Why is shotcrete used in construction

Everything about shotcrete

Properties of shotcrete

Shotcrete is not a special concrete with a special composition, but rather a concrete process. The concrete used is mostly conventional concrete, as regulated in DIN 1045-2.

However, production takes place in different ways, depending on the process, and the properties that result can vary depending on the production process used. This particularly applies to the strength of the concrete.

Application of shotcrete

Shotcrete is used in many areas. The spraying of concrete leads to both compaction and adhesion of the concrete to the desired spray base. This can save some work steps. In many cases, shotcrete is also used to stabilize rock walls, welded wire mesh can also be covered with shotcrete.

Shotcrete process

Shotcrete can be used in a variety of ways. The following procedures are common today:

  • Dry spray process
  • Wet spray process
  • Torkret process

Dry spray process

Here, cement and aggregates are blown dry through a feed line to a mixing nozzle, where the mixing water is added. In the dry injection molding process, the so-called rebound is particularly important, whereby a small part of the mixture is lost. The rest of the mixture is compacted by the rebound, which must also be taken into account. The cement content can therefore only be determined taking into account the rebound, the concrete mix must therefore be adapted accordingly.

The procedure is used very often because of its advantages. With the dry spraying method, large ranges can be bridged (up to 1400 meters), which also makes it possible to use it in impassable areas, for example to secure rocks. Low maintenance costs and low cleaning effort are also among the advantages of the dry spray process, as well as the inexpensive equipment for this process.

During use, however, there can be disruptive development of dust, and the relatively large rebound in the dry spraying process can also have a disadvantageous effect in some cases. It is usually around 20-25%.

Wet spray process

Here, the individual substances are mixed with water in advance and conveyed to the spray nozzle with a mortar (€ 7.79 at Amazon *) pump. There, compressed air is used to provide additional compression and the mixture is then blown through the nozzle.

The advantage of this method is clearly that a constant quality can be guaranteed, and the compaction can also be calculated exactly, which is not always the case with the dry spraying method. The concrete mix does not change with the wet spraying process. Technically, however, it is more complex and the equipment is more expensive.

Torkret process

The process was developed in 1919 and has been used in tunnel construction since the 1950s. Here, too, the components are transported dry, and at the end of the transport path, which is evenly filled with a pocket wheel, the dry mixture is moistened by a water ring and sprayed at the desired location.

Shotcrete can also be reinforced with fibers. For example, shotcrete can be turned into a particularly stable steel fiber shotcrete.

Author: Johanna Bauer

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