Concrete Pavement’s New Road Map
A new 10-year plan for concrete paving research will generate a new generation of concrete pavements.

by , Contributing Editor

A path for concrete pavement research during the next 10 years — in development since 2004 — has been accepted by the industry and will provide a plan for a new generation of concrete pavements in the years to come.

Commissioned by the Federal Highway Administration and stakeholders in the concrete pavement industry, this national research plan for the 21st century — The Concrete Pavement Road Map — will help pavement designers wend their way through the rapidly changing environment in which concrete pavements are designed.

The Concrete Pavement Road Map is a comprehensive and strategic plan for concrete pavement research that will guide the investment of approximately $250 million over the next 10 years.

Concurrently, a National Concrete Pavement Technology Center has been established at Iowa State University at Ames, which will facilitate and coordinate research and technology transfer taking place across the country, including that driven by the Road Map.

Both complement the ongoing effort to advance and publicize high performance concrete pavements. In late 2003, experience with HPC pavements began to be disseminated in a massive new portland cement concrete technology transfer program by the FHWA, called the Concrete Pavement Technology Program. Administered by the Construction Technology Laboratories in Skokie, Illinois, the program consists of research, product development, and technology delivery that will improve the performance and cost-effectiveness of concrete pavements.

In August 2005, the FHWA reported that some 30 research and demonstration projects had been implemented by CPTP, with a goal of reducing road user delays, reducing costs, improving pavement performance, and fostering innovation.

Also, concrete research is provided the new Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy For Users surface transportation legislation signed by President Bush in August.

The relevant passages on SAFETEA-LU research funding are found under Title V, Section 5203, Technology Deployment. Under the new Innovative Pavement Research and Deployment Program, SAFETEA provides for research to improve National Highway System pavements.

“The Secretary shall obligate for each of fiscal years 2006 through 2009 from funds made available to carry out this subsection, $4,100,000 to conduct research to improve asphalt pavement, $4,100,000 to conduct research to improve concrete pavement, $4,100,000 to conduct research to improve alternative materials used in highways (including alternative materials used in highway drainage applications), and $2,450,000 to conduct research to improve aggregates used in highways on the National Highway System,” SAFETEA-LU reads.

The same Title V provides research for alkali-silica reactivity, the bane of aggregate providers in the West and proven to afflict aggregates in every state of the continental U.S.

Dramatic changes in concrete

The Concrete Pavement Road Map is needed because concrete pavements have changed dramatically in recent years. For many years, the materials going into concrete largely were unchanged, consisting of portland cement, aggregate, and water, with air-entraining agents often added for durability. Placement of PCC pavements was unhurried and they were allowed to cure for days without having to bear traffic.

But the post-Interstate era has brought change to concrete pavements, as the paradigm has shifted from constructing new pavements on new alignments, to reconstruction of existing pavements under traffic.

“Today’s concrete mix designs must integrate a multitude of new, sometimes marginal materials, resulting in serious compatibility problems and reduced tolerance for variations,” the CP Tech Center said in describing this new environment. “Motorists are more demanding. They will tolerate only minimal road closures and delays due to road work, increasing the need for new paving methods that allow road crews to get in, get out, and stay out. And motorists want smoother, quieter pavements, pushing the industry to control pavement surface characteristics.”

Also, highway agency focus has shifted from building new pavements to rehabilitating and maintaining existing ones, which requires different designs, systems, materials, and equipment, the center said. “Environmental pressures — traffic congestion, drainage, and runoff issues — are affecting mix designs and pavement construction practices,” the center says. “Highway budgets are being squeezed at every level. The pavement community simply has to do more with less.”

CP Tech Center relaunched

The CP Tech Center — rechristened in late 2005 at an announcement at the American Concrete Pavement Association annual meeting in California — was founded as the Center for Portland Cement Concrete Pavement Technology in 2000 through the support of the Iowa Department of Transportation and the Iowa Concrete Paving Association. In 2005, the center was transformed into the National Concrete Pavement Technology Center with the support of the American Concrete Pavement Association.

Unlike its contemporary, the National Center for Asphalt Technology at Auburn University, the CP Tech Center doesn’t conduct research itself. Instead, it coordinates and directs activity, working with  partners to improve pavement design, mix and materials, construction, and maintenance to produce durable, cost-effective concrete pavements, and in particular, to make the vision of the CP Road Map a reality.

Even before the Road Map begins, the center is conducting over $8 million in research projects. The center anticipates some $10 million of the concrete research funds provided by SAFETEA-LU to help it leverage funding from other sources to support concrete pavement research efforts.

The CP Tech Center acts as a catalyst to bring together federal, state, and industry partners to leverage funds and pool interests, extending the value of research investments for a wide range of stakeholders. It will help build strong working relationships between the FHWA, state DOTs, the ACPA, state paving chapters/associations, and the research community. It hopes to facilitate cooperation and encourage coordination of research and technology transfer activities taking place across the country, and partner with interested universities to accomplish research tasks.

Twelve Tracks on Road Map

The new Concrete Pavement Road Map has 12 tracks of research that will set the stage for concrete pavements of the 21st century. The Road Map combines more than 250 research problem statements from state, local, federal, and private sector stakeholders into 12 fully integrated, sequential, and cohesive tracks of research which is hoped will lead to specific products that will dramatically affect the way concrete pavements are designed and constructed.

The 12 tracks of the Road Map, as articulated at the Transportation Research Board meeting in January 2006, are:

• Performance-Based Concrete Pavement Mix Design System. The final product of this track will be a practical yet innovative concrete mix design procedure with new equipment, consensus target values, common laboratory procedures, and full integration with both structural design and field quality control — a lab of the future.

This track also lays the groundwork for the concrete paving industry to assume more responsibility for mix designs as state highway agencies move from method specifications to more advanced acceptance tools.

• Performance-Based Design Guide for New and Rehabilitated Concrete Pavements. Under this track, the concrete pavement research community will expand the mechanistic approach to pavement restoration and preservation strategies. This track builds on the comprehensive work done under NCHRP 1-37A (development of the Mechanistic-Empirical Pavement Design Guide) and continues to develop the models from that key work.

• High-Speed Nondestructive Testing and Intelligent Construction Systems. This track will develop high-speed, nondestructive quality control systems to continuously monitor pavement properties during construction, so on-the-fly adjustments can be made to ensure the highest quality finished product that meets given performance specifications.

• Optimized Surface Characteristics for Safe, Quiet, and Smooth Concrete Pavements. This track will result in a better understanding of concrete pavement surface characteristics. It will provide tools for engineers to help meet or exceed predetermined requirements for friction/safety, pavement-tire noise, smoothness, splash and spray, wheel path wear (hydroplaning), light reflection, rolling resistance, and durability (longevity). Each of the functional elements of a pavement listed above is critical.

• Equipment Automation and Advancements. This track will result in process improvements and equipment developments for high-speed, high-quality concrete paving equipment to meet the concrete paving industry’s projected needs and the traveling public’s expectations for highway performance in the future.

• Innovative Concrete Pavement Joint Design, Materials and Construction. Potential products for this track include a new joint design, high-speed computer analysis techniques for joint performance, a more accurate installation scheme, and faster rehabilitation strategies. The problem statements in this track address the basics — joint design, materials, construction, and maintenance activities. The track also specifies research that will help develop breakthrough technologies and extremely high-speed joint repair techniques.

• High-Speed Concrete Pavement Rehabilitation and Construction. This track addresses a series of activities, from the planning and simulation of high-speed construction and rehabilitation, precast and modular options for concrete pavements, and fast-track concrete pavement construction and rehabilitation, to the evaluation and technology transfer of high-speed construction and rehabilitation products and processes.

• Long Life Concrete Pavements. The need for pavements that last longer between maintenance, restoration, or rehabilitation is integrated throughout the CP Road Map. However, this track draws attention to some specific research that may address pavement life approaching 60 years or more.

• Concrete Pavement Accelerated and Long-Term Data Collection. This track provides the infrastructure, such as data collection and reporting tools, and testing methods, for a future national program that will plan accelerated loading and long-term data needs, construct test sections, and collect and share data.

• Concrete Pavement Performance. This track addresses key elements of pavement management and asset management systems. Such systems determine if and how pavements meet performance characteristics for highway agencies and users.

• Concrete Pavement Business Systems and Economics. Roles and responsibilities are changing in the highway industry, affecting the way paving projects are designed, bid, built, and maintained. Contractors are being asked to assume more control of the operation and quality control inspections. By including warranty provisions in project contracts, owner-agencies are asking for additional assurance that pavements will be built and will perform as expected. This track captures some important research that should be considered as this process of transformation continues in the United States.

• Advanced Concrete Pavement Materials. The problem statements in this track address the development of new materials and refine or reintroduce existing advanced materials to enhance performance, improve construction, and reduce waste. This track will experiment with these materials on a large scale and will develop standards and recommendations for their use. It’s hoped the research will foster innovation in the development of additional, new and innovative concrete pavement materials.

Richard Meininger, P.E., a highway research engineer in the FHWA’s Office of Infrastructure Research and Development, and long-time engineer with the National Stone, Sand & Gravel Association and its predecessors, is leading efforts under the first track, which will focus on performance-based design systems for concrete pavement mixes.

Mark Swanlund, senior pavement design engineer in the FHWA’s Office of Pavement Technology, is working with Iowa State University and the American Concrete Pavement Association to leverage resources in the fourth research track, which will focus on optimized surface characteristics for safe, quiet, and smooth pavements.

Concrete’s environmental attributes

The environmentally benign attributes of portland cement concrete are being viewed as powerful marketing tools to promote use of concrete in pavements and other structures. This will accelerate as the nation integrates green philosophy and technology in the transportation infrastructure and building environment.

That concrete can be described as environmentally benign is a little ironic, as the manufacture of cement is a primary source of anthropogenic carbon dioxide. However, the industry points to the growing substitution of cementitious reclaimed industrial byproducts such as silica fume, coal combustion fly ash, and ground granulated blast furnace slag as a way of recycling formerly landfilled waste products, and of reducing the amount of cement needed in the first place, with accompanying reduction in the amount of energy consumed by the cement manufacturing industry, and parallel reductions in carbon dioxide and water vapor emissions from the fuels used in pyroprocessing, and from the calcining process itself.

And concrete pavements have other powerful green credentials that will work in their favor in coming years. For example, a new Cool Pavement Report: EPA Cool Pavements Study released in June 2005 describes concrete pavement’s capabilities in reducing the heat island effect which is said to contribute to urban hot spots and heat retention of built areas during summer.

“Cities can be several degrees warmer than surrounding regions due to the built environment and the concentration of human activity, a phenomenon referred to as an urban heat island,” the study says. “Pavements have become an important contributor to this effect by altering land cover over significant portions of an urban area. Analyses in cities such as Chicago, Houston, Sacramento, and Salt Lake City have shown that pavements for both travel and parking can account for 29 to 39% of urban land surface.”

Researchers have studied ways to reduce the urban heat island effect, and have identified vegetation, cool roofing materials, and cool pavements as mitigation strategies.

“Cool pavements can be achieved with existing paving technologies and do not require new materials,” the EPA study says. “Possible mechanisms for creating a cool pavement that have been studied to date are increased surface reflectance, which reduces the solar radiation absorbed by the pavement; increased permeability, which cools the pavement through evaporation of water; and a composite structure for noise reduction, which also has been found to emit lower levels of heat at night.”

Several conventional paving technologies now exist that can apply these mechanisms, the study adds, stating greater reflectance can be provided by conventional concrete, with its high albedo (rate of reflectance), roller-compacted concrete, concrete-over-asphalt (whitetopping and ultra-thin whitetopping), asphalt concrete and asphalt chip seals with light-colored aggregate, and asphalt pavements with modified color.

Other environmental benefits by high-albedo concrete pavements include reduced need for nighttime illumination. “More reflective pavements can enhance visibility at night, potentially reducing lighting requirements and saving both money and energy,” the report says. “European road designers often take pavement color into account when planning lighting needs. Better illumination from lighter pavements is sometimes considered valuable at private establishments as well, for security or customer appeal. Some sources cite nighttime illumination enhancements of 10 to 30% with more reflective pavements.”

Crumb rubber concrete ahead?

So-called crumb rubber concrete — newly described from Arizona — may also give PCC an environmental edge.

Crumb rubber admixture is a boost or bane to hot-mix asphalt pavements, depending on who you speak with (see Science Gives Asphalt Rubber Recycling a Thumbs-Up, October 2005). Now researchers at Arizona State University have developed a crumb rubber modified portland cement concrete that is lighter weight and recycles tire carcasses.

Concrete mixing and placing processes lead to inevitable voids entrapped in the concrete, typically 1 to 3%. Where temperatures vary widely, 5% total air or more is needed to allow the concrete to resist freeze-thaw damage. To achieve this high level of air content, air entraining agents are added to capture the necessary additional air. However, these additives weaken concrete, requiring the use of more cement to compensate. This drives up the price of concrete substantially, as cement is the costliest ingredient.

The ASU researchers researched an improved concrete mixture that addresses this problem by using crumb rubber modifier. Specific quantities of crumb rubber are added to the concrete mix. Improved thermal cycling resistance is achieved without the expense of additional cement. Additionally, the concrete is lighter, displays increased traction, reduced contact noise, and superior crack resistance. It is well suited for use in areas where repeated freezing and thawing occur, and can also be poured in larger sheets than conventional concrete, ASU says. As a side benefit, this technology provides an attractive end use for the millions of rubber tires discarded each year.

Crumb rubber concrete mixes can be used in a variety of applications, including sidewalks; parking lots; and roadways, which may last longer when created with crumb rubber concrete; and lightweight concrete products such as roofing tiles.

Crumb rubber concrete offers substantial improvements to conventional concrete, the researchers say, including:

• Improved thermal cycling resistance. Crumb rubber concrete is less likely to crack and shatter under repeated freeze/thaw cycles.

• Light weight.  There is a substantial weight savings compared to ordinary concrete.

• Low cost. The crumb rubber substitutes for a portion of the costly cement.

• Promotes recycling. The use of crumb rubber in concrete presents an economical use for the millions of discarded vehicle tires waiting for recycling.

Several test slabs have been completed at various Arizona locations, and the performance over a period of years has been monitored. Potential partners and licensees for the issued patent are being sought.

While crumb-rubber concrete may not make it into pavements at an early date, its light weight would make it ideal for precast products used in conjunction with road projects. Precast Jersey barriers would be easier to move into place if they were made of crumb rubber concrete. And sidewalk panels made of crumb rubber concrete could be simply lifted, rather than cut, when faced with utility work below.

New materials, new concretes

New materials are aiding the development of the next generation of concrete mixes.

For example, last summer, a new type of fiber-reinforced bendable concrete was used for the first time in Michigan, and University of Michigan scientists hope that their new material will find widespread use across the country.

The new bendable concrete looks like regular concrete, but is 500 times more resistant to cracking and 40% lighter in weight. Tiny fibers that comprise about 2% of the mixture’s volume partly account for its performance. Also, the materials in the concrete itself are designed for maximum flexibility. Because of its long life, the Engineered Cement Composites are expected to cost less in the long run, as well.

This bendable concrete was described briefly in an earlier article (see Trends to Watch in 2006: Engineered Cementitious Composites, December 2005).

U-M’s ECC technology has been used already on projects in Japan, Korea, Switzerland, and Australia, but has had relatively slow adoption in the United States, said engineering professor Victor Li, whose team is developing the engineered cement composites.

The ductile, or bendable, concrete is made mainly of the same ingredients in regular concrete minus the coarse aggregate, Li said. It looks exactly like regular concrete, but under excessive strain, the ECC concrete gives because the specially coated network of fibers veining the cement is allowed to slide within the cement, thus avoiding the inflexibility that causes brittleness and breakage, Li said. 

Fiber-reinforced concrete is not new, but Li believes that U-M’s ECC — under development for the past 10 years — is vastly superior to other fiber-reinforced concretes in development today. The key is that the ECC is engineered, Li said, which means that in addition to reinforcing the concrete with microscale fibers that act as ligaments to bond the concrete more tightly, scientists design the ingredients in the concrete itself to make it more flexible. The U-M holds four patents with three pending on ECC technologies, Li said.

Last summer, in Ypsilanti, the Michigan DOT used the ECC to retrofit a section of the Grove Street bridge deck over I-94. An ECC slab replaced the expansion joint and linked the adjacent concrete slabs to form a continuous deck. Because major problems can occur when expansion joints jam, significant savings may be possible by using ECC. Li said state suppliers are being trained to make the ECC concrete now.

“The ECC material has promise for solving some of the deck durability issues we face, such as premature cracking,” said Steve Kahl, supervisor, experimental studies group, with MDOT’s construction and technology division. “We’re hoping the ECC will work well, and possibly lower the cost when experience is gained on large scale production.”

While long-term studies are still needed, comparison studies by the School of Natural Resources and Environment’s Center for Sustainable Systems, in conjunction with Li’s group, show that over 60 years of service on a bridge deck, the ECC is 37% less expensive, consumes 40% less energy, and produces 39% less carbon dioxide (a major cause of global warming) than regular concrete. The study notes that the findings are based on the assumption that ECC lasts twice as long as regular concrete, a reasonable assumption given the known information, but it must be confirmed through further study.

Precast slabs revolutionize work zones

In the meantime, work pioneered under the FHWA’s Concrete Pavement Technology Program to develop precast pavement slabs that are not prestressed or post-tensioned now is in the field, utilizing slabs marketed by The Fort Miller Company.

The product, marketed under the name of Super-Slab, is appropriate for high-trafficked areas that are subject to punishing loads, and massive traffic counts that would be severely impacted by lane closures required for conventional concrete reconstruction.

“The slabs are suited for a majority of applications that have to be done quickly in real life,” said Peter Smith, P.E., vice president, product engineering and development, Fort Miller. “These include Interstate main lines, ramps, intersections, intermittent or continuous repair, and toll plazas.”

For example, a total of 378 slabs were placed on a 2-mile rehabilitation project on I-90 in Albany, New York in 47 night closures last year. A value engineering proposal utilizing the Super-Slab System, initiated by the contractor, resulted in the repairs being made in about half the time when compared to the specified rapid set concrete method. The entire six-lane highway was open during the hours of heavy traffic volume — every day.

Another project at Washington Dulles International Airport in Washington, D.C., demonstrated that Super-Slabs could be used for overnight replacement of active taxiway pavement. A 50- by 50-foot area on Taxiway Bravo was replaced in two nights with eight 25- by 12.5-foot by 13-inch-thick precast concrete sections.

And as part of the pavement replacement project on the West end of the Lincoln Tunnel in New Jersey, The Port Authority of New York and New Jersey specified precast pavement slabs at the entrance to the two Northern tubes. The contractor proposed the Super-Slab system to meet this precast requirement. A total of 54 slabs (8,285 square feet) was replaced in three locations during five weekend closures.

In late January, heavy load tests of the precast pavement slabs were being wrapped up in California by Caltrans. “Caltrans is finishing up a heavy vehicle simulator test, showing this concept is not just a precast slab, but can provide the kind of performance that may last 50 years, or 80 years,” Smith told Better Roads. “The time has come because the need is huge, and what we have been doing has not worked in the long run. But this concept in precast slabs will work and last a long time.”

Concrete Pavements in the Spotlight
 at October Chicago Conference

Long-lived concrete pavements will be in the spotlight at an international conference to be held in Chicago in October.

The International Conference on Long-Life Concrete Pavements will be held October 25 to 26 at the Donald E. Stephens Conference Center, Rosemont, Illinois, adjacent to Chicago-O’Hare International Airport.

Sponsored by the Federal Highway Administration, American Concrete Pavement Association, Concrete Reinforcing Steel Institute, Illinois Department of Transportation, International Society for Concrete Pavements, and Portland Cement Association.

This conference, organized as part of the FHWA’s Concrete Pavement Technology Program, will provide an international forum to address various aspects of concrete pavement design, construction, and materials technologies that result in long life for concrete pavements.

It’s targeted at pavement, materials, and geotechnical engineering professionals who are involved in various aspects of concrete pavement design, construction, testing and evaluation, and rehabilitation. They include federal, state, and municipal engineers; consulting engineers; contractors; materials suppliers; and academia. Implementable design, construction, maintenance, and rehabilitation techniques that result in long-lasting concrete pavements will be the focus of this conference.

U.S. and International experience on long-life concrete pavements — Topics include best construction practices to achieve long-life concrete pavements; innovations in materials and construction; lessons learned from early failures of concrete pavements; improved joint systems for long-life concrete pavements; surface characteristics and drainage requirements for long-life concrete pavements; effective maintenance, repairs, and rehabilitation to extend service life; and life cycle cost considerations for long-life pavements.

For more information, contact Shiraz Tayabji, P.E., Construction Technology Laboratories, Inc., 5565 Sterrett Place, Suite 312, Columbia, Maryland, 21044; voice 410-997-0400; fax: 410-997-8480; e-mail stayabji@CTLGroup.com .

A brochure is available at www.pavementpreservation.org/calendar/announcements/long-life-concrete-conference.pdf .

For More Information

An abundance of information about the bright future of portland cement concrete is at your fingertips. Visit these sites for more information.

The 112-page FHWA planning report on the structure of the Concrete Pavement Road Map — Long-Term Plan for Concrete Pavement Research and Technology: The Concrete Pavement Road Map: Volume I, Background and Summary, September 2005, Publication No. FHWA-HRT-05-052 — may be downloaded at www.fhwa.dot.gov/pavement/pccp/pubs/05052/ . It also can be downloaded as a .pdf file there.

 More information about the National Concrete Pavement Technology Center may be obtained at its Web site, www.pcccenter.iastate.edu/ .

 The brochure, The Concrete Pavement Road Map, may be downloaded from NCPT’s Web site at www.pcccenter.iastate.edu/publications/pc_road_map_execsumm.pdf .

 The American Concrete Pavement Association has a variety of tech tips and timely reports on concrete pavements. Visit them at www.pavements.com .

 A flyer on crumb-rubber concrete referenced above is available at www.azte.com/Documents/mechanical/M1-052_Zhu.pdf .

 The Cambridge Systematics report on Cool Pavements using portland cement concrete is available at www.epa.gov/heatisland/resources/pdf/CoolPavementReport_Former%20Guide_complete.pdf . 

The Road Science article Science Gives Asphalt Rubber Recycling a Thumbs-Up (October 2005) may be downloaded at www.betterroads.com/articles/oct05c.htm .

 The Road Science article Reclaimed Byproducts Boost Concrete Performance (January 2004) may be downloaded at www.betterroads.com/articles/jan04a.htm .

 The Road Science article Trends to Watch in 2006: Engineered Cementitious Composites, (December 2005) may be downloaded at www.betterroads.com/articles/dec05c.htm .

More details, and videos of the bending of bendable concrete as described in this article, may be viewed at www.umich.edu/news/index.html?Releases/2005/May05/r050405 .

Reprinted from Better Roads Magazine
March 2006

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