Different Salts

Those of us who live in the snow-belt are fairly familiar with rock salt. Large trucks distribute it on roadways to keep traffic flowing. I would curse the salt producers and the drivers of these trucks, not because of damage to roadways, but to my cars. Salts of just about any type are quite corrosive to metal. The chloride ion aggressively attacks poor quality steel. Many cars built in the '70s used poor quality steel, which made rusting body panels a nightmare. Cars built today seem to use better steel and steel that has corrosion resistant coatings that minimize salt damage. It is still a good idea to rinse off your car as soon as possible once it is coated with salt spray. Always rinse up under each fender and as much of the undercarriage as well.

A Safer Salt

Within the past few years a new deicing salt has been introduced to the USA. It is magnesium chloride. It joined the ranks of the other popular deicing salts: sodium chloride, calcium chloride and potassium chloride.

Magnesium chloride is attractive for several reasons. Testing conducted by the National Research Council's Strategic Highway Research Program showed that calcium chloride and sodium chloride caused lots more damage to concrete than did magnesium chloride. The sodium chloride - common rock salt - actually caused 63 times more damage than the magnesium chloride. This is a huge difference. The calcium chloride eroded 26 times more cement than the magnesium chloride. That is also a significant amount.

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Magnesium chloride is also less corrosive to metal such as tin, steel and aluminum (see Author's Note at the end of this column). The reason lies in the fact that it has less chlorides available than calcium chloride and sodium chloride. Remember, it is the chloride ion that attacks metals.

If you use significant amounts of salt or plan to, you need to paint all steel that is in contact with the concrete. This means that the steel bars or mesh used in concrete need to be primed with a rust inhibitive paint. Steel railing posts or aluminum posts need to be treated as well before they are cemented into place in a hole in a sidewalk or in a set of steps. Take this extra time and the corrosion will be minimal.

Plants, Animals & Carpets

Magnesium chloride is friendly to plants, streams, rivers and lakes. The primary reason for this is its lower chloride content. Magnesium itself is often found in many fertilizers.

Traditional deicing salts, like sodium and calcium chloride, leave white powder residue on carpets once they dry. Magnesium chloride doesn't do this.

Your pets should prefer magnesium chloride as well. It is not nearly as toxic as the other available deicing salts.

A Window of Vulnerability

Fresh concrete can be hurt by deicing salts if it is poured too late/early in the season. Concrete needs to be moist cured at or above 50 degrees F for a minimum of 7 days after it is poured. This curing controls and minimizes the release of water within the concrete.

Once cured, the concrete needs to dry for a minimum of 30 days before it is exposed to freeze-thaw conditions and deicing salts. Keep this in mind if you are pouring concrete early or late in the season!

Salt Toxicity

If you are not concerned with the environment, you should be. Each day there are more people on the planet. We need to adopt a sense of stewardship for future generations. You can do that by using products that are kind to the environment. Magnesium chloride is a deicing salt that is very non-toxic. In fact, it is the least toxic deicing salt - yet it is one of the most effective.

Look at the chart below to see how magnesium chloride - referred to as MAG - compares to other salts and some common household products you use and consume. Whatever you do, don't consume the top two items in the chart - cyanide and strychnine! The chart is courtesy of the Dead Sea Works.

Author's Note: In 2001, the USDA published an article entitled "Magnesium Chloride as a De-Icing Agent" that stated magnesium chloride led to "corrosion of steel and aluminum poles and pole hardware." Although used as an effective deicer, updated evidence after the publishing of this article on AsktheBuilder.com shows it can lead to harm of electric utilities. The article can be read here.

Also, a February 2003 Board of Montana Flathead County Commissioners minutes document called "Magnesium Chloride on Roads" on Corrosion-Doctors.org attests to magnesium chloride's corrosiveness on aluminum and steel. In a corrosion comparison done by Colorado D.O.T. and the University of Colorado, it was found that "road salt is more corrosive to the metals than mag chloride on a one time exposure." However, magnesium chloride corrodes over longer periods of time and Greg Fulton, president of the Colorado Motor Carriers Association, said it corroded aluminum on his vehicles as well as led to wiring failure. This document can be read here.

Related Articles:  Guidelines for Strong Concrete, Deicing Salt and Concrete,  Magnesium Chloride & Deicing Salt Companies

The Yellow Pages

The image just to the right is a clipping from my own Yellow Pages directory. It is published by Cincinnati Bell Directory, Inc. - a great company that provides me with a dial tone all the time! A larger ad quickly tells you that Cinti Wholesale Supply, and Koehl, Ed Inc. both carry deicing salts. They might carry magnesium chloride, but surprise - they don't! A smaller company with a minor listing - Ewers, Harry & Sons, Inc. - is the only company in Cincinnati, Ohio, that carries the newer deicing salt. You probably would have passed over them when trying to call around for magnesium chloride.

Open your Yellow Pages and start calling. It may require some patience on your part but you just may find that 'diamond in the rough' company like Harry Ewers & Sons, Inc. in your city or town.

Sources of Magnesium Chloride

To the best of my knowledge, magnesium chloride is only produced offshore. The primary source is the Dead Sea located in the Middle East. Those of you who remember your world geography should recognize this location - the lowest dry land below sea level. This giant drainage basin collects water and concentrates the mineral content within the sea as the surface water evaporates. The Dead Sea is rich in minerals - one of them being magnesium chloride. A company there - the Dead Sea Works - diverts water to evaporation basins and lets Mother Nature produce the raw salt. The company refines the magnesium chloride and then ships it to the United States and other countries that want to use this friendly deicing salt.

Get a 24-page guide right now that answers all your questions about Deicing Salts. Will it RUIN your concrete? Did you know that salt can SERIOUSLY harm you? What about your expensive landscaping? You can have all these answers and more in less than a minute. Buy it NOW.

Another company selling magnesium chloride is the Potash Import & Chemical Corporation. Go to their web site for a list of their warehouse locations, or to order their product.

Another magnesium chloride product is made by Interstate Products, Inc. You can order directly from their web site.

Related Articles:  Deicing Facts,  Guidelines for Strong Concrete, Deicing Salt and Concrete

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.

Get a 24-page guide right now that answers all your questions about Deicing Salts. Will it RUIN your concrete? Did you know that salt can SERIOUSLY harm you? What about your expensive landscaping? You can have all these answers and more in less than a minute. Buy it NOW.

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!