[Xelebes]

I was walking downtown on Saturday (I wasn't alone!) and I saw the construction site of the YMCA building. I found it odd that they were pumping cement in very non-ideal weather for cement-pouring. It was -10 C and there was snow forecasted later in the evening.

I work in the cement industry on the manufacturing of cement products (more specifically grouts and floor hardeners). I know that pouring concrete in subzero weather has many risks such as the concrete freezing, longer curing (hardening) times and threats of expansion-contraction cracking. So I was definitely concerned about the lack of heating units used to warm the concrete as it cured. I didn't see any.

Anyone care to comment on this?

[Kelvin]

What type of structure were pouring - slab? columns? mass pour? For example on an unreinforced mass pour, they may have decided it wasn't necessary and just let the natural heat of hydration take care of it. For caissons or grade beams, they may be able to just cover them with insulating blankets (however the ground should be thawed out prior to pouring). For just about anything else, they could have a real problem!

[Xelebes]

Not sure, I didn't really notice if there was rebar or not. Too busy looking for insulation or heating units. :)

[texcolo]

I test concrete for a living. The coldest I've tested in was 20 degrees Fareheit, and I was concerned about that. But, it was for an outdoor stairwell that was protected by a heated tent.

Some contractors will work in any circumstances.

[Kelvin]

Most specifications, esp. any in Canada or other northern climates, write in wording to either prohibit cold weather concrete or at least ensure that suitable measures are taken to protect it.

[Liz]

I saw sonmeone pouring a foundation the other day (about 20 F) without any warming blankets or measures to defrost, I feel like warning any potential buyers of that condo.

[Coldrsx]

Here in Edmonton, and that might be the YMCA in ref above, i know they can pour to ~ - 25 C.......with the right additives and heat/blankets.

[Xelebes]

I know the additives that they are supposed to use, but using that type of concrete gets rather pricey.

[Hardhatdan]

Usually what happens is they heat the slab from the underside. This is only not possible when pouring the lowest slab. I know last year I was doing pour watch on my sleeving and it was around -25 C.

[theWatusi]

I used to work for a McMansion Sprawl Building here in PA as a Job Super. Managment had us pouring foundatation walls in all weather. Schedule was king. Although anything below freezing we had the concrete subs order addatives from the batch plant and cover the forms with blankets when the pour was of, Leave the panals on for an extra day, Extra cure time before framing ect...

Hell we would dig a hole for footers in zub freezing and have the laborers cover the dirt with a mat of STRAW to protect from frost before the footers went in.

I would never ever in a million years pay over $500k for a home that was started in the winter.

No matter what the builers rep was.

[Dr. Smoke]

It's OK to pour ICF walls in this weather, but not good for any decks, and I don't care what admixes. Why isn't the City doing their job?!

[Calgarian]

Concrete generates a lot of heat when it cures, that's how they can cast it in freezing temperatures.

[Seasun]

This is the reason project owners hire 3rd party "special inspectors". On projects I've worked on the concrete and steel inspectors are the "eye and ears" of the city building department and the project structural engineer. They make cylinders of concrete during the placement of concrete and those cores should be stored for a few days in the about the same conditions as the permanent concrete is experiencing. Break tests indicate if the concrete is up to strength. Not an exact replication of conditions but a good indication.

During sub-freezing weather concrete plants use warm/hot water (plus admixes) just like during hot weather - ice is added to the mix.

[Robert Pence]

Concrete generates a lot of heat when it cures, that's how they can cast it in freezing temperatures.

Massive pours like dams sometimes have cooling pipes embedded to control the internal heat build-up from hydration.

[someone456]

Placing concrete in freezing conditions can be done, as long as there are procedures in place to deal with the conditions. These procedures are always reviewed by the Project Structural Engineer. The suspended slab forms require heating from below to ensure fresh concrete doesn't freeze from below. Also, the slab perimeter should have wind breaks installed to keep the surface from freezing. In milder cold weather, walls and columns might only need to be wrapped in insulated forms. In sustained freezing weather, the forms would need to be constructed with insulation panels. And the concrete is usually a special mix design that is suited to cold weather placement. It is usually cheaper to continue with construction than to shut down a site for 3 months. Also, the structure is the best thing to do in cold weather in regards to the overall construction process. The last thing you want to do in freezing weather is envelope work. All hand work that requires perfection or else it leaks.
My two cents.:tup:

[ReginaGuy]

Its done all the time here. You just need to use a cement with a moderate heat of hydration, maybe some admixtures, and a heated tent. There's no problem with pouring in sub-zero temperatures, either than the fact that more compicated and expensive

[harryc]

The Trump tower here in Chicago did'nt seem to miss a beat all winter, I don't recall the tower across the way stopping for the cold either. They do put blankets on.

The foundations for Waterview and 300 N LaSalle in Chicago were also put in during the winter.


The slideshow http://picasaweb.google.com/harry.r.carmichael/400DearbornHubbard shows a tower going up in Chicago.

From Jan 12 to Feb 12 ( some bitter cold ) the pace slows, but other than that it looks pretty consistant

[1ajs]

when it goes below -30 its insane to poor concreat

[nnnagig]

I want to use huge piles of sculpted snow as concrete forms, using rebar and some kind of poly film. Any thoughts? Of course a tent with heat will not work for me

[Kelvin]

The concrete will reach 60, 70, 80-Centigrade during the cure. I suspect your snow and ice wouldn't fare too well under those conditions.

[Glazier Man]

Concrete generates a lot of heat when it cures, that's how they can cast it in freezing temperatures.
I have heard many opinions on casting concrete in cold temps....you sure can tell who the engineer wanna be types are, and the ones who have hands on knowledge and understanding.

I agree with Johnny on the internal heat of curing concrete, as well, others have added value with thier input, i.e., insulating blankets and use of propane, or natural gas heaters under slab, insulating columns with straw, hmmmm, sounds a little primative, but I can imagine that it would work, as straw/hay also reacts and generates its own internal heat as well. Bottom Line...Building Erecting does not stop because it is raining or snowing out!!

P.S., Glazing in sub zero temps, well I can remember last year, winter of 2007 I think the air temp was -29 c, with the wind chill was -43 c, and yes, I was still outside Glazing. Damn Slave Driving Boss. I have since found another Glazing Company to work for.

[harryc]

Dec 7 - 2007 - Chicago Spire ramp.

http://lh5.ggpht.com/_8TC_VUmf9Fw/R1lQJeyiqhI/AAAAAAAAQWA/vDu_g-e_FoA/s800/P1150054.JPG