Rehab Work That Doesn't Take a Toll on Traffic Flow
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Speed and longevity are the key components of the rehabilitation program underway on the West Virginia Turnpike, Interstate77. The cracked and worn PCC pavement has to be replaced, and officials at the West Virginia Parkways were not interested in a "Band-Aid fix" that didn't solve the underlying problem. They could not, however, afford a solution that would tie up traffic for months on end.
That's why this summer, a ten-mile section of the Turnpike near Beckley, WV, is being rubblized and reconstructed with a full-depth HMA overlay. The work is being completed at an impressive rate--one lane mile per day--and traffic is flowing through the work zone.
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Rehabilitation of the West Virginia Turnpike, I-77, is being completed at an impressive rate - one lane mile per day - while traffic flows through the work zone.
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"If I had the resources, I'd start right now at one end of the Turnpike and rubblize every mile of PCCP and overlay it with Hot Mix Asphalt," said Col. William Gavan, General Manager of the West Virginia Parkways Authority.
"We have the data that shows the outstanding performance you get with rubblization and HMA overlays."
The data, in part, comes from an 18mile section of the Parkway that was reconstructed using this method in 1989. After more than nine years of heavy traffic, the HMA surface is providing a smooth ride and showing few signs of aging. The section of PCC pavement being replaced this summer is 16 years old.
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No Place for Detours
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Traffic and terrain compound the complexity of this reconstruction effort. The Turnpike is a vital north/south route for interstate commerce for the western third of the state, linking Charleston with I-81 to the south.
The importance of the road is reflected in the full name of its owner--the West Virginia Parkways, Economic Development and Tourism Authority. More than 81,000 vehicles travel the toll road every day; 82 percent are from out of state.
The 420-mile-lane turnpike winds through 88 miles of the Appalachians and some of the most beautiful mountain scenery on the East Coast. As it hugs the mountainsides and crosses 116 bridges, there are no nearby "alternate routes" or convenient detours available.
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The multi-head breaker (MHB) rubblizes a full 12-foot lane width of the worn PCC pavement on the Turnpike in a single pass.
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Comparing costs
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Past experience with diamond grinding sections of the Turnpike had proven to only be a temporary Band-Aid. A detailed comparison of every rehabilitation alternative showed that total reconstruction with PCCP or using a PCC overlay would be far too expensive, too time consuming, and create too many traffic flow problems. There was also a concern there would be a need to resurface the PCC within a few years.
Once motorists pay a toll, Col. Gavan explained, their expectations and demands go up. "They want a smooth ride." That's something the PCC pavement has not provided.
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The MHB's 1,000-pound hammers break the concrete into particles 3 inches or less above, and under 9 inches below, the reinforcing steel.
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Hot Mix Asphalt has another inherent quality that Col. Gavan values. "It's very forgiving. If you make a mistake, you mill it up and it's that simple. If you make a mistake with PCC, it's not easy to fix."
The Parkways Authority also ruled out a straight HMA overlay which would do nothing to prevent the slab cracking, joint deterioration, faulting, punchouts, and d-cracking in the PCCP, and eventually these faults would reflect through the new surface.
In West Virginia's experience, cracking and seating the PCC prior to a HMA overlay also had not completely eliminated reflection cracking. Extensive breaking or rubblizing the PCCP before overlaying with HMA met every criteria, and advancements in rubblization technology eliminated many traffic concerns.
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Keeping traffic moving
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A multiple-head breaker (MHB), capable of rubblizing the full 12-foot width of the PCC pavement lane in a single pass, is being used. This allows the contractor, West Virginia Paving, Inc. of Dunbar, WV, to work in one lane while the other lane stays open to traffic. More importantly, paving operations follow right behind the vibratory rollers that compact the rubblized surface further speeding the reconstruction and enabling both lanes to be open to traffic from Friday through Sunday when traffic volumes on the Turnpike are at their highest. In effect, the work is completed in four-day segments of rubblize, pave, open to traffic.
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A vibratory roller fitted with an Elliott "Z" pattern grid further reduces the surfaces particle size to 1 to 2 inches.
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"There are no exceptions, no excuses, said Dan Cooperrider, Vice President of West Virginia Paving. "We can close one lane during the week, but on Friday, it has to be open to traffic."
The MHB works like a guillotine, but instead of one drop hammer it carries 14. These 1,000 pound hammers are mounted laterally in pairs and attached to a hydraulic lift cylinder in two rows. Each pair operates as an independent unit and can develop between 2,000 and 7,000 foot pounds of energy depending on the lift height selected.
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Creating a new base
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As the MHB travels down the road on rubber tires at speeds ranging from 10 to 15 feet per minute, the falling hammers efficiently break up the pavement and create a granular dainage base.
Turnpike specifications call for the concrete to be broken into particles three inches or less above the reinforcing steel, and into particles 9 inches or less below the reinforcing steel.
Following close behind the MHB is a vibratory roller fitted with an Elliott "Z" pattern grid. Two passes by the Z-grid roller and a pneumatic-tired roller further reduces the surface particle size to 1 to 2 inches. Any soft spots quickly become apparent and are corrected.
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The rubblization process transforms the worn PCC pavement into a granular base ready for a HMA overlay.
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The rubblization work is being done by subcontractor Antigo Construction out of Wisconsin. Antigo holds a patent on the MHB, and will operate but not sell its equipment.
The only complaint Parkways officials have about the MHB is that it draws a crowd. Motorists have come to a halt to watch and even take photographs of the strange-looking machine with pumping arms pounding its way down the road. "You might want to consider putting up a curtain," was the humorous advice of Col. Gavan.
After a final pass with a vibratory roller, the surface is compacted and the fractured particles are "keyed" into place, and ready for the base course.
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Paving for heavy loads
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Traffic on the Turnpike increased 19 percent between 1993 to 1997, and the Parkways Authority specified a fulldepth, large-stone HMA mix capable of carrying up to 1.3 to 1.5 million ESALs a year.
The large-stone base mix, with a maximum aggregate size of 2 inches and PG 64-22 binder, comes close to matching a Superpave mix. It is followed with a leveling course compacted to 1 inch, and surface course with a skid-resistant aggregate.
West Virginia Paving is producing the HMA in a portable drum mix facility at a rate of 300 tons per hour. "The 2-inch rocks can be hard on an asphalt plant," admitted Mr. Cooperrider. Hauling the HMA to the paving site through traffic and up steep grades has also presented some challenges, but the paving has progressed at a rate of 400 to 650 linear feet an hour depending on the subgrade.
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The Turnpike's new surface is a full-depth, large-stone HMA mix capable of carrying up to 1.3 to 1.5 million ESALs a year.
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A transfer vehicle is being used to place the second base course lift to minimize segregation and on the surface course to ensure smooth flowing paving operations, said Mr. Cooperrider.
The paving work has stayed on schedule and Mr. Cooperrider full expects it will be completed by October 31, in far less time than any of the other rehabilitation options considered.
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Sharing their success
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Turnpike officials are so enthusiastic about the rehabilitation project underway, they joined with the Flexible Pavements Council of West Virginia, the contractor, and NAPA in hosting an Open House in June which attracted agency officials, consultants, and contractors from 15 states.
One of the guest speakers at the Open House was Marshall Thompson, Professor Emeritus of Civil Engineering, University of Illinois at Urbana Champaign, who has conducted numerous Studies on rubblization and found that if done properly, the rubblized material can be superior to a granular base.
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The 90 state DOT officials, contractors, and consultants taking part in the West Virginia Open House could see and feel how the rubblization process works under traffic.
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"You have to engineer these projects," cautioned Professor Thompson. It is important, he said, to test the existing pavements with Falling Weight Deflectometers and to take corings of the PCC and the subgrade.
Professor Thompson has carefully followed three rubblization projects on Interstates in Illinois, all of which are performing extremely well. "This process holds excellent promise, particularly for all the 30-year-old interstate pavements that are failing."
West Virginia Turnpike authorities are also convinced. Col. Gavan said another rubblization project is on the drawing board.
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Open House Visits Pay Dividends
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The old maximum that seeing is believing appears to hold especially true when it comes to trying new construction techniques.
Back in 1988, Industry members were invited by the Ohio Department of Transportation to inspect three different methods being used to rehabilitate worn PCC pavements with Hot Mix Asphalt in that state.
More than 140 engineers and agency officials took advantage of the opportunity to see demonstrations on I-70 of rubblizing, cracking and seating, and removing and recycling the worn PCCP into the HMA overlay.
Officials from the West Virginia Parkways Authority were among those who attended. The very next year they gave rubblization a try. That project won NAPA's highest honor, The Sheldon G. Hayes Quality Pavement Award, for the Authority and the contractor, West Virginia Paving, Inc. of Dunbar, WV.
West Virginia then, in turn, opened its rubblization project to visitors to demonstrate the new techniques in rubblization that have been developed since 1988.
Among those who traveled to West Virginia were members of the Colorado, Delaware, and Kansas Asphalt Pavement Associations, and representatives from the Kansas DOT.
"These demonstrations are very valuable. They are much better than a video, especially in these days of media hype and spin," said Don Popejoy, Vice President of Ritchie Paving, Inc., Kansas. "There's no substitution for being there.
"By walking out onto a project your eyes, hands, and feet are part of the process. You can talk with people, see the particle size, and feel the cars and trucks whizzing by. You can tell pretty quickly that this is a viable option that can be done under traffic."
The West Virginia experience will soon play a role in Colorado where DOT officials received a consultant's report from the Open House which they can refer to as they undertake a rubblization project on I-76 near Sterling.
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Source: National Asphalt Pavement Association, Focus on HMAT Vol.3, No.2
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