By Kirk Stelsel
Custom precast concrete solar tracker pads solve a utility company’s problem at the site of a retired landfill.
Innovation is a product of need. When the U.S. government needed a computer network, innovators created the foundation for the internet. Miracle medicines are created to cure diseases. Cars, electricity, the smart phone … behind every great innovation is an individual or company working to solve a perceived need.
Need also drives innovation in the precast concrete industry. Collaborations between precasters and customers to solve unique problems have resulted in incredible custom solutions. Dalmaray Concrete Products in Janesville, Wis., solved one such problem for a local utility company.
The unique problem
Aaron Ausen, vice president of Dalmaray, said the company fielded a call about custom precast footings for a solar field more than a year ago, but the project was canceled due to funding. Months later, he found himself reading about a similar solar field project in Beloit, Wis., in the local newspaper.
Thanks to a good working relationship with the local utility company, Ausen connected with its engineering team to find out more. Not only had the team not considered precast – the project also faced an issue not yet resolved.
The Rock River Solar Project is being built on top of a retired landfill with a liner buried 2 feet below grade. As a result, the typical solution of driving I-beams into the ground was not possible. In addition, the project called for a winter installation. It’s no secret that winters in Wisconsin are cold, so minimizing time spent on site and ensuring quality curing were important. Dalmaray’s custom precast solution minimized concerns and offered benefits no other alternative could provide.
“Precast was the only option at this time of year,” said Mark Miller, senior manager-estimating and pre-construction services for civil contractor Michels Corp. “Having the ballast blocks cast in a temperature-controlled environment and shipped to the site enabled the work to be completed in the winter.”
The custom solution
The precast concrete tracker pads required three months of custom engineering. Dalmaray’s team worked with Gary K. Munkelt & Associates to take every aspect of the project into consideration. Together, they engineered the precast, connection plates and bolt system for mounting the I-beams and solar panels to the pads.
The pads must withstand the loading scenarios and transfer the shear and overturning forces from the solar panel down while still allowing for adjustment for plumb. Designing the load transfer plate and anchor bolts to carry that load and still allow for adjustment is one of the challenges they were able to overcome.
“This is what excites me most about this project,” Ausen said. “To think we have designed this solution … now I’m watching it come to life in front of me.”
Dalmaray manufactured custom forms in its shop using a local steel supplier and local fabricators as needed. The pads are 13 feet long and vary in width. The thickness is 8 inches on the ends and 11 inches in the middle. Each pad has four bolts that secure a 1-inch plate with the mounting I-beam welded to it. In total, there will be 1,659 individual precast footings spanning seven solar arrays.
“There were actually 16 different types of tracker pads that varied in width and rebar configuration,” Ausen said. “The variance came in the height of the support post and location on the array. This was really challenging, trying to figure out which piece went where.”
Dalmaray and Michels were able to get everyone speaking one language through color coding. All layouts were color coded and Dalmaray coded the precast pieces with respective colorings. This made it easy for employees of both companies to identify where pieces should be placed.
Speed and scale
A sub-contractor also asked Dalmaray to precast transformer pads, pipe mounts and equipment pads. This made Dalmaray a one-stop shop for the majority of concrete items on site. Dalmaray cast 865 yards of concrete for the tracker pads and another 32 yards for the additional items. Despite it being the company’s largest project, all pieces were cast in seven weeks.
The project originally called for a 3,000-psi, 28-day-strength mix. Because precasting and shipping had a one-day window, Dalmaray produced a 6,500-psi mix that reached 3,000 psi in 22 hours. The company went through a week and half of batch qualification with the design team. According to Ausen, the site visit was an opportunity to highlight the advantages of precast. He said a lot of the attendees were amazed by what precasting is and what it can do for them.
“I was surprised by the level of value-added engineering provided by the precaster,” said Kim Halverson, project manager with Alliant Energy, the project owner. “The Michels/Dalmaray design went beyond structural and installation considerations and will provide decades of operations and management benefits.”
After two weeks of setting product, it was decided installation had to speed up. As a result, Dalmaray’s trucks began installing one trench while the contractor would set pads with an excavator. To start, Dalmaray was hauling 16-20 per day. Two weeks into the project, the company was hauling 80-100 per day.
“It’s really exciting because the scale is so huge, but also that we were able to be on the ground floor of designing the mega project,” Ausen said. “To see the whole life cycle of a project this size is impressive and rewarding. We are extremely excited for this project and we really think that this is precast providing a solution when people said ‘We don’t know what to do.’”
“The precast fabrication and installation have gone better than expected,” added Miller.
While Dalmaray sees the possibility for this product line to catch on should other solar field projects emerge, the greatest potential for the company is making its name as a custom solution provider.
“I find that custom precast has played and will continue to play a huge role in the success of our company and other companies if they are willing to accept the challenges that go with it,” Ausen said. “I talk to specifiers and engineers all the time and I can’t count how many times I’ve heard, ‘I didn’t know you can do that,’ or, ‘That could be precast?’ It’s a wonderful question to be asked.
“Thinking outside the box and solving insolvable issues is what precasting is all about.”
Kirk Stelsel is NPCA’s director of communication and marketing.