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South Dakota Department of Transportation
Project Synopsis
SD1998-07


Title: Optimization of AC Shoulder Design and Construction for PCC Pavements
Project Researcher: Kelly L Smith, ERES Consultants
Project Manager: Dan Johnston
Research Period: 5/1/1999 - 12/31/2001
Status:
Cost: $40,000.00

Problem Statement: The performance of Asphalt Concrete (AC) shoulders adjacent to Portland Cement Concrete (PCC) and Continuously Reinforced Concrete (CRC) pavements is extremely variable statewide with relatively good performance on some projects and severe shoulder subsidence and shoulder joint sealant failure occurring on others. Prior research projects such as SD90-13 and SD96-10 PCC/AC Shoulder Joint Seal Evaluation and SD95-04 Evaluation of South Dakota Department of Transportation's Shoulder Surfacing on New Construction looked at sealing the shoulder joint and the performance of different shoulder types but did not examine the causes of poor performance. The factors behind shoulder subsidence may be directly related to shoulder design and construction combined with regional climatic and topographical features. A shoulder design which provides good performance in a well-drained, relatively dry climate may suffer severe failure in a moist, poorly drained environment. In addition, some of the worst shoulder subsidence is associated with the use of a relatively impermeable base course such as cement or lime-treated bases. The recycled AC routinely used for constructing bases for AC shoulders adjacent to PCC pavements may be reducing the permeability of these bases and could contribute to poor performance.



Findings: The performance of asphalt concrete (AC) shoulders adjacent to Portland cement concrete (PCC) pavements has been extremely variable throughout South Dakota, with relatively good performance on some projects and severe shoulder subsidence and shoulder joint seal failure occurring on others. The factors behind poor shoulder performance may be directly related to shoulder design and construction, combined with regional climatic and topographical features. The research performed in this study sought to better define the causes of shoulder subsidence and joint seal failure, and to develop and implement a field study that tests the effectiveness of various design strategies and construction practices in reducing or minimizing settlement and seal failure. In the study, a total of 29 in-service shoulder structures located in the eastern half of the state were surveyed for condition and tested for load response characteristics using non-destructive deflection testing (NDT) techniques. The observations and resulting data were then used to formulate a set of shoulder design/construction strategies that could be tested as part of an actual paving project. Subsequently, a total of 11 different shoulder strategies were included in a mainline PCC paving project located on SD 37, north of Parkston. The construction of the test shoulders in fall 2001 were carefully monitored, and condition surveys and NDT testing of the shoulder sections were conducted at periods of 7 and 12 months following construction. This report discusses the results of the entire research effort and the recommendations made to the South Dakota DOT concerning their AC shoulder design and construction practices.

Research Objectives:
1  To explore technologies, construction practices and design modifications which may improve AC shoulder performance adjacent to PCC pavements.
2  To examine the need for different shoulder designs based on Regional and climatic factors.
3  To determine the effect of the time at which sealing occurs on PCC/AC shoulder joint performance

Research Tasks:
1  Review and summarize literature relevant to AC shoulder design and performance.
2  Survey 20 projects with AC shoulders exhibiting poor performance, primarily in the Aberdeen Region and examine the designs used in their construction.
3  Meet with the technical panel to review project scope and work plan.
4  Develop and submit plan notes for inclusion into an existing construction project. The plan notes should define a series of a minimum of nine test sections designed to evaluate significant design and construction factors and their effect on performan
5  Monitor and evaluate the construction of the test sections and document test results obtained during construction. Conduct any additional testing deemed necessary on materials and samples from test sections.
6  Monitor and evaluate the initial performance (including FWD testing) of the test sections through the following winter and note any significant differences.
7  Recommend practical guidelines and specification changes which will optimize the performance of AC shoulders.
8  Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions, and recommendations.
9  Make an executive presentation to the SDDOT Research Review Board at conclusion of the project.

Documents Available:
SD1998_07_Final_Report.pdf

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