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Publication Number: FHWA-HRT-05-052
Date: September 2005
A 10-year research plan of this size and complexity cannot be absorbed in one quick skim-through.1 This chapter is for readers who do not need all of the details but simply want an overview of the CP Road Map. Following is a summary of the road map, highlights of the research tracks and subtracks, and the general budget and timeline.
The CP Road Map consists of more than 250 problem statements organized into 12 topical research tracks:
The first nine tracks are time phased. The research will be conducted sequentially, and at the end of the track, a final goal (e.g., a fully functional product or products) will have been achieved. The last three tracks are not time sensitive.
The problem statements in each track have been organized into subtracks of specific areas of research. As described in the research management plan (chapter 8), each track will be managed by a track team leader or team leaders with a technical working group. Each track includes its own budget, begins with a framing study in which the work is planned in more detail, and includes specific implementation activities.
The various tracks are integrated in strategic areas. For example, reducing mix performance variability (track 1) will require equipment advances (track 5). Validating and calibrating mix design models (track 1) will require enhanced data (track 9). Constructing long life pavements (track 8) will require new mix and structural design techniques (tracks 1, 2, and 3).
Three important research topics included in these tracks, but not immediately perceivable, are:
These are described in chapter 8 of this report under “Cross-Referenced Database Tables.”
Each problem statement clearly defines the tasks that must be performed to produce a desired product or achieve a desired objective. Because this CP Road Map was not developed for a single budget or funding source, or with a particular client in mind, it was not possible to put this into a format ready for bid.
Developing detailed research statements may take six to eight experts 18 hours to develop, resulting in more than 100 person-hours of time and experience per statement.
It should be noted that many of the problem statements identify products that are self-standing and usable. It is not necessary to complete the entire track to obtain useful and important outputs.
Emphasizing any particular track could be at the expense of other equally critical ones. The 12 research tracks were divided into type 1 and type 2 tracks, however, to help communicate a general sense of priorities identified by stakeholders.
Type 1 tracks focus on systemwide quality control and pavement surface characteristics. Participants at the brainstorming events overwhelmingly supported the importance of integrating mix design, structural design, and construction control for enhanced pavement performance. The innovative 2002 Guide for Design of New and Rehabilitated Pavement Structures developed by NCHRP has prompted pavement engineers to think about pavement performance in a new way.(7) The top three tracks of the CP Road Map, therefore, will help lead the way to a new generation of concrete pavement solutions with systemwide quality control processes that ensure pavement performance. Because of the clearly emerging importance of pavement surface characteristics, based on interest in the concrete pavement industry and pressure from the traveling public, the surface characteristics track was included in the type 1 group.
The tracks are categorized as follows:
Table 1 provides an estimated budget per track in millions of dollars for a period of 7-10 years.
|Track||Estimated Cost* (Millions)|
|1. Performance-Based Concrete Pavement Mix Design System||$29.80-$67.80|
|2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements||$40.50-$59.60|
|3. High-Speed Nondestructive Testing and Intelligent Construction Systems||$19.60-$41.10|
|4. Optimized Surface Characteristics for Safe, Quiet, and Smooth Concrete Pavements||$25.40-$54.25|
|5. Concrete Pavement Equipment Automation and Advancements||$25.65-$56.15|
|6. Innovative Concrete Pavement Joint Design, Materials, and Construction||$10.00-$15.30|
|7. High-Speed Concrete Pavement Rehabilitation and Construction||$10.30-$20.30|
|8. Long Life Concrete Pavements||$10.50-$16.60|
|9. Concrete Pavement Accelerated and Long-Term Data Collection||$9.75-$15.50|
|10. Concrete Pavement Performance||$2.70-$4.15|
|11. Concrete Pavement Business Systems and Economics||$21.15-$31.20|
|12. Advanced Concrete Pavement Materials||$11.45-$23.25|
*All numbers are rounded.
These first four tracks require considerable integration across track lines. The modeling developed in one track invariably will be used in at least two other tracks to ensure proper analysis of performance.
Track 1. Performance-Based Concrete Pavement Mix Design System
This track will develop a practical yet innovative concrete mix design procedure with new equipment, consensus target values, common laboratory procedures, and full integration into both structural design and field quality control. As opposed to mix proportioning, mix design engineers a concrete mixture to meet a variety of property or performance targets. The process begins with the definition of the end product, and the various materials are then selected, proportioned, simulated, and optimized to meet the end-product goals. This track will develop mix design rather than mix proportioning. Figure 2 contains an illustration of a lab for developing advanced mixture designs.
Figure 2. Illustration. Advanced labs for advanced mixture designs.
This ambitious track also lays the groundwork for the concrete paving industry to assume more mix design responsibility as State highway agencies move from method specification to a more advanced acceptance tool. To do this, however, the concrete paving industry and the owner agencies must be able to refer to a single document for state-of-the-art mix design.
The track provides a plan for research in the following areas:
Innovative concrete mix material selections and mix design procedures will produce economical, compatible, and optimized concrete mixes integrated into both structural concrete pavement design and construction control.
Track Action Items
Track 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements
Under this track, the concrete pavement research community will attempt to develop a mechanistic approach to pavement restoration and preservation strategies. This track builds on the excellent comprehensive work done under NCHRP 1-37A (development of the Mechanistic-Empirical Pavement Design Guide).(8) The problem statements will continuously improve the models, designs, rehabilitation efforts, and all aspects of the work done under NCHRP 1-37A. This track relies on a detailed understanding of the Mechanistic-Empirical Pavement Design Guide, committing researchers to the power of modeling and predictions. However, the CP Road Map also identifies the need for simplified mix design procedures for cities and counties, as well as a design catalog approach. Because many materials properties are important to design success, it is critical that the research conducted under this track be closely coordinated with that done in track 1 (Performance-Based Concrete Pavement Mix Design System). Figure 3 demonstrates advanced models for performance-based design.
Figure 3. Illustration. Advanced models for performance-based design.
Empirical approaches to concrete pavement design are effective when the conditions remain nearly the same, the focus is on structural design, and the attention is not on understanding and managing distress or failure modes. The pavement design practice of today is primarily empirical, though the state-of-the-practice is moving toward mechanistic approaches. The primary source of much of today's pavement design is still the American Association of State Highway Officials (AASHO) road test of the 1950s. This one subgrade, one base, one climate, limited traffic design guide was created using better-than-normal construction practices. Data analysis techniques were also fairly basic and the incorporation of reliability was insufficiently understood. Moreover, the AASHO road test did not incorporate many of the concepts and products used in concrete pavement practice today, including concrete overlays, permeable bases, different cements, dowel bar retrofits, and other necessary repairs.
The state-of-the-practice today is moving rapidly toward M-E approaches, particularly with the release of the Mechanistic-Empirical Pavement Design Guide and the expressed interest of many States. These M-E approaches will allow the designer to account for new design features and characteristics, many materials properties, changing traffic characteristics, and differing construction procedures (such as curing and day/night construction). The designer also can now consider additional design features and focus more on pavement performance, including limiting key distress types.
In continuing this work, this track not only looks to the next generation of modeling improvements, but also seriously considers the integration of design with materials, construction, presentation, and surface characteristics. This track also explores the development of new highspeed computer analysis tools for optimizing pavement design that can address changes to multiple inputs and thus offer better data on potential life cycle costs and reliability.
Mechanistic-based concrete pavement designs will be reliable, economical, constructible, and maintainable throughout their design life and meet or exceed the multiple needs of the traveling public, taxpayers, and the owning highway agencies. The advanced technology developed under this track will increase concrete pavement reliability and durability (with fewer early failures and lane closures) and help develop cost effective pavement design and rehabilitation.
Track Action Items
Track 3. High-Speed Nondestructive Testing and Intelligent Construction Systems
The research community has studied various nondestructive testing (NDT) technologies for nearly 20 years. While this technology is beginning to impact pavement management equipment and some hand-held test equipment in construction technology, NDT technology has not been applied extensively to concrete paving. The advancing technology could benefit both the construction and inspection teams in several key ways. Figure 4 shows several examples of advancing technologies.
Figure 4. Illustration. Technologies for monitoring pavement data and making real-time adjustments during construction.
The equipment industry faces both a technical challenge and the challenge of investing in a methodology without being certain of a market. Establishing a working group that properly frames the issues, agrees on the technologies, and prioritizes the work efforts is critical for overcoming this investment challenge.
Both industry and government will benefit from NDT by reducing reliance on slow and sometimes poorly managed small-sample testing programs. NDT technology can also be incorporated into an intelligent construction system (ICS) that automatically adjusts the paving process while informing contractors and inspectors of changes and/or deficiencies in construction. Continuous and real-time sampling will be configured to detect changes to the approved mix design and the preprogrammed line and grade values. NDT technology will also allow industry and government to use the data collected for long-term pavement management and evaluation. In this regard, track 3 has significant links to track 10 (concrete pavement performance).
The NDT/ICS methods developed in this track can measure the following properties that impact concrete pavement durability and performance:
Many problem statements in this track relate to track 1 (Performance-Based Concrete Pavement Mix Design System) and track 2 (Performance-Based Design Guide for New and Rehabilitated Concrete Pavements). Software standards will also ensure that the public can link to any software that the private sector produces.
Finally, human factors are critical for both researching and implementing this track. Pavement engineers, materials testers, and contractors need to understand NDT fundamentals to avoid the black box syndrome-that is, trying to get a technology to do something that they do not understand in principle.
High-speed nondestructive quality control can continuously monitor pavement properties during construction to provide rapid feedback. As a result, adjustments made immediately can ensure a high-quality finished product that meets performance specifications.
Track Action Items
Track 4. Optimized Surface Characteristics for Safe, Quiet, and Smooth Concrete Pavements
FHWA and State highway agencies have learned from sophisticated opinion polling that American drivers value the quality of their ride experience. Over the past 2 decades, concrete pavement engineers have focused on improving pavement smoothness without jeopardizing surface friction or surface drainage characteristics. This difficult but important balancing act has led to advancements in smoothness indices, longitudinal tining, and measurement equipment, to name a few. However, the relationship between surface texture and surface characteristics, as well as concrete pavement performance, has not yet developed fully. While smoother concrete pavements are being constructed, the relationships between texture, noise, splash and spray, and friction require further study before widely accepted solutions become available. Figure 5 illustrates an optimized pavement surface.
Figure 5. Illustration. Optimized pavement surfaces for a safe, quiet, and smooth ride.
In some areas of the United States, drivers and residents have demanded a quieter ride and a quieter living experience. These demands often eliminate concrete pavement as a construction option, and in some cases have even led to the overlay of recently constructed concrete pavements. In the Phoenix, AZ, metropolitan area, for example, concrete pavements that have a harsh transverse texture make up nearly all of the freeway system. Because of noise complaints, these pavements are now being overlaid with an open-graded asphalt rubber wearing course. While this may seem radical to some, the approach is not new. Noise has been a major problem in some of the most densely populated areas of Europe for more than a decade. As a result, it has impeded concrete pavement construction there.
Most European nations now place thin asphalt-based wearing courses over their concrete pavements immediately after construction. However, some concrete surfacing solutions have been used successfully. These include thin, open-graded (porous) concrete wearing surfaces as well as exposed aggregate surfaces. Textures including fine longitudinal burlap drag and diamond grinding also are used to reduce noise.
To address noise impacts to highway abutters, FHWA regulations currently dictate the noise mitigation efforts required, if any, for new or expanded highway facilities. To date, these regulations have resulted in questions about whether noise walls are necessary, and if so, what their design should be. At the same time, automobile and tire makers have developed designs that meet more stringent friction (braking) demands, while at the same time reducing interior noise. The time is quickly approaching, however, when pavement changes will be needed to help reduce noise, and concrete pavement engineers will need to find innovative materials and optimize pavement textures.
To meet this responsibility, the concrete pavement engineer must balance smoothness, friction, surface drainage, splash and spray, and noise to develop economical and long-lasting solutions for concrete pavement surfaces. Any long-term solution must include research and experimentation that examines the integration of these elements into an array of viable incremental solutions. One consideration is developing standardized noise measurement and analysis techniques. Pavement engineers must also better understand fundamental engineering properties to assess noise, friction, and smoothness, isolating better texturing options and tailoring solutions to location, traffic, and renewal requirements. Pavement engineers must understand the functional and structural performance of various solutions over time, as the data from many studies are sufficient to examine the relationships between noise and the other surface characteristics, including pavement durability.
The issues that must be explored include developing various standardized measurement techniques, understanding the tire-pavement interaction with various texturing options, predicting the life expectancy of any solution, and identifying possible repair and rehabilitation strategies for these pavements. Moreover, if noise criteria are ever imposed as design-build criteria, integration with national noise mitigation standards must be considered, and rational and achievable construction specification language must be developed.
A better understanding of concrete pavement surface characteristics will provide the traveling public with concrete pavement surfaces that meet or exceed predetermined requirements for friction/safety, tire-pavement noise, smoothness, splash and spray, light reflection, rolling resistance, and durability (longevity).
Track Action Items
Type 2 tracks focus on diverse advancements, from equipment to construction processes to business and management systems.
Track 5. Concrete Pavement Equipment Automation and Advancements
Figure 6 illustrates several equipment and technology advancements.
Figure 6. Illustration. Equipment and technology advancements.
The problem statements in this track propose process improvements and equipment developments for high-speed, high-quality concrete paving equipment. Research on technologies like those listed below is needed to meet the concrete paving industry's projected needs and the traveling public's expectations for highway performance in the future:
Efforts in the area of equipment automation and advancements will require collaborative partnerships between equipment manufacturers, contractors, and State highway agencies. After equipment concepts have been established, it is hoped that contractors and industry will be willing to invest in the development of new equipment. Involving contractors and industry from the start is essential for ensuring the equipment is practical for actual implementation. This private funding also will help to deploy the new equipment into everyday practice much faster than if development and implementation costs were carried solely by the government.
Stringless, global positioning system (GPS) control of slipform paving equipment is just one example of many pioneering technologies that, if further developed and tested, could provide greater efficiency, lower costs, and increased performance for the concrete paving industry.
Concrete paving process improvements and equipment advancements will expedite and automate PCC pavement rehabilitation and construction, resulting in high-quality concrete pavements, reduced waste, and safer working environments.
Track Action Items
Track 6. Innovative Concrete Pavement Joint Design, Materials, and Construction
Concrete has a propensity to crack. Because controlling cracks is essential for pavement performance, joints are an important feature of concrete paving. As the FHWA Technical Advisory on Concrete Pavement Joints (T 5040. 30) explains, “The performance of concrete pavements depends to a large extent upon the satisfactory performance of the joints. Most jointed concrete pavement failures can be attributed to failures at the joint, as opposed to inadequate structural capacity.” (p. 1)(9)
Ideal joints must be relatively easy to install and repair, consolidate around the steel, provide adequate load transfer, seal the joint or provide for water migration, resist corrosion, open and close freely in temperature changes, enhance smoothness and low noise, and be aesthetically pleasing. Figure 7 contains a graphic interpretation of the goal in developing these techniques. Joint failure can result in faulting, pumping, spalling, corner breaks, blowups, and transverse cracking (if lockup occurs).
Figure 7. Illustration. Breakthrough techniques for designing and rehabilitating joints.
The problem statements in this track address new and innovative joint design, materials, construction, and maintenance activities. There is much room in this research for innovative concrete pavement joint design, such as in research addressing the coefficient of thermal expansion and shrinkage issues. Additional incremental improvements to joint design, such as tie bar design for longitudinal joints, are addressed under track 2 (Performance-Based Design Guide for New and Rehabilitated Concrete Pavements). Much of the proposed research in this track will develop important improvements, though the track also specifies research that will help develop breakthrough technologies. The problem statements also recognize that future joint repair will proceed quickly, and they propose research for accomplishing faster joint repair.
Here are a few of the concepts that will be investigated:
This track will identify, develop, and test new and innovative joint concepts for concrete pavements that are more cost effective, reliable, and durable than current alternatives.
Track Action Items
Track 7. High-Speed Concrete Pavement Rehabilitation and Construction
For nearly 15 years, the concrete pavement industry has confronted both facts and perceptions about concrete pavement construction under high-speed traffic conditions. While the industry's record is generally positive, perceptions still determine concrete use in many situations. The traffic growth data presented in chapter 1 show that, despite the gains made in the past decade, many more miles of pavement will be subject to high-speed rehabilitation and construction conditions.
The next generation of construction and rehabilitation tools combines the software and hardware required to simulate system design and predict problems that might surface during high-speed construction. High-speed computer simulation can troubleshoot a pavement's response to environmental changes as well. Effective construction management, however, remains critical for meeting the goals and objectives of this track.
Future high-speed construction challenges the industry to move away from slipform paving and identify ways to make precast construction a more viable alternative. Precast modular construction might not only replace ultra-high-speed construction but also improve product quality and extend the paving system. Figure 8 illustrates an example of modular construction.
Figure 8. Illustration. Modular construction: One of many potential high-speed rehabilitation techniques.
Research in this track will include the following areas:
Some high-speed construction issues are also investigated in other research tracks, and those efforts will be closely coordinated with those in this track. For example, track 1 (Performance-Based Concrete Pavement Mix Design System) and track 3 (High-Speed Nondestructive Testing and Intelligent Construction Systems) contain many elements required in a high-speed option.
This track will explore new and existing products and technologies that facilitate high-speed rehabilitation and construction of PCC pavements.
Track Action Items
Track 8. Long Life Concrete Pavements
Long life pavements are needed to handle the congestion and traffic loading that the pavements will experience in their lifetime. To meet a 30-year calendar design life, a pavement built in 2005 may need 70 to 100 percent more axle loads per mile than a similar pavement built in 1995. But rather than simply building pavements to handle axle loading, pavement design must address what the public sees-the time between repairs. Figure 9 illustrates this concept.
Figure 9. Illustration. Pavements that perform well for 60 years or more.
The following research areas needed to design and build long life pavements are developed in this track:
The research in this track will be coordinated closely with related research integrated across the strategic road map. For example, other research tracks propose the following advancements to achieve long life pavements:
This track addresses the operational conditions in which pavement performance is defined. For example, a 60-year pavement could be designed in several ways that determine its maintenance schedule:
Each of these options can be used in locations that experience light-to-moderate truck traffic today but anticipate long-term growth. However, it is not clear whether the time between fixes for pavements that are already heavily loaded can be extended beyond 25 years.
The problem statements in this track will identify both conventional and innovative pavement types, design features, foundations, materials, construction QC/QA, and preservation treatments that will reliably provide long service life (e.g., more than 40 years).
Track Action Items
Track 9. Concrete Pavement Accelerated and Long-Term Data Collection
Accelerated testing facilities (ATF) provide valuable performance data that allow engineers to improve current procedures and advance the state of the art. Throughout the 1980s and 1990s, many new accelerated testing programs with ATFs were installed. ATFs encourage innovation by eliminating the fear of failure associated with full-scale road testing, since ATFs can test innovations without the possibility of disastrous consequences that might occur on a real highway. ATFs also provide small-scale evaluation of full-scale designs to identify limitations and speed up the implementation of design improvements. At least 24 ATFs currently operate in the United States. Figure 10 conceptually represents such an ATF.
Figure 10. Illustration. Accelerated load testing and data collection to improve models and systems.
Test roads and data collection methods can be developed and expanded further. Additional data are needed for new materials, new test sections, model validation and calibration, innovative joint designs, and surface characteristics advancements. These data can contribute to many of the research tracks in the CP Road Map, which depend on quality data for validation or calibration and require experimental installations or access to long-term data.
This track provides the infrastructure for a future national program that will plan accelerated loading and long-term data needs, construct test sections, and collect and share data. The problem statements in this track will explore areas that will yield useful data and determine the amount of time needed to get it. Additionally, this track will research accelerated durability testing for concrete pavement materials and design.
The problem statements in this track will address:
The research in this track will collect, manage, and analyze concrete pavement performance data that will support the CP Road Map.
Track Action Items
Track 10. Concrete Pavement Performance
This track addresses key elements of the pavement management and asset management system. This system determines whether the sum of all the work done meets the required and desired concrete pavement performance characteristics for highway agencies and users.
In the past, concrete pavement performance requirements have focused on serviceability (i.e., ride quality) and friction. However, performance indicators, such as tire-pavement noise, tire spray, hydroplane potential resulting from wheel path wear, light reflection, fuel economy, and the availability of open traffic lanes (i.e., those not closed for construction or maintenance), are now of much greater interest to highway agencies and users. Future concrete pavement designs will be expected to provide for all of these functional performance indicators to produce surfaces and structures that meet the needs of highway agencies and users.
Structural and functional pavement performance is the output from all of the design, materials, and construction processes and can thus be predicted using mathematical and computer models that systematically analyze data to predict pavement performance.
Monitoring concrete pavement performance indicators using pavement management systems will be crucial to highway agencies. Developing a performance feedback loop to provide continuous condition reports will allow prompt improvements to existing pavements that fall short of user needs. Continuously monitoring pavement performance will also help improve concrete pavement design procedures (particularly functional considerations related to surface characteristics), construction standards and specifications, and rehabilitation techniques.
The research in this track will determine and address the functional aspects of concrete pavement performance, particularly factors such as tire-pavement noise, friction, smoothness, and others. Research will also provide rapid concrete pavement performance feedback and consider ways to schedule surface characteristics and conditions improvements. Developing feedback loops in highway agencies' pavement management systems will be crucial to monitor performance effectively and rapidly and suggest improvements that minimize lane closures. Figure 11 illustrates this comprehensive process.
The research in this track will provide the traveling public with excellent concrete pavement surface characteristics and minimal lane closures for maintenance or rehabilitation over the design life.
Figure 11. Illustration. Systemwide data collection and analysis to support long-term performance.
Track Action Items
Track 11. Concrete Pavement Business Systems and Economics
The problem statements in this track address business and economics issues in concrete paving. The research outlined here will quantify the value and benefits of concrete pavements and ensure that an adequate delivery mechanism is in place to supplement the low-bid system. This track, when implemented, will help clarify the relationship between concrete pavements and economic issues, capital availability, risk and risk transfer, and alternative contracting (see figure 12).
Figure 12. Illustration. Innovative business systems.
The research in this track will develop:
The research in this track will clarify the relationship between concrete pavements and economic issues, capital availability, risk and risk transfer, and alternative contracting.
Track Action Items
Track 12. Advanced Concrete Pavement Materials
If the concrete pavement industry continues to use the same types of materials, the same problems and limitations will persist in concrete pavement applications. Fortunately, innovative concrete paving materials are being developed continually to enhance performance, improve construction, and reduce waste (see figure 13). The problem statements in this track will develop new materials and refine or introduce existing advanced materials. Many existing materials that the problem statements study have been used thus far only on a small scale, such as in laboratory tests. Most existing materials have not been used in the United States, but have been used successfully in other countries. This track will bring new concrete paving materials into common practice by experimenting with them on a larger scale and developing standards and recommendations for their use. Moreover, this research will foster the development of new and innovative concrete pavement materials.
Figure 13. Illustration. Innovative concrete materials.
The problem statements in this track are grouped into three subtracks: performance-enhancing, construction-enhancing, and environment-enhancing concrete pavement materials. Performanceenhancing materials will improve pavement durability and long-term performance, perhaps extending pavement life further than conventional materials. Construction-enhancing materials will improve the construction process by reducing material requirements, labor requirements, or construction time. Finally, environment-enhancing materials show promise not only by reducing waste through pavement reclamation, but also for reducing raw consumer and industrial waste. Clearly, many of these materials fit in more than one category. A material that improves the construction process, for example, may also improve pavement durability and performance. Likewise, a material that uses consumer waste may also improve pavement performance.
The emphasis on environment-enhancing materials is significant. Not only are contractors and agencies paying heavily to dispose of reclaimed asphalt and concrete pavement, but other industries are looking for environmentally responsible ways to dispose of industrial and consumer waste to reduce the burden on landfills. Environmental concerns are expected to become more important in the next few decades as landfills fill quickly.
New materials will be evaluated and existing materials will be refined to improve concrete pavement performance, enhance construction, and lessen environmental impact.
Track Action Items
1 See volume II of this report for a detailed description of the CP Road Map and its tracks, subtracks, problem statements, timelines, and budgets.
Topics: research, infrastructure, pavements and materials
Keywords: research, infrastructure, pavements and materials, Concrete pavement, concrete mix design, pavement construction, pavement design, pavement performance, pavement smoothness, equipment automation
TRT Terms: research, facilities, transportation, highway facilities, roads, parts of roads, pavements