If the areas of the reinforced concrete envelope of a building that come into contact with the ground are designed in such a way that they are impermeable to water without additional coating, this is referred to as a white tank according to the DAfStb guideline (also known as the WU guideline).
The white tub is an alternative to the black tub . In the design of the White Tub, the concrete quality, reinforcement routing and joint formation are adapted in such a way that the crack widths are kept to a minimum in order to ensure impermeability to water.
The DAfStb guideline for water-impermeable concrete structures, or WU guideline for short, regulates the construction of water-impermeable structures that are waterproof without additional coatings. The monolithic reinforced concrete component itself (e.g. basement wall or floor slab) is designed to be impermeable to water. The classification according to the above-mentioned use and stress classes must be coordinated and documented between the planner, structural engineer and building owner.
The WU guideline only regulates the transport of moisture in liquid form. The Directive does not contain any further provisions on the moisture transport of other types and causes (e.g. vapour diffusion), which can also result in moisture being released on the room side. In the case of high usage requirements, the effects of these moisture transport processes must be limited to the necessary extent if necessary by indoor climate and building physics measures. Regardless of the conditions mentioned, additional indoor climate and/or building physics measures must be taken to prevent condensation, drying out of the building moisture or to ensure a dry indoor climate. These can be, for example:
Planning and monitoring by specialist companies: Companies that specialize in the planning and monitoring of watertight concrete components specify the necessary waterproofing measures and prepare binding planning documents for the service description and the Execution. They then monitor the practical implementation on the construction site and usually grant extended warranty periods and assume full liability. In this way, liability is transferred to companies with a lot of experience and specialist knowledge, planners and builders are relieved. In contrast, the costs are usually in a reasonable proportion.
The specialist company monitors the dewatering measures, the reinforcement installation, the joint bridging and the delivered concrete on the construction site, including its processing. As a rule, state-of-the-art auxiliary and measuring devices are used here, while concrete monitoring is organised in the background by the company's own concrete testing centre.
According to the WU guideline, the following parameters must be planned, documented and implemented:
Concrete quality: The concrete quality is usually determined by the structural engineer. These relate to the exposure class (e.g. XC), concrete quality (e.g. wu-Beton), the compressive strength class (e.g. C30/37), the consistency class (e.g. F3) and the maximum grain size.
Component dimensioning: The WU guideline specifies its own minimum component thicknesses, regardless of static requirements, which must be taken into account as minimum thicknesses during planning. See the knowledge pages ► 101 │Basement walls made of reinforced concrete and 100 | Foundation/floor slab.
Reinforcement guide: The reinforcement guide must be selected by the structural engineer in such a way that the perfect insertion and compaction of the fresh concrete and the integration of the joint tapes and built-in parts is possible without any problems and "fresh in fresh".
Crack width limitation: By choosing the measures, separation cracks can be avoided or at least limited, so that a wall consistency impermeable to water is created.
See ► WU Guideline, Crack Width Restriction
Waterproofing: Joint systems must be adapted to the water pressure and designed in a uniform and closed system. Movement joints should be avoided if possible. They should only be provided for where deformations between neighbouring components cannot be controlled by other design measures.
following points must be taken into account when executing water-impermeable structures:
Monitoring: DIN 1045-3 formulates a multi-level monitoring system with monitoring classes 1, 2 and 3. The requirements for checking the relevant fresh and hardened concrete properties increase with increasing monitoring class. When processing concrete of monitoring classes 2 and 3, monitoring must be carried out by a recognised monitoring body in addition to monitoring by the construction company
.Anchors and spacers: The construction of water-impermeable structures requires special care in monitoring. In addition to the correct arrangement of the reinforcement, the correct installation of the formwork anchors and spacers must also be checked. Especially in the case of structures subject to pressurized water, special anchors with water barriers are necessary. A selection of suitable anchors is listed in the DBV leaflet "Spacers".
Aftertreatment: Concrete must be treated regardless of the weather conditions. For example, floor slabs must always be covered after the concreting process to protect them from drying out too quickly. Walls should only be stripped after the specified time and also treated after stripping. Precise specifications on the type, duration and implementation of post-treatment are regulated in DIN 1045-3.
DIN 1045-2, Structures made of concrete, reinforced concrete and prestressed concrete - Part 2: Concrete - Specification, properties, production and conformity - Rules of application for DIN EN 206-1
DIN 1045-3, Structures made of concrete, reinforced concrete and prestressed concrete - Part 3: Construction - Rules of application for DIN EN 13670
DIN 1045-4, Structures made of concrete, reinforced concrete and prestressed concrete - Part 4: Supplementary rules for the manufacture and conformity of precast elements
DIN EN 1992-1-1, 2011-01, Eurocode 2: Design and construction of reinforced concrete and prestressed concrete structures - Part 1-1: General design rules and rules for building construction
DIN EN 1992-1-1/NA, National Annex - Nationally defined parameters - Eurocode 2: Design and construction of reinforced concrete and prestressed concrete structures - Part 1-1: General design rules and rules for building construction
DIN EN 1992-1-1/NA/A1, National Annex - Nationally defined parameters - Eurocode 2: Design and construction of reinforced concrete and prestressed concrete structures - Part 1-1: General design rules and rules for the construction of reinforced concrete and prestressed concrete structures Building construction, amendment A1
DIN EN 1992-1-2, Eurocode 2: Design and construction of reinforced concrete and prestressed concrete structures - Part 1-2: General rules - Structural design for fire
DIN EN 1992-1-2/NA, 2010-12 , National Annex - Nationally defined parameters - Eurocode 2: Design and construction of reinforced concrete and prestressed concrete structures - Part 1-2: General rules - Structural Design for Fire in the Event of Fire
DIN EN 13670, Execution of Concrete Structures
WU Directive (DAfStb Guideline for Water-Impermeable Structures Made of Concrete), November 2003 edition, Publisher: German Committee for Reinforced Concrete – DafStb at DIN German Institute for Standardization e. V.
Source: bauwion
