Critical to the vitality and economic health of the greater Pittsburgh metropolitan area, the Pennsylvania Turnpike Commission's Mon/Fayette Expressway & Southern Beltway Projects include seven different concrete pavement construction jobs, each of which are in varying stages of completion.
The following are just three portions of the projects:
Uniontown to Brownsville. The majority of this section of this section of the Mon/Fayette Expressway Project is currently under construction. The concrete used for road surfaces is Class AA, which has a mix design compressive strength of 3000 psi at seven days and 3750 psi at 28 days. A total of 30 bridge decks include a special high-performance, 9-inch-thick Class AAA concrete mix, which has a strength of 3600 psi at seven days and 4500 psi at 28 days.
The concrete is being batched on-site from temporary batch plants, a number of which are located at various points along the project. Specifications dictate the amount of slump and percentage of entrained air allowed, in addition to the minimum cure strengths needed based on the class of concrete.
Variables considered in the specifications include the ambient temperature (too cold and curing blankets may be used, too hot and ice may be added to the mix to keep it cool), the amount of time available for cure (faster yield mixes known as “hi-early” may be used), the distance to travel for concrete trucks, and finally, the method of placement.
I-70 to PA 51. Completed in 2002, this 17-mile section of the Mon/Fayette Expressway was constructed for a total of $588 million. Approximately 840,000 square yards of concrete pavement was placed from a Rex Model S batch plant centrally located to the construction site. Both fine and course aggregates were used in the approved concrete mix. Agitors and mixers were used in conjunction with hand pours as well as at the starting or ending bulkhead of a slip-form pour.
Concrete consistency for I-70 to PA-51 was controlled through precise action points. Air content was controlled at +/- 0.5% of target and slump at +/-¼ inch of target.
Paving operations began with a CMI PC450 belt spreader, starting from the end of the previous day's pour, placing concrete full width for the paving start up. A Gomaco GHP 2800 paver then proceeded over the concrete to begin paving. The final finisher on the back of the paver worked grout to the surface and closed any small holes that were found. Finishers and inspectors checked the concrete surface with a 10-foot straightedge and any rough spots were floated out with bull floats.
A cure machine operator applied texture to the finished surface of the pavement in 8-foot rectangular sections using a random tining format. Random tining was used instead of conventional texturing to reduce tire/pavement noise and to further enhance the ride.
PA-60 to US 22. Also known as the Findlay Connector, this portion of the Southern Beltway opened to traffic in late 2006. It begins at the Pittsburgh International Airport and proceeds 5½ miles to US 22. It's also the first segment of the planned 35-mile Southern Belt-way around the city of Pittsburgh.
The Findlay Connector was constructed in three sections and totaled $165 million, of which $20 million was earmarked for concrete applications. Approximately 525,000 square yards of 12-inch portland cement was placed.
For two thirds of the PA-60 to US 22 project, concrete was provided by a Rex Model S batch plant owned by Hi-Way Paving, Hilliard, Ohio. For the final third of the project, concrete was provided by Golden Triangle, Imperial, Pa., using a Vince Hagen batch plant. Both concrete plants were erected on-site. The concrete was passed through a preconstruction uniformity test for approval by the Pennsylvania Turnpike Commission and to ensure consistency in the mix.
The Hi-Way Paving mix design included a slag course aggregate and a natural sand fine aggregate while the Golden Triangle mix design included a gravel course aggregate and a natural fine aggregate.
Agitor and dump trucks hauled the plastic concrete from the batch plant to the paving train. Testing for both concrete mixes during batching also was conducted to ensure the material had proper slump and air content when delivered to the paver.
The Hi-Way Paving concrete was placed using a Gomaco 2800 New Generation slip-form paver for mainline paving and a Gomaco 6300 for ramp and shoulder paving. Spreaders included a Gomaco 2600 placer and an Allen Spreader in order to keep a consistent amount of concrete in front of the paver. Golden Triangle used a Gomaco 2800 slip-form paver for the mainline, a Gomaco Commander III paver for ramps and shoulders, and an Allen Spreader to increase production and improve quality.
Minimal hand finishing was required; finishers checked surface smoothness with straightedges. Forms were used for handwork in odd-shaped panels and tie-ins where slip-forming was not an option. Grade elevation was periodically checked by straightedges and stringline. Finally, profile index readings were taken shortly after the concrete reached strength for smoothness and acceptance.
- Owner: Pennsylvania Turnpike Commission
- Architect/engineer: PBS&J, Canonsburg, Pa.