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How is Concrete Poured for Skyscrapers?

Thanks to innovations in concrete, it seems like buildings are getting higher and higher every year. For the longest time, the CN Tower was the tallest free-standing structure in the world; now, it’s in the ninth spot! The Burj Khalifa in Dubai now claims the crown of the tallest structure in the world, with a height of an astronomical 2,717 feet (not counting the antenna). As opposed to the CN Tower, which can’t hold much more than an observation deck, the Burj Khalifa is a building that combines residential and commercial spaces.

It’s an impressive building, but this record could very well be broken soon. Whether or not that happens, the future of buildings still lies in the material that gave the CN Tower and the Burj Khalifa their strength: concrete. To get that concrete all the way up to floor 163, builders have had to use a lot of innovation.

 

Getting Concrete Into The Sky

Most skyscrapers are built around a steel frame, enabling them to go taller than typical buildings made from load-bearing walls. To get the concrete up to the floor where it is laid in place, builders use concrete pumps that get ready-mix concrete up through pipe. A team assists the placement by controlling a flexible hose on a boom while someone on the ground operates the pump.

As the building goes higher, pipes are added to reach the tallest floors. The construction of the Burj Khalifa broke this record when it pumped concrete 601 metres! The pipes also have to be cleaned regularly to prevent hardening, and solid piping made with thick walls is used so that it doesn’t break down as tons and tons of concrete are pumped through it on their way to the sky.

 

Do Skyscrapers Need Different Concrete?

The concrete has to be reinforced, which is when the concrete mixture poured around steel rebar. Reinforced concrete is strong in the face of compressive forces, but the weight of extraordinarily tall skyscrapers required advancements in concrete mixtures. For instance, to build the Burj Khalifa, builders needed 330,000 cubic meters of concrete! To bear all the weight, a mixture designed to have a high compressive strength has to be made.

Concrete is three simple ingredients: water, Portland cement, and an aggregate. The aggregate used can help create different strengths. In the construction of the Petronas Towers in Kuala Lumpur, Malaysia, the planners found that by adding very fine aggregate to the usual concrete ingredients, the tiny particles had an increased surface, making a stronger bond that would hold the weight.

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