Concrete Trends

An old construction standby, concrete adapts to changing needs and markets.

By Debra Wood

Blending additives to create a specific mix allows concrete to offer versatility for a myriad of applications, and recent market changes make it readily available and increasingly cost competitive.

“Block, tilt-up or poured-in-place seems to be gaining market share in commercial [construction],” says Bob Sitter, president of the Florida Concrete & Products Association of Orlando. Sitter credits some of the demand on Florida’s hurricanes and recent tornadoes. Concrete has proven to withstand wind loads better than other materials, sparking renewed interest in the product for residential and commercial applications. He also indicates no shortages of cement or concrete products.

The housing slump has dropped demand for concrete by 15 percent to 18 percent in Florida. Concrete sales for commercial projects have picked up about 8 percent to 10 percent, Sitter says. He adds that the Florida Concrete & Products Association’s print advertising campaign to pump up use of concrete block in office and retail construction has worked better than the organization expected.

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Nuclear Containment

In February, at Florida Power and Light Co.’s St. Lucie nuclear power plant on Hutchinson Island, Fla., Rinker Materials of West Palm Beach participated in a six-hour, 70-cu-yd monolithic pour of a cask handling facility. The team used pre-engineered forms for the 18-in.-thick, 17-ft-high, heavily reinforced walls.

“Radioactive materials may be handled on one side of the wall while other work occurs on the opposite side,” says Rusty Hurt, site project manager for FPL. It was the first large wall pour at the plant since the early 1980s.

The mix contained 0.5 percent boron carbide to provide shielding from two different types of radiation and superplasticizer to ensure flow through areas congested with No. 9 rebar at 11 in. on center on both faces of the figure-eight-shaped wall.

The pour was scheduled on a Saturday due to decreased traffic on the roads and at the plant, and it took place inside the facility’s security area and the radiation-controlled area. Further complicating the work, the morning selected turned chilly, with the temperature hovering at 35 degrees. The cold required close control of the pour rate, which was held to 4 ft or less per hour.

“The colder it is, the higher the pressures are [on the forms] because the concrete doesn’t have time to set up when the layers on top of the layers are being placed,” Hurt says. “We had to closely control our pour rate to make sure we didn’t damage forms.”

Underwater Condo Pour

At the 14-story Capri condominiums on Biscayne Bay in Miami Beach, Rinker Materials completed a three-phased underwater concrete pour for subcontractor Nicholson Construction Co. of Cuddy, Pa. G.T. McDonald Enterprises of Plantation, Fla., is the general contractor.

The underwater pour plugged the bottom of a 30-ft. excavation, explains Brian O’Gara, business development coordinator with Nicholson. The water could then be pumped out.

Ryan McCormack, area manager for Rinker Materials, says that the contractor used an underwater pour because it was more economical than dewatering the site.

Crews began by removing all debris and dirt until reaching bedrock, 11-ft. below sea level. Then the contractor drove sheet piling to act as the garage walls for the one-level parking garage.  

The job consisted of an elevator pit pour, followed by a 4-ft. seal placement of approximately 6,200 cu. yds. of concrete on December 2 and 3, and an additional 1,800 cu. yds. on December 19. The concrete is piped to the bottom.

“They have divers down there almost 24 hours a day to monitor the flow of the concrete to make sure it is level and smoothing itself out,” McCormack says. “It took four to six divers. They came up every half hour or so.”

Once the seal pour cured, crews drained the water and inspected the seal for any cracks or leaks. Then in January, when it was completely dry, crews placed a 7,700 cu. yd., 4-ft. structural mat foundation during a 30-hour pour. The structural mat consisted of two different mixes. Half contained a waterproofing admixture called Penetron, produced by ICS Penetron International, and the other did not, because the contractor decided to use a conventional betonite waterproofing system on half the pour negating the need for Penetron. Both mixes reached 5,000 psi in 28 days. The structural slab became the garage floor.

Pervious Pavement

Porous concrete, created with air voids, allows water to drain through it. Rather than water flowing off a parking lot into lakes or wetlands, it flows through the concrete to the soil below.

“Environmentalists like it because it traps a lot of impurities,” says Sitter of the Florida Concrete & Products Association. “Developers like it because in a lot of areas of the state they get credit and don’t need as much land put aside for water detention and retention. More is useable for parking and the building.”

The mix design is more expensive because it uses more cement.

Sitter says that its use is picking up speed. The Florida Concrete & Products Association will pave its new headquarter’s 40-space parking lot with pervious concrete.

Highways

Sitter says an expansion of Interstate 95 in Brevard County, Fla., will use concrete and be the state’s largest concrete highway project in 20 years.

“With the price of oil skyrocketing, the cost differential has gotten less in the last couple of years.

In December, the Florida Department of Transportation awarded Kiewit Southern Co. of Sunrise, Fla., the $148 million design-build contract to widen a 12.4-mi section of I-95 in Brevard County to six lanes. The project also includes some asphalt pavement.

On Interstate 75 in Bartow County, Ga., Archer Western Contractors of Atlanta is milling out 18-in. of asphalt and replacing it with concrete. The concrete inlay technique is used when problems develop deep in the asphalt, says Allan Childers, Georgia director for the Southeast chapter of the American Concrete Pavement Association. 

“If you are going to take out the material deep, it’s better to put back something that will last three to four times as long,” Childers says. “Concrete typically lasts 30 to 40 years plus, asphalt seven to 10 years on the interstate system.”

A milling machine removes the asphalt. A second machine comes behind and places the concrete, which contains an accelerant, so it sets up faster. Within four to six hours, traffic is back on the road.