Plastic shrinkage cracks are typically very narrow in width and barely visible. While nearly invisible, it is important to remember that plastic shrinkage cracks don’t just exist on the surface, they extend throughout the entire thickness of the slab.
An excessively wet mix is a contributing factor to shrinkage in concrete. While water is an essential ingredient in every concrete mix, there is such a thing as too much water. When the mix contains too much water, the slab will shrink more than if the correct amount of water was used. Hot weather is another big reason for plastic shrinkage cracks.
Control joints can be incorporated into the slab to prevent shrinkage cracking. The joints will open up as the concrete slab gets smaller.
2. Expansion concrete cracks
Just like a balloon, heat causes concrete to expand. When concrete expands, it pushes against anything in its way (a brick wall or adjacent slab for example). When neither has the ability to flex, the expanding force can be enough to cause concrete to crack.
Expansion joints are used as a point of separation (or isolation), between other static surfaces. Typically made of a compressible material like asphalt, rubber, or lumber, expansion joints must act as shock absorbers to relieve the stress that expansion puts on concrete and prevent cracking.
3. Heaving concrete cracks
When the ground freezes, it can sometimes lift many inches before thawing and settling back down. This ground movement brought on by the freezing and thawing cycle is a huge factor contributing to concrete cracking. If the slab is not free to move with the ground, the slab will crack.
Large tree roots can have the same effect on a slab. If a tree is located too close to a slab, the growing roots can lift and crack the concrete surface. Always consider this when laying a slab.
4. Settling concrete cracks
On the other hand, ground settling below a concrete slab can also cause cracking.
Settling cracks typically occur in situations where a void is created in the ground below the concrete surface. Think about when a large tree is removed from nearby and the roots begin to decompose or when a utility company digs a trench for their lines, pipes, etc. and don’t compact the soil when they refill it–these are examples of instances where settling cracks are likely to happen.
5. Concrete cracks caused by overloading the slab
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