Concrete in December

I live 40 miles east of Des Moines, Iowa and am thinking about starting the concrete for my new shop. We just finished the plateau last week. The dirt around my farm is extremely sandy as is the plateau, so I don"t think that frost heave will be a big concern. We are going to pour a footing that goes fairly deep and then extends 2" out of the ground as well as concrete throughoutt the shop area. Do you think that the cold will cause bad things on down the road with the concrete? Wait until spring?

The cement company can add calcium to the mix to be able to pour in colder weather but if it were me I would wait until spring.

As long as you don't place it over frozen ground, or allow it to freeze when initially placed, course they have admixtures and thermo blankets etc, and it does create heat while hydrating (chemical reaction while curing) you should be fine.

I always thought cooler, milder temperatures were better, as opposed to high heat, but temps above freezing, get below freezing you have to deal with it. Cooler temps, slower cure, water does not evaporate out, always seems like a better job.

Newell, so you think that I would have better results in the spring? Why? Just trying to learn more...

They pour a lot of cement round here in the cold winter months.Important thing thing is to keep it from freezing.Cover it with special (concrete) blankets,or straw.Sometimes in extreme cold,they will erect 'tents' and use a space heater.The 'concrete guys' tell me that the second night is most critical.

After a life in the concrete/excavating business, Yes you can very eaisly. Don't pour on frozen ground and protect for at least seven days after pouring if temps are below freezing.
Do not add calcium chloride, does not improve anything.

Here's a link to the standards used by the Dept of Defense. The general contractor I worked with for over 40 years did a lot of government work. We had to pour by these guidelines.

Calcium Chloride CAN be used, so long as kept under 2% mix. And care should be taken when using CC to prevent corrosion of any steel re-enforcing in the concrete.
Pour it out

I have poured concrete in the winter. It always turns out to be much harder to do and half the time you end up with a poor quality finish. I would not recommend doing it unless you have no other choice.

I poured two of my cattle floors in the winter. I had to hire it done because I did not have concrete blankets to cover it with. So that added to the cost. The contractor doing the work busted his butt fighting the cold. He covered it all and setup a tent with heaters the second day so they could work on the finish. He left the concrete covers on it for ten days after the pour. So I think he did all he could to make it work.

The second winter the finish coat started to flake off. I mean the top 1/2 inch or so. In big chunks that where some times larger than three feet in a spot. I had the contractor back out to look at it. He said that it had frozen even with the covers. That made the finish crack away from the base.

So I now have a eight inch thick cobble stone finish cattle yard. Every time I scrap manure I cuss myself for not waiting.

Also if you just leveled your building spot I would want it to settle down before I poured anything around it. The fact you have sand ground make that even more of an issue. The ground settles much slower. Did you compact the dirt in the fill or is it fresh cut with no back fill???

So unless you have to do it now I would wait until next spring to do the pour. It could turn out fine but if it does like mine and flakes off than you have the problem in your shop. If you just have to do something then just pour the footers and then do the floors next spring.

Going back to my AgMech 250 course from Iowa State I wouldn't even think of pouring concrete in December.

The first month is when over 90% of the curing process occurs. We tested three sets of cores over a month. One set was put under water, One allowed to air dry and one set was put in the freezer.

Don't remember the exact proportions but the difference in compressive strengths of these cores was significant. They were in the order listed above starting with the strongest to weekest. Unless you have a way to keep it from freezing for the first month I wouldn't even think about pouring this time of year.

hth

jt

You can protect it after pouring with a layer of plastic sheeting. For more protection, a layer of straw on top of the sheeting, with another layer of sheeting on top of the straw. Weight down the edges off the side of the pour. Air movement under the plastic is your enemy. As Larry and others said, never pour on frozen ground. We would excavate for the pour on day 1, and when we were to grade, compacted, and the forms set, we'd cover the pour area with plastic/straw/plastic. On day 2 we'd roll the plastic/straw/plastic back and make the pour. After it set enough to limit marking, we'd replace the plastic/straw/plastic. Like Delta Red said - the second or third night is when it is more vulnerable, not that you should be careless on the first night. We'd leave it covered for 7 days. It's serious business. Material and labor is too expensive to take chances. Your R/M supplier can give you good advice specific to your area.

I'm not Stephen, but yes, you'll have better results in the spring. Better working conditions, better opportunity to make a nicer finish, more flexibility on curing the slab, easier access for the trucks (usually). A lot can go wrong in a hurry on a winter pour. Contractors will always have a backup plan. Homeowners usually don't.

Contractors also will generally have ample labor force for dealing with extra work involved with special conditions, access to rental equipment, and a few experienced finishers who know how to react to unusual circumstances and conditions. Most homeowners or DIY-ers end up with the "well, NEXT time..." experience.

When short on hands on training, it's always better to do things under ideal conditions.

Or...hire it done can be cheaper than jack hammering a bad pour.

Can you pour the footings first and erect the building? Then when it is enclosed pour the floor? Easier to keep some heat in then. Make your footings 4 ft. below finished grade and you won't have any trouble with frost heaving. Add 2% calcium to the mix and use a stronger mix with concrete blankets on the finished pour and you will be ok. The 2% will speed up the set up time so plan accordingly. We have poured every month of the year here in SE. SD and never had a problem. Just don't pour over frozen ground or it will crack for sure.

We have put sawdust on it when temps are going to drop. No problem.
Richard

I could have gone into this a bit further earlier but time was limited.

My experience with concrete is based on high rise and commercial building construction, I've performed the work myself as well as being supervisor/project manager, overseeing contractors perform the work to adhere to the old 03300 CSI specifications, including admixtures, placing concrete in cold and hot weather. I've done footings, column footings, beams, strap beams, columns, decks and flat work from floors to sidewalks. I've had to perform and supervise this work under stringent controlled inspections required by city of new york dept of buildings, that must have technical responsibility reports (TR-1's) signed off by a licensed professional engineer holding a NY license, per NYS dept of education or whatever you call it. Inspection firm, has an inspector at the plant, the day of the pour, places a field technician on the job to take test cylinders, review reinforcing/shop drawing, design drawings, inspecting work being done against same and 03300 or similar specifications as well and any ACI (american concrete institute criteria) Cylinders must prove the design compressive strength, tests are done at 7 days, 14 days, 21 days and 28 days. The work and the above must be approved and signed off on or you will not get a certificate of occupancy, and this is just one inspection, there will be a stack of these TR-1's at the end. A little background for you.

Now, on properly compacted undisturbed ground with a suitable compacted, 95% or better sub base, (building pad) of material that will compact per above with optimum moisture, placed and compacted in 12" lifts, each lift can be tested with a troxler nuclear density meter and or 3 point or modified proctor test, to insure each 12" layer is properly compacted from undisturbed, this is part of the TR-1's required in NYC FYI, they are very serious about these things. OK, so now you have a properly compacted pad, of a suitable well drained material that has the density required given the compaction proven to support the load. YOur design may have footings, knee walls, pad in the middle, depends on what you are building, I'll use just a slab for example and this discussion, same rules apply to the other structural components.

The undisturbed, sub base (pad) is unfrozen and you have ideal, above freezing conditions, it can be in high 30's and work. You can form and place the concrete in these conditions. YOu may want at least a 4000 PSI (compressive strength) or even 5000 PSI if you can afford and your building will have heavier point loads on it, ( of course reinforcing, metal deformed bars/rebar will need to be installed per a design to meet a strength, one that will exceed the highest point load imposed, say by a dump truck wheels crawler or heavy ag equipment, shop equipment etc. etc.) Cost will likely be an issue, 4000 PSI may suffice or even be more than you need, but for flat work, colder temps, I think a stronger design, with sufficient rebar, not 6"x6" woven wire mesh, (W.W.M.) is better in colder temperatures, just opinion, things vary, so do contractor methods and means.

The caveat is that in colder temperatures, you want that pour started and placed as early in the day as you can get it, DO NOT place in the afternoon, you SHOULD place it early, before or at sunrise. Admixtures for cold temperatures may change this, but this is my methodology for placing concrete in the winter or in colder temperatures. The temperatures will be on the rise, and depending on conditions you may be able to achieve enough hydration, cure or what you call in in your neighborhood to get the power trowel on it. The caveat is that you may not be able to get onto it to do the finish as soon as warmer temperatures, and there will be a window that will be ideal, one that I prefer not to be midnight or 3 am LOL ! An experienced contractor who knows this work in all conditions is a wise choice to consult with or have do the work. Its possible to also get the advice to wait until spring or warmer temperatures, things vary widely.

You do not want the concrete to freeze, it will spall like JD Seller desrcribes, it will also do the same in high heat, whereas it hydrates too rapidly unless burlap and sprinklers are used for the several days its vulnerable. The judgment call in deciding on to proceed or wait will depend on weather, again you have admixtures and similar, but straight up concrete, its almost like doing hay, plan ahead as best you can. I don't mind it in the mid 30's, but it has to be insulated well if its going to get colder, in the following days, if its close to 40 one day, you pour, then it drops to zero, blankets, straw sawdust, and whatever, you do take a chance, better to remain close to freezing, below certain temperatures, you have to ask yourself or supplier, will the admixture perform, can I get a finish on it in ample time, place the protection over it to prevent freezing without damaging the finish, and will it freeze, one mistake could cost you, contractors in your area will know the limitations, there is no better person or company paid than one that knows this work, and has a proven record of successful installations in the various conditions.

Planning is key, if you want to proceed, and your building design is where you have a footing and load bearing components for the structure, you want to keep going in cold temperatures, then build or design to build where you can enclose, provide temporary heat to protect the slab, as said below, thats how most buildings under construction are planned, get the core and shell + roof established and work inside during the winter, some are so large the construction may span more than one winter and they have no choice but to work in winter conditions.


To insure compressive strength, you order a certain PSI concrete, say 4000 PSI. Get yourself empty test cylinders, you can hire a testing outfit, but if you want to save some money, get the cylinders, 4 will suffice, on large pours every so many cubic yards cylinders are taken, at intervals to represent a composite sample of all the concrete placed.

When the concrete truck arrives, at some point during the pour, fill these cylinders, 1/3rd at a time, then take a 1/2" dia. steel rod and pack each 3rd, 25X, so fill the first 3rd, rod 25x repeat for the next 2/3rds, then evenly screed off the top of the cylinder, place where its safe, prevent freezing, rain or what have you, you can then take these to a testing lab and ahve them broken 7,14,21,28 days or all at 28 days, small job. I think on any reasonable size job its prudent, for yourself or when a contractor is involved, will keep them on their toes, knowing the material is being tested. Something does go wrong you can rule out the material if it meets compressive strength.

I've done flat work (slabs, decks and similar) in colder temperatures, it can be done but there are rules to follow, it can be risky so you have to be prepared for the site conditions/weather etc.

Again, speak with an experienced contractor or person who knows this work, in your area, should be good advice.

I hate seeing all that work and money go to waste or have the material fail, what you do up front is key to it. ALso do not forget any future use items, all stub ups, pipe, electrical conduit, drainage, anything that needs to penetrate the slab, even an extra conduit or pipe you may want for something later, so much harder once the concrete is placed.

Hopefully some help, there are lots of opinions on the use of this material as well as various experiences, better to research it a bit and decide based on good information than to guess.

I just looked up the weather for your area and it says 21° tonight and below freezing for the next few nights. So I'd guess your ground is frozen which eliminates any possibility of pouring a slab. Footings and stem walls you most likely can do if the excavated base isn't frozen and the weather doesn't get much colder than the high 20's. Generally it will be more likely to freeze the second or third nights than the first. If light frost, still cover the top of the forms. When concrete freezes, it turns white and is more or less a dust that you can rub off.

For floors, the first thing is to have a good base. Usually six inches of clean gravel over good firm undisturbed soil or over engineered fill. Then proof roll it - heavy load and see if the compacted gravel base yields under the loaded wheels. If it does, excavate to firm soil and fill with clean compacted gravel fill. Calcium is basically salt and will only speed set up of the concrete. The building codes here will no longer allow us to use calcium where structural rebar is used - does the same thing road salt does to vehicles. If the weather is "iffy", we use hot water and Pozzutec© as an accelerator but you concrete supplier may have other similar materials. The buildings we do are mostly commercial and industrial warehouses and manufacturing.

If it's a shop floor, I'd assume you'll be running heavy equipment on it. You'd be much happier a year or two from now if you don't hurry and cut corners at the expense of doing it right.

insulate the concrete after it has set up with insulation,straw,etc, so that its temperature will not drop below 40 degrees for 6 days.
Do not use calcium chloride as it will corded steel and make the concrete surface porous.
using type 2 cement with air entrainment will increase durability and reduce spalling in freeze-thaw weather.
Taking test cylinders and air content is a good idea to verify what your buying from the supplier.

We pour concrete in colorado winter regularly. You can usally rent concrete blankets which are basically insulated tarps. You can place these black side up and will thaw the frost in your ground and protect it from further frost. Then once the concrete is poured you cover with the blankets until it is cured for 3 to 5 days. When it is really cold you can get electric heated concrete blankets and thaw machines.

I worked at a concrete plant for 25 years and you have given some excellent advice.Commerical and State concrete is inspected and done right almost all the time conversely residential and private concrete is usally poured out of spec about 95% of the time and the number 1 reason is because the finisher wants its wet and easy to put down.Personally on a slab of any size I'd only pour it in the Spring or Fall to avoid alot of weather related problems.

I'm more concerned about the slab itself done in winter rather than working the project. A lot depends on the cement company but I've seen some that I believe added too much calcium to the mix fighting the cold and it made the concrete softer. It didn't take very much abuse before it crumbled. Concrete takes a lot longer to cure than people think and if sometime in a week or two after it's poured it gets well below freezing it can ruin the slab. It's just better to make sure there is no chance of freezing weather after the slab is poured.

I would agree, adding water on site, it can and will offset the water/cement ratio, reduce compressive strength, one has to be careful with contractors and suppliers, more so in residential like you said and that is one reason why. A lower slump is fine if by design, but not ok if water is added on site, in my opinion.

I would further agree, and prefer more ideal weather conditions whenever possible. Extremes on either end of the thermometer cause extra work and worry, nice mild weather, 50's-70's so much easier to work with.

we always added super plasticizers if the contractor wanted more workability while lowering the water/cement ratio. They would make a 1 inch slump concrete flow like a 4 inch slump.
We insisted on them for prestress concrete products with 5000 psi strength and 12 hour turnover to reach 4000 psi.

You must have worked in a plant as well, I'm familiar with the other admixtures and so on, but usually the design mix by as specified, by contract documents will incorporate those admixtures, and be submitted for approval by the engineer of record reflecting that in the submitted design mix. Many specifications call for a proven mix design, using specific local materials to that plant, so if a contractor submits that mix design, from that plant its usually approved.

In the residential world, you can get all kinds of variables and situations because people and or contractors don't have enough knowledge of the material.

I do remember all the precast concrete plank I ordered was specified to be 5000 psi.

Hi Billy---I am a licensed professional structural engineer in NY so i wrote a lot of specs and supervised construction of a lot of projects. I am from LI and retired as the Director of Bridges and Structures for Suffolk County DPW. I just loved the design and fabrication of Prestress Concrete --you can really do a lot with it with economical pieces We used it for sheet piling, bridge abutments, bridge beams and pilings.

No kidding, I used to really marvel at large precast jobs in ENR and others locally, like the L.I.R.R. connector to Kennedy in Queens etc. Watched that go up.

I've done plank, box culverts, precast modular cells (nys max security correctional facility).

There is a large precast plant north of me up here, I used to deal with Strescon in PA, though the other precast outfit doing plank is near me up here too.

I am impressed with the versatility, I've had to modify precast plank in the field, per approved details that I had the engineer check and calculate, surprised that what was done checked out, not so sure I like precast plank and masonry buildings for seismic though, having built those.