December 2002

Ohio’s First Perpetual Pavement Draws National Spotlight

Interstate widening and reconstruction project provides a venue for testing the asphalt industry’s claim of never-failing pavement

By Fred F. Frecker, P.E.

The Ohio Department of Transportation is replacing about 2 miles of concrete pavement on I-77 near Canton, Ohio, with full-depth asphalt Perpetual Pavement.

Perpetual Pavement, a new concept to the road-paving industry, shows signs of catching on. The idea of a pavement that lasts a lifetime, making expensive reconstruction a thing of the past, has captured the interest of the construction industry.
Perpetual Pavement is designed in response to the motoring public’s call for an end to the repetitive and disruptive cycle of road construction. Its three-layer design forces distress to the surface where it can be maintained quickly and cheaply during off-peak traffic hours.
This increased durability will be accomplished through the use of mechanistic design. In a mechanistically based pavement, designers analyze how traffic strain will affect the pavement’s performance, taking into account material qualities and thickness. By designing the pavement to keep strain below the critical level, fatigue failure is avoided and perpetual performance can be assured. Structural and aeronautical engineers have used mechanistic design principals for years. It’s only a matter of time before it’s the standard in the paving industry.
Through use of mechanistic design, each layer in Perpetual Pavement’s three-layer system will be tailored specifically to local climate and traffic conditions. The base layer will be made of flexible, fatigue-resistant asphalt designed to resist bottom-up fatigue cracking. The middle layer will be made of high-modulus, rut-resistant asphalt formulated to support expected traffic. The surface layer — stone-matrix asphalt (SMA), open-graded friction course, or Superpave — will be designed to eliminate rutting, reduce splash and spray, absorb noise, and hold up to local weather and traffic conditions (Figure 1).

Figure 1: Each layer in a Perpetual Pavement’s three-layer system is designed mechanistically to stand up to local climate and traffic conditions. Source: National Asphalt Pavement Association

The combination of the three layers will force distress to the surface layer, where it can quickly be maintained at a low cost. The surface can be milled off, recycled, and replaced. This means that improved surface mix design can be incorporated into an existing Perpetual Pavement as it is developed over time.
“In the past we designed pavements with a different philosophy,” said Cliff Ursich, vice president of Flexible Pavements of Ohio. “After a certain amount of time or traffic loading, we knew the pavement would need to be replaced. Perpetual Pavement is designed never to fail. That’s going to translate into less traffic congestion and significant tax savings in the future. It’s no wonder there’s so much interest, because the implications of Perpetual Pavement are huge.”

Northstar Asphalt completed paving the northbound lanes of I-77 in October. Here, the company lays down the rut-resistant middle layer.

An Ohio Open House
Nearly 200 engineers from around the state and nation gathered in Canton, Ohio, recently for an open house event sponsored by Flexible Pavements of Ohio, the Ohio Department of Transportation (ODOT), the Federal Highway Administration, the Asphalt Paving Alliance, Ruhlin Construction (general contractor on the project) and Northstar Asphalt (paving subcontractor).
Ohio is one of a few states that have begun construction of this new pavement. The state’s first Perpetual Pavement is currently under construction on a segment of I-77 near Canton.
“This is the next generation in asphalt paving,” said Dr. David Newcomb, vice president of research & technology for the National Asphalt Paving Association, one of the technical presenters at the event. “Ohio is leading the way with the construction of this pavement, which will likely be the first of many.”
Perpetual Pavement is designed to avoid fatigue cracking and deformation of the base and subbase, Dr. Newcomb said. That means that transportation departments will only incur small, incremental costs over time for surface renewal of the pavement. Perpetual Pavement efforts are ongoing in six states — Illinois, Michigan, Wisconsin, Texas, Kentucky, and Ohio — and Europe, he said.
Open house attendees spent the morning in technical information sessions led by Perpetual Pavement experts, including Dr. Newcomb; Dr. Shad Sargand, Russ professor of civil engineering at Ohio University; and representatives from ODOT.
In the afternoon, attendees visited the construction site where Issam Khoury of Ohio University led an on-site demonstration of the tensile stress measured in the partially completed pavement. Fully loaded dump trucks were driven over sensors buried in the pavement. Data indicated that the distress level caused by these heavy loadings will be well below the critical level. The final layer, which was yet to be laid, will add more support to the pavement.
The project (ODOT 451 (01) Stark/Summit 17610/00.000) involves removing 2.3 miles of a four-lane concrete highway and replacing it with a new six-lane Perpetual Pavement. Construction on northbound lanes was completed during the 2002 construction season. In 2003, traffic will be diverted to the newly paved northbound lanes while the southbound lanes are rebuilt.
Before the change order to Perpetual Pavement, the original design called for a 17-1/4-in.-thick asphalt pavement on a 6-in. unbound aggregate base (ODOT spec 304) with the following profile, from the bottom, up:

• 4-in., free-draining base mix;
• 10-in. big-rock base mix (ODOT spec 302);
• 1-3/4-in. leveling course (ODOT spec 446 Type 2 heavy); and
• 1-1/2-in. surface course (ODOT spec Type 1 heavy).

The leveling and surface courses were to use a PG 70-22 polymer-modified binder.
The Perpetual Pavement design used on the I-77 project starts with a 4-in. fatigue-resistant layer on 6 in. of aggregate base. It is an ODOT spec 302 big rock mix made binder rich by designing at 3 percent air voids rather than the normal 5 percent and adding a density requirement of 94 percent. The middle layer is 9 in. of ODOT spec 302 big rock mix but with an added density requirement of 95 percent. Both these layers use a PG 64-22 binder.
Next is a 1-3/4-in. leveling course of 19-mm Superpave using a PG 76-22 polymer-modified binder. The wearing course is a 1-1/2 in., 12.5-mm Superpave mix also using a PG 76-22 polymer-modified binder.
Total pavement thickness is 16-1/4 in., 1 in. less than the original design. However, since use of Perpetual Pavement was a change order and the project was already under construction, ODOT wanted to keep the same elevations on the subgrade and surface. Consequently, an extra inch of middle layer (ODOT 302) was added to keep the thickness the same as the original design. The contractor did the change order at no additional cost to ODOT.
The entire project will cost $16,189,650, using more than 164,000 tons of asphalt. The 4-in. fatigue-resistant asphalt base layer was bid at $4.45 per square yard. The rest of the pavement, 13.25 in. of Perpetual Pavement layers, will cost $19.76 per square yard. This cost is approximately the same as it would have been using traditional asphalt paving methods.
“Several decades from now, when traffic is still running smoothly and there is no need to rebuild the pavement, we’ll see the real savings,” said Roger Sandburg of the Asphalt Paving Alliance. “You won’t have to delay traffic and spend tax dollars to fix a failed pavement. This road will be running smoothly long after we’re all gone.”

Open house participants observe an on-site demonstration by Ohio University researchers. Sensors in the partially completed pavement measure tensile stress from a loaded dump truck.

Fred F. Frecker, P.E is president and executive director of Flexible Pavements of Ohio