Cracks in concrete can be a major issue, ranging from unsightly to potentially dangerous. It is important to understand the causes of cracking in concrete and how to reduce the risk of cracks appearing. Shrinkage is one of the main causes of cracking, as concrete hardens and dries it shrinks due to the evaporation of excess mixing water. Excess water in the concrete mix can also increase the likelihood of cracking, so it is important to choose the right concrete mix for your project.
When a service pipe hole is drilled through the concrete, the coring process can cause damage to the concrete structure by creating cracks. Plastic shrinkage cracks are probably the most common reason for early cracks in concrete, as when concrete is still in its plastic state it is full of water. As the slab loses moisture during curing, it becomes slightly smaller and this shrinkage creates stresses in the concrete slab. When a brick wall or adjacent slab cannot flex, the force of expansion can be enough to cause the concrete to crack.
Reduced alkalinity of the concrete, either by carbonation or by the ingress of chlorides (salts), are also common causes of concrete corrosion. In order to reduce the risk of cracks appearing, it is important to properly prepare the subbase, ensure that the concrete is not too wet, use reinforcement where necessary, and properly place and space crack control joints and expansion joints. V-cutting along the crack line and then sealing it with an appropriate sealing material will allow movement and protect against further crack expansion and possible water ingress. Injection grouting is another repair option used to stop water leaks and involves injecting a highly water-reactive resin into cracks under pressure. Do not overdig and backfill with a few centimetres of soil; this will eventually settle and cause the slab to crack.
Careful timing is essential when using vibrators to ensure that the concrete re-sets under their action and that cracks close completely. In most cases where cracks appear in concrete, it is possible to identify the crack and establish its cause. It is important to consult a qualified and licensed professional to classify the severity of any crack and properly investigate its cause in order to determine the most effective repair method if necessary. By understanding why cracks occur in concrete and taking steps to reduce their risk, you can ensure that your project remains safe and structurally sound.