Novel Use Keeps Integrity of World’s Largest Concrete Pour
For a record-setting continuous concrete pour, Couts Heating and Cooling, Inc. installed more than 20 miles of Uponor radiant tubing to create a thermal cooling system that would ensure the integrity of the concrete as it cured. Applying this new technique, Couts not only smoothed the way for this rapid, massive project, it also benefitted from the ease of installation. The PEX tubing’s “extreme flexibility made it fast and easy to install around the rebar in the base of the structure,” said Mike Martin, Couts piping department manager.
Green Construction and Deconstruction
At 1,100’ tall and 73 stories, the Wilshire Grand Center in Los Angeles, CA, is the 10th tallest building in the United States and the tallest building west of the Mississippi. A structure of this magnitude requires precise engineering to ensure the building’s integrity while also incorporating creative and thoughtful design elements to meet the owners’ LEED® Gold certification requirements.
The first decision was to deconstruct the original, 1.1-million-square-foot building, built in 1951, instead of demolishing it, so that some materials could be recycled rather than go to the landfill. The concrete was crushed into material that can be sold as Class II Base for structural fills, roads, or building pads. The steel beams were sent to a local foundry and melted down to make recycled reinforcing bars. This “green” deconstruction of the old building saved the developer $4 million, making it not only good for the environment but also good for business.
Record-Setting Concrete Pour
After deconstruction, the focus turned to the design of the new, $1.2-billion structure. The base for the 2.1-million-square-foot building required a 21,200-cubic-yard concrete foundation located 84’ below street level. To place that kind of concrete mass required a world-record continuous pour.
Completed in less than 19 hours, the 82 million pounds of concrete set a Guinness World Record for the largest continuous pour in a 24-hour period. To ensure structural integrity of the foundation’s massive slab, the design specified a hydronic radiant cooling system to draw off the heat as the concrete cured—a new trend that is becoming more popular for large concrete projects such as building foundations and bridges.
According to Martin, the idea of thermal cooling came from an engineer in Minnesota who was looking to redirect the heat and keep an even temperature in the slab to prevent cracking after it cured. To keep the slab at the proper temperature, the team at Couts installed more than 100,000 feet of 3/4” PEX tubing from Uponor that intertwined through the rebar of the foundation. The tubing was used to convey 40° F water throughout the system to maintain an even temperature that was not to exceed 160° F as the concrete was poured and then cured.
“The lighter weight of PEX made it easier to move around the jobsite,” said Martin. “Also, PEX is very forgiving. The installers were walking on it and dumping concrete on it, and it never damaged the pipe. Plus, any kinks in the pipe were easily repaired with a quick shot of heat from a heat gun, which is a big advantage for PEX-A type tubing. This eliminated the need to add in couplings in the slab.”
Couts installed the radiant tubing at 6” on center and dropped it down 18’ from the 8” HDPE supply header before looping it back up. Once the radiant tubing installation was complete, the concrete pour began. It was a steady, organized plan that required more than 400 workers, eight concrete plants, 208 mixers, and more than 2,000 truckloads.
During the pour, the 40° F water, sourced from a chiller system featuring a 40,000-gallon storage tank, began running through the system. The thermal cooling system pumped water throughout the tubing for two weeks while being continuously monitored by 24 sensors to ensure proper system temperatures. After the two-week timeframe, the water was removed from the system and the tubing was filled with grout and remained in the slab.
Cooling Catches On
To date, the Wilshire Grand stands as a testament to new construction trends that promote business-smart sustainable design and “green” deconstruction, an idea that is likely to gain traction as older buildings make way for new structures. And, according to Martin, concrete thermal cooling will also continue to increase as more and more professionals look to smarter building practices to make structures of higher performance.
In fact, Martin noted, many general contractors are reaching out to Couts to install thermal cooling systems for similar applications. Since the Wilshire Grand, Couts has completed two bridges with concrete thermal cooling, and Martin estimated the trend will continue to grow.
For more information, visit www.uponor-usa.com.