White tub

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White Tank is a term from the construction of a water impermeable reinforced concrete structure . The decisive feature is the lack of additional sealing layers , since the load-bearing reinforced concrete structure also forms the sealing element. The system of the white tank is often used in sealing against groundwater or leachate , such as foundations and floor tiles , exterior walls of basements and top with earth heaped blankets . Water tanks and swimming pools can also be sealed in this way.

The term “white tub” is derived from the fact that the water-impermeable concrete used, in contrast to masonry cellar walls, does not require any additional sealing; Such seals are made with a bituminous and thus black sealing layer, so that this type of construction is referred to as a black tank . Visually, a white tub is gray like the concrete used.

In the current WU guideline of the DAfStb from 2017, the white tank is referred to as the WU tank .

features

The density of the white trays is by the use of water-impermeable concrete , the sealing of work and expansion joints achieved, the formation of water-tight penetrations and the restriction of crack width in the concrete. According to the guideline for water-impermeable concrete structures (WU guideline) of the German Committee for Reinforced Concrete (DAfStb), there are other options in addition to limiting the width of the cracks to create a white tank. It is possible to dispense with the crack limitation if cracks that have occurred are subsequently sealed as planned. As a result, a white tank in service class A can be created and the degree of reinforcement can be selected to be considerably lower. There is also the option of planning the position and number of cracks with so-called predetermined crack cross-sections. Here, too, a higher class of use and lower use of steel can be expected.

In addition to professional execution, planning is particularly important. This consists in the provision of measures to avoid cracks, the definition of joints in the components, coordination with the structural engineering and specifications for work cycles and post-treatment of concrete. The type of sealing of joints and penetrations must also be specified. It also includes an overall consideration of building physics and room climate.

Expert supervision of the work on the construction site is also advisable. Paving and compacting the concrete must be carried out carefully, especially avoiding any segregation of the concrete. Professional follow-up treatment is necessary.

Joint tapes , joint plates , swelling tapes or grouting hoses are used to seal the joints on the inside . A gray tank is the name given to external PVC profiles which are watertight against pressure water and are used to seal construction joints, building separation joints and crack cross-sections on structures made of water-impermeable concrete in accordance with the Building Regulations List A, Part 2, No. 1.4. In addition to the K-tub as a surface seal (because concrete often cracks in the surface, as is often the case with plastic elements used in concrete), this also includes pipe penetrations that do not seal on the inside, but on the outside, where the water is.

It used to be assumed that due to diffusion , pressure gradient and capillary absorbency, there was constant moisture transport through the component. According to recent studies, this is not the case as long as the components are sufficiently thick, for example 24 cm, and are free of cracks.

Cross-section through a basement wall made of waterproof concrete. As long as the area of ​​the capillary water transport does not overlap with the drying layer, there is no significant water transport from the outside to the inside. The core area prevents water from flowing into the drying area, from which it would diffuse into the interior air .

According to the “WU guideline” of the DAfStb, three areas can be assumed whose strength is independent of the hydrostatic water pressure on the component in contact with water. For a concrete C30 / 37 with a water-cement ratio of maximum 0.55, for example, the following ranges are to be expected:

  1. Area - Influence area of ​​the standing water: This area is divided again into the external pressurized water area (0-25 mm) and the capillary area behind it (≤ 70 mm). Interactions between the pore water and the cement phases lead to a significant reduction in capillary conduction.
  2. Area - core area: If the component is at least 20 cm thick, no water will pass through the core area, not even in the form of water vapor.
  3. Area - Diffusion area to the interior: a drying area forms on the inside (approx. 40 to 80 mm). The excess moisture of the mineral building material concrete escapes into the room air when the room is used dry. In the first years of dry use, an equilibrium moisture level is established. The concrete in area 3 has adapted to the usage environment.

conditions

Since November 2003, the requirements for white tanks in Germany have been regulated by the directive on water-impermeable concrete structures of the German committee for reinforced concrete.

After that, the stress is divided into two classes. Stress class 1 applies to pressing and non-pressing water as well as temporarily standing seepage water, stress class 2 to soil moisture and non-standing seepage water.

In addition, usage classes were determined depending on the function of the building and the usage requirements for the component. In usage class A, moisture transport in liquid form (water penetration) is not permitted. In usage class B, damp spots are permitted on the component surface, i.e. H. In contrast to usage class A, limited water penetration is possible. There is also the specially agreed usage class. For the classic white tub, stress class 1, usage class A, often applies, which, however, cannot be achieved with the frequently used construction method according to design principle B (crack limitation).

The recommended minimum thicknesses are:

Component Stress class In-situ concrete Element walls Prefabricated parts
walls 1 240 mm 240 mm 200 mm
walls 2 200 mm 240 mm 100 mm
Base plate 1 250 mm - 200 mm
Base plate 2 150 mm - 100 mm

See also

literature

  • German Committee for Reinforced Concrete V .: DAfStb guideline »Water-impermeable concrete structures«  (WU guideline) , 12/2017. The 2017 edition replaces the WU guideline from 2003 with the amendment from 2006. The guideline deals with planning, construction, dimensioning and execution. It is to be regarded as a supplement to the proof of usability according to DIN EN 1992-1-1 and represents the current state of the art .
  • German Committee for Reinforced Concrete: Explanatory Notes on the DAfStb Guideline »Water-impermeable Concrete Structures«, Issue 555, Beuth Verlag, 2006. A revised new edition is in preparation.
  • "Sealing of buildings" group of standards - DIN 18195 and DIN 18531, 18532, 18533, 18534 and 18535. These standards do not deal with water-impermeable concrete structures and are therefore not applicable.
  • DBV leaflet "High-quality use of basement floors", version January 2009, Deutscher Beton- und Bautechnik Verein EV, Berlin. The leaflet deals with building physics and other usage-related requirements for basements made of waterproof concrete.
  • DIN EN 1992-1-1: Dimensioning and construction of reinforced concrete and prestressed concrete structures - Part 1-1: General design rules and rules for building construction, (2011-01), Beuth-Verlag, Berlin (often also as Eurocode 2 or EC 2 designated)

Web links

Individual evidence

  1. ↑ a b Dr.-Ing. Christoph Alfes: The new WU guideline of the DAfStb , In: Cemex.de, German Committee for Reinforced Concrete eV, Berlin, February 22, 2018
  2. ↑ a b c Zement-Merkblatt Hochbau H 10 5.2019 - Water-impermeable structures made of concrete , In: Beton.org; accessed in March 2020
  3. ↑ Prof. Dr.-Ing. Rainer Hohmann: Waterproof structures made of concrete, innovations in the revised WU guidelines , 2019
  4. ↑ Yellow draft of the guideline as of 2016-10-13 , In: LBB-Bayern.de, Landesverband Bayrischer Bauinnungen