Concrete slab

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Concrete slabs are components made of concrete that are used as road paving , flooring or wall cladding .

production method

roughly sanded concrete slab

The most common method of manufacturing concrete slabs is the hermetic method . It is suitable for thicker panels around four to twelve centimeters thick. Production usually takes place on a rotary table press with usually seven, sometimes only five stations. Two different types of concrete are used: The relatively low viscosity facing concrete and the very dry backing concrete . The facing concrete later forms the visible upper side of the slab and is individually designed in terms of color and grain size. A uniform type of concrete is usually used for the back concrete.

First, the facing concrete is poured into the mold and distributed by shaking. Then the back concrete is poured in and the entire filling (usually in two steps) is compacted by pressing. Due to the high pressure of up to 1200 tons, part of the moisture migrates from the facing concrete into the back concrete, whereby the two layers are homogeneously connected. After opening the mold, the raw slab is removed, placed on a pallet made of metal, wood or (more rarely) plastic and placed in a warehouse so that the concrete can set.

The wet pressing process is similar to the hermetic process, but only one type of concrete is used here. This enables very thin panels to be produced. Since the concrete is still relatively thin when it is poured, most of the water must be able to escape from the mold during the pressing process .

Certain panels are also poured into molds (e.g. made of polyurethane ) and only removed after they have set ( wetcast process ). This has the disadvantage that a corresponding number of forms must be kept available.

In the past, concrete slabs were also stamped. However, this procedure is now considered out of date.

In order to avoid shrinkage cracks during the hardening process, fibers are often added to the concrete, which is called fiber concrete . The fibers absorb the tensile stresses that arise during curing and thus enable large panels to be produced.

Special effects

If the bottom of the mold is not smooth but has a pattern, this will be shown in relief on the finished panel. In this way you can achieve a sandstone- like appearance, for example .

A marbling effect can be achieved by spraying in additional paint before filling the back concrete.

With direct washing, the panels are processed with a high-pressure water jet immediately after removal from the press. The fine components of the concrete are removed from the surface, while the coarser grains are retained.

If the bottom of the mold is lined with paper that has been soaked with a setting retarder (e.g. sugar ), the front of the plate cannot harden. After the concrete has set, paper and non-hardened concrete residues can be removed by brushing and using water. This is how you get the classic exposed aggregate concrete .

Further processing

After setting, the panels can be processed in various ways. The main options are:

  • grind
  • Blasting with or without previous grinding. By using matrices, parts of the panel surface can also be blasted while others remain unprocessed
  • Rumbling, i.e. the mechanical tapping of the plate surface with a kind of hammer
  • Processing of the edges, e.g. B. by grinding bevels
  • Acid to remove cement residues or to achieve a greater roughness of the surface
  • The spraying of a coating to the resistance to dirt and weather influences to increase