What Is A Hollow Core Slab Construction Method?

What Is A Hollow Core Slab Construction Method?

What Is A Hollow Core Slab Construction Method?

A hollow core slab, also called a voided slab or a concrete plank, is a precast piece of prestressed concrete that is commonly used in the construction of floors in multi-story apartment buildings. It is particularly popular in countries where precast concrete is preferred for home construction, such as Northern Europe and former Eastern European socialist countries.

This type of slab is made by extruding wet concrete along with prestressed steel wire rope from a moving mold, and is then cut to the desired length using a diamond circular saw.

The slab has tubes with a diameter that is typically 2/3 to 3/4 the thickness of the slab running the length of the slab, which makes it lighter and more cost-effective due to reduced material and transportation costs.

It is typically 120 cm wide and has standard thicknesses of 15-50 cm, with reinforcing steel wire rope providing bending resistance. Hollow core slabs can also be made of reinforced concrete without prestressed steel wire and produced on a carousel production line to specific lengths, although the length is usually limited to 7-8 meters.

These types of slabs may need to be covered with a soft floor covering or floating floor screed to meet modern soundproofing standards, or a strip of rubber may be placed underneath the slab. The voids in the slab can also be used as conduits for installations or coated for use as ventilation ducts.

Advantages Of Hollow Core Slabs

Hollow core slabs offer several benefits in construction, including:

  • Cost savings and reduced weight due to their ribbed design
  • Improved fire resistance and sound insulation due to their thickness
  • Simplified electrical and plumbing installation as there is no need to drill into the slab.
  • Easy and quick installation with minimal labor required
  • Fast construction times.
  • No additional formwork or specialized machinery is needed for reinforcement.

Manufacturing Process Of Hollow Core Slabs

The process of manufacturing hollow core slabs involves the following steps:

·         Designing and planning the layout of the slabs using 3D CAD software, and creating a production plan for the factory.

·         Preparing the casting beds by cleaning them and applying an oil release agent, and running prestressing tendons down their length.

·         Applying load to the prestressing tendons using hydraulic pumps and jacks/cylinders, and locking them into place.

·         Batching and distributing the concrete mix to the casting machine.

·         Casting the concrete into the desired shape using an extruder, Slipformer, or Flowformer.

·         Adding any additional detailing to the slabs, such as openings or lift pins, using a plotter or vacuum suction machine/aspirator.

·         Curing the slabs by covering them with insulated covers and potentially applying additional heat.

·         Detensioning the prestressed tendons once the concrete has reached the desired strength.

·         Cutting the slabs to the correct length and angles using saws.

·        Removing the slabs from the casting beds using clamps and lifting beams.

  • In the factory, storage slabs can be transported by forklift trucks or side loaders on bogeys and then stacked on timber bearers in the stockyard.

Applications Of Hollow Core Slabs

Hollow core slabs are used in a variety of construction projects, including residential, commercial and industrial buildings as well as infrastructure projects. They are designed to withstand high loads and have up to 180 minutes of fire resistance.

Some common applications for hollow core slabs include industrial roof coverings, car parking structures, underground car parks, large commercial roof covers, continuous flooring, grandstands, floors for multistorey buildings and use with steel structures.

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