What causes cracks in a concrete slab and how can you repair the damage caused?

Three possible causes of cracks

It is not always easy to pinpoint the exact cause of cracks as several factors can contribute to it. Here are the five primary causes responsible for this issue:

1.Incorrect concrete mix

Choosing the right concrete is a lot more technical than it may seem, and it is directly correlated to the area’s intended use. For instance, depending on whether it is meant to harbour cars or pedestrians, the strength and thickness of the slab will depend on its intended use.

2. Poor-quality concrete

Failure to adhere to the correct ratios of cement, water, sand and aggregates will result in poor-quality concrete, affecting the durability of your project. It is usually recommended to use a ready-mix concrete from a concrete plant, such as the one offered by Premix, to ensure a precise mix. This guarantees the compressive strength that a manual concrete mixer cannot provide.

For instance, if your concrete contains too much water (an issue commonly-faced when site mixes are done), its strength is reduced. Aggregates then settle at the bottom of your mix, making the surface more prone to cracks.

Another common mistake faced is the improper cement dosage. If your concrete   does not contain enough cement, its strength is compromised. On the other hand, an excess of cement can lead to excessive shrinkage, which also causes cracks.

3.Poor  construction practices

  • Cover to reinforcement

Prior to pouring concrete, several measures must be considered to ensure the concrete’s longevity. For instance, you must ensure that proper reinforcements are used on the slab, you must check that there is appropriate cover on all reinforcements and conduits. All these steps must be carefully followed to ensure a well-constructed, sturdy, and durable concrete slab.

  • A lack of, or inadequate joints

Whether they are construction, expansion, contraction or isolation joints, their positioning is crucial for the floor slab’s adequate expansion, reducing the risks of cracks over time.

It is of course quite possible that cracks that appear on your concrete have nothing to do with the quality of the concrete or the construction process. For example, Impact, excessive load, or ground movement are other reasons that can explain crack formation. And fortunately, there are ways to limit these issues such as proper compaction.

How to repair a crack in a concrete slab?

Cracks are classified in two categories based on their severity: superficial or structural.

  • Superficial cracks

Shallow, narrow and short cracks mainly affect the appearance of your concrete slab. It is normal for concrete to develop these over time, and they do not weaken your slab. The good news? They can be easily repaired! To conceal them, you may use a waterproofing solution (which can be cementitious, acrylic, polyurethane, etc.)

  • Structural cracks

A structural crack can be identified by its length of several centimetres, as well as its depth. It can be a crevice or fissure, which then affects the slab’s structure. Repairing them may not always be possible, depending on whether the cracks are active or passive.

A structural crack is considered passive when it no longer grows further once it appears. Repairing it is usually not a problem.

An active structural crack, however, continues to grow and evolve once it appears. In this case, further investigation is required to identify the cause, or causes! Do not hesitate to consult a professional in this case!

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