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NCHRP 09-58 [Active]

The Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios

  Project Data
Funds: $1,500,000
Staff Responsibility: Edward T. Harrigan
Research Agency: Texas A&M Transportation Institute
Principal Investigator: Amy Epps Martin
Effective Date: 5/2/2014
Completion Date: 10/2/2017

OBJECTIVES
 
The objectives of this research are to (1) evaluate the effectiveness of recycling agents in HMA and WMA mixtures with high RAS, RAP, or combined RAS/RAP binder ratios through a coordinated program of laboratory and field experiments; (2) propose revisions to several relevant AASHTO specifications and test methods; and (3) develop training and workshop materials and deliver one workshop.
 
Since current practice generally limits recycled binder ratios to 0.3 or less, the scope of this research shall encompass asphalt mixtures prepared with recycling agents and RAS, RAP, or combined RAS/RAP at recycled binder ratios between 0.3 and 0.5. The performance of binders and mixtures containing recycling agents shall be compared to that of equivalent binders and mixtures (1) without recycling agents and (2) without RAS and RAP. It is anticipated that the majority of mixture testing in this research will be conducted on plant-mixed, laboratory-compacted (PMLC) specimens obtained from trial batches or production runs prepared in asphalt mix plants. Consistent laboratory conditioning procedures shall be applied to all specimens and changes in mixture properties with aging in the field shall be quantified. Field test sections shall be documented such that long-term performance studies can be conducted with these sections in future NCHRP research projects.
 
TASKS

Accomplishment of the project objectives will require the following tasks:
 
PHASE I
 
Task 1. Critically review the research and product literature and survey the current state of practice on the use of recycling agents in HMA and WMA mixtures containing RAS, RAP, or combined RAS/RAP. Analyze the results to determine (1) main classes of recycling agents; (2) their properties; (3) their effects on RAS, RAP, and combined RAS/RAP; (4) properties and performance of mixtures and pavements containing recycling agents; (5) methods for characterizing the properties of binders and mixtures containing recycling agents; and (6) potential limitations on the amount of RAS, RAP, and combined RAS/RAP used in asphalt mixtures with and without recycling agents.
 
Task 2. Based on the results of Task 1, propose a detailed work plan for a statistically designed laboratory experiment to characterize the performance of binders and mixtures prepared with selected recycling agents and RAS, RAP, or combined RAS/RAP. The plan shall address the following, at a minimum:
1.      Evaluation of key material and performance properties of recycling agents, binders (including modified binders), and mixtures (including liquid anti-strip agents), and appropriate test methods,
2.      Comparison of the properties of binders and mixtures prepared with recycling agents to those of equivalent binders and mixtures prepared (a) without recycling agents and (b) without RAS and RAP, and
3.      Assessment of potential limitations on the effectiveness of recycling agents.
 
Task 3. Submit an interim report that includes the findings of the Task 1 literature review and the proposed Task 2 work plan. Meet with NCHRP 1 month after submission to obtain approval to proceed with Phase II.
 
PHASE II
 
Task 4. Conduct the work plan approved in Task 3 and analyze the results to determine:
1.      How the use of recycling agents affects the performance of asphalt binders and mixtures prepared with RAS, RAP, or combined RAS/RAP and how the performance compares to that of binders and mixtures prepared (a) without recycling agents, (b) without RAS and RAP, and (c) without both recycling agents and RAP and RAS, and
2.      Any practical limits on the effectiveness of recycling agents in asphalt mixtures incorporating high RAS, RAP, and combined RAS/RAP binder ratios.
 
Task 5. Prepare an interim report of the results and findings of Task 4. In the report, propose a detailed work plan for a statistically designed field experiment that addresses the following issues, at a minimum:
1.      Selection of field projects to evaluate the effectiveness of recycling agents in HMA and WMA mixtures with high RAS, RAP, or combined RAS/RAP binder ratios and documentation of all pertinent aspects of the plant production and pavement construction.
2.      Characterization of asphalt binders extracted and recovered from RAP and RAS stockpiles.
3.      Characterization of the recycling agents used and identification of the key properties of recycling agents needed to ensure good performance.
4.      Characterization and comparison of the asphalt binders extracted and recovered from asphalt paving mixtures prepared with RAS, RAP, and combined RAS/RAP, with and without recycling agents.
5.      Comparison of the measured degree of blending of the virgin and recycled binders to that predicted from measured mixture properties and predictive equations (e.g., the Hirsch Model), with and without recycling agents.
6.      Characterization and comparison of the laboratory performance of asphalt mixtures containing RAS, RAP, and combined RAS/RAP, with and without recycling agents. Evaluation of the short-term field performance of asphalt mixtures produced with RAS, RAP, and combined RAS/RAP, with and without recycling agents.
7.      Comparison of the performance measured on PMLC and PMFC (plant-mixed, field-compacted) specimens with that measured on LMLC (laboratory-mixed, laboratory-compacted) specimens.
 
Meet with NCHRP 1 month after submission to obtain approval to proceed with Phase III.
 
PHASE III
 
Task 6. Conduct the work plan approved in Task 5 and analyze the results to determine the effectiveness of recycling agents in asphalt mixtures containing high RAS, RAP, or combined RAS/RAP binder ratios, through a comparison of the laboratory and field performance of binders and mixtures containing recycling agents to that of equivalent binders and mixtures (1) without recycling agents and (2) without RAS and RAP.
 
Task 7. Based on the results of Task 6, propose revisions and associated commentary to AASHTO MP 15, “Use of Reclaimed Asphalt Shingles as an Additive in Hot Mix Asphalt,” AASHTO PP 53, “Design Considerations When Using Reclaimed Asphalt Shingles (RAS) in New Hot Mix Asphalt (HMA),” AASHTO M 323 “Superpave Volumetric Mix Design,” and AASHTO R 14, “Classifying Hot Mix Recycling Agents.” The revisions shall specifically address the use of recycling agents with high RAS, RAP, or combined RAS/RAP binder ratios in HMA and WMA.
 
Task 8. Develop training and workshop materials and best practices for the use of recycling agents with RAS, RAP, and combined RAS/RAP and deliver one workshop.
 
Task 9. Prepare a final project report that documents results, summarizes findings, draws conclusions, and presents (1) the proposed revisions and associated commentary to AASHTO MP 15-09, PP 53-09, M 323, and R 14 and (2) the training and workshop materials and best practices. An appendix to the report shall include electronic files of all test data and results collected and measured in the research on appropriate media.

 
STATUS: Work is underway. 

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