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Five Causes of Concrete Cracking

Five Causes of Concrete Cracking

Concrete cracking is an interesting topic that holds great importance in the world of construction and infrastructure. Concrete cracking does not only affect the aesthetic appearance of your concrete, it also impacts its structural integrity. Which is why it is important to know what causes cracks in concrete and how to avoid it. Unfortunately it is not always a straightforward answer. In some cases a combination is present which makes it harder to identify the exact cause. We will outline the five main causes of concrete cracking and provide our top tips on how to minimise the risk for your concrete.


Plastic Shrinkage Cracking

Plastic shrinkage cracking occurs whilst, as the name suggests, the concrete is still in its plastic state. The plastic state refers to the state of concrete when it is still wet, before it sets and hardens. When the concrete sets, the water in the concrete dries and leaves behind a void between the aggregate. If there is too much water in the concrete mixture, these empty spaces will be bigger and can lead to concrete cracking. The empty spaces can be found throughout the entire block of concrete, however, they will only be visible on the surface.

Thermal Cracking

When concrete undergoes rapid temperature changes, it expands and shrinks accordingly. Hot weather, humidity and wind each affect your concrete and can increase the chances of thermal cracking.

Chemical Reaction Cracking

Chemical reactions can be caused by the materials used in the concrete mix and by materials the concrete may have come in contact with. An example of a common chemical reaction is the alkali-silica reaction. When the alkalis in cement comes in contact with specific types of aggregate, a chemical reaction can occur. This chemical reaction creates a gel-like substance, which can expand in the presence of moisture. This expansion causes internal pressure within the concrete, leading to cracking and potential structural damage. Moat often finds the relevant concrete supplier for your projects.

Corrosion of Reinforcement

Sometimes steel reinforcements are used in concrete to strengthen the structure. However, if the steel reinforcement corrodes , it will start to form rust and thereby expand. This expansion causes internal pressure within the concrete and can result in the cracking of your concrete.

Overloading or Structural Overstress

Excessive loads or volume changes can cause the concrete to crack under the weight placed upon it. This is often the case in structural elements such as beams, columns and slabs as they often are the bearer of weight. Inadequate designs and structural planning are the main cause of cracking due to overloading.

Top tips to avoid cracking

Knowing the causes of concrete cracking can help you avoid compromised structural integrity, aesthetic appearance and durability of your concrete. Once a crack has formed, it can allow water and other chemicals to penetrate the concrete, leading to further deterioration. At Concrete Taxi we want your concrete to last, which is why we have summed up some measures and tips to avoid concrete cracking;

  • Proper mix

By using a concrete mix that has the correct water to cement ratio, you minimise the risk of plastic shrinkage and thermal cracking. Concrete Taxi’s experienced drivers mix the concrete on-site, allowing them to adjust the strength of the batch to fit your project’s needs. Save yourself the hassle of mixing up the correct concrete mix and use Concrete Taxi’s small batch concrete delivery service!

  • Surface preparation

Level the surface, use compacted road base underlay. Use correct sized mesh. Never pour concrete over gras/soil. The organic material under the slab will rot, creating voids and will cause cracking.

  • Use Correct Strength Concrete

20 MPa minimum for walkways, 25 MPa for trafficable areas, 32 MPa for structural elements and wherever cracking minimisation is needed.

  • Ensure correct slab thickness

125mm minimum for driveways, 200 mm for carports. Minimum concrete slab thickness is 75mm, slabs thinner than 75 mm will not have the strength and will crack.

  • Slab moisture retention

Always put moisture barrier (plastic sheet) under the slab. The barrier retains water in the concrete, allowing it to set properly. In the absence of a barrier soil sucks water out of the bottom layers of the slab, causing uneven setting and cracking immediately upon setting.

  • Control temperature and moisture

While it is especially important to protect your concrete against temperature changes during its plastic state, ongoing protection is necessary to ensure long-term durability. To safeguard your cured concrete you can consider applying sealants or coatings, ensuring adequate drainage and of course regular maintenance.

  • Regular maintenance

By regularly inspecting your concrete, you can identify and address potential causes of cracking and new cracks before they escalate and become a bigger issue.


By keeping these causes in mind and implementing preventive measures, you can minimise the chances of cracking. Concrete Taxi is here to help you create your next small batch concrete or ready mix concrete delivery project and ensure more durable and long-lasting concrete structures.



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