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South Dakota Department of Transportation
Project Synopsis
SD1997-03


Title: Optimization of Recycled Asphalt Concrete and Base Materials for Bases of New Asphalt Concrete Pavement
Project Researcher: Erland Lukanen, Braun Intertec
Project Manager: Dan Johnston
Research Period: 5/1/1997 - 1/31/2000
Status:
Cost: $59,983.00

Problem Statement: Recycled asphalt concrete pavement and base materials have been used as a source of new base materials in asphalt concrete pavement construction for more than a decade in South Dakota. Typically, a blend of the recycled material (70%) with virgin aggregate (30%) is used for the new base. Construction of the new recycled base section is usually accomplished by placing virgin granular base material either above or below the recycled blend on state projects, whereas, counties frequently use only the recycled blend. Although the structural capacity of these new bases on the state system appears to be good there are numerous reports of anomalous transverse and longitudinal cracking within months after construction. Also, there are numerous reports of structural failure at the county level. The use of these recycled materials provides a significant cost savings with minimal environmental impact, but no investigation of factors which provide the best quality of recycled base has been conducted. Some of the factors include but are not limited to: type of recycling machine, horsepower, rate of travel, existing pavement thickness, quality of the material, gradation of the material before and after recycling, moisture content, laydown thickness, density, and recycled/virgin blend ratio.

It is important to determine the best procedures for constructing recycled bases and whether the current methods are contributing to random cracking or structural failure. Also, there are questions concerning the tendency of the recycled blend to compact into a section which performs more like asphalt concrete rather than granular material. When the recycled blend is placed immediately below the new asphalt concrete both layers may be acting more as a single full depth asphalt pavement rather than separate layers. On the other hand, when a virgin layer is placed between the recycled blend and the new asphalt concrete the impermeability of the underlying recycled blend may adversely affect pavement performance.

The purpose of this research is to optimize the use of recycled asphalt concrete and base materials and develop recommendations for changes to our current construction practices which will achieve an improvement in the quality and performance of these bases.



Findings:

Research Objectives:
1  To examine the relationships between construction practices and performance of existing pavements with recycled bases.
2  To determine the effects of the milling/recycling operation on the quality of recycled asphalt concrete base materials.
3  To determine the effects of different ratios and sizes of virgin aggregate blend material on the base quality.

Research Tasks:
1  Meet with the technical panel to review project scope and work plan.
2  Review and summarize literature relevant to recycling asphalt concrete and base materials for use as new base materials.
3  Conduct interviews with necessary department personnel and recycling contractors concerning South Dakota‚Äôs recycling practices and past recycling projects.
4  Establish a historical database on recycled base projects on the state highway system throughout South Dakota.
5  Conduct material testing on a minimum of 10 reconstructed pavements across South Dakota. The pavements will be selected in conjunction with the panel and will contain the recycled blend material.
6  Develop and submit plan notes by September 1, 1997, for inclusion into an existing construction project. The plan notes should define a series of test sections designed to evaluate significant recycling construction factors and their effect on perfor
7  Monitor and evaluate the construction of the test sections and conduct necessary testing (including FWD testing) of materials before, during, and after recycling.
8  Monitor and evaluate the initial performance (including FWD testing) of the test sections through the following winter and note any significant differences.
9  Recommend practical guidelines and specification changes which will optimize the use of recycled materials.
10  Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions, and recommendations.
11  Make an executive presentation to the SDDOT Research Review Board at conclusion of the project.

Documents Available:
SD1997_03_Final_Report.pdf

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