weather and concrete?

[phantom309]

These great threads on concrete have me wondering...:

I'm starting on a pole barn. Am currently putting in the poles and will follow a little later with a concrete slab.

Q1) Is it a problem if I pour concrete in the post holes when it will freeze later that night? FYI, generally in these parts, our normal freezes are mid 20's or higher.

Q2) After the poles are in, I'm going to put up forms, then rough in the plumbing, set the rebar in place and then pour the slab. During the process it will be impossible to recompact most of the pad which was prepared with 200yds of select fill and compacted.

We will likely get some rain and/or snow before the slab is poured. Do I need to be concerned what this will do to the compaction of the pad? Especially so when the plumbing and/or rebar goes in which will prohibit any additional compacting?

Is it OK to just wait out the weather and then pour when conditions are OK or will I have problems due to the rain, snow, etc on the pad since it was compacted??? (fingers crossed) Surely it's not necessary to do all of the dirt, plumbing and concrete work without any wet weather in between?

Thanks!

Mark

 

[cowboydoc]

I wouldn't pour concrete when it's going to freeze. Your concrete will crack and won't be much better than just filling your holes with dirt.

You REALLY need some heavy compaction BEFORE you put any kind of concrete down. If you don't have an extremely solid base it will shift and ruin your concrete.

I would definitely be very concerned with rain and snow. With frost heeving and the compaction effect putting water on will have I think you will have a big problem. Can't you wait to put the plumbing and all in when it warms up? That way all frost heeving will be done and you can recompact and do it right.

 

[phantom309]

Hey Cowboydoc-

Thanks for the note. The pad was put down and compacted well. Spent a few days running a 20K lb vibrating sheeps foot compactor back and forth over it as the fill was brought in and spread. Dirt guys are guessing 98 - 99% compaction. Will have it tested before the pour.

RE freezing concrete. I live in Texas. Granted, it's the highest and coldest part of Texas (near Amarillo), but it's pretty rare for the ground to freeze much here. On the local ag weather report every morning, the 2in soil temp is usually mid 30's. It takes a big Blue Norther to freeze even the top few inches of soil.

Lastly, it'll take me two or three more weeks to set the poles so by that point, it'll be late Feb and very unlikely that we'll get any extended hard freezes. The concrete guys plan to recompact a bit before they forms are put in place, plumbing is done, etc. It's that window of time from the final compaction to pour, where the more likely issue is rain instead of freezing rain or snow that I'm wondering about.

Not sure how much that would change your advice, but there it is!

Mark

 

[cowboydoc]

Yea that changes things quite a bit. In that case I wouldn't worry too much about the freezing. Where I'm at we can get to teens and - #'s for highs. In that case your concrete isn't going to set very well.

With regard to compaction you are probably ok. Snow and rain are going to matter though. As good as it is compacted snow and rain can make a difference. How much time are you looking at between setting forms and pouring? Most concrete guys I know and every concrete project I've done we don't set the forms until the day before or maybe two days before we are going to pour.

 

[phantom309]

Thanks for the advice. Things are sounding somewhat better!

</font><font color="blue" class="small">( How much time are you looking at between setting forms and pouring? Most concrete guys I know and every concrete project I've done we don't set the forms until the day before or maybe two days before we are going to pour. )</font>

After the forms are in, we'll do the rough in for the plumbing and then the rebar and finally the pour. With me doing much of the work and only being able to work on it a few days per week, , it could easily be a couple or three weeks.


Thanks again!

Mark

 

[LarryD]

I wouldn't stop the project based on the temps your going to get. Since concrete generates heat in the curing process, a little cover should work. Straw has good insulating properties, over plastic if you're woried about the finish. I have an ACI .pdf that covers cold weather concreting. Can I attach a 365kb file in a PM?

 

[Dartagnan]

Hey Larry, can you PM that to me too? please?

TIA
Dart

 

[bebster]

Here in Massachusetts I've had to really watch this issue. Bottom line, it's ok to pour concrete as long as the night of the pour it doesn't get below freezing, and also for the next day or 2. The chemistry is such that by that time the concrete will have reached a PSI of 500 where it has strength enough to resist colder temps. But if it freezes before it reaches 500 PSI, it's in trouble.

If I were you, I'd just time the pour during a "warm" spell (that's what we call it here when it gets into the 30's!). In a pinch, you could probably push it into the high 20's since the concrete will generate its own heat.

 

[LarryD]

This file is has lots of technical information regarding cold weather concrete and your local batch plant should be aware of it contents and requirements. Cold weather concrete
If you're expecting a few days above freezing and can insulate your work, your concrete company should be able to provide a suitable batch that will hold up for years.

 

[bugstruck]

As long as there is not frost in the soil and you are not going to experience any below freezing weather for the next 48 to 72 hours I would say you're good to proceed. The concrete will generate it's own heat, even on a 4" slab, but it also will be vulnerable to evaporative cooling after the first several hours of being placed, so a 33 degree night with a steady breeze might, might mind you, put a little frost at the surface about dawn if you did a morning pour the day prior. Also at temps below 45 degrees waiting for concrete to set enough to hard trowel makes paint drying look like a fast process. This can impact the final quality of the finish. You're a lot dryer there than we are in Maryland so maybe it's not quite the issue, but as you approach freezing temps the chemical heat of the cure is being depended on to add to the evaporation process. It can't compare with good atmosphere in it's ability to do that. Here, we prefer to pour slabs on days with say 50 degree plus high temps. It's a much more tolerable situtation. Slabs are by far the most vulnerable. Footers in you area, I'd pour them on the nearly the worst of days if the trench or post hole was fresh (no time for frost to take hold) and throw a little straw in if it was going below freezing that night. That is if the footer does not present the sides (forms) above grade. No chance of any problems there. If it is above grade formed you need to be more careful but not quite so much as the slab on grade.

Good Luck