Concrete Question

Getting ready to pour concrete in a barn with a block foundation and wood siding. The temperature here is near 55 during the day and 32-34 at night. If the concrete is poured early in the day will it cure enough to be ok with the low night temperatures? The block foundation is above grade with the barn built on top pole barn style so the fresh concrete will be shielded from the outside by 1-2 concrete blocks. The wood siding has ¼ in gaps so it provides little protection. If this is not acceptable I will just use the gravel base till weather gets warmer and concentrate on putting metal siding on.

If you pour early in the day it will definitely be good the first night. I would tarp it late the first night ,then scatter straw on top of the tarp for a few days. Have
done this on outside slabs with no problems.

If it must be poured in the cold they can add calcium IIRC ? to aid in cold weather. Ask your concrete dealer about it.

It won't freeze at those temps as the concrete generates heat as it cures,but you might want to spray some water on it about dark and that'll help plus keeping the slab wet will
help it cure out better.

Can't answer the temperature question, but I would advocate waiting till spring for the benefit of moisture. More water in the ground for the concrete to draw from during curing.

although, in a bar the dirt probably isn't very wet to begin with.

Speak to your supplier and ask about the cold weather ad mixture. They'll know if you need it or not, and likely you won't. With this temperature range, it's very likely you won't have any freezing. As concrete hydrates (cures) it will create heat, but with a slab it will be less than something substantially larger like a pier or footing or similar. You don't want the concrete to freeze during that initial cure, once it's hydrated, at lower temperatures, you'll get a slower cure (28 days it takes to reach its design strength). In hot weather, you'll always see on highway or road jobs like bridges, the use of burlap and soaker hoses to keep it from hydrating rapidly. I prefer cooler temperatures for concrete work as you don't have to worry about that.

Placing the concrete early in the day (7:00 A.M.) is ideal under these conditions, it will be setting up and going through the hydration process as the day time temperature rises. You should be able to get to the finishing part at an ideal time as well if you start early. I've had pours that were done in similar conditions, one of which they were on the power trowels after midnight. Had the subcontractor placed the concrete early in the day, it would have been a lot sooner, the colder temperatures just delayed being able to finish.

If you are still concerned, see if you can get thermal blankets and cover the slab after finishing. Might be overkill for these temperatures, but given you are just around freezing, using thermal blankets would insure nothing freezes.

Check with a local contractor and see if you can rent some insulated blankets.

Inside the barn at night it won't get to freezing for quite some time yet.

A whole lot of concrete trucks running here now, last minute jobs. The high is in the mid 30s for the past week now, low is touching the teens.

Here is my understanding:

Concrete when it cures is a chemical process, the water doesn't just dry out of it but it is like a fire, some chemical reactions are going on
slowly.

This chemical reaction creates some heat, so concrete pour at 25 degrees or so isn't such a bad thing. It will warm itself above freezing. As
long as you have something, a frame or a concrete blanket over it to keep the heat from wicking away fast over night. The surface could freeze
up if totally exposed and chip up.

However, after a week or so, the chemical process slows down and less heat is generated, but there may still be a fair amount of unconverted
water left in your concrete. -That- is when it can freeze and hurt your concrete? This is when you really need to protect it from bitter cold for a
few weeks.

At the temperatures you mention, there is no worry about any issues.

But what wil you have in a week, or three weeks from now? Same temps and you should be fine, but if the temp dips down to 10 degrees or so,
you could have issues?

The antifreeze in the water in the concrete is a miserable deal, I would avoid that if I could.

Paul

pour it in the morning and by eve you can cover with hay or straw and let it cure.All depends on just how
cold it gets anything above 25 it will be ok.

Have them add some calcium. Up to your contractor
how much he wants to put in. I believe the
maximum is 3%. Also have him put blankets on it
when he is done to retain the heat.

Hope this helps

Vito

Whenever I've poured concrete when the temp was iffy, the ready mix company has always included an additive if they thought it was needed.

If you are pretty sure it won't get any colder than that I would avoid the calcium and just pour it. It would have to get well below freezing before you would need to modify the cement.

pour it and forget it it will be just fine

Around here they put Calcium in the mix for cold days. The ready mix supplier puts it in as requested along with the number of bags of
Portland per cu. yd. Had a pour job once for my house extension. Contractor forgot to have the C added. We were finishing most of the night
trying to get that stuff to cure.

Here in Idaho we usually use hot water and 2% calcium when it gets colder. Like others have said pour it earlier in the day and by late you will be set up enough that you can actually get on it and cover it.

Steven

i am no expert, but have poured my share of mud here on my farm. Remember mud poured this late will cure much slower. It will harden just fine, just slower. If the ground doesn't freeze neither will your mix. Also keep in mind that cement will make heat as it chemically cures. After it skins over you can lay plastic, old sheets, even old rugs down to protect it. Dont worry, go for it, just dont drag your feet. jack frost is coming soon. A few weeks might drop temps where you have to add chloride. Al

I would pour it . 50? to 55? are perfect for curing concrete. Pour as early as possible have them take the flyash out of the mix (they will charge you more for this) If using a 4000psi mix ,consider a 4500 mix , the use of chloride(you can get as little as a 1/4% up to 2% ) is a great accelerator but is corrosive, so keep that in mind if you are using rerod and wire for reinforcement. If the plant is offering hot water (at a cost) It is usually a good idea. Definitely cover your concrete if exposed to temps below 32?. keep in mind once concrete reaches 500psi set strength (about the hardness for you to walk on it to start finishing) it will go thru a freeze thaw cycle and continue to gain strength.

If it is inside just use a heater to hold the temp above freezing. One slamander heater would do the job and could be started just before dark and be good for the night or put some plastic over it on the foundation above it for the night.
Though I would not fear to much of a problem at that temp. I would guess your bigest issue will be just before daylight in the morning.

concrete should generally be kept at least at 45 degrees for 7 days for it to cure properly. The chemical reaction in the concrete will produce some heat so covering it with thermal blankets or even straw will suffice at those moderate cool temperatures---external heat is also an alternative---be sure to keep it moist for those 7 days for it to develop strength rapidly

I Got the barn finally ready to pour and Got the 14 yards of concrete down today. Just came in. Concrete plant said it would be good down to 25 F. All should be good as the weather is not to turn bad till next Thursday. Thanks for all the advice.

Good to hear. Always nice to go into winter with a project done.