Structural Concrete Cracks: What are the Causes?

15 January 2021

Concrete is normally comprised of fine and coarse aggregate that is combined with a fluid cement before the final material hardens and solidifies over time. This material has been maximised by the construction industry due to its known durability, strength, and versatility. Some known applications of concrete include pavers, pipes, drains, and other structural parts of a building or infrastructure.

But even though concrete has the durability and strength to make it last longer, it is still prone to damages. One common issue with concrete is that it tends to sustain cracks, especially if there are forces that can trigger the material easily. Structural concrete cracks can jeopardise the safety of a given structure. Therefore, knowing the causes of these cracks can help prevent their occurrences.

Some of the most common causes of structural concrete cracks are as follows.

Plastic Settlement

As previously stated, the materials used in concrete are combined with a fluid cement before they set in and solidify. During the initial setting of concrete, there will be instances where free water would still rise and ultimately cover its surface. While most cases of water bleeding are normal, there are times where they can cause problems. The separation of the said water weakens certain layers of concrete, making it possible for the material to crack. Plastic settlement cracks typically happen in deep section pours.

Plastic Shrinkage

Structural concrete cracks can also develop whenever there is rapid early drying and low rate of bleeding during the solidifying phase. These situations happen whenever the rate of the surface to volume in concrete elements is high. And if the evaporation rate from the surface of the concrete exceeds the rate of bleeding, then plastic shrinkage will most likely occur. The presence of plastic shrinkage can effectively cause the concrete surface to shrink and ultimately crack.

Drying Shrinkage

Concrete normally shrinks whenever it loses moisture. However, concrete structures are typically provided with reinforcement and crack control joints, which somehow restricts them from shrinking. Long-term drying shrinkages can occur in thin floor slabs and walls, mostly due to the presence of ineffective joints. Other factors that would promote drying shrinkage include the overall cement and water content, size of aggregate, the spacing of the reinforcement steel, use of admixtures, temperature, and humidity.

Thermal Contraction

Cracks in concrete pours happen whenever their internal temperature rises and drops slowly while the external temperature cools rapidly. As the cooler parts of the concrete contracts more than the warmer parts, the stresses caused by the contraction would then turn into structural concrete cracks. One reason behind the temperature changes and differences would be the presence of varying ambient temperatures.

If your need to resolve these issues, then you can contact us at Fairdinkum Technical Services. We are a boutique organisation with operation centres located in New South Wales and Queensland, with over 35 years’ experience in engineering design and construction, providing technical engineering design. We also offer construction support for small scale domestic improvement projects for homeowner builders.

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