtures (3) identify corresponding practical characterization methods for virgin binder, rejuvenator, RAM, combined virgin/RAM binder, and aggregate, and protocols for mixture sample preparation, conditioning, and testing (4) develop guidelines to adapt the durability testing to specific project conditions, interpret the results, and compare them with durability performance thresholds Submit a technical report of the results and findings. Task 5. Based on the results of Task 4, prepare (a) a proposed AASHTO standard practice for designing durable high RAM content asphalt mixtures and a revision of the proposed AASHTO Standard Practice for Characterization of Asphalt Mixtures with High Recycled Materials Contents and Recycling Agents that addresses mixture durability, (b) any necessary revisions to supporting AASHTO standard test methods, and (c) commentary supporting the new and revised practices and test methods. Task 6. Submit a final report that documents results, summarizes findings, draws conclusions, and presents: (a) proposed new and revised AASHTO standard practices and test methods for consideration and possible adoption by the AASHTO Committee on Materials and Pavements and (b) supporting commentary. An appendix to the report shall include electronic files of all data used in the project and the results of the analyses conducted with the data. Note: The contractor shall meet with NCHRP within 2 months of submitting the draft Task 7. Present a virtual workshop to AASHTO Committee on Materials and Pavements describing the research results and the project products.

Language

  • English

Project

  • Status: Proposed
  • Funding: $750000
  • Contract Numbers:

    Project 09-65

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Harrigan, Edward

  • Start Date: 20201214
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01739634
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 09-65
  • Files: TRB, RiP
  • Created Date: May 18 2020 3:06PM