Ohio Takes Perpetual Pavement
 Another Step Forward
Extensive research has gone into Ohio DOT's
second perpetual pavement project

by Cliff Ursich, P.E.

The much-heralded next generation of asphalt paving technology is now serving traffic on one Ohio highway and will be soon on a second. The state’s newest perpetual pavement is the subject of even more attention than the first, as Ohio’s road construction industry develops its understanding of this new technology and the impact it will have on Ohio roads. Local governments are getting involved, too, as perpetual pavements are being designed for local roads in the Cincinnati and Cleveland areas.

The state’s first perpetual pavement, a stretch of I-77 near Canton completed in 2003, attracted nearly 200 engineers to a jobsite open house as well as the attention of statewide and national media. However, the groundbreaking for Ohio’s newest perpetual pavement seems to have more significant implications. An 8-mile stretch of U.S. 30, bypassing the city of Wooster, in Wayne County, is being constructed on a new alignment as an Ohio Department of Transportation demonstration project. The westbound lanes will be asphalt perpetual pavement.

Crafting the design procedure

In early 2002, an ODOT task force began the process of developing the perpetual pavement design procedure and the specifications that would be used on a demonstration project. The task force consisted of four subcommittees. One was charged with developing a thickness design procedure using mechanistic design principles. Another subcommittee developed material specifications for each layer of the pavement. A testing design subcommittee identified laboratory testing protocols to verify design assumptions, developed accelerated load test procedures to confirm laboratory testing results, and established an outline for ongoing testing of a pilot project. An additional subcommittee was charged with identifying potential projects for which perpetual pavement would be appropriate and subsequently chose the section of relocated U.S. 30 in Wayne County.

The committee included representatives from ODOT, the Federal Highway Administration, and the asphalt industry, as well as an impressive list of national and academic experts. The committee was chaired by engineers from ODOT’s Pavement Engineering Section and the group included representatives from the National Center for Asphalt Technology, the Asphalt Institute, the Heritage Research Group, the University of Akron, Ohio State University, the University of Cincinnati, Ohio University, the University of Toledo, and Flexible Pavements of Ohio.

Since perpetual pavement is designed to have an inexhaustible structural life, the task force determined that legal load plus 20% would be the critical load for perpetual pavement, with 70 microstrain as the limiting strain at the bottom of the pavement. With these limits set, it was determined using elastic layer analysis that the asphalt concrete pavement thickness would be 16.25-inches thick on a 6-inch-thick crushed aggregate base when built on a soil having a CBR range of 4 to 6.

The committee determined the following specifications for each layer of the pavement buildup:

6-inch building platform: ODOT Item 304, a highly crushed densely graded granular base, with under drains.

4-inch bottom — fatigue resistant layer: ODOT’s large stone base mix, Item 302, made binder rich by designing it for 3% air voids; 94 to 97% constructed density.

9-inch middle — high modulus layer: ODOT’s large stone mix, Item 302, using a PG 64-22 asphalt binder; target density 93 to 96%.

3.25-inch top — sacrificial layer composition:

— 1.75-inch intermediate course: ODOT 19-mm Superpave, Type A, with PG 76-22M polymer modified binder; target density 93 to 97%.

— 1.5-inch wearing course: ODOT 12.5-mm stone mastic asphalt with a PG 76-22M polymer modified binder; target density 93 to 97%.

Validating the design concept

The U.S. 30 demonstration project is under construction and is expected to open to traffic in the fall of 2005. After construction, validation of the thickness design concept is the final step. To accomplish this, ODOT has awarded three research contracts to Ohio University to evaluate the perpetual pavement.

The objective of the first research project is to determine the mechanical properties of the materials used in the construction of the U.S. 30 test pavement. In this project, the researcher is to review the design assumptions used to determine the pavement buildup and identify the mechanical properties needed to validate the design procedures. A sampling and testing plan was developed to determine the mechanical properties of all pavement layers needed to validate the design procedure. ODOT, the paving subcontractor, Shelly and Sands Inc., and Ohio University researchers collect the necessary samples as construction progresses.

The second research project seeks to collect environmental and load response data from test sections on the U.S. 30 demonstration project by developing a pavement instrumentation plan and installing the instrumentation during construction of the project. Being measured are pavement and subgrade temperature, aggregate base and subgrade moisture, frost depth in the aggregate base and subgrade, groundwater table, strain and deflection in the asphalt due to load, pressure at the interface between the aggregate base and subgrade, and climate. The Ohio University research team has been installing the instrumentation as construction proceeds.

The third and final research project validates the perpetual pavement design procedures. The predicted pavement response will be compared to the actual field response under traffic loads. The analysis uses the mechanical properties of materials determined in the construction of the test pavement, the load response data collected from the instrumented test sections, coring data supplied by ODOT, and any specification deviations to the materials and/or construction methods.

While the U.S. 30 demonstration project was still being designed, an opportunity presented itself to use the perpetual pavement design on a section of I-77 that was already under construction. The paving subontractor on that project, Northstar Asphalt, proposed using the perpetual pavement design as a no-cost change on the project and the change was accepted by ODOT. Ohio University conducted a research effort on the Interstate 77 project that is similar to that proposed for the U.S. 30 project. In August, 2003, a test section consisting of 6 inches of dense-graded aggregate base, 13 inches of bituminous aggregate base, and a 1.75-inch intermediate surface layer was instrumented. Instrumentation included strain gauges, pressure cells, and thermocouples. In December 2003, data was collected from these sensors in response to a load applied using an ODOT single-axle truck having an axle weight of 26,000 pounds. Pavement response indicated that the strains at the bottom of the asphalt layer were approximately half of what is considered to be a maximum design value — 70 microstrain.

A whole lot more

In addition to the thickness design methodology, ODOT is seeking to evaluate other attributes of perpetual pavement that affect management decisions. The U.S. 30 demonstration project will be observed through 2006, with extensive data collected in four categories — cost, safety, user delay, and ride and condition. The evaluation criteria developed by ODOT address every significant measurable element needed for determining the manageability of perpetual pavement.

Project Evaluation Criteria

Cost:

• Initial construction cost

• Rehabilitation cost

• Force account maintenance (hours and cost)

• Salt usage (hours and cost)

• Truck fuel usage

• Pavement marking costs

• Lighting

Safety:

• Fatal accidents

• Nonfatal accidents

• Property damage accidents

• Pavement skid

User Delay:

• Pavement construction duration

• Rehabilitation duration

• Queues during rehabilitation

Ride & Condition:

• Pavement profile

• Pavement condition rating

• Pavement damage

• Sub grade moisture

• Weather

• Noise

Long-lived asphalt pavements aren’t new to Ohio. The state has enjoyed very long life from its conventionally designed asphalt structural bases. As the perpetual pavement design protocols are refined for Ohio conditions and materials, it is expected that long-lived pavements will become more reliable and economical than ever before.

“Ohio has a long history of long-lived, full-depth, and deep-strength asphalt pavements; so, we expect perpetual pavement to receive a superior evaluation in every category,” says Fred Frecker, Executive Director of Flexible Pavements of Ohio. “We have a high degree of confidence that perpetual pavement is a cost-effective way for Ohio to maintain a high level of user satisfaction.”

Engineers of the famed AASHTO Road Test revolutionized pavement engineering with the development of the service-ability concept. They defined successful pavement performance as that which serves the user. The Ohio DOT is right on point with its pursuit of perpetual pavement research. Perpetual pavements are built to serve the user by providing inexhaustible structural life with only the need to occasionally refurbish the wearing surface. The research effort in Ohio is sure to return dividends to Ohio’s motorists, and provide additional data to the ever-increasing body of knowledge being accrued on the national level.  

Cliff Ursich, P.E., is executive vice president of Flexible Pavements of Ohio.

Reprinted from Better Roads Magazine
November 2005

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