Major Development Relies On Efficient Concrete Placement
In June 2006, explosives were used to excavate rock for a 100-foot-deep hole for the below-grade parking garage of what will eventually be the Wachovia Corporate Center (WCC). To date, 600,000 pounds of explosives have been used to remove in excess of 500,000 cubic yards of rock. Located in the heart of downtown Charlotte, NC, the WCC will be part of a yet-to-be-named major mixed-use urban development spanning two full city blocks. The development will have an impressive 250,000-square-foot footprint, while the WCC itself will also have an extraordinary footprint of 60,000 square feet.
With an estimated completion date of June 2009 for the WCC and its parking deck, the WCC is sure to add that extra spark to Charlotte's ever-expanding downtown skyline. The other buildings in this mixed-use development will finish later in 2009 and into 2010.
The yet-to-be-named mixed-use development will consist of six buildings – the WCC, African American Cultural Center, Knight Theatre, Bechtler Museum, The Mint Museum, and a residential condominium which is in the early design stages.
Choosing A System
“Because of the 100-foot deep hole we excavated for the underground parking garage, we were challenged with finding the solution to getting concrete to the various structures that would be rising out of the deep hole,” says Chuck Gaston, project superintendent for Batson-Cook Construction (Batson-Cook), the general contractor for the mixed-use development.
According to Gaston, the key in finding the most efficient solution for getting concrete down into the hole was finding a company that has dependable and highly versatile concrete placing equipment.
“We considered a handful of companies to fill the role of placing system and concrete pump supplier/operator for this project, but only one was able to step up to the plate – Coastal Carolina Pumping,” comments Gaston. “They have a reputation as one of the main professional companies in the Charlotte area, along with the experience, personnel and technology to handle a project of this magnitude.” Batson-Cook and Coastal Carolina Pumping, Inc. (CCP) had also worked together on the Hearst Towers high-rise project, also located in Charlotte, NC.
According to Keith Bauer, COO of the Charlotte-based CCP, the following Putzmeister placing equipment from their fleet has been used on the mixed-use development project:
Six pin towersFour Putzmeister Series II detach 36/40Z-meter placing boomsOne BSA 14000 trailer pump
“Our Putzmeister concrete placing equipment has never failed us and has always exceeded our expectations,” notes Bauer. “Each year we're using our placing equipment more and more. I think professionals in the construction industry are really recognizing what placing system technologies can do on massive projects such as this one.
“We worked together with Batson-Cook's knowledgeable team to determine the most efficient locations for each of the towers to maximize boom reach for the mixed-use development,” adds Bauer. “We also had to make sure we took into account that the entire project site was surrounded by city streets.”
CCP has had three of its six placing towers installed for the mixed-use development project. Tower A is freestanding 140 feet high and is mounted on a foundation anchor system in the WCC structure. This tower will eventually become a hydraulic climbing system. Tower B is freestanding 80 feet high and is mounted with a foundation anchor system. It is located in what will be the low-rise portion of the WCC. Tower C is the newest tower that's been installed and stands 20 feet tall in the low-rise portion of the WCC, as well.
According to Bauer, after CCP and Batson-Cook found the ideal layout for the towers and placing booms, their next challenge was designing the pipeline that would service each of the booms.
“Based on where the placing booms needed to be, we were able to determine where the pipelines should be positioned for the towers,” comments Bauer.
Placing Booms In Action
According to Gaston, CCP arrived on the project site in February 2007 to place the foundations for the eight-level underground parking garage for the WCC. Since CCP arrived on site, they have placed about 30,000 cubic yards of concrete with their placing booms and truck-mounted boom pumps – ranging from their 32Z-meter to their 61-meter – and have been pumping and placing concrete six days a week. When all is said and done, CCP will have pumped and placed 90,000 cubic yards of the total 120,000 cubic yards of concrete needed for the mixed-use development.
One of the 40-meter placing booms is on Tower A and the other is located on Tower B. According to Bauer, Tower A has placed about 25,000 cubic yards of concrete and Tower B has placed about 5,000 cubic yards of concrete so far.
“Placing the 90,000 cubic yards of concrete with placing booms on this project has allowed us to increase the amount of crane time available for other structural components,” says Gaston. “This is a huge plus.”
One of the challenges with the actual pours, according to Brus, is the city's noise ordinance. “With only a 14-hour window of opportunity for our pours,” says Brus, “we must have our scheduling down to a science.”
On September 19, 2007, a 250-cubic-yard pour occurred early at 3 a.m. for the first above-ground floor for the WCC.
According to Brus, their 40Z-meter truck-mounted pump delivered the concrete from the basement up to its detached placing boom instead of the BSA 14000 trailer pump that they would normally use, because of the noise ordinance.
“The 40Z-meter placing boom's horizontal reach of 115 feet 2 inches and vertical reach of 122 feet 8 inches has helped immensely in placing the concrete exactly where it needs to be as well as placing it as efficiently as possible,” notes Brus. “Using the boom's truck-mounted pump was an invaluable benefit based on the time the pour occurred.”
On the afternoon of September 20, 2007, the BSA 14000 was silenced no more and back in action. The trailer pump delivered 50 cubic yards of concrete up to the 40Z-meter placing boom for the first section of vertical elements for the first above ground floor.
The next day the remaining 50 cubic yards of concrete for the vertical elements of the first above-ground floor for the WCC was pumped by the BSA 14000 and placed by the 40Z-meter placing boom.
According to Brus, the vertical pours are usually split up into two days.
On the BSA 14000's performance Bauer says, “The BSA 14000 has pumped the 16,000-psi concrete required on this project extremely well and has exceeded every expectation I've had. You can tell this powerful machine is made for this kind of work.”
Placing The Right Mix
According to Gaston, there are multiple concrete mix designs being used for the WCC.
“We're using concrete designs varying from 5,000-psi lightweight concrete mixes up to 18,000 psi,” says Gaston. “We have every confidence that CCP and their equipment will easily place every type of mix used on this project.”
According to Bauer, the 5,000-psi concrete mix is being used for the slab on decks, which is a high-early mix. The columns on slab pours use a 12,000-psi concrete mix, and most of the vertical pours are at 16,000-18,000 psi with the exception of a few walls at 7,000 psi and 10,000 psi.
“The 12,000- and 16,000-psi mixes are extremely sticky – similar to lava – and really fight us trying to push them through the pipeline,” notes Bauer, “but our pumping equipment never gives in and easily gets it to the point of placement.”
Looking Into The Future
“Usually developments of this size are found in large metropolitan markets and not mid-size cities like Charlotte,” says Bauer. “We have taken this project as an opportunity to exhibit that our fleet of concrete placing equipment can deliver the results needed no matter how extreme the conditions. As the project progresses further, we will continue to exceed expectations with our equipment.”
As the excavating continues to take place for the mixed-use development, the remaining three placing tower foundations are being prepared for assembly.
With this project just starting, you can bet there will be many more challenges in store for CCP's innovative placing system technology, but have no doubt, their equipment is up to the test.