The Pennsylvania Turnpike is one of the older limited-access highways in America, with its first four-lane, 160-mile stretch opened to the public in 1940. Over the years, the highway has been lengthened to its present size of 515 miles. Most of the later-built highway sections are in good condition. However, the 1940 vintage roadway is in need of reconstruction because the surface-water drainage system is inadequate and the reinforced concrete pavement is beginning to fatigue beyond making cost-effective repairs. The inadequate surface-water drainage system has exacerbated roadway problems because of freeze-thaw conditions.
In Part I of this story, published last month in Roads & Bridges, it was reported that 100 of the 160 miles would be rebuilt over the next 10 years for an estimated cost of $1.44 billion. It was further pointed out that a major reconstruction problem for the Turnpike Commission was in dealing with the poor subgrade conditions (clay) encountered. This problem is being resolved by incorporating lime/pozzolan or lime/pozzolan/portland cement into the upper 15 in. of the subgrade for stabilization and strength.
A well-stabilized subgrade with acceptable strength characteristics is necessary because the new highway features Superpave (flexible pavement) instead of the concrete pavement (rigid pavement) it is replacing. Superpave was selected by the Turnpike Commission for a host of reasons, but the two most compelling are: Asphalt paving is readily maintained at any time and even overlays in the future can be made in the wee hours of the night when traffic flow is at a minimum; and it carries an affordable life-cycle cost. Since the motorists pay tolls for the use of the highway, the Turnpike Commission is sensitive to their wants. The commission sees the motorists as its customers. Understandably, encountering long lines of bumper-to-bumper traffic, due to daytime road maintenance activities, is unacceptable.
The first contract let for rebuilding the 100-mile highway was designated 76/85. It is a 9-mile section and calls for rebuilding the two eastbound lanes and the two westbound lanes between the New Stanton Interchange and the Donegal Interchange. The paving contractor for this contract is Lindy Paving, a Trumbull Corp. company located in Newcastle, Pa.
Better Materials, good paving
Quality control of the paving process is Lindy Paving's first consideration when each new paving project starts. Top-performing paving equipment is paramount for getting high-quality paving results. Equipment to be considered includes the plant for producing hot-mix asphalt (HMA), special equipment for delivering the HMA directly into the paver, the paver and the rollers used for compaction. Equally important, said Lindy Paving's Joe Conti, is the paving crew's performance, especially the operators of the equipment. Good equipment and poor operators or poor equipment and good operators are not formulas for achieving good paving results, he said.
As for this project, the HMA supplier is Better Materials Corp., Connellsville, Pa. The company bought a used Astec Turbo 400 Six Pack portable asphalt plant from this project's prime contractor, Angelo Iafrate Construction Co. Originally, Iafrate bought the plant new specifically for this project. Iafrate did the paving the first season, but for the final season the contractor decided to subcontract both the HMA production (Better Materials) and the paving of it (Lindy Paving).
One of the main reasons for choosing the Six Pack is its portability. Iafrate projected it might take on other contracts, yet to be let, that are associated with this $1.44 billion, 100-mile project. Most of these future contracts will include about 10 miles of roadway reconstruction. Since the plant might be relocated every 18 months to a new turnpike project, efficient plant portability was considered very important by Iafrate.
The plant includes a Turbo 400 Double Barrel drum mixer, cold feed, scalping screen, baghouse, cyclone, surge bin, drag conveyor and control house. Options supplied include a RAP bin, fuel tank and an AC holding tank. This plant's rated throughput capacity is 400 tph.
Dan Skovira said he planned to use the new plant just as Iafrate intended to, as a portable plant. Skovira is the asphalt products services manager for Better Materials and is responsible for 10 different asphalt plants including the Astec Six Pack. This is the only company-owned plant he calls "a 100% portable plant."
"I can haul this complete plant to another location in 10 truck loads even though there are many options added to it. Despite its portable design, this plant is built rugged. It also is very reliable. We are producing HMA at a rate of 400 tph and are experiencing near 100% plant availability," he added.
With this plant, Iafrate produced over 250,000 tons of HMA in the first season, and this season Better Materials produced another 160,000 tons. The base course for this project is made with BCBC 64-22 and 20% RAP added. The Superpave is a polymer 76-22 mix with 15% RAP added.
Stick to static
The turnpike has certain equipment-usage specifications to which the contractor must adhere. One is the use of a material transfer vehicle (MTV) for loading the HMA into the paver. An MTV is purposely specified by the turnpike for reducing aggregate segregation within the mix, which is commonplace while loading the mix into the paver, and to ensure a more even temperature throughout the mix. In turn, this mix uniformity enables the mat to be compacted to a uniform density.
Lindy Paving owns two Roadtec SB-2500B Shuttle Buggy MTVs that are being used on the project. Conti said the Roadtec Shuttle Buggy is an important link in the paving train for assuring a high-quality pavement. Accordingly, the company uses the Shuttle Buggy on many other paving projects even when the project does not specify its use.
Here are some quick facts about the Roadtec SB-2500: it weighs 79,000 lb, it is powered by a 275-hp diesel engine and it is 4wd. The main hopper surge capacity is 25 tons, and the truck unloading conveyor rate is 1,000 tph. Functionally, the HMA is remixed in the hopper with a triple-pitch anti-segregation auger that reduces aggregate segregation and helps maintain an even temperature throughout the mix.
Unlike many DOT agencies, the Turnpike Committee will not allow paving contractors to use vibratory rollers in the vibratory mode on any asphalt paving if the mat-lift is 3 in. or less.
"We have tried compacting asphalt paving in the past using vibratory rollers in the vibratory mode with little success. While vibratory rollers are fine for compacting the base course we find it creates a bumpy road when compacting a binder or wear course. I realize that some newer model compactors have very high frequency modes but we have not tried them yet. It is possible these new compactors have corrected the problems we encountered with older technology rollers," explained Gene Mattson.
Indeed, some make roller technology is advanced, according to Conti. The high-frequency feature is one reason Lindy Paving bought new Sakai vibratory rollers. Sakai rollers feature selectable vibration frequency modes for producing 2,400, 3,200 and 4,000 vpm.
Another Turnpike Commission specification relevant to rolling Superpave is the use of a static three-wheel roller for the breakdown. Not having such a roller in the fleet, Lindy Paving turned to the Sakai dealer, Highway Equipment Co., Zelienople, Pa., for selecting the best roller. The model selected was the R2H, which has a gross weight of 30,920 lb, including added water for ballast. An important attribute of this roller is its full 83-in. coverage even when turning the machine because of an articulated center-design system.
Mattson said the turnpike gets superior results using a three-wheel roller as the breakdown (lead) roller. "On some Superpave projects we eliminated the three-wheel roller, and the results were very disappointing. I am convinced that for superior pavement smoothness, a three-wheel roller should be used. Such a roller eliminates the shoving and scuffing that is associated with other roller designs. The pavement smoothness results that Lindy is getting on the project speak for themselves."
Lindy is indeed achieving ideal smoothness results on this project. The specifications call for 28 in. deviation per mile. The actual results being recorded average 12 in. For achieving these results, the paving train configuration includes a Roadtec SB 2500, a Blaw-Knox paver, the Sakai R2H 3-roller and two Sakai vibratory rollers that include models SW800 and SW850.
The rollers are not operated, of course, in the vibratory mode when compacting the 2-in.-thick, 25-mm binder course and the 2-in.-thick, 19-mm wear course. Nevertheless, even in the static mode, these rollers perform well because of their oversized roller diameters. The SW800 has an effective width of 67 in. and the SW850, 79 in., and weigh 23,930 lb and 27,560 lb, respectively.
Here, the same rollers are used in the vibratory mode when compacting the base. It should be pointed out, however, that while Lindy is meeting with extraordinary success with the smoothness of this roadway, the company has had many other successes on paving projects in Pennsylvania and West Virginia. Besides the NAPA award, the company has earned six other awards for excellence in paving. All of the awards were received on projects where the rollers were used in the vibratory mode and a three-wheel roller was not included.
Every piece of equipment used for mixing the HMA, transferring it to the paver, laying the mat and compacting it, were pivotal for realizing the excellent paving results experienced by Lindy.
Of course, as Conti stressed, the equipment performances depend on good operators who can optimize each machine's potential.
