In an effort to educate our customers, Liberty Ready Mix would like to ask you to read the following information. Concrete is one of the biggest investments that home and business owners can make, and protecting that investment should be as important to you as it is to them.

Causes Concrete Flatwork Damage?

Freeze/thaw cycles during cold months are the most common cause of damage to the surface of concrete flatwork. Concrete is a porous material that will absorb moisture at the surface. When the absorbed moisture freezes, in exerts a tremendous expansive force, which weakens the surface and sometimes leads to scaling. Concrete less than one year old, and particularly concrete poured after November 1st, is particularly vulnerable to freeze/thaw cycle damage.

About De-icing Products

De-icing products can be composed of a variety of different chemicals that are harmful to concrete. State, county and municipality street departments frequently use magnesium chloride based materials in the past, a chemical that exacerbates the probability of damage to concrete as a result of snow and water drippings from vehicles.

The most damaging effect of using de-icers is not the chemicals themselves, rather that they increase the number of freeze/thaw cycles experienced by flatwork during cold months.

Repetitive cycles amplify the weakening effects caused by freezing moisture at the surface of the concrete. As a general rule, de-icing products should not be applied to exterior concrete flatwork that is less than one year old.

Liberty Ready Mix prides itself on providing quality products to its customers. We use concrete mixes for exterior flatwork that meet or exceed industry standards for compressive strength and air-entrainment. Air-entrained concrete mixes contain tiny air bubbles that provide spaces within the concrete for expanding water to move into, thereby reducing the expansive stresses associated with freezing moisture in the concrete.

Protecting Your Exterior Flatwork

You should inform all of your customers to take the following precautions. This will help to reduce the number of call backs that you get, in turn reducing tear-out and replacement losses.

DO NOT USE ANY DE-ICING PROCUCTS IN THE FIRST COLD WEATHER SEASON UNDER ANY CIRCUMSTANCES. Again, using these products exacerbates the weakening effects of freezing moisture on concrete surfaces by increasing the number of freeze/thaw cycles.

NEVER USE ANY DE-ICING PRODUCT CONTAINING AMMONIUM NITRATE, AMMONIUM SULFATE, OR MAGNESIUM CHLORIDE. These agents chemically attack concrete and cause damage above and beyond the effects of freeze/thaw cycles.

DO NOT PARK VEHICLES ON DRIVEWAYS. Snow and water contaminated with road salt and de-icers will drip from vehicles leaving concentrated areas of salt or de-icer brine that will facilitate multiple freeze/thaw cycles at the surface of the concrete.

MINIMIZE VEHICLE TRAFFIC ON THE DRIVEWAY UNTIL COLD MONTHS HAVE PASSED FOR ANY CONCRETE POURED AFTER NOVEMBER 1. Concrete requires an ambient temperature of 50 degrees of 30 days for the curing process to complete. If the ground is frozen, as it often is after November 1, the compressive strength of concrete is at a minimum. A weak concrete surface combined with uneven areas of frost-heaved sub-base can lead to severe damage when subjected to the stress caused by the weight of an automobile.

APPLY A PROTECTIVE SEALER TO THE SURFACE OF THE CONCRETE. Liberty Ready Mix would be happy to assist you with more information about sealers and their application.

Every spring, we experienced a number of call-backs from owners complaining about scaled surfaces on exterior, slabs-on-grade (mainly driveways). In fact, this problem is common among ready mix producers in the Des Moines area, Iowa, and the entire Midwest. This is disappointing to us at Liberty Ready Mix, and eliminating scaling has become a top priority.

There are many contributing factors to why the winters are so severe in terms of scaling. The main reason is the weather. From mid-November through January, we have prolonged cycles of rain/freezing rain/sleet followed by hard freezes. The freezing rain and slush accumulate so quickly that concrete which normally has quick run-off, now has ponding water hard frozen to the surface. As the saturated surface freezes, the water expands, causing stresses in the surface of the slab. This is scaling.

We know how to produce concrete which is resistant to scaling, and, for the most part, we do produce scale resistant concrete. What we have found, however, is that we have concrete that meets specifications as it was placed, exceeded specifications when it hardened, yet suffered moderate scaling. Independent testing of cores is pointing to two major problems; excessive jobsite added water (water added to the mixer and to the slab surface), and lack of curing.

Construction practices that were “good enough” in the past are causing us (concrete producers and contractors) problems and costing us money today. Because of the changes in the materials and environment and what new concrete is subjected to today, it is imperative that we go back to the basics of placing and curing.

Recent changes in our industry:

  1. Today’s cement is ground finer than in years past. Fast-track construction schedules demand that concrete mixes achieve design strengths at earlier ages, as well as contractors want quick setting concrete to get their finishers off the job (and clock) as soon as possible. Cement producers react to these demands the cheapest way possible…. by grinding cements finer. However, quick setting concrete does not always necessarily mean more durable concrete.
  2. Unwillingness of contractors to properly cure new concrete. There is nothing that Liberty Ready Mix can put into new concrete that will have a greater, positive impact than curing. The benefits of curing are most evident at the surface of the slab. A properly cured slab will have more complete hydration of the cement, will be less porous, have better abrasion resistance, and will maintain the good air void system necessary for freeze-thaw resistance. This has to be done!!
  3. Iowa Department of Transportation’s expanded use of salt brine. Applying this material to roadways makes snow and ice removal easier and cheaper. However, it appears to be at the cost of new concrete surfaces. An easy solution would be to quit using this type of de-icer. However, when it comes to public safety and shrinking snow removal budgets, you quickly realize that this is not likely.

Today’s concrete IS DIFFERENT than concrete produced in years past and it is being placed into harsh service conditions at a much sooner time frame. It is up to us to adapt to the negative changes which are not going to go away.

We recommend that all exterior slabs on grade, including residential, be properly cured. Curing is maintaining an environment favorable for strength development, which includes moisture retention AND protection from temperature extremes (mainly cold temps).

  1. Wet curing is the best cure, but is rarely possible.
  2. Plastic sheet curing works well when done properly. Plastic sheeting should extend beyond the slab edge and be secured so that air does not blow under the plastic. This is a good cure method when a post treatment will be later applied.
  3. Membrane-forming cures, which are applied to the slab (at or above the recommended coverage rate) after finishing are the most cost effective type cures. If a sealer is to be applied later, however, this material usually must be removed.
  4. Penetrating sealers work very well in preventing scaling, particularly when heavy salt use is anticipated. Salt is carried into the slab by water. Penetrating sealers prevent water penetration, and doing so prevent salt from getting into the surface. These types, however, need to be applied after a cure period of weeks to months.

We have researched effective cure products, and found these locally available products to offer cure benefits and/or sealer which will protect from scaling:

  1. Any membrane forming cure which conforms to ASTM C-309, available from any of our local construction materials supply stores. Applied to newly finished concrete
  2. Sikagard 701W, available from Liberty Ready Mix. Penetrating sealer applied to concrete after 10 to 14 day cure.
  3. Chem-Crete Pavix CCC100 available from Logan Contractor Supply. Penetrating sealer applied to cured concrete.
  4. Saltguard, available from Stetson Building Products. Penetrating sealer applied to cured concrete.
  5. One-Step, available from Liberty Ready Mix. Combination cure and penetrating sealer applied after final set. Offers some curing benefits and sealer benefits. New product not locally tested, but sounds promising.