Concrete - the ideal anchoring base
Concrete is characterized by its high strength, flexible application and excellent fire protection properties. Concrete is a mixture of water, cement, aggregates (gravel and sand) and possibly special chemicals (retarders, accelerators, pore formers...). When not hardened, it can be cast into almost any shape imaginable, making it ideal as a building material. Generally, concrete is used in combination with reinforcing steel. The result is reinforced concrete or reinforced concrete. The reason for installing the reinforcing steel is the very limited load-bearing behavior of the concrete in tension. If cracks develop in a concrete structure, the concrete can no longer transfer forces at this point and the component would fail. In reinforced concrete, these tensile forces are transferred to the reinforcement. This creates a very stable and ductile component. Cracks always appear in common concrete components such as floor slabs. However, these are usually very small at 0.3 mm or less. This is ensured by the design of such reinforced concrete components.
Even if the cracks do not negatively affect the load-bearing behavior of the concrete part - or are inevitably part of it - they influence the choice of fasteners.
In the field of fasteners, a distinction is made between dowels that are only rated for non-cracked concrete and those that are also rated for cracked concrete. Dowels with approvals/evaluations ( ETA ) in non-cracked concrete may only be used in components where the structural engineer has proven that no cracks can occur during the service life. This can be the case, for example, in reinforced concrete columns or walls. For most concrete components (such as ceilings), however, cracked concrete must be assumed and the fasteners selected accordingly. The reported performance of fasteners in cracked concrete is generally significantly lower than that in non-cracked concrete.
In general, the following applies to all types of heavy-duty fastening:
If the fastening is a safety-relevant fastening, ie life and limb are at risk in the event of failure or high economic damage is to be expected, this should only be carried out by trained specialist personnel.