Seriously, there are two associations that promote concrete and its correct use. They are progressive and their recommendations are backed up with tens of thousands of hours of scientific investigation and testing. The two groups are the Portland Cement Association (PCA) (www.cement.org) and the American Concrete Institute (ACI)(www.concrete.org). Here are some guidelines they suggest you follow, if you want trouble-free concrete in cold climates:

Low Water to Cement Ratio

The cement in concrete is the glue that holds everything together. The more water you add when you mix, the weaker the concrete will be for a given amount of cement. Think of cement as sugar in iced tea. If you add just a little sugar the sweetness level is weak. Add lots of sugar and you get some sweet stuff!

A Four Inch Slump - The MAXIMUM Allowed

Slump refers to the stiffness of the mix. The lower the number the stiffer concrete is. You can actually mix and pour concrete with a 1 or 2 inch slump! Have you seen highway median work where the crash barrier is done with a forming machine? The concrete is so stiff that it can stand four feet tall moments after it is poured - yet it attains a high strength once cured and dried. You don't need lots of water to make concrete strong. The addition of water to a 5 inch or higher slump just makes it easier to pour.

Six Bag or 4,000 PSI Mix

You must have enough cement in each cubic yard to make sure it is strong. For concrete exposed to freezing temperatures you want a minimum of six bags (564 lbs.) of cement per cubic yard or a design strength of 4,000 pounds per square inch.

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Air Bubbles

Special chemicals can be added to concrete as it is mixed. These chemicals create micro-air bubbles within concrete. The air spaces become shock absorbers as water freezes within concrete. Make sure your concrete is ordered with air - often called air entrained concrete.

Proper Finishing

Just as you can't add extra water to mixed concrete, you can't add water during the finishing process. This added water dilutes the cement paste in that localized area.

Slope

Concrete slabs need to have good drainage. This means that they need a slope of 1/8 inch per lineal foot minimum to shed water. Pooled water that freezes on the surface is bad....bad.......!

Adequate Curing

As concrete dries, it needs water to complete the chemical transition called hydration. If you let too much water escape from the slab before the chemical reaction is complete, it simply doesn't become as strong as it should be. You can cure concrete by covering it with plastic, wet burlap that stays wet or by spraying it with a liquid curing compound. Don't forget this important step!

No Silicone!

If you feel the need to seal your concrete, do not use silicone sealers. These are film formers. You need a breathable sealant or water repellent. Top performers are those that contain silanes and siloxanes. These are chemicals that are similar to silicone.

Related Articles:  Deicing Facts,  Deicing Salt and Concrete,  Magnesium Chloride & Deicing Salt Companies

Did you know that the performance of many building and remodeling materials is deeply rooted in basic chemistry and physics? Now hold on there, this isn't going to be a reenactment of your boring high school chemistry class. Give me a chance here. OK, take roof shingles and flashings. Many people look at me funny when I tell them that the only reason they work is because of gravity. If rain water goes backwards up a roof, you will have a leak!

In my opinion, concrete is probably one of most fascinating building materials. While it appears to be a very basic material, nothing could be further from the truth. High quality concrete doesn't happen by accident. It is a highly sophisticated chemical compound.

Think Jello®

Have you ever made instant gelatin or pudding? Well, you take a powdered mixture, mix it with water, stir it up, and before you know it, you have a semi-solid compound. You are an amateur chemist and you didn't even realize it!

There is a difference, however, between concrete and Jello®. The cold temperatures in your refrigerator speed up the transition of the liquid mixture into a semi-solid material. With concrete, cold temperatures slow this transition. In the case of concrete, it can be disastrous.

Concrete is a strong material because of its chemistry. When you mix water with the cement powder, you start an irreversible chemical reaction. Tiny crystals begin to grow. These crystals attach to one another, the sand and the gravel in the mixture. When everything goes right, you basically have created a compound hard as a rock!

Ice Crystal Pressures

Speaking of crystals, let's digress and talk about ice crystals. When water freezes it turns into ice crystals. This transition would be no problem except for one thing. As the ice forms, the volume of the water grows by nine percent! The ice tends to push or break things that get in its way. The force can be enormous.

In the case of freshly poured concrete, ice can destroy your slab. Enough cement crystals must be allowed to grow within the concrete to withstand the forces of growing ice crystals. It can be a race against time. Most concrete chemists and engineers agree that if the concrete can attain a minimum strength of 500 pounds per square inch (PSI), it can resist ice damage.

Did you know that some chemical reactions require heat to complete, while other reactions create heat? Guess what? The chemical reaction of concrete formation creates heat! It is called the heat of hydration. This heat can be trapped and used to fight off the threat of ice. All you or your concrete contractor has to do is to cover the fresh concrete with insulated blankets. Nothing to it!

Common Surface Defects

Concrete which has been damaged by cold weather commonly has surface defects. The most common defect is spalling. Spalling is simply the peeling or loss of the top finished layer of the concrete. It usually happens because the upper surface of the concrete froze before enough crystals grew to give this layer a strength of 500 PSI.

Popouts are another common surface defect. A popout is created when a piece of aggregate (rock) in the upper surface of the concrete explodes as a result of freezing. Some pieces of aggregate have a tendency to absorb water. This water freezes, expands and BOOM! Gravel companies go to great lengths to try to remove this type of rock from the gravel. However, they don't always catch every piece.

Deicing salt damage is another common surface defect related to cold weather. Scaling of your concrete can happen even if everything was done correctly. As concrete is exposed to air, it gets harder. This process is called carbonation. The carbon dioxide in the air reacts with the concrete and creates limestone (calcium carbonate). Some forms of limestone are very hard!

This carbonation process, however, usually takes one year to produce any substantial differences in strength. So, if you use deicing salts or they drip from the under side of your car onto your new slab, you may have a problem.

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Other Cold Problems

Let's say you do everything right. You order heated concrete (either the mix water is heated and/or the sand and gravel is heated by the supplier), you even put extra cement in the mix, you finish the concrete correctly, and you insulate it for three to five days. You still can have problems!

The cold temperatures slooooow down the crystal formation in concrete that gives it its strength. Sure, you hit the 500 PSI mark okay, but your slab or foundation wall may need higher strengths to resist cracking.

So, in colder weather, you must try to keep your concrete protected from loading as long as possible. Avoid backfilling foundations. Don't allow heavy trucks to drive across sidewalks or driveways. Protect your investment!

Tips on Pouring Concrete in Cold Weather

I have poured many a concrete slab in cold weather. It is always a challenge. The cold temperatures make working that much more miserable. If you get wet, you really become miserable. No doubt this type of activity is not for the faint hearted! What's worse, once the pour begins, there is no turning back. That concrete coming down the chute is like liquid gold! A mistake or goof can cost thousands of dollars.

Frozen Ground or Snow

Don't pour concrete on frozen ground. Not only can the ground freeze the concrete from the bottom up, you can have catastrophic cracking when the ground thaws. There will no doubt be hollow spots beneath the concrete. Driving over the hollow spots will create tension, which in turn creates cracks.

Pouring concrete over snow simply adds unnecessary water to the concrete. We have already discussed why this is not a good idea.

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Foundation Walls and Cold Weather

Is your house going to be built in cold weather? Watch out for pouring foundations in cold weather! Remember a foundation wall is simply a vertical slab. However, they have a disadvantage. They are exposed on three sides once the forms are pulled! Foundation forms should be well insulated and left on for three to five days if at all possible.

If your foundation contractor removes the forms too quickly, the concrete will have absolutely no protection! If they must remove the forms, absolutely install the insulation blankets immediately. If you have extended cold weather don't allow the foundation to be backfilled. Temperatures below 14 degrees F completely stop the hydration (crystal growing) process. Once temperatures rise above that, the chemical reaction resumes, but very slowly. It could take a long time for your foundation walls to gain enough strength to resist the pressure of backfill dirt.

Low Slump + Lots of Help = Success

Low slump concrete is hard to work with. It's backbreaking work. But in cold weather is can mean the difference between success and failure. Think of it, why not hire (or have your contractor hire) two to three additional people for the one to two hours it will take to place the stiff concrete. Once in place, screeded and bull floated, those guys can take off. What did it cost? $100 - 150? Is that worth it to insure that you will not have bleed water problems? Low slump concrete will allow you to finish the slab quicker. That will allow you to get blankets on the slab quicker. It's a good idea!

Checklist for Installing Concrete in Cold Weather

Prior to Placement of Concrete

Don't place concrete on frozen ground or snow. Cover excavated soil with straw to retain heat prior to pouring.

Have all blankets, tarps, enclosures ready before the pour. Every minute counts after the concrete is finished!

Be prepared to wait for the concrete to set. Don't expect to "get in and get out". Cold temps will slow set time!

Installation and Placement of Concrete

Be sure to order air-entrained concrete. Tiny air bubbles grow within the concrete which help win the war against ice crystal damage.

Order heated concrete, preferably between 55 to 75 degrees. Order concrete with an extra 100 lbs of cement per cubic yard. This will help develop both early and long term strength.

Order concrete with a low slump or water content. Excess water is your enemy in cold weather! Don't worry, the concrete will not "get away" from you. Remember the colder temperatures slow the set time.

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Wait for the warmest time of the day if possible to place the concrete. Cold temperatures and wind will suck the heat from the concrete rapidly!

Do not trowel surface bleed water back into the concrete! This bleed water must evaporate or be gently removed (with a hose or a squeegee) from the top of the concrete. Troweling this water into the surface will significantly weaken the top layer of the concrete! Ordering concrete with a low slump will prevent excess bleed water.

Protection after Placement

Use polyethylene plastic or liquid membrane curing compounds. Do not use ponding water or wet burlap.

Cover the concrete with insulating blankets as soon as the curing procedure is complete. Edges and corners need extra protection!

Use vented heaters to provide warmth. Excessive carbon dioxide buildup will cause surface defects! The concrete will dust at a later time!

After the curing period (five to seven days) allow some air to get to surface for drying purposes. Try to "dry" the surface before exposing concrete to freezing temperatures.

Gradually remove insulating blankets. Thermal shock (exposure to cold temperatures too rapidly) can lead to concrete cracking.

Do not expose cold, fresh concrete to early loads. Remember, the concrete is getting stronger each day. It may take weeks or months for it to gain the strength it is designed for. Be careful!