Hollow-core slab
The hollow core, also concrete hollow core or concrete hallway, is a uniaxial armored precast concrete with standardized dimensions, which is produced in precast plants. Today it is regarded as technologically obsolete. Hollow core slabs have been largely replaced by concrete slab and semi- precast slab elements.
Construction
Hollow core slabs are half Precast concrete quality-controlled, which are used on the construction site to the formwork by massive ceiling of reinforced concrete. Looking at the cross section of rectangular concrete elements, so round hollow chambers between the reinforcing rods are arranged at regular intervals, extending through the entire length of the concrete element. So that material is saved and the weight is reduced. The longer the hollow core ( span ), the stronger are the desktop elements designed to increase the intrinsic stability.
Development and use
Hollow core slabs have been developed to simplify the previously common, usually made of wood slabs for solid ceilings situ concrete. The time required to create the slabs decreased and less concrete for grouting it was needed. Concrete planks occurred mainly in the industrial and multi-storey basement in intermediate and roof ceiling with regular axis dimensions apply. Due to the relatively low weight of the individual elements of this without heavy lifting equipment ( cranes ) were mounted. Through the development of panel formwork systems, custom-made prefabricated floor slabs or concrete slab hollow core slabs have lost much of its importance. Only on construction sites without use of a crane, for example in private construction, a hollow plank ceiling can still be economical. The concrete floors are available in different lengths are placed on or in steel beams ( joists ) that were positioned for a ceiling plan on the wall tops. The concrete elements are laid in the rule manually or with simple lifting and brought in the installed position. The resulting walk formwork is equipped with additional reinforcement after reinforcement plan, can be provided with pre-installation for plumbing, electrical and ventilation and is then filled with concrete to form a monolithic ceiling. At lower spans can be eliminated by the present in the hollow core slabs steel reinforcement to provide additional support for encapsulation with the upper concrete.
Prefabrication
The production takes place in a precast plant in series production and monitored quality. The usually in lengths up to 160 cm (maximum 300 cm) concrete planks produced are poured into appropriate molds, in which pre- construction steel bars as reinforcement and moldings for the cavities are inserted. Depending on the span of the hollow core slabs have to allow a thickness between 6 cm and 10 cm and weights up to 100 kg ( maximum about 180 kg) to a processing without cranes. The width is a uniform 33 cm. After curing and partial curing of the hollow core slabs are removed from the mold and removed from the molded body, whereby the characteristic circular hollow chambers formed. After about 28 days the concrete has reached its ultimate strength.
Benefits
- More economical construction by a faster and support free assembly against classical Ortbetonschalung.
- Easy transportation of the individual elements
- Applicability without heavy lifting equipment, even in hard to reach places
Disadvantages
- The hollow core slabs and therefore the finished ceiling, in contrast to floor slabs and concrete slab on a rough bottom, the receiving iron beams remain visible. If this is undesirable, must be cleaned or covered.
- The manual operation during assembly is significantly higher than for the larger prefabricated elements, the mounting times are higher.
- Individual measurements or ceiling cutouts outside of the plank grid must be laboriously created on site by editing the hollow core slabs.