What do the different types of concrete mean?

When fixing to concrete, it is important to know the difference between cracked and non-cracked concrete. What does it mean for your installation, and which fixing should you choose? Remember that an anchoring element approved for cracked concrete will also work in non-cracked concrete – but we do not recommend using an element designed for non-cracked concrete in cracked concrete.

Here we go through the key terms related to installation in concrete and advise on how to choose the right fixing, for example:

• Cracked and non-cracked concrete: what does it mean and how does it affect the choice of fixing?
• European Technical Assessment: what does it mean that an anchoring element has an ETA, and what types of technical assessment exist?
• Effect on the fixing: important things to keep in mind when fixing to concrete so that the installation is durable.

Are you a structural designer and need advice on fixing to concrete? Contact us at Zrubko.sk – we can also provide you with documentation from the manufacturer ESSVE.

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What is cracked and non-cracked concrete?

Non-cracked concrete

Non-cracked concrete is concrete without visible cracks, found in areas subjected predominantly to compression. Examples are walls and columns, in which cracks rarely form. In these parts of the structure we can therefore use concrete anchors that do not have to withstand additional stress. However, it is always worth checking that the chosen anchoring element has the relevant ETA.

Cracked concrete

Cracked concrete is concrete in which cracks form as a result of tensile stress. They can appear in various parts of the structure, especially in slabs and near beams, and their width is usually no more than 0.3 mm. Although the cracks are barely visible to the naked eye, they significantly reduce the load-bearing capacity of the fixing. In cracked concrete, therefore, use anchoring elements that are expressly approved for such a structure – only then will the fixing be safe.

If we are not sure whether the concrete will remain non-cracked, it must always be treated as cracked. When we do not know the condition of the concrete with certainty, we must choose an anchoring element for cracked concrete, which is safe in both cases.

In our range you will find several options for fixing to cracked concrete, for example the EUS concrete screw, the ONE chemical anchor and the EST-1 wedge anchor. The product information clearly states whether the fixing is suitable for cracked concrete.

European Technical Assessment (ETA) – what does it mean?

The European Technical Assessment (ETA) confirms that a product meets the requirements of EU technical standards. It is proof of the quality and load-bearing capacity of the product. For concrete anchors, we distinguish between two main assessments:

• ETA option 7 – for non-cracked concrete, which has no cracks and remains permanently in compression throughout its service life.
• ETA option 1 – for cracked concrete, in which cracks form as a result of stress. This option requires stricter testing, so products with this assessment are more expensive, but they guarantee a higher load-bearing capacity in more demanding conditions.

Products with an ETA are clearly marked on the packaging and on the product pages, which makes choosing the right concrete anchor easier.

How does concrete affect the load-bearing capacity and durability of a fixing?

Service life of the building and cracks in concrete

Cracks in concrete affect the load-bearing capacity of a fixing throughout the service life of the building, not only during installation. That is why it is worth carefully assessing the forces the concrete will be exposed to and choosing the anchors accordingly. Remember that loads can cause new cracks to form over time.

Embedment depth

The deeper the anchor is embedded, the higher the load-bearing capacity of the fixing. So make sure you drill to the correct depth for a stable installation.

Drilling depth

After drilling, do not forget to clean the drilling dust out of the hole, as settled dust can impair the quality of the fixing. The correct hole depth is crucial so that the anchoring element can anchor reliably in the base material, i.e. in the concrete.

Edge effect

Placing an anchor close to the edge of the concrete can significantly reduce the load-bearing capacity of the fixing. This phenomenon is called the edge effect.

Double the load-bearing capacity?

Two anchors instead of one do not always mean double the load-bearing capacity. When overloaded, each anchor pulls a cone out of the concrete – if the anchors are close together or near an edge, the cones overlap or are cut off and the group carries less than twice the load of a single anchor. You only achieve the full load-bearing capacity of each anchor with sufficient spacing (according to EN 1992-4 usually three times the effective embedment depth; the exact value is given in the anchor's ETA). The concrete class also affects the load-bearing capacity. Keep this in mind when planning the installation.