Creating a New Generation of Concrete pavements

Paving Article December 28, 2000
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Concrete pavement research and innovation have produced an im-pressive record of technical ad-vancement

Concrete pavement research and innovation have produced an im-pressive record of technical ad-vancement. Significant advancements in concrete pavement design and evaluation, material properties and construction techniques have greatly improved the nation’s transportation system by producing pavements that are safer, durable and cost-effective.

In this, the post-interstate era, research must focus on preserving, rehabilitating and enhancing highways, airport pavements, streets and local roads. At the same time, road-users, who have become increasingly dependent on America’s surface transportation infrastructure, also have become less tolerant of delays, performance problems and the expense of poor pavements.

Today there are new research needs and priorities, as well as new dynamics in research funding. Working together, public agencies and the private sector can accomplish the required applied research that is needed to ensure that concrete pavement will continue to meet our evolving transportation needs.

The need for applied research

Roadbuilding professionals, both in the public and private sector, recognize the increasing need for applied concrete pavement research. In 1998, the need was firmly acknowledged by Congress. The Transportation Equity Act for the 21st Century designated $5 million per year through 2003 for applied concrete pavement research. These resources allow for key applied research projects that improve concrete pavement technology and the transfer of the knowledge obtained from such research.

The American Concrete Pavement Association (ACPA) fully supports ap-plied concrete pavement research. In 1997, a blue-ribbon panel of ACPA members, in partnership with public agencies, transportation research groups and academia, developed a "Blueprint for Concrete Pavement Research, Technology, and Innovation."

This document identified five goals for applied concrete pavement research:

  • Discern the best of today’s practices;

  • Reduce initial costs without compromising performance;

  • Reduce user delays during PCC pavement construction and maintenance;

  • Develop cost-competitive PCC options for all paving applications; and

  • Increase the certainty that PCC pavement will achieve design expectations.

To achieve these goals, the Innovative Pavement Research Foundation (IPRF) developed an "Action Plan for Research." This document, which has been widely dispersed throughout the transportation community, contains 70 specific research projects. When complete and implemented, this research will achieve the five goals described in the "Blueprint for Research."

Public/private partnership

The pressing concrete pavement research needs, coupled with the increased resources designated in TEA-21, provides a unique opportunity for the public and private sectors to work together to improve our transportation system. Through an active partnership, the concrete pavement industry and public officials have identified and prioritized the most pressing research needs. This partnership has led to an historic cooperative agreement for applied concrete pavement research between the Federal Highway Administration (FHWA) and the IPRF.

The IPRF presents an excellent vehicle to conduct applied research through the cooperative agreement with FHWA. It’s a non-profit organization devoted to concrete pavement research, advancement and transfer of concrete pavement technology, as well as public education on the use of portland cement concrete pavement. The IPRF is jointly owned by the ACPA, Portland Cement Association (PCA) and the National Ready Mixed Concrete Association (NRMCA).

The IPRF administers the cooperative agreement program using a process similar to the well-established meth-ods of the National Academy of Science’s Transportation Research Board. Project panels play a major role in the conduct and expected quality of the applied research. Processes and procedures have been set forth to ensure the smooth operation of the panels and contracts entered into under each task.

Applied research projects

In early 1999, the FHWA, IPRF and other industry representatives determined the specific research agenda for the early portion of the cooperative agreement. Using the IPRF "Action Plan for Research," and recognizing research under way by FHWA, NCHRP and other agencies, seven research projects were identified. The projects were considered top priorities toward reaching the five goals outlined in ACPA’s "Blueprint for Research." These seven projects, designated as Tasks 1-7, include:

Task 1 - Traffic management studies for reconstructing high-volume roadways;

Task 2 - Impact of texturing and surface treatment on reducing wet-weather accidents;

Task 3 - Performance and design of whitetopping overlays for heavily trafficked pavements;

Task 4 - Tests or standards to identify compatible combinations of individually acceptable concrete materials;

Task 5 - Accelerated loading tests of ultra-thin whitetopping (UTW);

Task 6 - Costs and benefits of various components of concrete pavements; and

Task 7 - Field trials of concrete pavement product and process technology.

Further breakdown of the seven tasks for the seven research tasks are as follows:

Task 1 - Renewal of urban interstate highway pavements and other urban freeways and expressways is an issue of growing national concern as more of the 21,000 centerline miles of this critical pavement network exceeds its design life. The temporary disruption caused by reconstruction often results in costs to the highway user and the local community that dwarf the capital cost of renewal. An innovative approach that provides a long-lived pavement and minimizes traffic and community disruption is needed.

Concrete pavement contractors suggest there are a variety of innovative construction and traffic management methods possible to reconstruct a significant section of urban freeway with long-life pavement. Unfortunately, there is general skepticism among some engineers that long-life pavement reconstruction can be accomplished with minimal user disruption.

Task 2 - According to the FHWA, the purpose of texturing road surfaces is to enhance driver safety by reducing wet-weather accidents. Presently, many state agencies assume that higher skid numbers from standard locked-wheel trailer tests represent safer surfaces in terms of wet-weather accidents. However, this assumption is unproven and there are few data available to relate surface textures or skid numbers to wet-weather accident rates.

Task 3 - Whitetopping, concrete overlays of asphalt pavements, has been used extensively throughout the U. S. Essentially, there are three types of whitetopping—conventional, thin, and ultra-thin. Conventional whitetopping is typically greater than 8 in. thick. The design of these overlays has been based on conventional procedures, which assumes the existing asphalt pavement is a stabilized base course.

Ultra-thin whitetopping is a more recently developed class of whitetopping. They are typically between 2 and 4 in. thick and have been applied to intersections, ramps and other areas. where the asphalt pavement has not performed adequately. Thin whitetopping overlays are between 4 and 8 in. thick. They have typically been used on low volume primary and secondary roads and are usually designed using conventional whitetopping design procedures. Research has found that bonding or interaction between the existing pavement and the overlay and short joint spacing contribute significantly to the overlay performance. This is not properly accounted for in current design practices.

Task 4 - In most cases, there are no limitations to the combination of materials to produce workable and durable concrete. However, certain combinations may produce undesirable chemical reactions that can lead to short-term problems such as early stiffening (false set or flash set) or long-term problems such as alkali aggregate reaction.

Task 5 - Ultra-thin whitetopping overlays are a relatively new composite pavement design using a 2- to 4-in.- thick concrete overlay of asphalt pavements. The original ultra-thin overlay concept, developed in 1990, was for light traffic situations. In practice, some ultra-thin projects have been constructed on heavy truck ramps, and even high-speed highways. Early performance of these pavements has been excellent, exceeding most expectations.

An element of uncertainty exists in the prediction of ultra-thin overlay load-carrying performance because it is a composite system. Modeling the composite system requires determining which layer (concrete or asphalt) will develop distress that will affect the pavement serviceability. It also is difficult to model the existing asphalt layer, which deteriorated with time and traffic before the ultra-thin overlay was placed.

Task 6 - There is a variety of design choices or features for concrete pavement. State agencies should select from these available features when designing highway, street and road pavements. In many cases, a standard design is propagated in a state agency over many years. There becomes little institutional knowledge of the purpose and interrelationship of the standard sections’ features, particularly on expected cost and performance.

Task 7 - In many cases, implementing new technology into the highway industry presents the following Catch 22: "A contractor cannot use technology unless it is specified, but a state cannot specify or allow a new technology until it is tried and proven."

Task 7 seeks to encourage state agencies to partner with their local contractor and material/equipment supplier constituents to implement new technology for the betterment of the highway user.

Specific target areas include load transfer optimization and materials; alternate concrete mixtures; surface finishing techniques; materials utilization; geometric and thickness alternatives and thin overlay construction.

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Overlay Init