A recent article in Concrete Construction Online News titled “Concrete Pavement Performance” touts extensive data is being developed through the “Long-Term Pavement Performance Program (LTPP Program)”. The article is a collaboration by Jeff Uhlmeyer, P.E., State Pavement Engineer-Washington State DOT; Kevin Senn, P.E., Principal Engineer-Nichols Consulting Engineers (NCE); Larry Scofield, P.E., Director of Pavement Innovation-American Concrete Pavement Association (ACPA) and Director of Engineering & Research-International Grooving & Grinding Association (IGGA), Phoenix, AZ; and Kristen Dispense, Account Manager-Achieving Operational Excellence (AOE)-American Concrete Institute (ACI). One important way of disseminating all this information is Local Learning Tech Days—state-hosted SPS-2 Tech Days—which involve both presentations and field evaluation of SPS-2 test sections. These provide the opportunity to assess which design features have performed the best, as well as which pavement preservation strategies are most effective.
During a May 2019 Ohio SPS-2 Tech Day workshop/open house—associated with the
Federal Highway Administration’s (FHWA)’s “Long Term Pavement Performance (LTPP) Program”,
the number one question was posed:
“Why and how do pavements perform as they do?”
… a difficult question and finding an answer means that the program’s research has spanned decades
and generated extensive data—with more to come.
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— LTPP PROGRAM OVERVIEW —
Started in the late 1980s:
The LTPP Program is the world’s most comprehensive investigation of more than 2,500 test sections of in-service highways in the United States and Canada with two components:
• General pavement studies (GPS): Examined existing roadway sections
• Specific pavement studies (SPS): Included multiple test sections at one location
LTPP was established as part of the original Strategic Highway Research Program (SHRP) to determine how and why in-service pavements perform the way they do, and was transitioned to FHWA management in 1992. LTPP data was also the primary source used to develop AASHTOWare PavementME design software, and continues to be used to improve the programs ability to predict eld performance.
Test sections are typically 500 feet long, and detailed information is collected either by the FHWA or the state and provincial highway agencies.
The information includes:
• Materials properties
• Traffic volumes and loading
• Weather
• Any rehabilitation or maintenance
• Performance data
The SPS-2 experiment examines the effects of:
• Subsurface drainage
• Warp and curl
• Dynamic load response
• More
The design factors studied include:
• Concrete strength
• Base type
• Drained versus undrained construction
• Lane width
• Shoulder type
• Pavement thickness
• Details of dowel bar
• Details of tie bar placement
Site factors studied include:
• Coarse-versus-fine soils
• Climate zone
Early 1990s through 2000:
SPS-2 pavements were built from the early 1990s through 2000, with data collection beginning during construction, and continuing to the present day.
2013:
While the SPS-2 project was designed to study structural factors, the second piggy-backed study was launched in 2013. The Washington State DOT leads this study, along with DOTs of Arizona, California, Colorado, Georgia, Kansas, and North Carolina. These states learned that, given the age and relatively good condition of the SPS-2 test sections, pavement-preservation techniques could be undertaken to learn the optimal timing for the use of pavement preservation treatments and the resulting improvement. To examine pavement preservation strategies—the techniques include:
• Diamond grinding or diamond grooving
• Partial or full-depth repair
• Dowel bar retrofit
• Joint sealing or resealing
• Slab stabilization
• Longitudinal crack stitching
• Buried treasure
All of this data is uploaded annually to InfoPave, a website where users can access the:
• Pavement performance data and findings from data analyses
• Complete library of LTPP publications
• Many additional pavement-related tools
• Detailed construction reports
• Materials sampling and testing plans developed for each project
May 2019:
At the above-mentioned May 2019 Tech Day in central Ohio, attendees were able to examine pavement test sections on U.S. 23—a stretch of pavement where during the 2018 average daily traffic was 28,599 vehicles, 16% being truck traffic. Approximately three miles of portland cement concrete (PCC) in the northbound lanes were part of this SPS-2 experiment to evaluate these five design features:
• 8-inch versus 11-inch thickness
• 550 psi versus 900 psi flexural strength concrete
• 12-foot versus 14-foot travel lane widths
• Base types
• Drainage
Some of the information shared at the Ohio Tech Day included:
• Jointed plain concrete pavement (JPCC) constructed on a layer of permeable asphalt treated base offered superior smoothness compared to sections constructed on lean concrete base or on dense-graded aggregate base.
• JPCC had low joint faulting and less cracking
• Wider slab sections showed less faulting than conventional width slabs
• Thicker slabs demonstrated better crack resistance than thin ones
• Recommendations were made for dowel alignment: minimize longitudinal restraint and avoid misalignment and place dowels parallel to both the pavement surface and the longitudinal axis. Maximum shear load transfer capacity occurs when the dowels are centered longitudinally and placed at mid-depth.
For more information on SPS-2 Tech Days, please see the December 2018 MAP Brief PDF titled Performance Experience and Lessons Learned from SPS 2 Test Sections of the Long-Term Pavement Performance Program (LTTP): cproadmap.org/publications/MAPbriefDecember2018.pdf
More to be Done—Future Plans:
Studying Pavement Preservation:
Pavement preservation is a critical part of keeping roads smooth, rideable, and structurally sound over the long term. The current recommendations on how and when to perform preservation techniques, however, assume all pavement types and strategies perform equally. This leads to over-simplification and anecdotal approaches in lieu of solid data and analysis. Continuing SPS-2 studies will perform cradle-to-grave analyses of the test sections and the preservation treatments used, with a focus on pavement life extension and cost-effectiveness. The results will be used to establish pavement management system triggers.
To maximize the opportunities afforded by the research, road owners must allocate funding for planned preservation cycles and develop a feedback loop between members of the design, construction, maintenance, and administration teams. Intervention cycles need to occur earlier in the performance period than they have in the past, and owners and agencies must rigorously collect and analyze data to justify this schedule shift.
For InfoPave, please go to: infopave.fhwa.dot.gov/
Started in the 1980s, the LTPP project will be a continue … is, and will be, the world’s largest ongoing concrete preservation research project!! States and other stakeholders who want to participate in the experiment, please contact:
Jeff Uhlmeyer: E-mail: UhlmeyJ@wsdot.wa.gov | Phone: 360-709-5485
For the Concrete Construction online article, please go to: https://www.concreteconstruction.net/projects/infrastructure/concrete-pavement-performance_o