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Asphalt Pavement Recycling with Reclaimed Asphalt Pavement (RAP)
Environmental stewardship is designated as a major focus area of the United States Department of Transportation (DOT) strategic plan. According to the Environmental Protection Agency (EPA), environmental stewardship is the responsibility for environmental quality shared by all those whose actions affect the environment. The Federal Highway Administration (FHWA) supports and promotes the use of recycled highway materials in pavement construction in an effort to preserve the natural environment, reduce waste, and provide a cost effective material for constructing highways. In fact, the primary objective is to encourage the use of recycled materials in the construction of highways to the maximum economical and practical extent possible with equal or improved performance. As part of the FHWA recycled materials policy, the FHWA actively promotes asphalt pavement recycling and technology.
There are three key requirements that must be satisfied for asphalt pavement recycling to be successful. Recycled asphalt pavements must:
In order to satisfy these requirements, the FHWA has identified the following specific objectives to encourage asphalt pavement recycling:
Specific goals include increasing the amount of highway construction and rehabilitation projects that use RAP and to increase the amount of RAP used in specific projects.
This webpage provides information on the use of RAP in flexible pavements. For more information on pavement recycling, please see the FHWA pavements recycling website.
Readers wishing to learn more about in-place recycling techniques are referred to FHWA's guidance documents: Cold In-Place Asphalt Recycling Application Checklist, Hot In-Place Asphalt Recycling Application Checklist, and Cold In-Place Recycling State of Practice Review. Additional information may also be found in the Asphalt Recycling and Reclaiming Association (ARRA) publications: Basic Asphalt Recycling Manual, Full Depth Reclamation Manual, and Cold Recycling Manual.
FHWA Involvement and Support of RAP Activities
Reclaimed Asphalt Pavement (RAP) Expert Task Group
In 2007, the FHWA Office of Pavement Technology initiated an Expert Task Group (ETG) on the use of RAP in the construction and rehabilitation of flexible pavements for highways and roads. The ETG is comprised of experts on the use of RAP in asphalt paving mixtures from State DOTs, FHWA, the American Association of State Highway and Transportation Officials (AASHTO), National Asphalt Pavement Association (NAPA), and National Center for Asphalt Technology (NCAT). The purpose of the ETG is to advance the use of RAP in asphalt paving applications by providing highway agencies with critical information regarding the use of RAP, technical guidance on high-RAP projects, and direction on research activities. For more information on the RAP ETG, please see: http://www.ncat.us/RAP/.
Showcasing Performance of High RAP Asphalt Pavements
One goal of the RAP ETG is to initiate several field projects throughout the US using high percentages of RAP (25% or more) in order to increase awareness of the benefits of RAP in HMA production and develop best practices for designing, processing, and handling RAP in HMA. FHWA, NCAT, and ETG members are working with State DOTs on field projects to showcase the performance of high RAP mixtures and document their design, construction, and performance. The objectives of the field projects are documentation of the mixture design process, production, construction, performance testing, and best practices learned for future mixture design and quality control procedures.
The FHWA Mobile Asphalt Material Testing Laboratory provides support in the form of mixture design replication and performance testing for the high RAP field projects.
For more information on field projects or for assistance in planning a high RAP field project in your state or region, please contact Audrey Copeland.
Table 1. High RAP Field Projects - This table provides a list of the locations of high RAP field projects, the percent RAP used in each project, and the dates of construction.
Improved Mix Design, Evaluation, and Materials Management Practices for Hot Mix Asphalt with High Reclaimed Asphalt Pavement Content - NCHRP Project 9-46
The objectives of National Cooperative Highway Research Program (NCHRP) Project 9-46 are to (1) develop a mix design and analysis procedure for HMA containing high-RAP contents that provide satisfactory long-term performance and (2) propose changes to existing specifications to account for HMA containing high-RAP contents. High-RAP content is defined as greater than 25% and may exceed 50%.
The mix design procedure is expected to be an adaptation of AASHTO R 35, Superpave Volumetric Design for Hot-Mix Asphalt. The mix analysis procedure is expected to (1) include performance-related tests and key criteria to address permanent deformation, fatigue cracking, low-temperature cracking, and moisture susceptibility and (2) identify any promising method or procedure developed to assess the durability of HMA.
A mix design and analysis procedure will then be prepared in the form of an AASHTO Standard Practice for use by practicing engineers and technicians. The specification will be an adaptation of AASHTO M 323, Superpave Volumetric Mix Design. Practical guidelines for proper material management and processing of RAP (such as contained in NAPA Quality Information Series 124, Designing HMA Mixtures with High RAP Content: A Practical Guide) will also be developed.
For more information on the specific tasks, please see: http://www.trb.org/TRBNet/ProjectDisplay.asp?ProjectID=1624.
Research and Development to Improve RAP Usage - Asphalt Research Consortium
The mission of the Asphalt Research Consortium (ARC) is to, over the next five years, build upon prior asphalt and modified asphalt research as well as prior asphalt pavement research in order to substantially improve the understanding of the mechanisms of asphalt pavement failure modes; and employ this improved understanding of pavement failure modes to devise user-friendly, validated test methods applicable to all materials (including engineered materials) and construction methods to predict pavement performance.
In particular, by using fundamental engineering principles in design of mixtures, superior performance and reduced impact on the natural environment can be optimized using a high concentration of recycled asphalt mixtures. A goal of the ARC is to develop guidelines for high level use of recycled pavement mixtures and validate these guidelines using laboratory damage resistance testing and field full scale trials. For more information, please see: http://www.arc.unr.edu/.
Low Temperature Properties of Plant Produced RAP Mixtures - North Central Superpave Center
The FHWA in conjunction with the North Central Superpave Center (NCSC) and Heritage Research Group (HRG) jointly are investigating and evaluating plant-produced HMA mixtures containing varying percentages of RAP to investigate low-temperature performance of the mixes. So far, results appear to confirm the current suggested guideline for the use of RAP in the amount of 15% or less that states that "no change is required in the binder PG or in the mixture design". However, in the case when higher amounts of RAP (i.e. greater than 25%) are used, the stiffness properties of the mixture increase (significantly in some cases) and it may be necessary to lower the PG of the binder or use blending charts to (i) determine the amount of RAP to use based on the virgin binder grade or (ii) determine the virgin binder grade and amount based on the desired amount of RAP.
The results highlight some challenges in using high amounts of RAP. A primary concern is the performance of high RAP mixtures in cold climates. The addition of high amounts of RAP to an HMA mixture usually increases the mixtures stiffness. In cold climates, this may contribute to the occurrence of low-temperature cracking. Another concern is due to the uncertainty of what occurs between the virgin and the RAP binder during mixing in a HMA plant.
Current activities include expanding this project to include materials from multiple HMA suppliers in order to gain valuable insight on producing HMA mixtures with RAP and to substantiate the results of the original project now referred to as Phase I.
Cold Climate Performance of RAP under Controlled Testing Conditions - Minnesota Road Research Facility (MnROAD) Study
The Minnesota Department of Transportation specifies the maximum amount of RAP allowed in a mixture based on the pavement layer and traffic level. In addition, binder grade affects the maximum amount of RAP allowed. MnROAD plans to conduct a 5-year project to study the performance of RAP and determine if the present specified limits on RAP are justified. Several asphalt concrete test sections will be built and contain 30 percent RAP but vary in binder grade and fractionated RAP content. It is anticipated that the results of this research will lead to the modification of current specifications to include fractionation of RAP aggregate and/or new percentage requirements for high-RAP asphalt.
Resources and Guidance Documents
Reclaimed Asphalt Pavement (RAP)
National Cooperative Highway Research Program (NCHRP) publications
National Asphalt Pavement Association (NAPA) Publications
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