The producer used high-range, water-reducing and superplasticizing admixtures in producing the SCC. Standard Concrete's engineers relied on the polycarboxylate polymer technology and formulation to provide maximum water reduction and extended slump retention at low dosages.
The admixtures were a critical part of Standard Concrete's mix design that also yielded a number of benefits to hardened concrete. These include higher ultimate strengths for greater engineering design flexibility and structural economies, more durable, dense concrete with reduced permeability, and fewer surface defects.
Using SCC reduced the time required to cast the beams, virtually eliminated the need for vibration equipment and associated noise, and significantly reduced dry-finishing costs. The concrete was specified to 6500 psi for release and 8500 psi at 28 days. Actual strengths averaged 7000 psi within 15 to 18 hours of being cast, and 13,000 psi after 28 days.
Slump flow was 22 to 26 inches, air content 3% to 6%, maximum temperature 95° F, and yield ±2%. Crews conducted static-segregation and J-ring tests throughout the project. The concrete also easily passed a specified Mustafa Pull-Out or stand-bond test.
The producer recognizes the benefits of SCC and now plans to use it in more mix designs as more designers across the country become more comfortable with it. “The concrete met all of our specifications, and the beams looked great,” says Pieterse. “As a result of the reduced waste, speed of construction and increasing acceptance of self-consolidating concrete, we're using it whenever and wherever possible.”
Standard Concrete Products also used a new, full-bed-length rolling form system to cast the prestressed beams. When the concrete reached its release strength, the forms were opened hydraulically, rolled to the next bed, and set up for the next pour. The beds were inline, so a crew could roll the form easily to the next bed in just 30 minutes.Barge transport
Another key to the producer's on-time performance was a unique transportation system. The company's production facility has deep-water access on the Theodore Industrial Canal on the west shore of Mobile Bay. Production crews can hoist the beams from inventory storage directly onto delivery barges.
The Biloxi Bay Bridge project required more than 100 barge trips, each carrying five to seven beams. This is the norm for the producer, which ships about half its products in this manner, anywhere from Louisiana to Florida, and up the Mississippi River to Vicksburg, Miss. “It's much more economical than road transportation,” says Pieterse. The producer outsources all of its barge operations.
Production crews worked under tight delivery schedules. Tug boats pushing two barges at a time took 10 to 14 hours to move the beams from the plant to the jobsite, where crews unloaded them and placed them into position.
“This helped us reduce transportation costs,” explains Pieterse. “And the combination of the prestress strand design, efficient forming system, and self-consolidating concrete allowed us to accelerate the production schedule and stay ahead of schedule.”
Although the Biloxi Bay Bridge was a high-profile project, Standard Concrete Products is manufacturing concrete for other Hurricane Katrina-related projects along the Gulf Coast, from Panama City, Fla., west to Louisiana. These include major piers and marinas. And this goes on while the producer itself battened down the hatches for Hurricane Gustov this past Labor Day weekend. The pre-cast plant did not have to ride out the monster hurricane three years ago; it was built after Katrina struck.
Bruce Strickland is national marketing manager for Sika Corp., which provided the admixtures used on this project. For more, visit www.sikaconstruction.com. For more on Standard Concrete Products, visit the producer's Web site at www.standardconcrete.net.