February 25, 2013

Concrete work in colder climates can be challenging

CONCRETE FEATURE

P-BAN ENTERPRISES LTD.

Pouring and finishing concrete becomes more challenging as temperatures drop.

CAROL CHRISTIAN

correspondent

In an area where it's common for temperatures to drop to -42C and lower, pouring and finishing concrete successfully can be challenging.

There’s always the possibility of frozen concrete and frozen chutes. Also, a pump not pumping concrete for even 10 minutes in Fort McMurray freezes.

It’s like when people leave a tap trickling so the running water keeps the pipes from freezing underground, said Garry Jacobson, general manager, P-Ban Enterprises, the largest pump, place and finish concrete company in Northern Alberta.

“It’s the same principle for the concrete pump except when the pump freezes, we’re in big trouble because now we’ve got all these four-inch pipes full of concrete.”

They have to all be folded up, driven back to the shop and put inside the heated wash bay.

When they start thawing out a couple of hours later, every piece of pipe has to be dismantled and washed out otherwise it will harden.

“You’ve lost your boom pipe. That’s a $10,000 hit,” he said.

Also, the pumps have tank heaters in them to ensure the water doesn’t freeze and special heaters are installed in the hydraulic tanks to heat the fluid.

Most of the company’s work is two hours away from the shop.

Once at a site, Jacobson said crews do a boom pre-heat procedure for about half an hour to ensure it is warm enough to accept concrete, otherwise it will freeze as soon as it hits the steel.

Both he and Jason Kraby, operations manager, noted that contract waivers say when it gets below –20C, the customer is going to be responsible for freeze-ups because there are too many things out of the company’s control.

Concrete freezes faster than it sets for the most part, Kraby added.

“We depend on Lafarge and Burnco and Inland to make sure that they’re going to be supplying us with concrete fast enough so we don’t have to stop,” said Jacobson.

Kelly Neilands, ready mix division area manager for Burnco, said the biggest obstacle they face is ensuring the temperature of the concrete is correct when it arrives. The company won’t deliver cold concrete because it won’t set up properly, cure properly and it doesn’t meet strength requirements.

Sometimes there are extenuating circumstances, explained Neilands, such as the distance travelled.

“If we’re being asked to deliver three hours south, and with the wind it’s 40 below, there’s a good chance we can’t deliver within spec,” he said.

There’s also the same equipment challenges any operator faces in cold weather.

“We ensure we park everything inside and we ensure everything is fully operational before we pull it out. We heat up all the oils, hydraulic systems. If it becomes a point where our hydraulics are starting to squeal, then we know they’re working too hard and we’re going to make some decisions based on that,” he said.

The size and scheduling of some oilsands projects results in winter pouring.

Jacobson said some of P-Ban’s customers intend to have their plants operational by spring or summer, meaning work such as concrete finishing has to be done in the winter.

The size of those projects can be challenging for heating and hoarding.

They have to build a tent-like structure that has to be fairly lightweight and relatively quick to put up and dissemble. It has to also withstand winter storms and winds.

The construction of the hoarding has to be large enough to cover the pour area and then some to ensure adequate coverage. The concrete could be frozen five minutes after its poured.

When concrete is frozen and thawed, it can become crumbly and dusty or have Jack Frost designs in it instead of a smooth trowel finish.

With heat pumping into the hoarding, it’s almost uncomfortably hot.

In the winter, air movers are used to reduce humidity and power trowels are used for finishing, but even with exhaust scrubbers, carbon dioxide and carbon monoxide build up.

“Our guys wear gas monitors so they know when the exposure to carbon monoxide is there,” said Kraby.

However, when the doors are opened to let fresh air in, a chin-level fog bank is created when that chilling breeze meets warmer air.

“You can’t see the floor,” he said.

The company asks the customer to create a ventilation system using frost fighters to pump heat into the building to create positive pressure, pushing the exhaust fumes out through a roof hatch or window.

Around October, P-Ban starts circulating cold weather information sheets to all its customers, informing them of the requirements for cold climate work, whether zero to –20C or from –20 and below.

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