Crews in Calgary were busy on the weekend with the country's largest continuous concrete pour of a building foundation.

About 1,000 truckloads of concrete were used for the building's foundation. (CBC)The record-setting work is for the Bow office tower, which will become the new office building for oil giant EnCana. The pouring of 14,000 cubic metres of concrete — enough for the foundation of 2,800 homes — began Friday night and was to continue through Sunday.

"This is probably the biggest milestone we will achieve this year, and that's pouring what we call a raft slab," said Michael Brown of developer Matthews Southwest.

The slab will take 36 hours to pour and in the end will cover 2,787 square metres (30,000 square feet) at a depth of about three metres.

"When you include reinforcing steel, the concrete supply, the pumps, everything that's happening, it's about a $10-million foundation," said Kerry Gillis, senior vice-president of Ledcor Construction.

The foundation alone will cost an estimated $10 million. (CBC)Over the next three years, more than 500 workers will be building the 58-storey building. The projected final cost is expected to top $1.1 billion.

Mayor Dave Bronconnier has called the project on the east side of Centre Street "very ambitious" in a city with a very robust economy.

"To have a project with this size, scope and magnitude delivered on time, that is very impressive," he said.

Only two other continuous pours of concrete have ever been bigger — one in Dubai for the Al Durrah Tower and another in Las Vegas for the Howard Hughes Centre.

When completed, the Calgary building will be the tallest single-tenant office tower in Western Canada.