InfraStructures - September 2013 - Crossrail On the Right Track with JCB - Canada's Equipment Magazine

New G&Z Paver Meets Tough Specifications

Stuart MacKenzie
Special Collaboration

When a contractor faces a tough concrete paving spec – and a very tight schedule to boot – it makes for a difficult project in every respect. Yet those were the challenges confronted and overcome by Sherwood Construction Co. in the construction of Runway 18L-36R at the Tulsa, Oklahoma, International Airport.

Last March, Sherwood began work on the removal and replacement of 457 m of the old runway, which consisted of 46 cm of dowel-jointed concrete pavement. The contractor first removed the old concrete and the 15 cm layer of cement-treated base under it. That left 30 cm of aggregate base, which stayed in place.

“We had 70 days to do all the construction – removal of the old runway, replacement with 46 cm of new concrete pavement, and getting it ready for aircraft,” said Scott Middleton, project manager. “We didn’t make the schedule; we came in late. But we had anticipated taking about 15 days more than they gave us. We knew that going in, and that was figured into our bid. We worked 12 to 14-hour days, six days a week. The penalty for not meeting the deadline was $10,000 per day.” With this in mind, Sherwood knew they needed a slipform paver that would maximize available paving time and minimize width change time.

G&Z Selected for Versatility & Quick Width Change Capability
For the Tulsa runway and other projects to follow, Sherwood bought a new S850QB concrete paver from Guntert & Zimmerman. The contractor wanted a versatile paver, one that could change paving widths relatively quickly, said Ron Whisenand, Sherwood’s paving superintendent. “Instead of taking days to change widths on our paver, now we do it in hours on the S850,” he said. “We’re able to stay on our schedule and the paver is more versatile too.”
Sherwood set up the Tulsa runway to pave eight lanes of 5.7 m each for a total of 45.7 m wide. Using stringline with a 1.8 m offset, the contractor paved four pilot lanes first. It took three or four days for the first of the pilot lanes to gain enough strength to pave filler lanes.

Tackling Tough Specifications
The tough part was the specification set forth by the Federal Aviation Administration. Here is how it reads: “Surface smoothness deviations (on hardened concrete) shall not exceed 6 mm from a 4.9 m straightedge placed in any direction, including placement along and spanning any pavement joint edge.”

Another portion of the spec addresses edge slump: “When slipform paving equipment is used, not more than 15% of the total free edge of each 152 m segment of pavement, or fraction thereof, shall have an edge slump exceeding 6 mm, and none of the free edge of the pavement shall have an edge slump exceeding 9.5 mm.” Keep in mind, that is 6.4 mm of edge slump on fresh concrete standing 46 cm tall.

“The Guntert & Zimmerman paver met every challenge we had – and it satisfied the owner,” Mr. Whisenand said.

S850 Pushes High Quantity of Concrete
Still, meeting the edge slump spec was not easy, Scott Middleton said. Sherwood was using an eight-sack mixture, for high early strength, and the concrete was relatively dry – it had just a 19 mm slump with the slump cone test.

“It slows you down because you have to stack so much concrete in front of those corners to make sure you get plenty of concrete up in there to form those corners right,” Mr. Middleton said. “Of course you’re paving 46 cm thick, so you have a lot of concrete head in front of the paver. It makes you walk slower with that paver to make sure you don’t start slipping the tracks because that’s a lot of head in front of the machine.”

The S850 was up to the task. “When you had plenty of concrete in front of the paver, and had your build-up in the corner set properly, and if your plant is maintaining a uniform slump, the paver will do it quite easily,” Mr. Middleton said. “And that’s with very little finish work behind it. It took a bit of trial and error to get to that point because with a brand new paver we had to dial it in, get the overbuild right, and make sure we were producing consistent concrete.

“Once we got it dialed in, and once we knew what slump the plant was producing and would stay at, the process worked fine,” said Scott Middleton. “We ended up dialing in for a 19 mm slump. If we got much more than that, we couldn’t hold the corners very well.”

“Our older paver would not have been able to meet that edge slump spec,” said Mr. Middleton. “So yes, we’re happy with the new paver.”

Sherwood sawed transverse joints at 6.1 m intervals down the pavement. Dowel bar baskets were placed on 46 cm centers across the pavement in the transverse direction. And the contractor drilled and inserted tie bars between lanes at 76 cm intervals in the longitudinal direction.

The Tulsa Airport Authority provided full payment for producing a smooth ride on the runway, and exacted a penalty for a ride that exceeded deviations from a blanking band on a profilograph. To reach full pay, Mr. Whisenand said total deviations from a 5 mm blanking band could not exceed 11 cm per kilometer. The pavement required minimal grinding – just at the headers.

Production averaged between 164 to 228 m3 per hour, and ranged up to 274 m3 per hour. The batch plant was located 1.6 km off the project, and Sherwood hauled concrete with 16 dump trucks. For the filler lanes, Sherwood used a placer-spreader.

“The paver performed perfectly,” Ron Whisenand said. “Everyone was ecstatic with the performance of the paver. Our company owners, our client, and the FAA, and also the engineering consultant, were all very happy with the product that was laid down.”