How to Reduce Shrinkage and Thermal Cracking in Concrete?

Whenever you deposit concrete in a form, gravity tends to cause all heavier particles such as cement or aggregate to segregate and sink, which tends to displace water.

Water that has nowhere to go often ends up on the surface. Also known as bleeding water, this will typically evaporate. As any bleed water evaporates, it will develop a negative pressure within the paste.

All water that gets evaporated will get replaced by any additional water within the mixture. However, when the rate of rising water does not match the evaporation rate, your concrete mixture will dry out and shrink.

Our experts from Big D Ready Mix Concrete have identified six major contributors to instant surface moisture evaporation. They are:

Low water to cement ratio

If your cement to water ratio is excessively low, then it means that your structure will not have enough water to replace what already has been evaporated.

High cementitious content

The more cement you add to your mix, the more paste you will end up with. However, it would help if you remembered that the paste in concrete is often much more prone to shrinkage.

High temperature

As your cement structure hydrates, it will generate a large amount of heat. If heat is not controlled, it will cook the water off, just like allowing a pan of water to sit on the stove for an extended amount of time.

Low humidity

Chapped knuckles and lips are easily one of the worst parts of winters. It tends to occur when dry air wicks away moisture from your skin. The same happens to your concrete structure.

Wind

Outside and inside, air currents blowing over the surface of your concrete structure will blow away any moisture. It is one of the main reasons you need to take precautions when casting a concrete structure outside.

Effects of shrinkage and cracking

The most common effect of shrinkage and cracking is the unsightly appearance of the surface of the concrete. Cracks tend to form as soon as the cement reacts to the water.

Depending on the structure, these cracks can range anywhere from a few inches to several feet in length.

When the wind blows over the surface of the concrete, you will notice these cracks follow a pattern, running perpendicular to the flow of wind.

However, if the wind is swirling, you may notice cracks forming a random pattern along the structure’s surface, developing from several different directions.

Cracks tend to occur on horizontal areas of the structure where water is still evaporating. Even though cracking caused by shrinkage does not immediately threaten the overall structure, it may reduce the total lifespan of the product.

Just as our skin helps protect our body from any bacteria or germs, the surface of concrete plays a critical role in preserving the rebar against any harmful substance.

Any cracks on the surface provide an opening for corrosive materials and dirt to enter the structure. This can be dangerous since it might further lead to corrosion of your reinforcing steel underneath.

Any expanding oxidizing steel can lead to additional cracks, which will further cause more exposed steel and corrosion.

If you do not take the required measures on time, this will eventually reduce the total service life of the structure significantly.

Countermeasures that you need to consider

You need to take proactive measures to minimize any possibilities of shrinkage and cracking.

Add fibers

Adding some fibers to your mix is an excellent way to increase the tensile strength of your structure. It will prevent tensile stress from exceeding the total power of your mix.

For this, you need to understand all attributes of the fiber and how to batch them correctly into the concrete since it will affect the water demand for the mix.

Sunshades and windbreaks

Sunshades and windbreaks can be placed around the concrete structure to help reduce the total velocity of wind while protecting the surface from excessive sunlight.

Many professionals use damp burlap to protect concrete structures from the sun’s heat and ensure a perfect moist curing condition.

Fog sprays

Using a fog spray can help you increase the relative humidity of the air surrounding the concrete structure.

Since high levels of humidity tend to correspond with a lower rate of evaporation, it would be best if you keep your concrete in a humid environment.

Allowing your structure to cure as soon as possible while maintaining consistency is the best way to ensure a reliable and high-strength concrete structure.

A common mistake that most people make is not paying attention to bleed water that has worked its way back into the first layer of concrete.

This tends to increase the top layer’s overall water to cement ratio, causing a significant reduction in total strength and other critical issues.

It also creates an issue by getting rid of water that would ideally evaporate, increasing the structure’s temperature, making it more prone to cracking.

However, if you notice that cracks have already occurred, you can always use fillers and sealants to protect it against any further damage. If you have any more questions related to concrete, feel free to get in touch with Big D Ready Mix Concrete.

Are you looking for an expert’s opinion? Contact Big D Ready Mix Concrete today!

Here at Big D Ready Mix Concrete, we have a team of highly trained and experienced professionals who are ready to assist you with your residential and commercial concrete and construction-related needs for all types of projects.

We can provide you with high-quality wall mixes that not just cure well but will also give you a solid, long-lasting result.

We have been serving the Dallas area since 2002. Give us a call at 972-737-7976 or contact us online and one of our professionals will guide you through the process.

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