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SWUTC Research Project Description

Performance Studies and Future Directions for Mixes Containing RAP and RAS

University: Texas A&M University

Principal Investigator:
Fujie Zhou
Texas Transportation Institute
(979) 458-3965

Funding Source: SPR Program

Total Project Cost: $203,873

Project Number: 0-6738

Date Started: 9/1/12

Estimated Completion Date: 8/31/13

Project Summary

Project Abstract:
Hot-Mix Asphalt (HMA) produced with RAP and RAS can significantly reduce the cost of asphalt mixtures, conserve energy, and protect our environment. However, there is substantial speculation that the recent introduction of higher RAP and RAS contents to Specification Item 341 mixes has had a negative impact on the life of HMA overlays. But, no hard data is available to substantiate the speculation and some claims. The other aspect of RAP/RAS is compactability during construction. These stiffer mixes will be more difficult to construct and therefore could be expected to have poorer overlay density and worse longitudinal joints than regular virgin HMA. The use of Warm Mix Asphalt (WMA) technologies will help on compaction issues but these mixes will not be homogeneously blended between the virgin binder and the recycled binders from RAP/RAS due to the low mixing temperatures.  As the Texas Department of Transportation (TxDOT) moves into more and more RAP/RAS usage with different mix types it is necessary to learn from the experiences of the past 3 to 4 years, to determine what is working and what is not, and to study how variations in mix design options, plant production and construction process have impacted the performance life.

Project Objectives:

Specifically, the major objectives are to:

  1. Evaluate the impact of RAP/RAS used in HMA and WMA on durability/performance problems of the mixes through field survey:
    1. Do we have durability problems? If so, how significant are they?
    2. Where the RAP/RAS is working; where not; where to best use?
  2. Evaluate the impacts of RAP/RAS mixes’ performance and identify approaches to improving the durability problems in terms of mix design (increasing target densities, using softer binders, reducing recycled binder content, etc);
  3. Develop the best practices for industry in terms of materials handling (including RAP/RAS processing and stockpiles management), plant production, and construction process;
  4. Investigate the cost-benefit of pre-treatments of the RAP/RAS stockpile with rejuvenators in terms of binder blending and overall mix quality;
  5. Verify maximum allowable recycled binder content in the specification in terms of binder blending and rheology of the total combined binder including WMA technologies.

Task Descriptions:

Task 1: Literature Review

Task 2: Meet with Project Monitoring Committee within Six Months

Task 3: Evaluate Durability Problems of RAP/RAS Mixes

Task 4: Evaluate the Impacts of Changes in Mix Design on the Durability of RAP/RAS Mixes

Task 5: Verify Maximum Allowable Recycled Binder Content in the Specification in Terms of Binder Blending and Rheology of the Total Combined Binder Including WMA Technologies

Task 6: Investigate Cost-Effective Improvement of Using Rejuvenators in Binder Blending and Mix Engineering Properties

Task 7: Construct Field Test Sections to Validate the Approaches for Improving Durability Problem of RAP/RAS Mixes

Task 8: Recommend Specification Changes

Task 9: Develop and Teach RAS Workshop

Task 10: Write and Submit Reports

Implementation of Research Outcomes:
In the last several years reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) have been widely used in asphalt mixes in Texas. The use of RAP/RAS can significantly reduce the initial cost of asphalt mixtures, conserve energy, and protect our environment. There are always two main concerns: variability of RAP/RAS and durability (or cracking) of RAP/RAS mixes. This study focused on the durability of RAP/RAS mixes.

Impacts/Benefits of Implementation:
This research reviewed the new specification for asphalt mixes in Texas and then a revised field experimental test plan for validating TxDOT’s new specification is recommended.

Web Links:
Final Technical Report