A kilometer and a half of bridge parapets need to be constructed, just before the end of the construction season? No problem for the Sangamo Construction Company. The stringline-free construction of monolithic profiles is a quick and economical process with the Wirtgen Slipform Paver SP 15i, equipped with the "AutoPilot" 3D control system.
Based in Springfield/Illinois, Sangamo Construction had been contracted to build several bridges including the parapets required: five bridges in central Illinois with a combined length of some 850 m plus another 700 m in the southern part of the state. The parapets were 1 m high, 48 cm thick at the bottom, tapering to a width of just under 27 cm at the top, and had a perpendicular rear wall. As much as 260 m3 of concrete were processed just for the construction of the four 150 m-long parapets on the twin bridges on Interstate Highway 55 near the small town of Lincoln.
The Wirtgen slipform paver constructs a 1 m-high monolithic profile around the pre-installed reinforcement using the special parapet mold. The parapet measures 48 cm at the bottom, tapering to 26 cm at the top.
SP 15i hits the mark with diverse range of applications
The paving work was performed by a Wirtgen Slipform Paver SP 15i with AutoPilot which Sangamo had purchased from the North American Wirtgen Group sales and service company, Wirtgen America, along with an extra mold for parapets and another for curb and gutter profiles. "We have been in the concrete construction business for a long time and are particularly experienced in the field of bridge construction," reports John Jilg, Project Manager at the Sangamo Construction Company. In the past, a small team constructed the sidewalks, curbs and gutters. But then Sangamo concluded a contract for a number of smaller repair jobs in urban areas.
Once we knew that we would be carrying out these tasks in addition to our bridge construction work – which always includes safety barriers in the form of bridge parapets – we decided to purchase a slipform paver.
John Jilg, Project Manager, Sangamo Construction Company
The decision to buy the smallest model in Wirtgen's concrete paver fleet was mainly prompted by the flexible range of applications offered by the offset paver SP 15i. "The three crawler tracks and the possibility of mounting the molds on either side of the machine are huge benefits," explains the Project Manager. He felt that a larger model with four crawler tracks would not have been the right choice, particularly for work on narrow roads, which are often obstructed by parked cars in urban areas. This would disrupt the flow of traffic too much. But with its SP 15i, Sangamo is always flexible. "We have used the slipform paver to construct curbs and gutters in Springfield, but we can also use it to build 1 m-high parapets," adds Jilg.
The Wirtgen SP 15i with AutoPilot can pave the parapet without stringlines, greatly reducing both the construction time and the costs involved.
Wirtgen's stringline-free paving technology is a winning feature
The possibility of stringline-free paving was another key aspect. Developed by Wirtgen, the AutoPilot is a user-friendly, cost-effective 3D control system for offset applications and the construction of monolithic profiles such as concrete safety barriers, curbs, gutters and channels. The GPS-based system ensures maximum precision and efficiency, not only when creating straight or complex curved concrete profiles, but also when constructing closed configurations. There is no need for a digital terrain model, as the profile path or configuration is programmed on the spot. The Autopilot permits fully automated top-quality paving in radii down to as small as 600 mm. And without stringlines, too: The time-consuming and labor-intensive surveying, installation and removal of stringlines can now be completely dispensed with.
The Sangamo Construction Company first encountered the SP 25i with AutoPilot in Las Vegas. "We took a look at the machine at Conexpo and obtained some in-depth advice on its possible applications from the Wirtgen experts," says Jilg. Shortly afterwards, Sangamo took another much closer look at the advantages of the slipform paver with 3D control system during a live demonstration at Wirtgen America's headquarters in Nashville. "We wanted to see the SP 15i in action on site and make sure that it matched our requirements. And our expectations were met in full," concludes Jilg with satisfaction.
The correct set-up on the job site ensures high-precision measurements. The reference station is an integral part of AutoPilot, Wirtgen's stringline-free 3D control system.
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