What Is Hollow Core Slab?

Hollow core slabs also know as “voided slabs” or “concrete planks” are prestressed precast concrete slabs panels having usually circular openings and are typically used in construction of floors and roof in multistory construction.

Typical precast prestressed hollow core slab panel Image credit: megaprefab.com



Hollow core slabs have major advantages and are used widely where prestressing technology is available. It has following advantages

  • These slabs provide economical and efficient floor and roofing systems
  • The underside of slab can be used as a finished ceiling using paints and acoustical sprays.
  • Due to presence of void through out the panel, it has excellent fire resistance.
  • Voids act as insulator for sound as well as it reduces sound transmission from one apartment to another (in case when used in building).
  • They are precast and prestressed concrete members with continuous voids which can accommodate electrical or mechanical runs.
Hollow core slab panel accommodating electrical and mechanical runs. Image credit: weilerprecast.com


Properties and Specification

Thickness of hollow core slabs vary from 4 to 15 in. The grout which is used for filling voids is usually 1:3 cement sand mortar with maximum 2000 psi capacity. For the main hollow core slab 5000 psi is must. These slabs may or may not have structural or non-structural topping having strength of about 3000 psi.

The span to depth rations of hollow core slabs are in the range of 30-50 while for hollow core roof slabs it is 40-50.

Dry extrusion or wet placements are usually two methods for construction, the later one is preferred.Voids of any shape can be induced by using an appropriate form-work placed in the bed. The strands are then pre-tensioned. Usually Low relaxation strands of about 0.5 in diameter are used.

Concrete used after setting up form-work is usually self-consolidating or self-compacting concrete.



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Civil Engineer MSc from National University Of Sciences And Technology.