For a continuous concrete pour to be successful, all the different participants in it must coordinate with pinpoint precision. When that coordination must extend 24/7 over eight-and-a-half days, perseverance must be added to the mix. 

“All of the concrete trucks are logged with the time they are batched and then the time they arrive at the job site,” Continental Construction Project Manager Jim McKnight points out. Continental Construction is the prime contractor on the construction of 15 concrete silos being built on the Gulf Coast for the Port of Gulfport in Gulfport, Miss. Chemours, which was spun off from DuPont, will lease the silos from the port. The silos are designed to hold ilmenite, iron titanium-oxide and other raw materials that are used in the production of titanium dioxide pigment, a whitening agent in paints, paper and plastics. The construction cost for the concrete silos is approximately $44 million.

 The slip form pour for 12 silos that are 139 feet tall began July 7 and was completed in eight-and-a-half days. The pour for the other three that are 159 feet tall began July 20 and was completed in nine-and-a-half days. The combined capacity of the new silos will be approximately 183,000 tons.

Approximately 550 people worked on the 12-silo pour for approximately 200 hours, half of them on each 12-hour shift. Another 250 people worked for approximately 225 hours during the three-silo pour. Outside of the silo pours, approximately 100 workers were on the site fabricating steel for hoppers and preparing forms. 

Foundation First

Before the silos were poured, Continental Construction began pouring their foundations Jan. 21, 2015, over piles constructed by another company. The foundations were completed by spring, and preparation work and form construction for the silos extended until the month of July. 

A total of 8.8 million tons of rebar were delivered for the project, and 45,000 yards of concrete were poured to build the silos, their foundations and ancillary structures around them. A joint venture of two local companies, Bayou Concrete LLC and Gulf States Ready Mix, supplied the concrete from plants that were eight to 15 miles away from the site. “A pour of this size does not come along very often,” McKnight says. “This is the largest slip form project that we have been awarded.”

The concrete was pumped up to hoppers on the silos, discharged into buggies, rolled to the site and shoveled by the workers. This technique was necessary because the forms were too complicated to pump the concrete directly in. Additionally, the final height of the silos exceeded that of the pumps. 

The project had five subcontractors who worked on the silos. “We had subcontractors that slipped the concrete walls for the three silos, placed the large foundations and some of the interior columns and slabs for us, performed field erection of the steel hoppers and multiple subcontractors that placed reinforcing steel,” McKnight says. 

The silos were topped off with concrete decks supported by steel beams. Continental Construction is continuing to pour concrete for interior columns and elevated slabs and doing formwork until the scheduled completion in April. The project is being managed by the joint venture of Yates/Anderson with Brown, Mitchell and Alexander Inc. as the lead design and engineering firm.

Samples Tested

Quality was assured at every step of the pour. Samples of the continuously poured concrete were taken every 100 cubic yards and poured inside a cylinder for compressive strength tests. These tests were performed seven and 28 days after the concrete hardened inside the cylinder to confirm that the required 5,000 psi of compressive strength was being met.

The timing of the project was challenging. “It was a construction schedule that we felt was aggressive,” McKnight concedes. “Since our initial planning, we’ve remained on schedule.”

McKnight is pleased with the way the pour was completed. “The greatest success was the people that were on the project,” he emphasizes. “We had a lot of good subcontractors and suppliers that helped us out. It was a joint effort by key personnel onsite and in the office.”