Toronto Four Seasons Hotel and Private Residences Toronto | 203.9m | 52s | Lifetime | a—A

Why is the rebar so dense?

Technically speaking, that rebar is no more dense than the thinnest 10M bar as it's all made out of the same steel.

Obviously you're referring to its large diameter. I believe that the rebar shown in that picture would be used to anchor the foundation into the bedrock, and not to construct a rebar cage for use in reinforced concrete.
 
He could've meant the density in terms of the apparent narrow spacing between bars as well. In the one picture it does appear as though the bars are very tightly spaced in the mat.

And there are different grades of rebar, so the density of the bar itself can vary. Offhand I know there's 300R, 400R, 500R, 400W and 500W. There's a mark on every piece of rebar, close to the end, that tells you what it is.
 
From National Post on November 29

Yorkville turns into a concrete jungle today

At 7 a. m. today, an armada of trucks carrying concrete will descend from three directions on Yorkville to begin the Big Pour: the continous filling-in of a deep hole at the corner of Bay Street and Yorkville Avenue, in one of the most ambitious single-day construction projects in Toronto.

After two months of planning, 120 trucks and 180 workers will lay the 10,000-tonne foundation of the Four Seasons Hotel and Private Residences in Yorkville over 12 hours. The 4,100-cubic-metre area will be filled at a rate of 500 cubic metres per hour.

The finished building will be a 55-storey, 356-suite skyscraper housing condominiums and a hotel.

"It's a special project," said a very excited Paul McMurray, project manager at Menkes Life Storeys construction company.

"Since the planning stages, we've been online comparing what we're doing to other projects, and there doesn't seem to be anything out there that compares to this.... I'm watching it all come together out my office window, and seeing how it's moved along and came together has been super exciting."

Six trucks will be backed into six pour locations around the site shortly before dawn, while the rest of the trucks will either be on the road or loading up at three concrete plants in Toronto and Newmarket.

Between 40 and 50 trucks will unload at the pour site each hour. Seven police officers will control their movement.

They are not unloading just any kind of concrete. Called Agilia, the concrete is self-levelling, but has never been used on such a large scale. It had previously been used for a project laying 1,200 cubic metres of concrete, but the Four Seasons pour will require almost four times more material.

Despite the new technology, Mr. McMurray anticipates no problems.

"It's special because it doesn't require mechanical compacting, it just levels out on its own and it's done. We just have to keep filling in the void."

The project will shut Yorkville Avenue between Yonge and Bay for the 12-hour period. Davenport Road, Scollard Street and Yonge Street will all experience heavy volumes of traffic throughout the day, as the trucks will be continually running between the construction site and the three concrete batch plants.

"The sooner we get this work done, the sooner we can get this street open," said Angie Antoniou, the city's manager of Transportation Services.

"Rather than doing this in smaller groups, they get the closure so it's easier for them to come and go. It's compressed but there's a lot more activity happening."

Planners made sure to prepare for all eventualities, including fickle weather. The temperature of the concrete mix will be controlled at the plants. The company decided to do a single, large-scale pour instead of many smaller projects to avoid interfering with Yorkville's heavy holiday traffic.

"If we did this project in two parts, I believe we wouldn't be allowed to do any work requiring closures in December," Mr. McMurray said.

"Once we calculated and planned and finally discovered we could do it all in one go before the real Christmas rush starts here in Yorkville, we just went all out with this very ambitious plan."

http://www.nationalpost.com/news/can...tml?id=1008475

Pictures of the event can be found at SSC:

http://www.skyscrapercity.com/showthread.php?t=267216&page=38
 
December 9 2008 update

that's one BIG hole ... seems like excavation is completed and work has coimmenced on the first parking level (P__ whatever that is ~) :D

IMG_2857.jpg
 
Caught this Nov 30

I can't remember seeing a pour like this in some time. I counted 30 trucks on site with more arriving.

3073625954_5ac240096d_b.jpg
 

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