Post Tensioning Services Limited


On Falomo Ramp Bridge, Victoria Island, Lagos, the voids ensured 35% lighter structure.

The voids were produced in lengths of 6 meters and jointed on site.

700 linear meters were produced in 1 week and installed in 10 days.


In Partnership With


Voids are light weight and can be installed without a crane.

The voids shall be firmly attached in position to avoid floating in fresh concrete.

Solid joints and end caps are the key items for a successful void.


PTSL produces circular void formers of different diameters ranging from 400mm to 1200mm and different length depending on the project. Special dimensions can be custom produced.

PTSL provides installation services as well.


The voids are produced by a spiral machine which rolls galvanized steel strip in form of cylinders.

The pipe is corrugated to increase its radial stiffness and avoid its deformation and flattening under pressure.

The gauge of steel and the corrugation depends on the diameter of the void.

Pipes are jointed together on site.

The ends are closed by a steel plate.

The seams are water tight preventing infiltration of water inside the void.


For long spans, one of the commonest way of lightening a solid slab is to use void formers.

Lighter structure means better structural performance, less dead load, smaller foundations and savings in concrete and reinforcement.


Although void formers appear to be impermeable, it is actually not 100% watertight, the voids should therefore be provided with drainage holes at their lower ends.