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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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|Publication Number: FHWA-HRT-05-006 Date: July/August 2005|
Publication Number: FHWA-HRT-05-006
Issue No: Vol. 69 No. 1
Date: July/August 2005
Iowa is leading an effort aimed at increasing the long-term performance and durability of concrete roadways.
Concrete research often is conducted using mixes developed in a lab. When road crews mix concrete on a paving project in the field, however, the amount of mixture is much larger in quantity, and weather and other conditions are less controllable. As part of a study called Material and Construction Optimization for Prevention of Premature Pavement Distress in PCC Pavements (MCO), researchers are determining which conditions affect the quality of these new concrete mixtures.
In some of the States, we heard concerns about the quality of concrete, and we found that part of the issue was the fact that materials were changing,” says Gordon Smith, president of the Iowa Concrete Paving Association. “For example, we have admixtures that we didn’t use 30 years ago. Then we used portland cement only, whereas today we may use portland cement, fly ash, and ground, granulated blast-furnace slag. Instead of just having one cementitious material, there may be three. As we mix these changing materials today, we are finding that some of the things we used to do in the past do not always work now. The industry needs to have a better understanding [about] how those materials work together.
Researchers and Missouri Department of Transportation personnel work together outside the Mobile Concrete Research Lab to cast specimens for testing the development of maturity curves and strength gain from age.
To identify possible solutions to common problems like this, in 2003 the Federal Highway Administration (FHWA), Iowa State University, and other partners launched a 5-year pooled fund study known as the MCO project. In the study, researchers are evaluating conventional and new technologies and procedures to help State departments of transportation (DOTs) prevent premature distress in concrete pavements. Ultimately, the research will lead to the development of a suite of tests that will enhance the long-term performance of concrete pavements.
Federal, State, regional, and local transportation agencies, academic institutions, foundations, and/or private firms jointly fund studies through the Transportation Pooled Fund Program, with the focus of the research on solving problems of widespread interest within the transportation community.
The Midwest Concrete Consortium (MC2), a group of Midwestern States that has been gathering biannually for the last 8 years to share experiences and concerns about concrete and concrete pavements, initiated the MCO study through the Transportation Pooled Fund Program. The States in MC2 decided to work together through a pooled fund study to improve the group’s collective understanding of the materials its members were using in concrete mixes, and the consortium then recruited additional States and partners to join the effort.
FHWA, 17 State DOTs, the American Concrete Pavement Association (ACPA), and State and regional concrete paving associations are sponsoring the MCO study. The Iowa DOT serves as the lead State for the project, and the Center for Portland Cement Concrete Pavement Technology (PCC Center) at Iowa State University is responsible for management and execution.
The study consists of three phases. In Phase 1, now complete, researchers collected data, developed testing procedures, and implemented pilot projects. In Phase 2, now underway, researchers are further developing the test procedures and conducting field demonstration projects. An additional aspect of this phase involves dispatching teams of engineers to help States evaluate problems that arise on concrete paving projects. During Phase 3, expected to begin in 2006, the researchers will focus on technology transfer and help States implement successful testing programs. The MCO project will wrap up in 2008.
“There’s a tremendous value in doing this type of research through a pooled fund because you’ve got a group of interested investors at the very beginning of the project,” says Smith. “And if we’re coming up with answers about how to do something better, I truly believe that those States and contractors involved in the study will respond more quickly to lessons learned than if we’d tried to tell the story later. There’s real ownership.”
Participants in the Midwest Concrete Consortium, the group that initiated the MCO pooled fund study, met in Detroit, MI, and are shown here touring the Mobile Concrete Research Lab on September 21, 2004.
The realization that pavements need to be durable rather than simply strong is partially responsible for a change in how projects are contracted, and the MCO study will likely advance this trend.
In the past, concrete pavement specifications usually were based on the strength and thickness of the pavement. But today that is not enough. “You can make a concrete that is strong but not durable,” says Shannon Sweitzer, P.E., State roadway construction engineer at the North Carolina Department of Transportation (NCDOT). “For instance, if you don’t have the appropriate air entrainment, the concrete doesn’t have an air void structure that will resist freezing and thawing cycles. Therefore, the concrete pavement will likely deteriorate, and you’ll be replacing it in a short period of time.”
New and improved procedures for evaluating the durability of a concrete mixture will help. “We’ll be able to shift emphasis from prescriptive specifications to performance-based specifications,” says Seamus Freyne, Ph.D., a civil engineer at the Oklahoma Department of Transportation (ODOT) and an adjunct professor at the University of Oklahoma.
“The method specifications that we’ve lived by for years and years were developed when there wasn’t a lot of variation in sources or types of materials,” adds the Iowa Concrete Paving Association’s Smith. Those specifications required the contractor to produce concrete by mixing specified materials in definite proportions with predetermined types of equipment and placing methods.
“But the method specifications didn’t address the fact that some of those materials might react differently when combined as a concrete mix,” he continues. “What we’re really trying to do with the MCO study is to look at the holistic aspect of concrete by determining what materials work best together.”
This may be particularly important for contractors who increasingly are asked to expand their roles in paving projects. “There’s a shift in philosophy today that makes the contractor more responsible for the quality of the material,” Smith says. “While contractors today are still being required to meet specifications by mixing certain ingredients and following certain procedures, they also are being encouraged to assure that the pavement works and performs to expectation when the project is complete. And this study will help to reduce the risk to contractors by helping them to better understand how these materials work together.”
In 1988 FHWA introduced its first Mobile Concrete Laboratory. Technicians traveled across the country helping States test their pavements. According to lab technicians, the first FHWA mobile lab served the agency’s needs well, but the extensive travel caused sufficient wear and tear that it eventually had to be replaced.The original lab now serves as a stationary facility at the FHWA Turner-Fairbank Highway Research Center.
In the early 1990s, FHWA created its second, larger mobile concrete lab, measuring 15 meters (48 feet) long. With several years of experience under its belt, FHWA designed the second lab with improved functionalities. The newer lab is large enough to serve as a small classroom on wheels, traversing the country to introduce Federal, State, and local transportation personnel to state-of-the-art concrete materials and technologies and to conduct field and laboratory testing. Lab technicians continue to update the facility as new technologies become available.
FHWA’s Mobile Concrete Laboratory has three main goals: to advance technologies and procedures for long-life pavements, to conduct nondestructive testing, and to assist States with implementing the Mechanistic-Empirical Pavement Design Guide, developed through the National Cooperative Highway Research Program. (For more information about the guide, see “Designing Tomorrow’s Pavements” in the September/October 2004 issue of PUBLIC ROADS.)
The lab accomplishes these goals by visiting concrete pavement laboratories and project sites and conducting technical demonstrations. “We tailor what we do for each State depending on what it needs,” says Suneel Vanikar, concrete team leader at FHWA. “This may include training on equipment or software. Sometimes we conduct training seminars not on the site of the trailer but in a DOT building.” The FHWA lab also loans equipment to States and contractors so they can try the equipment before purchasing it.
“We help industry associations and contractors by showing them the latest advances in testing,” Vanikar says. “Contractors play a key role because ultimately they implement a lot of these new technologies.”
The notion of having a mobile lab is catching on within the States. Missouri, for example, recently created its own lab, albeit smaller than the FHWA prototype at 5 meters (16 feet) long. “It’s a mushroom compared to FHWA’s trailer,” says Patty Lemongelli, director of research, development, and technology at the Missouri Department of Transportation (MoDOT).
According to Lemongelli, necessity was the mother of invention for MoDOT’s lab. “We found ourselves out in the middle of nowhere, as we often do with field testing, and we needed to shuttle specimens to the nearest testing facility,” she says. “It was extremely inconvenient, and also dangerous to the specimens to transport them at such early ages.”
In response to this need, a couple of resourceful technicians at MoDOT proposed converting an equipment-hauling trailer into a mobile lab. The idea worked, and today the lab provides a convenient way for MoDOT technicians to conduct maturity testing and other research-related activities in the field. The lab includes a secondhand compressive strength machine, equipment for testing slump and air content, and a computer. MoDOT also recently modified the lab to accommodate air void analysis in the field.
“Our lab isn’t as sophisticated as FHWA’s mobile lab, but it’s dependable and functional,” Lemongelli says. “Given the minimal resources put into it, it’s a great addition to our research capabilities.”
In 1988, FHWA first used the concept of a mobile concrete laboratory to demonstrate new concrete technologies to personnel in field offices and working on projects in North Carolina, Virginia, and Iowa. Using FHWA’s Mobile Concrete Laboratory for technology transfers, demonstrations, and testing proved to be very successful over the years. And as technologies changed, the lab conducted additional visits to States, including a site visit to the I-26 project in Ashville, NC, in July 2002.
A mobile lab has been a key component of the MCO project as well. Sponsors from the concrete industry purchased a mobile research laboratory and donated it to Iowa State University to support the MCO study. Because part of the study includes conducting field tests to assess strength and durability, Iowa State University’s Mobile Concrete Research Lab (Iowa Mobile CRL) was specifically designed for the study. The research team modeled the Iowa Mobile CRL’s features and capabilities after FHWA’s Mobile Concrete Laboratory.
This photo of the interior of Iowa’s Mobile Concrete Research Lab shows the work space and some of the testing equipment.
Not as large as FHWA’s model, the 13-meter (44-foot)-long Iowa Mobile CRL was tailored to meet the specific needs of the study team and to be as small as possible for facilitating easy access to field sites. In addition, the Iowa Mobile CRL is not outfitted for mixing concrete because the team’s focus is on sampling materials at construction sites.
Researchers using the Iowa Mobile CRL can perform a comprehensive suite of tests. One of the key pieces of equipment is the air void analyzer (AVA), an important technology that measures the volume, size, and distribution of air voids in concrete in the field.
According to Smith, several pavements built in Iowa in the late 1980s and early 1990s started to deteriorate prematurely, within 5 years. “We would not have expected that kind of deterioration for 20 or 30 years,” he says. “After much analysis and significant research, we found that the common flaw in all of those pavements was that the air system in the concrete was not of good quality. We found that even if the pavements included enough air content, the distribution, sizing, and spacing of air bubbles was inadequate for a concrete mix that would resist freeze/thaw cycles.”
The AVA is a sensitive machine that researchers historically considered accurate only when installed in buildings, thus limiting its use in field situations. Because vibrations, such as those caused by wind, can dramatically skew the results, the trailer containing the Iowa Mobile CRL was designed with a portal in the floor to accommodate the AVA equipment. When the Mobile CRL is parked, the base of the AVA rests on the ground through the hole and is surrounded by a weather shield so it is protected but not touching the trailer.
“The AVA enables us to look at the concrete in its plastic state, while we’re building the pavement,” Smith says. “We can determine whether there is good sizing and spacing of air bubbles in the mix. Although it isn’t going to help with the concrete we put down 3 hours ago, the AVA test, which takes about an hour, enables the contractor to respond with changes in the mix so he doesn’t build a whole mile of pavement with a poor air void system. It’s almost a real-time analysis of the concrete mixture.”
These researchers are using a drill to obtain core samples on a concrete test road. The core drill is one of many pieces of testing equipment available in Iowa’s Mobile CRL. The truck that tows the lab also provides water for the drilling process, as shown here.
In addition to the AVA, the Iowa Mobile CRL includes a variety of other testing equipment, including a weather station, a wireless computer with global positioning system (GPS) and data analysis software, various sieves to determine coarse and fine aggregate gradations, a microwave oven to determine water-to-cement ratios, a penetrometer to test the setting time for mortar, a core drill and concrete saw, a curing tank, and calorimeters to determine the heat signature of mortar and concrete. The Iowa Mobile CRL also features a 113,400-kilogram (250,000-pound)-capacity compression tester to measure compressive and flexural strength development.
Technology transfer has been a key component of the project from the beginning. “With so many States involved, everybody is bringing something different to the table and sharing experiences,” says NCDOT’s Sweitzer.
During Phase 1, the team gathered data on State research related to concrete mix properties and paving practices, and compiled a detailed inventory of technologies and procedures for mix design, materials control, concrete testing, and field control. The team also obtained details on past projects that exhibited some form of early pavement deterioration. From this data, the researchers can better understand and assess the causes of pavement distress to ensure that proposed testing will address real-world problems.
The air void analyzer, shown here in Iowa’s Mobile CRL, measures the distribution, sizing, and spacing of air bubbles in concrete pavement mixtures.
Fulfilling an additional aspect of the project, the Mobile CRL visited each of the participating States at least once. In North Carolina, for example, researchers from the Iowa Mobile CRL demonstrated the suite of tests and applied them to two projects currently underway. “We actually got to see the tests being performed,” says Sweitzer, “which was an excellent technology transfer opportunity for our construction engineers and technicians who are involved in the placement of concrete on a routine basis.”
According to Sweitzer, North Carolina found that the AVA, microwave water/cement ratio, maturity, and unit weight tests were the most useful procedures performed onsite. As a result of the site visit, North Carolina now implements maturity testing in its specifications and will be evaluating the AVA, unit weight, and microwave water/cement ratio tests on several projects during the 2005 construction season.
The Iowa Mobile CRL also visited Wisconsin for 2 weeks and happened to be in the right place at the right time on one project. One morning the researchers were traveling along the previous day’s paving when they saw a number of vehicles parked beside the new pavement, including a sheriff’s car. They were investigating tire tracks in the newly placed concrete. Apparently a vandal in an off-road vehicle had jumped the vertical edge of the new road and driven for about 213 meters (700 feet) on the fresh pavement.
Staff from the Iowa Mobile CRL extracted a number of core samples from both the damaged and undamaged areas, and testing revealed small tears and cracks directly beneath the tire tracks, indicating that removal and replacement of the pavement was warranted.
The Iowa Mobile CRL also visited Missouri to conduct a demonstration project. A heavy storm passed through the area on the first night of the visit, dropping rain at a rate of nearly 11 centimeters (4.5 inches) per hour and providing an opportunity for lab personnel to demonstrate the effectiveness of a device for recording precipitation. Gauging rainfall is important because weather conditions during the first 72 hours of a pavement’s life can have a significant impact on its long-term performance. On an actual paving project, MoDOT could analyze the slab’s cracking potential by keying the weather information into FHWA’s HIPERPAV software, also included among the lab’s equipment.
MoDOT recently launched its own scaled-down version of a mobile concrete lab, with equipment to conduct maturity tests and other research-related activities. FHWA officials are pleased to see States taking the initiative to create labs that suit their own needs. “We know that FHWA can’t take care of all the work that’s out there, so we’re encouraged to see that others have been inspired to take it to the next level,” says FHWA’s Vanikar.
The research team also is formalizing technology transfer through, among other activities, creating a state-of-the-practice manual.
|A New Manual for Designing Concrete Pavements|
Through the MCO project and other efforts, researchers are making significant advancements in materials selection, mix design, and construction technologies for concrete pavements. Information about these advancements, however, may not always reach practitioners in a timely manner, so implementation in the field often lags behind.
Currently under development, the manual will introduce State and local DOTs, contractors, and consultants, including engineers, quality-control personnel, suppliers, and technicians, to new technologies, tests, and practices for identifying materials, concrete properties, and construction practices that can lead to premature pavement distress. In addition, the reference manual will impart the knowledge and skills necessary to implement new technologies, tests, and practices in the field and help practitioners troubleshoot and prevent problems.
“Experts from across the Nation contributed to writing this manual,” says NCDOT’s Sweitzer, who reviewed an early draft. “I see the manual as being a very beneficial tool, not just for States in the study, but nationally. It’s user friendly, and it will be an excellent tool.”
A number of features differentiate the forthcoming manual from existing references. First, it describes concrete pavement construction as an integrated system in which materials selection, mix design, and construction practices all affect one another in multiple ways. The manual provides straightforward, easy-to-understand information about materials’ effects on mixture design, construction, and service life, and describes critical mix properties that help predict the overall quality of the final product. Further, the manual compiles information about new technologies, tests, and practices, as well as how and why to implement them.
The manual identifies and solves mixture problems at the design phase and at time of production, identifies when and how to adjust the mixture according to weather and other factors, and uses testing and performance prediction technologies and procedures to address problems with concrete pavements.
Information gathered through the MCO project represents the core content of the manual, including current standards and best practices from participating States and laboratory evaluations of materials- and construction-related tests.
The team developing the manual expects to complete a preliminary draft in time for the 8th International Conference on Concrete Pavements in August 2005 at Colorado Springs, CO. At the conclusion of the pooled fund study, the team will update the manual to include final results from the project, and the document will be incorporated into a new, state-of-the-practice publication covering all aspects of concrete pavement design and construction.
NCDOT’s Sweitzer and the others expect that the findings from the MCO study are likely to change the way States mix and construct concrete pavements. “I envision [NCDOT] taking the results of this study and actually implementing them in our specifications for concrete pavement,” he says. “So instead of just performing tests to evaluate strength and thickness, there may be additional tests we’ll need to conduct to evaluate durability. I think it’s really going to enable us to evaluate our pavements in a smarter fashion so that we end up with a higher quality product.”
The MCO team plans to visit more States in the coming years, and some States are already well on their way toward incorporating new tests into their pavement designs. Oklahoma, for example, has purchased new equipment to improve the durability of concrete overlays on its bridges. “Through this study we’ve learned about a couple of new tests, including the bond or pull-off method and the air void analyzer,” says ODOT’s Freyne. “With the bond test, we can assess the quality of the existing concrete bridge deck prior to an overlay, and [then later evaluate] the bond between the new and old concrete after the overlay.”
In the end, the study team expects the MCO project to result in more durable concrete pavements across the country.
Jim Grove, P.E., is a paving engineer at the PCC Center at Iowa State University and leads the pooled fund study for the MCO project. His experience includes serving as the PCC paving field engineer in the Iowa DOT Office of Construction and the PCC engineer in the Iowa DOT Office of Materials. Grove is a member and past chairman of the Transportation Research Board Committee on Portland Cement Concrete Pavement Construction. He has an M.S. in transportation engineering and a B.S. in civil engineering, both from Iowa State University.
Mark Anderson-Wilk is an editor for the PCC Center at Iowa State University. He leads development of the PCC Center’s research and technology transfer publications. Anderson-Wilk has a master’s degree in English from the University of Minnesota.
Marcia L. Brink is the communications manager for Iowa State University’s Center for Transportation Research and Education, administrative home of the PCC Center and the U.S. Department of Transportation’s University Transportation Centers Program serving Iowa, Kansas, Missouri, and Nebraska. Brink has a master’s degree in English from Iowa State University.
For more information about the MCO project, visit www.cptechcenter.org/mco/index.htm or contact Jim Grove at 515-294-5988, firstname.lastname@example.org. For information about Iowa’s Mobile Concrete Research Lab, contact PCC Research Engineer Bob Steffes at Iowa State University at 515-294-7323, email@example.com.