Solidifying the Future
Concrete Innovations Across the Country Get the Job Done

By Candy McCampbell, contributor, South Central Construction. The McGraw-Hill Construction publication can be read online by visiting www.southcentral.construction.com

Concrete Domes in Birmingham
The $16.5 million activity center project at Faith Chapel Christian Center in Birmingham, Ala., is unlike the majority of church expansion projects.

This one requires the construction of six monolithic concrete domes totaling 120,000 sq. ft. across 16 of the church's 140 acres. The additions are being built next to the church's existing 87,000-sq.-ft. domed sanctuary, the largest single dome in the country at the time of its construction three years ago.

The new domes - three are 144 ft. and three are 164 ft. in diameter - will house a children's play area, entertainment areas complete with a pair of NBA-size basketball courts, a 12-lane bowling alley and commercial kitchen and a connecting lobby.

To build the domed roofs, construction manager Monumental Contracting Services of Birmingham, Ala., and contractor South Industries of Menan, Idaho, install a roofing membrane - called an Airform - on top of the wall forms. Polyurethane foam is then applied to the interior surface of the membrane, which then acts as a base for attaching the roof's reinforcing steel.

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Work is currently under way on the fourth dome, which will be inflated this month, said William Robertson, president of Monumental Contracting Service.

"You have to have constant air pressure to keep it inflated, and you have to inflate it 24 hours a day," Robertson said. "The contractor has to monitor the intake and outflow to keep the pressure even."

To access the air structure, the contractor must enter through a double door airlock, which keeps the air-pressure inside at a constant level. Steel-reinforcing rebar is attached to the foam using a specially engineered layout of hoop and vertical steel rebar.

Shotcrete - a special spray mix of concrete - is applied in 1-in. layers over the mats of reinforcing steel. Some areas of the dome can be as much as 24 in. thick, he said.
Drying time varies, depending on the circumference of the dome, but usually two layers can be applied each day.

Robertson said the side walls for each dome - built in the same way with layers of shotcrete and steel mesh - range from 10 to 14 ft. high, depending on the building's use.

The monolithic layered-construction method required about 575 cu. yds. of concrete per dome, or 3,450 cu. yds. for the project. Each dome also requires about 55 tons of steel, or about 330 tons for the project.

Construction of a dome takes about two months from start to finish, Robertson said. The last one should be completed by June, when interior finish work will start. The entire project is scheduled for completion in December.

LPDJ Architects LLC, of Salt Lake City, Utah, is the architect for the center.

"The uniqueness about this client is they are an all-cash deal," Robertson said. "There is no debt service."

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