InTrans / Jun 22, 2018

UHPC overlay equipment makes US debut in Iowa

Technologies can be implemented quicker when all parties work together.

Iowa State University’s Institute for Transportation (InTrans) and the Iowa Department of Transportation (DOT) in partnership with engineers of Wapello and Buchanan counties in Iowa, Iowa Highway Research Board, and Federal Highway Administration have been national leaders on the development and implementation of Ultra-High Performance Concrete (UHPC) projects.

One of their recent pioneering efforts is to use UHPC as a bridge deck overlay. So, it was only a matter of time before their technique got implemented in the field on a primary bridge, which involved international companies LafargeHolcim and Walo Bertschinger (WALO) that specialize in UHPC materials and construction automation, respectively.

All four united on a project currently underway in Sheldon, Iowa.

“I think the technology implementation is successful because everybody is participating with commitment and enthusiasm,” said Dr. Sri Sritharan, the Wilkinson Chair of Interdisciplinary Engineering at Iowa State’s Department of Civil, Construction, and Environmental Engineering.

The agencies, companies, and more met in Sheldon in early June to get a glimpse of first-ever appearance of UHPC overlay equipment developed by WALO that was in operation to place the overlay mix developed by LafargeHolcim.

“This is the next step in the process: getting it ready for this market after completing the basic research, so it can be adopted statewide,” said Vanessa Goetz, operations research engineer with Iowa DOT’s Iowa Highway Research Board that has funded a research monitoring project for the deck overlay effort.

Before the site-visit, a day-long workshop highlighted various projects in Iowa and across the country that have used UHPC and offered some insights about the material, the equipment, and the potential for more fully adopting UHPC in bridge projects. About 50 people attended.

More study is needed but all speakers agreed that there is a lot of potential for using UHPC. The material costs more than conventional concrete but there’s a consensus that it can be used cost effectively.

In the overlay concept, a thin layer of UHPC is placed on bridge decks as a protective layer, making them waterproof and helping to save on any additional costs by sparing the expense of deck repair and full deck replacement.

One-of-a-kind equipment

Walo Bertschinger, the owner of the eponymous company now in its fourth generation, said his company first got interested in UHPC on a bridge rehabilitation project in its home country of Switzerland.

The challenge was the four-lane, 550,000 square-foot Chillon Viaducts could not be fully shuttered during construction if a major deck rehabilitation were required.

The solution was to strengthen it with a reinforced UHPC top layer, so that it could be done in parts. But it brought on a new challenge—the need for equipment that could better handle this new material and do the work relatively quickly.

“We had to design a new machine, but you can’t design a machine without knowing the material,” Bertschinger said.

That led them to connect with LafargeHolcim that had developed different UHPC mixtures dubbed Ductal.

The project ultimately was so successful that it was showcased in the First UHPC North American International symposium held in Des Moines, Iowa in 2016. That led Sritharan to Bertschinger. At the time, Walo was interested in expanding into the US market and Sritharan was wrapping up an earlier phase of UHPC bridge deck overlay research.

The Sheldon, Iowa project represents the first time the WALO UHPC overlay equipment has been used in the US. The company is working on the project as a subcontractor of Cramer & Associates.

“This is kind of the next stage, and we’ll see what’s next,” Bertschinger said. “This is a start up. It’s a start up for everybody, because the material is not that simple, and we constantly learn and adapt.”

Iowa’s UHPC history

Ahmad Abu-Hawash, chief structural engineer at Iowa DOT’s Office of Bridges and Structures, said Iowa’s interest in UHPC dates back to 2004. But it wasn’t until 2016 it used the material on a bridge deck overlay project in Buchanan County — the first in the US that followed the recommendations of Sritharan’s research.

The location was intentional. The DOT wanted to try this new material on a secondary road; though there’s less traffic, it does see a fair amount of heavy truck and agricultural traffic.

The project in Sheldon, on the Floyd River in northwest Iowa, is the DOT’s first UHPC overlay on a primary road. The bridge is 205 feet by 44 feet. The overlay is designed to be 1.75 inches thick.

The projects have been funded in part through the Federal Highway Administration grant Innovation Bridge Research and Construction/Deployment. Aside from overlays, Iowa DOT has also done a UHPC waffle deck in Wapello County.

“We were interested in UHPC because it’s more durable,” Abu-Hawash said. “It’s performing as expected. We’re hoping it can give us longevity.”

Sritharan said as the development of UHPC deck overlay continues to move forward, the question of long-term performance is one his research is also looking to address, as well as how to reduce the cost of field implementaion. Sensors have also been placed in the Floyd River bridge overlay project to further study the performance of UHPC deck overlay.