At 73 stories and 1,100 feet in height, the new Wilshire Grand project in downtown Los Angeles will be the tallest structure west of the Mississippi when its doors open in 2017. Following deconstruction of the existing Wilshire Grand Hotel in 2013, construction of the new mixed-use building, designed by AC Martin Partners, Inc., commenced in February 2014 with the world’s largest continuous concrete pour. The project’s general contractor, Turner Construction Company, worked with The Conco Construction Companies, one of the largest pumping and belt companies in the U.S., to coordinate the fleet of pumps, including 16 Putzmeister America, Inc. units, required for the record-breaking, 21,200-cubic-yard mat pour.
To lay the foundation for the massive Wilshire Grand project, Turner and Conco devised a plan for the continuous 21,200-cubic-yard mat pour, which was located 80-95 feet below street level. For the past several months, crews have prepared the site by digging an 18-foot-deep pit and lining it with seven million pounds of reinforcing steel.
During the massive pour, 12 Putzmeister truck-mounted concrete boom pumps ranging from 32Z-47Z Meters, two Putzmeister placing boom towers, and two Putzmeister trailer-mounted concrete pumps were strategically placed both inside and above the excavation.
A total of 19 pumps were utilized for the pour. Six pumps at street level fed six pumps, including two Putzmeister MX 34/38Z Placing Boom Towers, two 32Z- and a 36Z-Meter Truck-Mounted Boom Pump, located deep in the excavation. Two Putzmeister BSA 14000 Trailer Pumps at ground level also relayed concrete into the pumps located inside the excavation.
“We utilized Putzmeister equipment due to its durability and reliability,” says Michael Marchesano, Turner’s general superintendent. “With a continuous pour of this magnitude, you need to be able to count on your equipment to keep doing its job, even under demanding conditions.”
The pour included 227 ready mix trucks making more than 2,100 trips and pouring 82 million pounds of concrete during an 18 ½-hour period.
“Each truck made 10 to 14 concrete drops, traveling through the night between eight different concrete plants within a 20-mile radius,” says Marchesano. “The first batch of concrete poured onto the site came from a plant in Vernon, Calif. that poured the first concrete in Southern California ever.”
The structural engineering team, Brandow & Johnston, elected a continuous pour to ensure the mat foundation would yield the maximum strengths. To guarantee the entire pour cured at the same rate, a special 6,000 psi, 90-day mix was used. Special admixtures were used to ensure the temperature during the process of hydration didn't exceed the parameters designed for the mix. Without those admixtures the mat slab could have experienced thermal cracking and lower strength, which could impact the structural integrity of the pour. Following the pour, a cure blanket and a thermal control system were put into place for 15 days.
The mat pour qualified as the largest continuous concrete pour in history and officially claimed a GUINNESS WORLD RECORD.
High-traffic, congested location
Given that Los Angeles is the second most populous city in the United States, the construction team anticipated logistical challenges when planning the large mat pour at the project’s downtown location. To minimize the impact on businesses and residents, they began the pour on a Saturday evening and concluded around noon the next day.
“Because the concrete must be poured within 90 minutes of being mixed, trucks had to arrive on time,” Marchesano explains. “In case of freeway jams, alternate routes were mapped.”
Not only was outside traffic a concern, but job site congestion also was a challenge. Equipment had to be carefully chosen to accommodate the site’s needs.
Now that the foundation is in place, the crew will begin working on the attached parking structure and 73-story building that will make up the Wilshire Grand project. Both of the existing Putzmeister MX 34/38Z Placing Boom Towers that were used for the mat pour will remain in place while the crew builds up.