Selective service

Nov. 13, 2008

The project requirements called for the removal and replacement of almost 2 miles of existing roadway. The section of roadway is one of the busiest thoroughfares through Fort Riley and connects the town of Ogden, Kan., with the main barracks housing 20,000 soldiers and part of the base’s company headquarters. The old roadway was quickly deteriorating. The road’s poor condition, combined with steep grade and a hairpin curve, was the source of several accidents.

The project requirements called for the removal and replacement of almost 2 miles of existing roadway. The section of roadway is one of the busiest thoroughfares through Fort Riley and connects the town of Ogden, Kan., with the main barracks housing 20,000 soldiers and part of the base’s company headquarters. The old roadway was quickly deteriorating. The road’s poor condition, combined with steep grade and a hairpin curve, was the source of several accidents. Snow and ice often caused the road to be closed down for safety purposes, but that caused congestion on other roads around the base.

Smoky Hill LLC, a heavy contractor based out of Salina, Kan., won the contract to remove the dangerous road and replace it with concrete. The project involved straightening portions of the new roadway while trying to decrease the steep slope. The new road had to be built as far away as 100 ft from the existing one in some places. Smoky Hill also hired a subcontractor to blast and remove 25 ft from a rock hill, then used that material to fill in an additional 20 ft of area. Even with that measure, they are still having to slipform a portion on a 6% grade. Superelevations and crowns in the new grade and pavement created additional challenges. A roundabout and tank crossings were other unique aspects of the project.

Smoky Hill’s paver of choice for their concrete slipform paving has always been GOMACO. This year the family owned company decided to add a third paving crew and purchased a new GOMACO GP-2600 two-track paver.

“We do a lot of urban pavement,” Garett Cloyd, project superintendent for Smoky Hill, explained. “We specialize in chopped-up projects and we do a lot of conveyor paving, because we have no room for a placer/spreader in a lot of areas where we work. We need a paver that is diverse and able to be changed pretty readily.”

Their two-track paver is equipped with a front-mounted conveyor system to help deal with their different projects’ tight conditions. The conveyor system on the paver has a belt that can be extended for concrete trucks to unload on. Once the truck is empty, the belt is retracted and the truck can drive on through. The belt places the concrete onto the grade in front of the paver. The auger/strike-off moves the concrete across the width of the open-front mold on the paver. The system gives Smoky Hill a placer/spreader option without having to find the space for an extra piece of equipment on the project.

Militarized base

Before any concrete paving can take place, the grade has to be properly prepared. Smoky Hill had some demanding specifications from the Army Corps of Engineers that had to be met on the two different layers of base material. They used their GOMACO 9500 to trim each layer of base to the exacting specification.

“The Corps of Engineers would inspect after every time we trimmed,” Cloyd said. “They would dig down and check the depth of the lime. If we were deficient more than 0.25 in., there was a penalty. The same was true for the second layer of rock. Each 12-ft-wide trimming pass for both layers of base material was inspected for depth accuracy.”

The Corps never found their grade to be deficient.

Stringline set on the project controlled the trimmer’s steer and cross slope. Carefully setting the stringline allowed Smoky Hill to trim the grade with the same crowns and superelevations that the paver would put into the concrete roadway. Topcon sonic sensors helped control the grade, which ensured an accurately trimmed base.

“This road had eight supers in it, and some of them were pretty lengthy,” Cloyd said. “We also had multiple places where we went from a crown, transitioned into a super and then went back to a crown again. We watched the stringline very closely and were pretty detailed with it to make sure the lime and the rock were where they needed to be.

“We had a tank crossing that needed to be 0.5-in.-thicker pavement than the rest of the road. We just marked that out ahead of time. The trimmer operator just dialed the sonics down 0.5 in. when he trimmed the lime so it was a little bit deeper. We laid our rock on top of that and did the trimming in one pass. We didn’t have to go back to cut the tank crossing out. We also trimmed our aggregate shoulder as we went, so it was all one pass off the same stringline.”

Catering to tanks

When it was time to start paving on the project, Smoky Hill took on the biggest challenge first: the roundabout. They had slipformed one before with their GOMACO GP-2500 paver, but this would be their first roundabout, on the first pour of the project, with the new GP-2600.

“It was the first pour on the job and we had a lot of people watching us, from Corps of Engineers personnel to civilians,” Cloyd said. “It went very well. The roundabout had a 100-ft radius, and we started and stopped paving in the exact same spot. They’re big enough around that by the end of the day we just had to put burlap out and wash the paver. We left the paver there for three or four days until we got our needed cure time on the concrete. Once we got cure time, we made a ramp, tracked the paver out of there and moved it to the site of the next pour.”

With the roundabout complete, paving on the rest of the roadway started. All of the concrete pavement on the project was 24 ft wide and 9 in. thick. Production averaged between 110 and 120 cu yd per hour. A portable batch plant was set up onsite to supply the concrete. The mix was a Corps of Engineers-approved design with slump averaging 2.5 to 2.75 in.

Another interesting aspect of the project, and something not found on an ordinary road project, was the tank crossing.

“There’s a tank crossing through the roadway, an intersection for the tanks to travel across while moving from their battalion headquarters on the base out onto the firing range,” Cloyd said. “The Corps wanted the intersection to have a little bit thicker concrete, 0.5 in., and it has a little bit different steel in it for extra reinforcing.”

The paver is equipped with a frame-mounted bar inserter on the front. It placed a transverse bar every 24 in. for the longitudinal joint. A timing wheel on one of the paver’s tracks measured out the spacing of the bars automatically.

A second wheel on the track is part of Smoky Hill’s vibrator monitoring system. They are using a Minnich Auto Vibe II system, which helps them control vibrator vpm, as well as monitors and stores their vibrator data.

“It wasn’t a specification on this Corps of Engineers project, but the Kansas Department of Transportation started requiring it a few years ago,” Cloyd explained. “They wanted to be able to have a readout of our vibrator frequencies and other measurements. With this Auto Vibe II, we just take the card out, take it into the office and we can print them out a chart showing all of our information.”

The concrete paving portion of Smoky Hill’s first project with their new paver is now completed and they have moved on to other work within the state of Kansas.

About The Author: Krueger is with GOMACO, Ida Grove, Iowa.

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