Concrete put to test

Hey there, time traveller!
This article was published 09/10/2010 (5715 days ago), so information in it may no longer be current.

111It’s pure simplicity: Water and cement are combined and as that hardens, a stone-like material is left behind. Its performance qualities and malleability make it perhaps the most perfect building material ever.

And at the Canadian Museum for Human Rights, concrete was put to the test.

In all, PCL Constructors, the general contractor, will pour more than 18,000 cubic metres of concrete at the museum site; 5,000 cubic metres alone in the form of poured caissons and precast piles will be used in the foundation.

But it is not the magnitude of the concrete that makes this project special. It is the size and shape of some of the concrete forms.

One wall, referred to as the east wall of Route D, one side of the Buhler Hall, is a section of an upside-down cone. That means the concrete is not only curved, but it is smaller at its base than at the top and tilted at a precarious 23 degrees. Pouring this concrete required meticulous planning and a steady patient hand.

Concrete is typically set by pouring it into forms made from sheets of plywood. Steel rebar is set into the concrete to give it extra resilience. For the museum, special hardware and supports were used to hold five-metre sections of plywood in place and these are further supported by super studs, enormous expandable metal posts that are bolted into the floor and then used to support the walls as they are built up. As each section sets, the studs are put in place, and the forms are moved along, and then up, until the wall is completed. The super studs remain to hold the concrete in place until permanent steel supports are installed.

The same process was used for the Hall of Hope, or the wedge canyon as the construction team calls it. Tall concrete structures are typically erected floor by floor. This means that after one floor of concrete is poured, steel is tied in to the top at right angles and then the next floor is poured. This process could not be used for the Hall of Hope.

This towering concrete valley was built, without steel supports, to a height of 57 metres. This also required PCL to steady the looming concrete walls with temporary supports, which are then strategically removed as primary supporting steel is put in place. The hall was given an extra dramatic feature with the addition of graphite to the concrete mix, giving the walls a sombre black tone. White alabaster ramps, lit from within, criss-cross the canyon.