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Concrete Pavement Technology Update
Traffic Management on High-Volume Roadways
The Traffic Management Studies for High-Volume Roadways project, sponsored by FHWA, in collaboration with the Texas Transportation Institute, has made significant contributions to the state of knowledge regarding the effectiveness of traffic and construction management strategies for rigid pavement preservation, rehabilitation, and reconstruction in high-traffic environments.
The investigation was successful in many ways. Through teamwork and extensive research, the project was able to accomplish the following key tasks:
These activities and related findings are documented in reports, case studies, technical briefs, and conceptual studies. To further facilitate technology transfer, these products are being made available on navigable DVDs. The products are in the publication process and will be utilized in workshops that are being developed for delivery to State highway agencies and industry organizations to address the following issues:
For more information on products from the Traffic Management Studies project, contact Sam Tyson, FHWA Office of Pavement Technology (email@example.com).
Concrete Pavement Road Map Leads the Way
Implementation of the CP Road Map is underway. FHWA is funding critical, short-term administrative services for implementation through the CP Tech Center, Iowa State University’s National Concrete Pavement Technology Center. The newly appointed executive committee met in March 2007.
A unique model for managing the research tracks outlined in the Road Map has been developed, where, instead of a dedicated pool of funds for research with a single oversight organization, sponsors will collaborate to fund projects based on their common goals and priorities. The mix design and analysis track (1), recently organized, serves as an example of the new working model: 1. Expert champions identified themselves for participation. 2. Champions organized track leadership (in this case, a three-way partnership between the FHWA, State DOTs, and industry). 3. The champions agreed on a mechanism for funding administrative support. Efforts will be coordinated among the three partners. FHWA will identify needed improvements and simplify user interfaces for mix design models, such as COMPASS, HIPERPAV, and others. The States will ensure that critical new tests are ready for implementation. Industry will develop a comprehensive mix design manual that incorporates up-to-date modeling and testing information compiled by FHWA and the States.
For more information about the CP Road Map and how to get involved, contact Dale Harrington, Snyder & Associates (515-964-2020) or the CP Tech Center (515-294-8103).
Joint Sealing: New Outlook on an Old Approach
The sealing of transverse contraction joints in concrete pavements has been standard practice throughout much of the United States for many years. The common belief is that sealing joints improves concrete pavement performance by reducing water infiltration into the pavement structure, thereby reducing the occurrence of moisture-related distresses such as pumping and faulting. Additionally, sealing is believed to prevent the infiltration of incompressibles (i.e., sand and small stones) into the joints, thereby reducing the likelihood of pressure-related joint distresses such as joint spalling and blowups. While these assumed benefits appear logical, the question of whether sealing joints is cost effective for all pavement designs and climatic conditions remains unanswered.
In hopes of finding an answer to this lingering question, FHWA sponsored a research project to evaluate the effectiveness of joint sealing. Initiated in 1993, the following project objectives were developed:
To accomplish these project objectives, the following research activities were conducted.
Assessment of State of the Practice—The first two tasks of the study focused on determining the state of the practice in joint sealing activities around the country. First, a comprehensive literature review was conducted to review and summarize existing published studies on transverse joint sealing practices, with special attention to their performance and cost-effectiveness. Second, a survey of concrete pavement construction contractors and equipment and materials suppliers was conducted to solicit industry opinions of concrete pavement joints and sealing, sealant types, sealing practices, performance, and costs.
Field Inspection and Testing—Between February 2004 and June 2006, field testing was conducted on 117 different individual test sections, with 26 different projects located in 11 States. These projects represent a range of concrete pavement designs, sealant material types, and transverse joint configurations. For each test section, the host State highway agency conducted falling-weight deflectometer testing, while the project team conducted field survey activities that included mapping all distresses in the outer lane, measuring joint faulting and nominal joint widths, and evaluating joint sealant performance in detail.
Data Analysis—The collected distress and deflection data were analyzed to assess the effects of joint sealing alternatives on joint spalling, joint seal damage, faulting, and midslab and joint deflections. In addition to the condition and deflection data analyses, the cost-effectiveness of joint sealing practices was also examined.
Based on an initial evaluation of the data, the following general preliminary observations and results were provided:
Also, it should be noted that most of the pavement sections evaluated in this study were relatively young (between 5 and 13 years old) and did not exhibit a tremendous amount of distress prior to the testing.
A draft final report for this study was submitted to FHWA in May 2007, and the final report is expected in fall 2007.
For further information on the joint sealing project, contact Jim Sherwood, FHWA Office of Infrastructure Research and Development (firstname.lastname@example.org), Sam Tyson, FHWA Office of Pavement Technology (email@example.com), or Kurt Smith, ApTech (firstname.lastname@example.org).
Equipment Loan and Demonstration Activities
The CPTP Equipment Loan Program was established in 2005 to promote implementation of promising, implementation-ready technology. The program enables State DOTs to evaluate new testing devices first hand, without having to purchase the device. DOTs can request a demonstration or a loan. The standard loan period is 1 month, and the CPTP Technology Implementation Team provides onsite training and technical support for loans. Devices available are the MIT Scan-2, air-void analyzer, impact-echo for slab thickness measurements, and maturity meters.
To date, the most popular loan item has been the MIT Scan-2 (see below), a state-of-the-art, nondestructive testing device for measuring the position and orientation of dowel or tie bars encased in concrete. The device is accurate and easy to use, and the results can be printed using the on-board printer immediately after scanning. Three units of MIT Scan-2 are available for loans and demonstrations. So far, the device has been demonstrated or loaned to 21 States and Ontario; loans to 4 other States are pending.
The MIT Scan-2 (shown here), air-void analyzers, impact-echo devices, and maturity meters are available to State highway agencies on loan from the CPTP program.
In most cases, DOTs have borrowed MIT Scan-2 simply to try out the device. However, the device has proved useful in settling questions regarding dowel or tie bar placement even on these trials. In other cases, DOTs requested the scanner because of specific concerns over dowel placement on a current project. On projects where dowel bar inserters (DBIs) were used, MIT Scan-2 results were particularly useful both for verifying the dowel bar positions and for optimizing concrete mixtures, which is very important to achieve good dowel alignment when using DBIs. As a result of CPTP’s equipment loan program, Florida, Colorado, and Wisconsin plan to implement the use of MIT Scan-2. Several other States are also interested in acquiring their own MIT Scan-2 and are using the loan equipment to conduct further evaluations.
The CPTP equipment loan program proved valuable to the States by helping them resolve problems. For example, in one case, MIT Scan-2 results showed severe problems with tie bar placement over a significant length of a project where no problems had been suspected. On another occasion, the project engineer suspected that one end of dowel baskets had been run over during paving. The MIT Scan-2 results clearly showed that the baskets were damaged during paving. On several DBI projects, MIT Scan-2 showed excellent results with respect to dowel alignment, giving the DOT and the contractor peace of mind.
To arrange a demonstration or to borrow testing equipment, contact Sam Tyson, FHWA Office of Pavement Technology, at 202-366-1326 or email@example.com.
Texture Research Pursues Quiet Pavements
A great deal of pavement research, including the efforts of the Concrete Pavement Technology Program, is directed at achieving quiet pavement practices, especially in urban, high-trafficked areas. The FHWA’s Technical Advisory T 5040.36 (Surface Texture for Asphalt and Concrete Pavements) provides information on state-of-the-practice of surface texture–friction on pavements and guidance on selecting techniques that will provide adequate wet pavement friction and low tire–surface noise (FHWA 2005). However, before these techniques are embraced, there must be an overall understanding among the pavement community of the cause of the noise generated at the tire–pavement interface. Additionally, the public must accept that pavement safety concerns are increasingly more important than noise issues and that sometimes both needs cannot be met simultaneously.
There are two major areas of tire–pavement noise concern: the noise experienced by vehicle passengers, often referred to as on-board sound intensity (OBSI) and noise experienced by those in close proximity to a highway, sometimes referred to as wayside noise. In 2005, the Institute for Safe, Quiet, and Durable Highways at Purdue University summarized much of the recent tire–pavement noise research in the report, “An Introduction to Tire–Pavement Noise.” That report established relevant topics in acoustics and noise, explained how noise is created at the tire–pavement interface, summarized the concepts used to create reduced noise pavement, described tire–pavement noise measurement methods, and presented an overview of U.S. traffic noise policy.
The effect of texture on tire–pavement noise is complex. In general, macrotexture (related to pavement finishing operations) wavelengths of 2 mm to 10 mm (0.08 to 0.40 in.) tend to decrease the exterior noise generated at the tire–pavement interface, while increased megatexture (roughness) of 50 mm to 500 mm (2.0 to 20.0 in.) has shown to increase interior noise in vehicles. Much of the current research is directed at achieving an optimized texture that could provide a pavement that is both quiet and safe. In fact, Larson, Scofield, and Sorenson note that because texture has such an effect on both noise and friction, the two issues must be considered together to fully address highway users’ concerns (Larson et al. 2004).
Paul Wiegand of the National Concrete Pavement Technology Center at Iowa State University summarized typical tire–pavement interface noise by conventional concrete pavement texture type, using test data on approximately 1,000 concrete pavement sections.
Wiegand indicates three zones of OBSI noise, as shown in Figure 1. Zone 1 is described as the innovative level (less than about 99 dbA) where research is needed to develop textures to meet the proposed levels. Zone 2 (99 to 105 dBA) is described as the zone that includes many conventionally textured concrete pavements that are cost effective and provide a balance between noise, friction, and smoothness. Zone 3 (more than 105 dBA) is described as the zone to avoid. It includes pavements that exhibit the highest noise levels. These pavements tend to have highly aggressive textures such as transverse grooving. While he notes that much research is yet needed, Wiegand concludes that many noise issues can be addressed through diamond grinding of existing pavements and a drag (burlap or turf) for longitudinal tine finish of new construction (Wiegand 2006).
Figure 1. Pavement texture and three zones of on-board sound intensity (Wiegand 2006, p.2).
In January 2005, FHWA issued a memo entitled “Guidance on Quiet Pavement Pilot Programs and Tire–Pavement Noise Research,” which notes that current FHWA policy does not allow the use of pavement type or surface texture as a noise abatement measure. The memo encourages State participation in the Quiet Pavement Pilot Program (QPPP) or in quiet pavement research.
The QPPP provides for a monitoring period of at least 5–10 years during which the State would collect data on acoustic, textural, and frictional characteristics and document public reaction. The memo continues, “If policy change is to occur, results of the QPPP or additional research must demonstrate the safety and durability of each ‘quiet pavement,’ as well as its noise reduction capability. The safety and noise reduction of the pavement must last in perpetuity. In the short term, any policy change will be State specific, i.e., the change will only apply to a given State DOT(s) for a specified pavement type or texture. If warranted, changes in national policy may be considered in the future.”
Other research underway includes the National Cooperative Research Program Project 1–44, which addresses the development of rational procedures for measuring tire–pavement noise and will demonstrate applicability of the procedures through testing of inservice pavements. This work is scheduled for completion in late 2007. In addition, the Concrete Pavement Road Map work at Iowa State University includes Track 4, Optimized Surface Characteristics for Safe, Quiet, and Smooth Concrete Pavements, which will result in a better general understanding of concrete pavement surface characteristics.
To supplement ongoing research, FHWA is offering a new workshop to increase agency knowledge of tire–pavement noise and noise abatement strategies. Developed by the Office of Pavement Technology and the Office of Natural and Human Environment in conjunction with the Transtec Group, “Tire–Pavement Noise 101” is designed to help pavement engineers and noise practitioners improve their understanding of pavement noise and learn ways to reduce it. “The workshop is intended to bring noise practitioners and pavement engineers together and fill in the knowledge gaps between the two parties,” says Mark Swanlund of FHWA. More information is available at http://www.fhwa.dot.gov/environment/noise/tp_noise.htm.
Bernhard, Robert J., and Roger L. Wayson. 2005. “An Introduction to Tire–Pavement Noise.” The Institute for Safe, Quiet, and Durable Highways, Purdue University, West Lafayette, IN.
FHWA Technical Advisory T 5040.36, Surface Texture for Asphalt and Concrete Pavements, June 2005 (www.fhwa.dot.gov/legsregs/directives/techadvs/t504036.htm)
Larson, Roger M., Larry Schofield, and James B. Sorenson. 2004. “Pavement Surface Functional Characteristics.” Presented at Fifth Symposium on Pavement Surface Characteristics, Toronto, Canada, June 2004.
Shrouds, James M. 2005. “Guidance on Quiet Pavement Pilot Programs and Tire–Pavement Noise Research.” Federal Highway Administration’s Office of Natural and Human Environment, Washington, DC.
Wiegand, Paul. 2006. “Concrete Solutions for Quieter Pavements on Existing Roadways.” National Concrete Pavement Technology Center, Ames, IA. (http://www.cptechcenter.org/publications/quieter_pavements_tech_brief.pdf (.pdf, 0.5 mb)).
On the Road: A New Mobile Concrete Lab
FHWA’s Mobile Concrete Laboratory (MCL) is a key component in the technology transfer program designed to bridge the gap between the development and implementation phases of new technologies. The MCL is a fully functional concrete laboratory uniquely housed in a 15‑m (50-ft) trailer that is equipped with both conventional and innovative testing equipment for use with fresh and hardened concrete. Following a series of earlier versions that had been in use since the late 1980s, the MCL staff from FHWA’s Office of Pavement Technology has recently taken delivery of a new MCL.
The MCL has proven to be a highly effective means for introducing FHWA’s customers and partners in State highway agencies (SHAs), industry organizations, and academia to innovative concrete testing equipment. The MCL provides onsite testing demonstrations and training to complement field and laboratory training received by SHA personnel and others. MCL staff also oversee an equipment loan program for SHA personnel, and they showcase innovative testing equipment at regional and national conferences and SHA-sponsored events. The inaugural showcasing event for FHWA’s newest MCL was at the spring convention of the American Concrete Institute held in April 2007 in Atlanta, Georgia.
For more information about FHWA’s mobile lab and how SHAs can schedule demonstrations of testing equipment for fresh and hardened concrete, visit FHWA’s Web site:
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