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CPTP Status Report - Task 65 Engineering ETG Review Copy

Chapter 2 - CPTP Focus Areas

Introduction

The CPTP initiative encompasses a broad range of projects, ranging from materials research to field testing of new technologies, from the development of computer programs to the implementation of technology transfer activities. For purposes of categorization, the CPTP initiative is divided into the following six focus areas relating to various aspects of concrete pavements:

Over 30 projects, referred to as tasks, are currently included in these focus areas, and each is closely tied to the overall goals and objectives of the program. The following sections describe each of the six focus areas, and highlight some of the projects that make up each focus area along with significant contributions that have been made to the program. Appendix A lists the CPTP tasks and identifies the associated focus area(s) of each task, with specific project details provided in Appendix B. Appendix C provides information on non-CPTP projects being conducted by others that complement the current CPTP projects.

CPTP Focus Area 1: Advanced Designs

CPTP Focus Area 1: Advanced Designs
  • Performance and Design of Whitetopping Overlays for Heavily-Trafficked Pavements (Task 3).
  • Accelerated Loading Tests of Ultra-Thin Whitetopping (Task 5).
  • Instrumentation of UTW in Colorado (Task 7C).
  • Accelerated Load Testing of Ultra-Thin Whitetopping (Task 55).
  • Incremental Costs and Performance Benefits of Various Features of Concrete Pavements (Task 6).
  • Field Evaluation of Elliptical Steel Dowel Performance (Task 7G).
  • Influence of Sealing Transverse Contraction Joints on the Performance of Concrete Pavement (Task 9).
  • Revision of ISLAB 2000 for Subbase/Pavement Interaction (Task 10).
  • High Performance Concrete Pavements (Task 53).
  • Development of Standard Test for Concrete Coefficient of Thermal Expansion (Task 56A).

Projects in this area are looking at ways to improve or advance pavement structural designs. In some cases, this may include projects developing advanced design or analysis methods, while in others it may refer to projects incorporating the use of new or innovative materials or construction procedures. Highlighted projects within this focus area are described below.

Whitetopping and Ultra-Thin Whitetopping

Under CPTP Tasks 3, 5, 7C, and 55, research is being conducted on the improved design and rehabilitation of whitetopping overlays (concrete overlays of existing hot-mix asphalt [HMA] overlays). This technology is seeing significant growth as an effective rehabilitation measure for distressed HMA pavements, and can consist of conventional whitetopping, thin whitetopping, and ultra-thin whitetopping (UTW). Conventional whitetopping has the longest history of use (dating back to 1918) and is designed essentially as a new pavement on a stabilized base, assuming an unbonded condition between the concrete and the existing HMA pavement. Thin whitetopping is a moderately thin PCC overlay (thicknesses between 102 and 203 mm [4 and 8 in]) that is placed on a milled HMA pavement. The bond between the concrete and HMA pavement is relied upon in the design procedure, and short joint spacing (between 1.8 and 3.7 m [6 and 12 ft]) is used. UTW is similar in concept to thin whitetopping in that the concrete is bonded to a milled HMA, and that bonding is relied upon in the design process. PCC overlay thicknesses are between 50 and 102 mm (2 and 4 in) and square slabs (between 0.6 and 1.8 m [2 and 6 ft] on a side) are employed.

View of a ultrathin whitetopping pavement, showing joint layout.

The focus of much of the research in the CPTP has been on the improved design of thin and ultra-thin whitetopping, particularly in the area of bond development and bond contribution to load-carrying capacity. Additional work has been done documenting "best practices" for the repair and rehabilitation of ultra-thin whitetopping overlays.

Joint Design

Several projects within the CPTP are looking at improved and more cost-effective joint designs. For example, in Task 7G and Task 53, the use of different types of dowel bars are being investigated; these include not only the use of elliptical-shaped dowel bars (which are expected to reduce critical dowel-concrete bearing stresses by distributing loading over a wider area) but also the use of alternative dowel bars constructed of a non-corrodible material or containing a non-corrodible cladding for protection against corrosion. Pavement projects incorporating these different types of dowel bars have been constructed and are now being monitored to evaluate their long-term performance and overall cost-effectiveness.

Dowel basket with coated dowel bars.

Also being investigated in the area of joint design is the issue of transverse joint sealing (Tasks 9 and 53). This has been the subject of widespread debate within the pavement community, and the CPTP includes several projects directly evaluating the performance of concrete pavement sections with and without sealed transverse joints. Results from these studies are expected to provide improved guidance on when transverse joint sealing may and may not be cost-effective.

Benefit/Cost Tradeoffs of Design Features

The addition of design features (such as dowel bars, drainage, stabilized base, and so on) to a new concrete pavement are expected to have a positive effect on pavement performance, but the addition of such features also increases the overall cost of the pavement structure. Under CPTP Task 6, an evaluation tool is being developed that can be used to assess the relative costs and benefits of incorporating different design features into a concrete pavement design. The tool provides insight into general performance and cost trends associated with those modified pavement designs and, as such, can assist design engineers in developing more cost-effective concrete pavement designs.

Mechanistic Design

Several projects conducted under the CPTP are contributing to the development and implementation of mechanistic pavement design procedures, such as the 2002 Design Guide for New and Rehabilitated Pavements. For example, enhancements to the ISLAB 2000 finite element computer program have been funded, and that program serves as the stress computation "engine" for the 2002 Design Guide rigid pavement design procedure. Moreover, a procedure has been developed (and adopted by AASHTO as a provisional specification) for the determination of the concrete coefficient of thermal expansion, a key materials input in the 2002 Design Guide.

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Products and Contributions of CPTP Focus Area 1
  • Improved procedures for design of whitetopping overlays (in development).
    • UTW Design guide (available, pending final review).
    • UTW Software (available, pending final review).
    • Colorado's thin whitetopping design procedure calibration (in development).
  • Various UTW Performance Reports from FHWA accelerated load testing program (available now).
    • An Analysis of Ride Quality of the Ultra-Thin Whitetopping Overlays at the FHWA Accelerated Loading Facility.
    • Identification of Pavement Failure Mechanisms at FHWA Accelerated Loading Facility Ultra-thin Whitetopping Project.
  • Database of UTW performance under accelerated loading (in development).
  • Status of High-Performance Concrete Pavements (available now).
  • Alternative Dowel Bars for Load Transfer in Jointed Concrete Pavements (available now).
  • Guidelines for determining need for transverse joint sealing (in development).
  • ISLAB 2000, enhancement to the finite element analysis tool (available now).
  • AASHTO provisional specification on determination of concrete thermal coefficient of expansion (available now).
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Updated: 04/07/2011
 

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