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Publication Number: FHWA-HRT-11-065
Date: April 2012
A 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 CP Road Map, highlights of the research tracks and subtracks, and the general budget and timeline.
The CP Road Map consists of more than 270 problem statements. These were originally organized into the following 12 topical research tracks:
Over the course of the last 5 years of implementation, the CP Road Map has evolved. The current organization includes the following tracks:
The problem statements in each track have been organized into subtracks of specific areas of research. As described in the research management plan (see chapter 8 of this report), each track is 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-lasting overlays (track 8) will require new mix and structural design techniques (tracks 1 and 2).
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 h to develop, resulting in more than 100 h 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.
Table 1 provides an estimated budget per track in millions of U.S. dollars for each of the 12 tracks.
|Track||Estimated Cost* (Millions)|
*All numbers are rounded.
Track 1 subtracks are as follows:
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 QC. As opposed to mix proportioning, mix design engineers will create a concrete mixture to meet a variety of property or performance targets. The process begins by defining the end product. Next, the various materials are selected, proportioned, simulated, and optimized to meet the end product goals. This track will develop mix design rather than mix proportioning. Figure 2 shows a lab for developing advanced mixture designs.
Figure 2. Illustration. Lab for advanced mixture designs.
This track also addresses concrete pavement materials selection, including the use of recycled materials, SCMs, and new and innovative materials that will help mixture designers to better achieve performance requirements. Materials selection maintains a certain emphasis on sustainable materials, complimenting research conducted under track 12.
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 owneragencies 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:
Track 1 Goal
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 1 Action Items
The track 1 action items are as follows:
Track 2. Performance-Based Design Guide for New and Rehabilitated Concrete Pavements
Track 2 Subtracks
Track 2 subtracks are as follows:
Under this track, the concrete pavement research community will develop a mechanistic approach to pavement restoration and preservation strategies. This track builds on the comprehensive work done under NCHRP 1-37A (development of the MEPDG), which subsequently led to the AASHTOWare® design software DARWin-METM.(1) The problem statements serve to 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 MEPDG, 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. 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 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, although 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 constructed using better-than-normal construction practices. Data analysis techniques were also 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 (DBRs), and other necessary repairs.
The state of the practice today is moving rapidly toward mechanistic-empirical (M-E) approaches, particularly with the AASHTOWare® release of the design software DARWin-METM and the expressed interest of many States.(1) 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 now can 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 it seriously considers integrating design with materials, construction, presentation, and surface characteristics. This track also explores the development of new high-speed 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.
Track 2 Goal
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 2 Action Items
The track 2 action items are as follows:
Track 3. Intelligent Construction Systems and Quality Assurance for Concrete Pavements
Track 3 Subtracks
Track 3 subtracks are as follows:
The research community has studied various ICSs and nondestructive testing (NDT) technologies for nearly 30 years. While this technology is beginning to impact pavement management equipment and some hand-held test equipment in construction technology, ICS and NDT technology have 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 ICS and NDT by reducing reliance on slow and sometimes poorly managed small-sample testing programs. ICS can adjust the paving process automatically 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. ICS and NDT technology will also allow industry and government to use the data collected for long-term pavement management and evaluation.
The 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 tracks 1 and 2. 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 ICS fundamentals to avoid the black box syndrome–that is, trying to get a technology to do something that they do not understand in principle.
Track 3 Goal
High-speed nondestructive ICS can continuously monitor pavement properties during construction to provide rapid feedback. As a result, automatic adjustments can ensure a high-quality finished product that meets QA and performance specifications.
Track 3 Action Items
Track 3 action items are as follows:
Track 4. Optimized Surface Characteristics for Safe, Quiet, and Smooth Concrete Pavements
Track 4 Subtracks
Track 4 subtracks are as follows:
FHWA and State highway agencies have learned from opinion polling that American drivers value the quality of their ride experience. Over the past three 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, among other areas. However, the relationship between surface texture and surface characteristics, as well as concrete pavement performance, has yet to develop 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 quieter rides and living experiences. These demands often eliminate concrete pavement as a construction option and, in some cases, has 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 used to make up nearly all of the freeway system. Because of noise complaints, these pavements have now been largely overlaid with an asphalt rubber friction 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 two decades. As a result, concrete pavement construction has been impeded 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 and exposed aggregate surfaces. Textures, such as fine longitudinal burlap drag and diamond grinding, are also 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 on the Federal aid system. To date, these regulations have resulted in questions about whether noise barriers 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. In the near future, pavement will be observed to help with noise reduction. This will require concrete pavement engineers to take responsibility to find innovative materials and optimize pavement textures.
To meet this responsibility, concrete pavement engineers 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 understand fundamental engineering properties better to assess noise, friction, and smoothness, isolating improved 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.
Research must aim to develop various standardized measurement techniques, understand the tirepavement interaction with various texturing options, predict the life expectancy of any solution, and identify 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.
Track 4 Goal
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 4 Action Items
Track 4 action items are as follows:
Track 5. Concrete Pavement Equipment Automation and Advancements
Track 5 Subtracks
Track 5 subtracks are as follows:
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 the following technologies are 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 developing new equipment. Involving contractors and industry from the start is essential for ensuring the equipment is practical for actual implementation. This private funding will also help introduce the new equipment into everyday practice much faster than if development and implementation costs were solely carried by the government.
Stringless global positioning system control of slipform paving equipment is just one example of many pioneering technologies that, if further developed and tested, could increase efficiency, lower costs, and increase performance for the concrete paving industry.
Track 5 Goal
Concrete paving process improvements and equipment advancements will expedite and automate concrete pavement rehabilitation and construction, resulting in high-quality concrete pavements, reduced waste, and safer working environments.
Track 5 Action Items
Track 5 action items are as follows:
Track 6. Innovative Concrete Pavement Joint Design, Materials, and Construction
Track 6 Subtracks
Track 6 subtracks are as follows:
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 (JCP) failures can be attributed to failures at the joint, as opposed to inadequate structural capacity"(p. 1).(9)
Joints can also fail prematurely. Deterioration of concrete pavement joints has been reported nationwide, particularly in the northern States. Pavements affected include State highways, city and county streets, and parking lots. While it should be emphasized that only a small number of concrete pavements are affected, the distress is common enough to warrant research to identify preventative measures.
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 to address 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. 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.
Some of the concepts that will be investigated include the following:
Track 6 Goal
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 6 Action Items
Track 6 action items are as follows:
Track 7 Subtracks
Track 7 subtracks are as follows:
In the current economic climate, the need to maintain and preserve existing highway infrastructure assets has taken on a much greater importance. This is reflected by highway agency budgets shifting funding from new construction and/or reconstruction to maintenance and preservation. This shift in priorities emphasizes the importance of establishing reliable procedures and developing new and innovative methods for concrete pavement maintenance and preservation.
Proper maintenance and preservation treatments can significantly extend the life of concrete pavements, even well beyond their intended design life. There is a need to identify and implement proven maintenance and preservation practices and techniques and ensure proper application of those treatments.
Furthermore, many enhancements to existing maintenance and preservation treatments are envisioned. Automation of distress and maintenance need identification, and automated application of maintenance and preservation treatments can greatly reduce the cost and expedite the application of treatments, as well as enhance safety for maintenance workers.
Research in this track will include the following:
There is significant crossover with the problem statements presented in this track and other tracks; notably, problem statements from track 2 related to the effect of improvements in maintenance and preservation treatments on pavement design, problem statements from track 5 related to advancements in equipment automation for maintenance and preservation, and problem statements from track 9 related to the effect of maintenance and preservation on pavement life. Figure 8 illustrates one pavement preservation strategy.
Figure 8. Illustration. Dowel bar retrofitting used for pavement preservation.
Track 7 Goal
Track 7 will focus on optimization and deployment of maintenance and preservation treatments for concrete pavements in order to preserve the asset and maximize its lifespan.
Track 7 Action Items
Track 7 action items are as follows:
Track 8. Concrete Pavement Construction, Reconstruction, and Overlays
Track 8 Subtracks
Track 8 subtracks are as follows:
For more than 20 years, the concrete pavement industry has confronted both facts and perceptions about concrete pavement construction under high-speed construction 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 of this report show that, despite the gains made in the past decade, concrete pavements across the country will continually need rehabilitation under high-speed construction conditions.
Furthermore, while asphalt pavement has traditionally been viewed as the only solution for overlays of existing pavement, over the past decade, tremendous advances have been made in the understanding and usage of concrete pavements. Concrete overlays present a solution that facilitates high-speed rehabilitation by eliminating the need to remove the existing pavement prior to constructing a long-life concrete pavement. Figure 9 illustrates a bonded concrete overlay.
Figure 9. Illustration. Bonded concrete overlay over composite pavement.
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 accelerated 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 not only might replace ultra high-speed construction but also improve product quality and extend the paving system.
Research in this track will include the following:
Some high-speed construction issues also are investigated in other research tracks, and those efforts will be coordinated closely with those in this track. For example, tracks 1 and 3 contain many elements required in a high-speed option.
Track 8 Goal
This track will explore new and existing products and technologies that facilitate high-speed rehabilitation and construction of concrete pavements.
Track 8 Action Items
Track 8 action items are as follows:
Track 9. Evaluation, Monitoring, and Strategies for Long-Life Concrete Pavement
Track 9 Subtracks
Track 9 subtracks are as follows:
Long-life pavements are needed to handle the congestion and traffic loading that pavements experience in their lifetime. To meet a 30-year calendar design life, a pavement built today may need 70-100 percent more axle loads per mile than a similar pavement built 10 years ago.
One method for evaluating the performance of a particular pavement design is through accelerated loading at test tracks or accelerated loading facilities (ALFs). ALFs 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 ALFs were installed. ALFs encourage innovation by eliminating the fear of failure associated with full-scale road testing, since ALFs can test innovations without the possibility of disastrous consequences that might occur on a real highway. ALFs also provide small-scale evaluation of full-scale designs to identify limitations and speed up the implementation of design improvements. At least 24 ALFs currently operate in the United States.
Data collection methods for monitoring both test roads and in-service pavements can be developed and expanded further. Continuously monitoring pavement performance will help improve concrete pavement design procedures, construction standards and specifications, and rehabilitation techniques. Developing a performance feedback loop to provide continuous condition reports will allow prompt improvements to existing pavements that fall short of user needs. Additional data are also needed for new materials, new test sections, model validation and calibration, innovative joint designs, and surface characteristics advancements. This 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 from in-service pavements.
The research areas needed to design, build, evaluate, and monitor long-life pavements in this track are as follows:
Figure 10 illustrates long-term pavement performance (LTPP).
Figure 10. Illustration. Pavements that perform well for 60+ years.
Track 9 Goal
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 provide the traveling public with a long-life concrete pavement requiring minimal lane closures for maintenance or rehabilitation over the design life.
Track 9 Action Items
Track 9 action items are as follows:
Track 10. Concrete Pavement Foundations and Drainage
Track 10 Subtracks
Track 10 subtracks are as follows:
This track addresses both foundations and drainage elements of concrete pavements. It has long been established that principal components of a long-life concrete pavement include a uniform foundation and proper measures taken for drainage. Given the sheer variety of potential conditions that can be present on any given job (e.g., soil type), there is no "one size fits all" solution. This track explores research and technology related to these important topics, with a particular emphasis on tasks that can be readily applied in a site-specific manner. Figure 11 illustrates research and technology related to concrete pavement foundations.
Figure 11. Illustration. Quality foundation and drainage system.
The research in this track will determine and address both foundations and drainage aspects of concrete pavements, particularly factors such as subgrade, subbase, base construction, subsurface, and surface drainage. It includes measurement design and construction methods, as well as measurement techniques.
Track 10 Goal
The research in this track will provide pavement engineers with the tools to better design, construct, and evaluate foundations and drainage systems for concrete pavements.
Track 10 Action Items
Track 10 action items are as follows:
Track 11. Concrete Pavement Economics and Business Management
Track 11 Subtracks
Track 11 subtracks are as follows:
The problem statements in this track address economics and business management 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. Figure 12 illustrates innovative business systems.
Figure 12. Illustration. Innovative business systems.
The research in this track will develop the following:
Track 11 Goal
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 11 Action Items
Track 11 action items are as follows:
Track 12. Concrete Pavement Sustainability
Track 12 Subtracks
Track 12 subtracks are as follows:
At its core, sustainability is the capacity to maintain a process or state of being into perpetuity. In the context of human activity, it has been expressed as development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Although not universally accepted, sustainability is often characterized as a three-legged stool supported by economic, environmental, and social considerations or pillars. Although there is often synergistic cooperation between the three pillars, it is also true in practice that a balance must be struck between competing interests. The system is in danger of toppling if only one or two of the pillars are considered because it will be unbalanced.
FHWA recently initiated a dedicated program to explore sustainability aspects of concrete pavements. Within this program, it is maintained that the key to successfully increasing the sustainability of concrete pavements is to consider all three pillars of sustainability by having the tools and data needed to quantify each and understand the relationships of one to the others. Sustainability, in the context of this track, is the use of materials and practices in concrete pavement design, construction, operation, preservation, rehabilitation, and recycling (which are performed now) that reduce life-cycle costs, improve the environmental footprint, and increase the benefits to society (which researchers need to learn to do).
Research into sustainable practices should not only consider new construction, but it should also include the concrete pavement network, which already exists. For example, a significant portion of the Nation’s highway system is more than 40 years old, with some portions over 50 years old. The interstate and State primary road construction era of the 1950s, 1960s, and 1970s, much of which featured the use of concrete pavements, was followed by a period of rehabilitation featuring repeated asphalt resurfacings of these pavements. It must be recognized that through the appropriate application of sustainable preservation techniques, the service lives of concrete pavements can be extended for decades without the need for rehabilitation. It is also recognized that as traffic loadings increase, it might be necessary to add structural capacity to the existing pavement. This can be accomplished by selecting improvement techniques such as concrete overlays. The approach of extending the service life of the original pavement, and therefore maintaining equity, is fundamental to increasing the sustainability of an existing system. By choosing an appropriate preservation strategy, the low maintenance attribute of a concrete pavement can be preserved, as opposed to using strategies that can eventually lead to the complete reconstruction of the pavement. Figure 13 illustrates a life-cycle assessment (LCA) of concrete pavements.
Figure 13. Illustration. LCA of sustainable concrete pavement alternatives.
Track 12 Goal
The goal of this track is to identify and quantify characteristics of concrete pavement systems that contribute to enhanced sustainability of roadways in terms of economic, environmental, and societal considerations.
Track 12 Action Items
Track 12 action items are as follows:
1See volume II of this report (Report No. FHWA-HRT-11-070) 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, Dynamic modulus, MEPDG, LTPP, Hot mix asphalt, Artificial neural network (ANN)
TRT Terms: research, facilities, transportation, highway facilities, roads, parts of roads, pavements