Pouring concrete in winter. Question..,

[sawtooth]

Ok so our new home is almost finished so its about time to pour the driveway. This in VA so seeing some freezing temps. The contractor says no worries as they use additives to keep things from freezing. So my question is does these additives hurt, make weak, or damage the concrete long term? Should i be worried about this?

Thanks

 

[murphy1244]

I have never seen a Cement Truck out in the cold.

 

[Bigkrank]

They just poured 740 yards in an addition at work last week. I would never pour concrete on frozen ground though.

 

[adirondackmtnman]

Ok so our new home is almost finished so its about time to pour the driveway. This in VA so seeing some freezing temps. The contractor says no worries as they use additives to keep things from freezing. So my question is does these additives hurt, make weak, or damage the concrete long term? Should i be worried about this?

Thanks

I'm guessing that they're speaking of a set accellerator, and if dosed corretly, they should have no impact on the finished product. Do you have frost in the ground? If not, have them throw some blankets over it to keep it from freezing. Anything too cold, I personally would want to hold off until spring.

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[sawtooth]

I'm guessing that they're speaking of a set accellerator, and if dosed corretly, they should have no impact on the finished product. Do you have frost in the ground? If not, have them throw some blankets over it to keep it from freezing. Anything too cold, I personally would want to hold off until spring.

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The top of the ground is frozen right now due to the cold snap that came through. However, we will have highs in lower 60's by weekend so it will thaw out. I know he plans to do it on a warmer day but it till may be around freezing at night. Just worried these so called additives may become a issue down the road as the builder will be long gone by then.

 

[CurlyDave]

I would wait for warmer weather.

There is a divergence of interests here. You want the best outcome possible. The contractor wants to be paid as soon as possible. Never forget this difference.

I have no doubt that he can get an acceptable result in cold weather, although from what you said at first about "additives" he might not be as experienced as you think. He should have been able to name the additive used (out here it is calcium chloride), and specifically what it does.

I am also certain that the result will be better if you place the concrete when it is warmer.

For a general contractor building a spec house, it really doesn't matter when they pour, the result will last long enough to sell the house. OTOH, you really care how good it looks 10 years out.

 

[mark54]

I would not recommend it. Here in the Chicagoland area the readymix suppliers cutoff date for backing up the performance on their product is November 1st as they cannot predict 30 consecutive days of above freezing weather. Wait until spring when the ground thaws and the temps are 40F and rising and you will be fine. I did this work for 30 years and know what I'm talking about. Mark54

 

[adirondackmtnman]

The top of the ground is frozen right now due to the cold snap that came through. However, we will have highs in lower 60's by weekend so it will thaw out. I know he plans to do it on a warmer day but it till may be around freezing at night. Just worried these so called additives may become a issue down the road as the builder will be long gone by then.

The additives are ok, like I said, as long as they're dosed correctly. The admixture and dosage rate should be printed on the batch ticket, and it wouldn't hurt to call the ready mix plant and ask them what they will use. I would prefer a non-chloride accellerator, as it will protect the rebar/mesh from the corrosion a chloride based accellerator will cause. If the ambient temperature during the night hovers around freezing at night, you'd probably be ok due to the heat of hydration. If its a concern, blankets will do a good job. If the contractor is any good, he'll know that. I'd be more concerned with proper subbase prep than the cold right now.

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[adirondackmtnman]

P.S. if you wait, be sure he doesn't come back when it's scalding hot outside, the heat is just as bad as the cold

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[Zick]

I would wait for warmer weather.

There is a divergence of interests here. You want the best outcome possible. The contractor wants to be paid as soon as possible. Never forget this difference.

I have no doubt that he can get an acceptable result in cold weather, although from what you said at first about "additives" he might not be as experienced as you think. He should have been able to name the additive used (out here it is calcium chloride), and specifically what it does.

I am also certain that the result will be better if you place the concrete when it is warmer.

For a general contractor building a spec house, it really doesn't matter when they pour, the result will last long enough to sell the house. OTOH, you really care how good it looks 10 years out.

Excellent advice! :thumbsup:

 

[8N Ren]

Depends on the temp. My buddy poured 40 X 30 in mid October here 3 years ago and the temp was falling to -8°C ( 17 for you guys). Laid insulated tarps over it so it doesn't get touched with frost, no cracks or chips at all.

Where are you located Sawtooth?

Hey Murph! I guess you have never traveled into Canada in the winter lol

 

[aginn]

I have see an inept contractor poor at 10 degrees F and the end product was a spalling product that had to be torn out and redone. Like others have said, if he knows what he is doing, additives can get you a decent product. If he doesn't know what he is doing it will be an immense problem for you. Do you trust the guy enough to gamble with that much money?

 

[Mike476]

The additives won't hurt your concrete, wait for the 60 degree days (that's summer weather for crying out loud ) and you'll be fine.

We built our home through late winter into early spring, poured the footings and concrete walls in Nov before the frost got into the ground, poured the slab after framing / siding etc in Jan, was a coooooold day. That was 13 years ago, still as good as the day we poured it.

 

[timswi]

The additives won't hurt your concrete, wait for the 60 degree days (that's summer weather for crying out loud ) and you'll be fine.

We built our home through late winter into early spring, poured the footings and concrete walls in Nov before the frost got into the ground, poured the slab after framing / siding etc in Jan, was a coooooold day. That was 13 years ago, still as good as the day we poured it.

Same experience here..Was a -26 wind chill when we poured my basement..Right contractor/right supplier, no problem...The trucks lined up outside started to rattle due to the temp...We got it all in and have had no issues 13 years later. Given that the basement was the future home for the furnace, there was no heat during all of this.

 

[msmith1wa]

You have gotten some good advice already. If they do use an accelerator it should be a non chloride one.

Do not let them place the concrete on frozen ground.

The text below is what Washington DOT requires for cold weather concrete placement. Use it as a guide, a lot of what it says is overkill for your driveway, but if freezing temps are predicted overnight I would ask for insulating blankets for at least 3 days.


6-02.3(6)A2 Cold Weather Protection
This Specification applies when the weather forecast predicts air temperatures below
35°F at any time during the 7 days following concrete placement. The weather forecast is
based on predictions from the Western Region Headquarters of the National Weather Service.
This forecast can be found at National Weather Service - Western Region Headquarters.
To achieve adequate curing, the temperature of the concrete shall be maintained above
50°F during the entire curing period or 7 days, whichever is greater. The concrete temperature
shall not be allowed to fall below 35°F during this time. Prior to placing concrete in cold
weather, the Contractor shall provide a written procedure for cold weather concreting to the
Engineer. The procedure shall detail how the Contractor will adequately cure the concrete and
prevent the concrete temperature from falling below 35°F. Extra protection shall be provided
for areas especially vulnerable to freezing (such as exposed top surfaces, corners and edges,
thin sections, and concrete placed into steel forms). Concrete placement will only be allowed
if the Contractor’s cold weather protection plan has been approved by the Engineer.
The Contractor shall not mix nor place concrete while the air temperature is below 35°F,
unless the water or aggregates (or both) are heated to at least 70°F. The aggregate shall not
exceed 150°F. If the water is heated to more than 150°F, it shall be mixed with the aggregates
before the cement is added. Any equipment and methods shall heat the materials evenly.
Concrete placed in shafts and piles is exempt from such preheating requirements.
The Contractor may warm stockpiled aggregates with dry heat or steam, but not by
applying flame directly or under sheet metal. If the aggregates are in bins, steam or water coils
or other heating methods may be used if aggregate quality is not affected. Live steam heating
is not permitted on or through aggregates in bins. If using dry heat, the Contractor shall
increase mixing time enough to permit the super-dry aggregates to absorb moisture.
The Contractor shall provide and maintain a maturity meter sensor, continuously recording
time and temperature during the curing period, in the concrete at a location specified by
the Engineer for each concrete placement. The Contractor shall also provide recording
thermometers or other approved devices to monitor the surface temperature of the concrete.
During curing, data from the maturity meter and recording thermometer shall be readily
available to the Engineer. The Contractor shall record time and temperature data on hourly
intervals. Data shall be provided to the Engineer upon request.
Starting immediately after placement, the concrete temperatures measured by the maturity
meter and recording thermometer shall be maintained at or above 50°F and the relative
humidity shall be maintained above 80 percent. These conditions shall be maintained for a
minimum of 7 days or for the cure period required by Section 6-02.3(11), whichever is longer.
During this time, if the temperature falls below 50°F on the maturity meter or recording
thermometer, no curing time is awarded for that day. Should the Contractor fail to adequately
protect the concrete and the temperature of the concrete falls below 35°F during curing, the
Engineer may reject it.
The Contractor is solely responsible for protecting concrete from inclement weather during
the entire curing period. Permission given by the Engineer to place concrete during cold
weather will in no way ensure acceptance of the Work by the Contracting Agency. Should the
concrete placed under such conditions prove unsatisfactory in any way, the Engineer shall
still have the right to reject the Work although the plan and the Work were carried out with the
Engineer’s permission.

 

[DJ54]

More than likely flake calcium chloride. Used as an accelerator, and for pouring in cold weather. We've used it pouring bridge decks in the winter, so it is acceptable.

They used it in my shop floor two years ago, although it was warm. The driver put it in after he got here. I noticed a few small walnut sized chunks go in. Floor looks great, except one spot/hole that has just appeared over the winter. I suspect it is where one of those small chunks came close to the surface, and just now let go. Reckon' I'll just fill it with some concrete caulking, or something similar when it warms back up.

 

[Danny C]

Concrete should never be placed on frozen ground and should never be exposed to consistent freezing temperatures for the first 28 days or so. It will take nearly that long for the concrete to achieve sufficient strength to withstand the expansion caused by water in the concrete and aggregate freezing.

Calcium chloride should never be used on concrete with steel reinforcement because it will cause said reinforcing steel to rust, which will adventually expand and cause delamination (will take 30-40 years). Calcium chloride is an accelerant that is often used in 1% concentrations in cool weather to expidite the finishing process, etc. A 2% concentration is typically used in below freezing conditions, often with hot water used in the mix, to make sure it doesn't freeze during the hydration (curing) process; that would be disastorous!

For durable concrete, you need to:
1. Make sure the concrete is of sufficient design strength for your area. Call 3-4 ready-mix plants and get their reccomendation for strength. I wouldn't go with anything under 4,000psi and personally would preferr 5,000psi concrete for the minimal price difference.
2. Make sure the concrete is air entrained, which will prevent surface spalling and cracking do to freeze/thaw damage. As will a higher strength concrete.
3. Make sure the water/cement ratio is no more than .40
4. Make sure the finishers do not add water to the mix or the concrete surface while finishing. This will reduce strength, will increase the likelihood for surface spalling and cracking.
5. Get a minimum of 4-5 references from the concrete finisher, prefferably jobs that are 5+ years old that you can go look at.
6. Make sure the contractor introduces Control Joints into the concrete within 12-24 hours after placement, depending on temperature and that they be no more than 10ft aprat and as close to square as possible. The joints must also be no less than 1/4 of the thickness and no more than 1/2 the thickness of the concrete slab. This will prevent plastic shrinkage cracks and will prevent settlement and expansion/contraction joints in the future.
7. Make sure the subbase is adequate for your region. Again, do some checking. A fully loaded ready-mix truck should not sink into the subbase any more than 1/4". When you kick your heel into the subbase, it shouldn't dig in very much at all.
8. Your concrete slab should be no less than 4" thick and if you will be driving or parking anything heay on it, you should consider a slab 5-6" thick.

The hydration process (curing) of concrete is an exohermic reation, which generates it's own heat. If temperatures are just at freezing, you can use calcium chloride and an insulated tarp and will be fine so long as temperatures are not below freezing for prolonged periods of time.

With all that said, having been a concrete professional for over 25 years in the residential, commicerial, industrial and government sectors, I would hold back the money for the driveway and have them install it in the spring when temperatures are consistantly 50F (10C).

My two cents....

 

[adirondackmtnman]

More than likely flake calcium chloride. Used as an accelerator, and for pouring in cold weather. We've used it pouring bridge decks in the winter, so it is acceptable

All the DOT bridge decks here in NYS are placed with coated rebar to avert corrosion, as well NYS spec calls for a non-chloride accellerator. We use a lot of salt on our roads up here in the winter, and it plays havoc with the bridges especially. Given the the OP's climate, I wouldn't spring for coated bar, but I personally wouldn't want the calcium chloride.

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[marcomjl]

Some people over do it on here. Pouring concrete in the winter is nothing new. Inside pours are a no issue. For outside pours every concrete plant adds an additive (calcium chloride) to accelerate the cure. It does not cause any issues at all with the concrete. Also they mix wit hot water. As long as the ground is not frozen (it can be thawed if the contractor has thermal blankets), can be poured as long as it is above 25 degrees. You can go lower but it involves special equipment. On a cold day you can pour first thing in the morning, let it get the sun all day and cover it with an insulated blanked +/- hay on top. Its possible with a good installer who knows what he is doing. If you can deal without the driveway for now don't sweat it and pour in late winter/early spring without a concern.