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|Federal Highway Administration > Publications > Public Roads > Vol. 67 · No. 2 > CPTP Update|
by Cheryl Allen Richter and Suneel Vanikar
Humans have been building roads since the Romans, so some may assume that the highway community knows everything there is to know about pavement. Not so. Pavements are highly variable in smoothness and durability, depending on the origin of the materials used to construct them, weather conditions such as temperature and humidity during and after construction, and how well (or not so well) the materials were compacted. Construction of pavements that are safe, smooth, and durable requires good design, sound selection of materials and mix design, and well-controlled construction processes.
The Federal Highway Administration's (FHWA) Concrete Pavement Technology Program (CPTP) is helping designers, material suppliers, contractors, and State agencies improve portland cement concrete (PCC) pavements by addressing some of the critical gaps in knowledge. The CPTP authorized under the Transportation Equity Act for the 21st Century (TEA-21) is funding research on approximately 30 projects for 6 years to improve the performance and cost-effectiveness of concrete pavements. During the first years, FHWA and the Innovative Pavement Research Foundation conducted the CPTP jointly. In the summer of 2002, FHWA assumed sole responsibility.
The CPTP will produce practical and readily usable tools, guidelines, methods, and software to be used in the selection of materials, mix and pavement design, construction, and operation. The goals are to reduce user delays and costs, improve performance, and foster innovation. The July/August 2002 issue of PUBLIC ROADS discussed selected CPTP projects in depth, and this followup article describes the program's progress and highlights over the past year, starting with selected CPTP projects in advanced pavement design systems.
The Concrete Pavement Technology Program was developed and is being implemented by FHWA in cooperation with the State departments of transportation (DOTs), American Association of State Highway and Transportation Officials (AASHTO), industry, and academia. "This program is an excellent example of a public-private partnership," says Tommy L. Beatty, FHWA's director of pavement technology."The CPTP has produced numerous technologies that will make a significant impact on the transportation program."
Advanced Pavement Design Systems
These projects are pioneering changes in structural design, materials, and cost analysis. The industry can expect guidance, tools, and test methods to support the design and evaluation of highly cost-effective and durable concrete mixtures and analytical tools to perform sound economic evaluation of alternative pavement designs.
Currently, nearly all State highway agencies require transverse joint sealing, which adds about 2 to 7 percent to the initial construction costs of pavements and even more in resealing activities. If narrow, unsealed joints on short-jointed concrete pavements can perform as well as sealed joints, States may save millions of dollars in construction and maintenance costs. By eliminating or reducing the need for joint maintenance, this change also will improve safety by reducing the need for lane closures that are inherently dangerous to both drivers and maintenance crews.
A 3-year CPTP study on the cost effectiveness of sealing transverse contraction joints is one of several projects that will help agencies determine when, where, and how to seal pavement joints. In this study the lead on the program, Dr. Katie Hall, and her colleagues will take a close look at the performance of 35 to 40 experiments in 12 States on sealed and unsealed joints. CPTP-funded demonstrations in Illinois, Kansas, and Ohio on high-performance concrete pavements, for example, are comparing sealed versus unsealed joints.
In the 1950s Wisconsin DOT (WisDOT) engineers questioned the cost effectiveness of sealing joints in PCC pavements. Since that time Wisconsin has built numerous test sections and documented findings to determine the effects of unsealed joints on pavement performance. In 1990 WisDOT adopted a department policy of not sealing PCC joints in new construction and maintenance. "We are convinced that leaving joints unsealed is the most cost-effective way to deal with joints in PCC pavements," says Steve Krebs, WisDOT pavement engineer.
A 1997 report, Stephen F. Shober's The Great Unsealing: A Perspective on PCC Joint Sealing, documented Wisconsin's findings and started a national controversy. "Although Shober took a lot of heat for his stand, this research intrigued us in Illinois because we have the same weather conditions," says Matt Mueller, Illinois Department of Transportation (IDOT) pavement engineer.
At that time IDOT was conducting a study of how much water was passing through its concrete and full-depth bituminous pavements. A flow meter on the under drains revealed the presence of significant water passing through the typical sealed joint pavements. Recognizing that seals fail to keep the water out, IDOT decided to do its own joint sealing studies and asked crews on then-current projects to install a few 61-meter (200-foot) sections with narrow unsealed transverse joints. In 1997 the first test section on IL 64 near St. Charles compared three variations: joints with no seals, preformed elastomeric (rubbery) joint seals, and a reservoir sealed with rubberized hot sealant. Three subsequent test sections of unsealed and sealed joints followed in 1997 on IL 59 at Naperville, in 1999 on US 67 at Jacksonville, and in 2000 on IL 2 at Dixon.
According to David Lippert, engineer of physical research with IDOT, the test sections have done so well that IDOT has adopted a no-seal standard effective for all jointed-concrete projects let after January 1, 2003. Estimated savings top $1 million per year. The specified saw cut is so narrow at 5 millimeters (0.19 inch) that only sand-size material can enter—not large enough to spall the surface of the concrete.
"We learned right away that many standard saw blades are wider than we would like," says Lippert, "so we notified our construction personnel to make sure the narrow blades are used."
In the past, the roughness from overfilled poured joints and the tire slap noise from preformed joint sealant were major concerns, according to Lippert. "It would ride rough until the snowplows or the traffic wore down the seal, but with the no-seal joints the ride is smooth and definitely quieter."
Dr. Hall thinks that the national study may show different options are more cost effective in different regions depending on the climate, the subgrade soil, the aggregates used in the concrete, and the joint spacing.
Concrete Materials and Mix Integration
Five projects under Marcia Simon, PCC pavement laboratory manager at FHWA, are examining the integration of materials to improve PCC pavement mixes. Incompatibilities of materials within mixes can result in early stiffening, excessive retardation, early-age cracking, and detrimental effects on the air void system.
Researchers are examining deficiencies in existing testing methods for assessing concrete material suitability, production and placement methods, finishing, and influences of temperature and humidity. For example, since the American Society for Testing and Materials (ASTM) C-359 test for early stiffening of portland cement may not apply to cementitious materials with chemical admixtures, research will evaluate the mini-slump cone test for identifying material combinations that produce early stiffening. The researchers will write guidelines for evaluating material combinations for concrete pavements and recommend methods of communicating the information to the concrete pavement industry.
Vibrating Slope Apparatus
The second generation of the vibrating slope apparatus developed by the U.S. Army Corps of Engineers is a promising tool for assessing the workability of paving concrete. The University of Texas, Iowa State University, and the Turner-Fairbank Highway Research Center are evaluating a vibrating slope apparatus with updated electronics and software. The apparatus quantifies workability by measuring the time for a measured mass of concrete to move out of the chute under certain vibration energy. The study is assessing concrete slump, chute angle, vibration force, and test procedures. When evaluations are complete, the vibrating slope apparatus will debut on the road as a component of FHWA's Mobile Concrete Laboratory.
Concrete Mixture Optimization
With such a wealth of material from multiple sources, pavement and materials engineers need a practical tool to select the optimal mix for a given paving project. Facing so many choices in chemical admixtures, fly ash, cements, mineral additives, water/cement ratios, and aggregates, how do work crews avoid incompatibilities in concrete mixes?
"Contractors may rely on hunches or past experience, so we're developing a tool to give them rational choices," says Dr. Robert Rasmussen, P.E., of The Transtec Group, Inc., an FHWA consultant.
Rasmussen is gathering literature for an expert database and inviting field input from a technical advisory panel of State DOT concrete engineers, contractors, and trade association representatives. The goal is to produce by 2005 a user-friendly computer program to optimize the mixes. With the software, the user will be able to identify the starting-point for site-specific conditions quickly and optimize the mix based on chosen targets such as cost, strength, workability, durability, long-term performance potential, and numerous other properties.
"We're excited about this project as it will reduce our risk of producing incompatible mixes," says advisory panel member Pete Capon of Rieth-Riley Construction, an Indiana paving contractor. "Now we go through the time-consuming and necessary task of gathering materials, doing trials, and then determining what we can and cannot do in material combination. This tool has been needed for a long time and is a big leap forward."
The optimization software will enable a user to plug in a new ingredient such as a change in fly ash, imported materials, or a different cement source, and predict the potential for problems. According to Capon, users of this tool could move from State to State and do theoretical mix designs with ease and produce reliable numbers for estimating and construction. During the contract bidding process, DOTs might use the tool to predict problems and specify those combinations that cannot be used for construction.
Mobile Concrete Laboratory
An integral part of the research and development part of the program, this traveling project is primarily a tool to obtain real-world test data for use in developing and refining CPTP research products. Additionally, the Mobile Concrete Laboratory also acts as a deployment and technology transfer instrument by introducing Federal, State, and local transportation personnel to state-of-the-art technologies in materials selection and mixture design. In this role, the lab focuses on shortening the acceptance time for new technologies through onsite demonstrations. Therefore, the Mobile Concrete Laboratory is both a research and development and a technology transfer tool.
"One of the major technologies we're presenting now is the air void analyzer," says Gary Crawford, FHWA project manager for the lab. (Last year AASHTO's technology group selected the air void analyzer as a new technology with a big payoff.) Although previous tests could identify the air quantity in fresh concrete, they did not measure the size of the bubbles or the spacing between them—characteristics that predict freeze-thaw resistance. The air void analyzer enables a user to determine that a problem exists and enables the user to adjust the admixtures to improve the concrete before placing the pavement instead of afterward, when it is too late.
"The implementation panel for the air void analyzer is developing an AASHTO provisional specification so the States will start using this equipment," Crawford says. See www.aashtotig.org for more information.
The Mobile Concrete Laboratory also is assisting States with technologies such as maturity meters—heat sensors embedded in fresh concrete to measure heat gain, which can be used to estimate strength. According to Crawford, instead of relying on traditional methods of casting cylinders or beams and breaking them at 6 or 7 days to confirm strength, a State or local agency using the temperature probe may learn that sufficient strength has developed to open up that pavement in 2 or 3 days, saving 4 days of construction time and inconvenience to the traveling public.
To encourage DOTs to try out the analyzer, maturity meters, and other testing equipment to determine if they want to invest, the laboratory will loan the equipment, ship it to a site, and send a technician to work with the onsite staff. If the State wants to educate its employees on a number of tests, it can ask the lab to schedule a site visit. Typically the Mobile Concrete Lab visits four to five field projects per year, staying at each from 2 to 4 weeks. From November through March, the lab sets up in parking lots to showcase its technologies to attendees at the American Concrete Pavement Association's meetings and State conventions.
The laboratory staff documents the results from every site visit in a report describing how new technologies were utilized. These reports, combined with technical presentations, papers, and magazine articles, are key to the success of the Mobile Concrete Laboratory and have been an effective way to share this information with the transportation community.
During fiscal year 2003, the lab scheduled eight equipment loans to highway agencies to evaluate nondestructive impact-echo tests for measuring thickness of existing concrete pavements in lieu of destructive core tests. The laboratory set up displays and made technical presentations at conferences in Colorado, Illinois, New Jersey, New York, North Carolina, Pennsylvania, and Texas. During the remainder of the fiscal year, the lab will travel to Florida and back to New York and Pennsylvania. Other States—California, Indiana, Iowa, New York, and North Carolina—have requested lab participation on field projects.
Advanced Quality Systems
CPTP projects will promote improvements in the as-constructed quality of concrete pavements through advances in the availability and application of technology, analytical tools, and guidance for quality control. Contributions to date include the HIPERPAV II software, workshop materials addressing nondestructive and innovative testing, a prototype software tool to guide the selection of materials and procedures for curing, and increased knowledge and experience with performance-related specifications.
This user-friendly software application released in the late 1990s runs on the Microsoft® Windows® operating system and can be used as a tool to help highway agencies avoid premature failure of concrete pavements. The software user can input site- and time-specific weather data and information on the specific concrete mix to be used on the project. The software models the changes that take place as the concrete sets and cures, enabling the engineer to assess the likelihood of early-age cracking in real time so that adjustments to the mix design, paving schedule, and curing practices can be made if needed. For example, if work crews anticipate thunderstorms in the late afternoon followed by a cold front, with HIPERPAV they can determine the effect on the concrete and make a decision to cover with tarps or insulated blankets. On a hot summer day, they may change the timing of placement to paving at night.
Powerful new modules for HIPERPAV II will predict the early-age performance of jointed plain concrete pavement (JPCP) and its performance beyond the first 72 hours and also the early-age performance of continuously reinforced concrete pavements (CRCP). The new release will include an implementation package for training field personnel.
Although HIPERPAV II is not a structural design tool, it may be used in the design phase to help the designer identify potential materials-related problems and make appropriate adjustments to the mix or structural design to prevent cracking. In a forensic mode, HIPERPAV may diagnose a cracking problem so that the same mistakes are not repeated on a future project.
The developers of the software conducted workshops with a beta version of HIPERPAV II in Iowa, Michigan, and Pennsylvania, and then modified the tool based on the feedback. The initial release of HIPERPAV II was in the summer of 2003. After further refinement based on feedback from additional workshops, the final software version will be delivered by January 2004.
In the highway industry, implementation of new technology encounters a "Catch-22" situation. A work crew cannot use new technology unless it is specified, but a State cannot specify or allow a new technology until it is tried and proven. FHWA study manager Sam Tyson, in partnership with multiple academic and engineering firms, is solving the dilemma with pilot tests of new technologies. In a field trial, an FHWA work crew tests a technology under development by taking it to a local work crew or State staff and working with them on a trial project. Then FHWA uses the feedback to improve the product.
Field Trial: Magnetic Tomography
Dowels may be a small item in concrete pavements, but their placement is critical for spanning the joint and providing proper load transfer. Misaligned dowels can lock up the joint and cause premature failure, but identifying how accurately they are placed is difficult. A new technology, magnetic tomography, developed by a German manufacturer for locating unexploded ordnance, promises to become an important monitoring tool during construction.
"We're excited about magnetic tomography because it can show us the precise location of the full length of the dowel in three dimensions within a tolerance range of perhaps 1 millimeter (0.039 inch)," Tyson notes.
At a presentation for the Transportation Research Board in January 2003, the German manufacturer—MIT Sicherheit Besser of Dresden—demonstrated that using this imaging device to locate a dowel bar in concrete shows the dowel as clearly as magnetic tomography shows a bar surrounded by air since concrete has no magnetic qualities.
Although FHWA has not yet tested magnetic tomography in this country in a field trial, the device is a proven technology in Europe where the manufacturer has implemented it in dowel bar locations for numerous projects. By using this imaging device during construction, a work crew can pick up problem placement caused by equipment malfunction and correct the problem early on instead of miles down the road.
Field Trial: Monitoring Maturity Using the TEMP System
Another field trial will take the maturity test to a new level by adding software and miniature sensors to monitor pavement temperature during curing. A member of the work crew will set the button-sized devices into the concrete during placement and then monitor the curing temperature using computer printouts in graphic formats. An FHWA contractor is developing the "Total Environmental Management for Paving" (TEMP) software and is planning field tests with two State DOTs. The software program can be set up to answer a question such as: "I want to open this pavement to traffic 48 hours from construction at 2 p.m. on Tuesday. Can I do that?" Using measurements from the temperature sensors, the software will be able to give the user an exact time—earlier, the same, or later—when the new pavement can be opened to traffic.
"We hope this system will be adaptable to remote sensing," Tyson adds, "maybe picking up these data points through long-range wireless technology, thus allowing monitoring from a centralized workstation."
Several studies are looking at alternative dowel bar materials. In March 2002, FHWA published preliminary findings from field trials in Illinois, Iowa, Kansas, Minnesota, Ohio, and Wisconsin in a report titled High Performance Concrete Pavements. A recently initiated study with Iowa State University will examine elliptical steel and elliptical fiber-reinforced plastic (FRP) dowels.
Enhanced User Satisfaction
Minimizing traffic disruptions due to pavement construction, reconstruction, rehabilitation, and maintenance meets the Long Life Pavement Program goal of enhanced user satisfaction. Projects include using precast concrete panels to expedite highway pavement construction and for full-depth repair, weekend intersection reconstruction, optimal traffic management when reconstructing urban highways, and tools and techniques to achieve smooth pavements.
Placing Precast Concrete Panels in Highways
Last year's PUBLIC ROADS article, "Texas Tests Precast for Speed and Usability," examined a pilot project by the Center for Transportation Research (University of Texas, Austin) on a Georgetown, TX, frontage road. The work crew installed 700 meters (2,300 feet) of precast pavement on both sides of a new bridge. To aid with alignment when assembled, the precaster fabricated the panels with continuous shear keys in the edges. The panels were pretensioned crosswise during fabrication and post-tensioned lengthwise during construction.
California is proposing a project similar to the Georgetown pilot for I-10 in the Los Angeles area, and Missouri also is considering a field trial using the precast method pioneered on the Georgetown project, according to Mark Swanlund, FHWA study manger.
Michigan State University will take the next research step, a field trial using precast for full-depth repairs, when its researchers direct pilot projects in Michigan and Colorado. Instead of pretensioning and post-tensioning, the precast panels will incorporate steel reinforcement and load transfer. Dowel bars will be cast into the slab at the casting yard so that the dowels can be positioned perfectly horizontally and aligned to prevent the joints from locking. On the job site, the dowels will fit into slots cut into the adjacent pavement, then be sealed with grout.
"I find this field trial exciting, as I worked with full-depth temporary repairs using precast panels with the Virginia Transportation Research Council in the 1970s," says FHWA's Sam Tyson. "Those repairs had no load transfer, so the 18-wheelers would cause movement, and we would take the panels out in a year or so and use them in a different location. With the advances in technology, the Michigan State project will be a permanent repair."
Swanlund adds, "Installing precast panels in both the construction and maintenance modes eliminates the time-consuming curing step from the field construction phase of the project while maintaining high-quality concrete." Precast panels can be cast in a controlled environment at the casting yard, stockpiled, and then taken to the job site when needed. With this technology, work crews will be able to install durable repairs in record time on interstates and highways in busy urban areas, reducing delays and traffic costs.
Traffic Management Optimization For Reconstructing Urban Freeways
Often the temporary disruption caused by pavement reconstruction results in costs to the highway user and the local community that dwarf the capital costs of renewal. Concrete pavement contractors are suggesting innovative construction and traffic management methods to reconstruct heavily traveled sections of urban freeways using long-life pavement. Unfortunately, many engineers doubt long-life pavement reconstruction can be accomplished with minimal disruptions for motorists. Success in providing a quality long-life pavement with minimal disruptions may decrease user costs and improve safety significantly by reducing workers' exposure to traffic during construction.
The University of California-Berkley demonstrated the feasibility of rehabilitating 2.8-lane kilometers (1.7-lane miles) within a construction window of a 55-hour weekend and documented the productivity benefits. In a followup project, the Texas Transportation Institute will undertake and document a demonstration project, survey motorists and residents, develop a matrix model on methods to involve the public, and provide methods of technology transfer—including a national open house—to communicate the model to the highway construction industry. Technology transfer products may include reports, summary papers, brochures, posters, audio/visual presentations, slideshows, videos, CD-ROMs, DVD-ROMs, or a Web site, and possibly all of these and other tools. Completion is expected by March 2005.
Smoothness Criteria for Concrete Pavements
This project will identify the characteristics of objectionable longitudinal profiles, ways to measure those factors, the causes, and ways to avoid creating them. The study will establish appropriate limits for smoothness specifications and determine methods to identify and correct localized roughness in concrete pavement.
Research has shown that concrete pavements that are built smooth initially will stay smooth longer than pavements that are built rough initially. To provide smoother pavements many States employ incentive and disincentive provisions in their construction contracts. These provisions provide a financial incentive to contractors who exceed the require pavement smoothness while penalizing those who build a pavement rougher than specified. Forty-five of 52 State DOTs utilize smoothness specifications for construction acceptance of concrete pavement.
Most DOTs currently use a profilograph or other response-type roughness meter to measure the smoothness. However, there is a growing trend to change the measurement device to inertial profiler and to more advanced roughness indices, the International Roughness Index (IRI). AASHTO currently is considering adoption of a provisional standard for pavement smoothness based on inertial profilers and the IRI.
These are some of the questions that researchers will investigate:
Enhanced Capability of the Technical Workforce
The conclusion of CPTP research is just the beginning of improving the Nation's concrete highways. To implement the emerging technologies with end users in the transportation community, FHWA is seeking a partner to mastermind a project titled, Technology Transfer, Deployment, and Delivery.
Since the CPTP research projects currently underway are expected to yield 25 to 30 products, they will group them logically into workshops, slide presentations, Web sites, guideline literature, and other publications. The CPTP group envisions that a DOT or industry group might one day schedule a 2-hour executive-level presentation of all the products coming out of CPTP's 6 years of research and then select products of interest for hands-on workshops for engineers from State highway agencies, civil engineering professors, and members of industry trade associations. Other products may reach the end user through tradeshow exhibits, videos, teleconferencing, CD-ROMs, and technical reports.
Nondestructive and Innovative Testing Workshop
In the mid-1990s, several State highway agencies participated in 1-day workshops on nondestructive testing. Based on this success, FHWA decided to broaden the scope with a 2-day hands-on workshop presented on a national basis to interested highway agencies. The Maryland State Highway Agency hosted the first pilot 2.5-day workshop April 9-11, 2002. The Mobile Concrete Laboratory staff presented a second abbreviated pilot workshop for the Ontario Ministry of Transportation on October 17, 2002.
By incorporating the feedback from the pilots, the 2-day presentations were refined. Once a presenter is onboard to take the workshops nationwide, FHWA will send out an announcement of times and locations for 20 to 30 workshops.
The Nondestructive and Innovative Testing Workshop will present information on the following devices: maturity, pulloff (bond test), air void analyzer, and impact-echo and concrete thickness gauge. A session on new and emerging technologies will discuss FHWA's nondestructive evaluation (NDE) Validation Center activities (HERMES II ground-penetrating radar, infrared thermography, and wireless measurements systems), pullout, workability device, cover meter, spectral analysis of surface waves, the Road Surface Analyzer (ROSAN), dynamic friction tester, and the circular track meter.
The Road Ahead
Although the completed CPTP projects have reduced user delays and costs, improved performance, and fostered innovation, transportation agencies still need an innovative roadmap for the road ahead. Iowa State University, with input from stakeholders and partners, is charting that path from the current state-of-the-practice to a new generation of concrete pavements to develop FHWA's Long-Term Plan for Concrete Pavement Research and Technology.
The plan will answer questions from decisionmakers: "Where do we go from here? What funding do we require? What are the needs for tomorrow's pavements?"
The plan will look ahead 10 to 15 years as it guides concrete pavement research, development, and technology activities, both within and outside the Concrete Pavement Technology Program, and FHWA's post-TEA-21 Infrastructure Technology Program. Plan development will include an extensive outreach effort to ensure that the final product fully meets the needs of the pavement engineering community. Completion of the plan is slated for June of 2004. Visit www.pccpavement.com for information as the plan unfolds.
Paul Teng, P.E., director of FHWA's Office of Infrastructure R&D, concludes, "The CPTP is an excellent blend of FHWA experts and industry practitioners that has resulted in a program and products to enhance concrete paving technology."
Cheryl Allen Richter, P.E., Ph.D., is the team leader in portland cement concrete pavement research and development at the Turner-Fairbank Highway Research Center in McLean, VA. She has worked 11 years for FHWA, 10 of them as part of the Long-Term Pavement Performance Program staff. Prior to joining FHWA, she worked for the Strategic Highway Research Program and the New York State Department of Transportation. She earned her B.S. and M.S. from Cornell University and her Ph.D. from the University of Maryland.
Suneel Vanikar, P.E., leads the concrete group at FHWA's Office of Pavement Technology. An FHWA employee for 23 years, he directs the product development and technology transfer projects of the CPTP program. He is actively involved in fast-track paving, nondestructive testing, and high-performance concrete and is a member of American Society of Civil Engineers, American Concrete Institute, and Transportation Research Board committees. He has authored numerous publications and frequently speaks at national and international meetings. He earned his M.S. degree in civil engineering from Colorado State University.
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