They're ready to do the concrete rumble on Arch Street.

Contractors for Comcast Corp.'s new skyscraper on the 1800 block will pour 400 truckloads of concrete over 10 to 12 hours beginning early Saturday for a 10-foot-thick, 15-million-pound foundation mat.

This foundation mat for the city's tallest skyscraper will attach the building's structural support - its core - to city bedrock.

Officials said Thursday that it will be one of the largest concrete pours in city history.

Comcast announced the plans for the Comcast Innovation and Technology Center in January. Liberty Property Trust is a 20 percent owner in the project and the tower's developer. Comcast owns 80 percent.

Foster & Partners of London is the architect for a "vertical stacked campus" that seeks to replicate suburban-style offices in a high-rise. Thornton Tomasetti, one of the world's leading firms for developing skyscrapers, designed the structural engineering for the new tower from its Philadelphia office.

The building will be 59 stories tall, or 1,121 feet, and topped by a 222-room luxury hotel.

"Rain or shine, we're pouring concrete," said Fran Pietrini, president of B. Pietrini & Sons, of King of Prussia, the concrete contractor for the $1.2 billion project.

"Once we start the pour, we have to make sure it is in a fluid state. You can't let it [the concrete] get hard, so it needs to be a continuous motion."

A crew of 40 to 50 workers will pump the 4,000 cubic yards of concrete into the foundation and smooth it, removing inconsistencies and potential weaknesses. Contractors say wet concrete is not to be layered onto dry concrete.

Prep work will begin at the construction site at midnight Friday and the concrete pouring will begin at 2 a.m. The 1800 block of Arch Street is expected to be closed for the duration of the concrete pour. That stretch is planned to reopen at 5 p.m. Saturday, officials said.

SJA Construction, of Philadelphia, and Action Supply Co., of Sharon Hill, will supply the concrete, and B. Pietrini will operate four pumpers to deliver the concrete to the foundation mat.

To make sure there won't be an interruption in the flow of concrete to the site, SJA and Action Supply will produce the concrete in plants in South Philadelphia and Port Richmond and two in Sharon Hill, officials said.

There will be 50 concrete trucks making the 400 deliveries, with about two-thirds of the trucks coming down Arch Street and the other third approaching the construction site by 19th Street. At any given moment there should be about six concrete trucks emptying their loads.

B. Pietrini, which has 14 concrete pumpers, including a new one for the tower's construction, will have an extra pumper at the construction site on Saturday for an emergency.

If all goes smoothly, the concrete pour could be done in less than 10 to 12 hours, Pietrini said.

"This is a dream job we got," he said. "It's a very big pour."

BY THE NUMBERS

The new Comcast tower will be 59 stories tall. Building the foundation mat for the structure will involve:

400

Truckloads

of concrete.

10

Thickness in feet of foundation mat.

15M

Weight in pounds of foundation mat.

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