WHAT IS SLIP FORM CONSTRUCTION?

Slip form construction is also known as continuous formed construction. It is a construction method of in which concrete is poured into a continuously moving form.

This method consists the continuous placing of concrete in a shallow mould having the same plan as the building to be constructed. This kind of moulds are rigid and hard to resist the pressure of fresh poured concrete and this formwork is in continuous slip manner towards up so it has been called slip form. This mehod is suited for high rise building to construct its core walls on continuous rates which saves time and reduce project tenure. 

Slip Form | Slip Form Construction | Slipform Concrete Construction

The formwork rises upward continuously ata rate of 300 mm per hour. It allows for the continuous pouring of concrete into walls of a structure and only stops when the full required height of the structue has been reached. The height of the formwork is designed in such a manner that while top of the formwork is being filled by concrete the lowest layer of concrete poured earlier has already gained an initial set.

Concrete slip form sliding formwork - Bitschnau GmbH

Procedure :
  • Assembly can only start once the foundations are in place and the wall starter is in correct alignment.
  • Slip form shuttering is aligned with the help of yokes.
  • Horizontal crossbeams connect these yokes.
  • Hydraulic jacks are attached to these crossbeams for simultaneous upward movement.
  • Height of the slip form is ranging between 1.1 to 1.5 meter.
  • Yokes and crossbeams also used to support  the working platform.
  • Structure should be rigid and shape maintained at all times.
  • Make sure there is no lag or else it prevents the structure from free upward movement.
  • It is also possible to reduce the thickness of wall constructed. The form arrangement have designed to reduce the wall thickness on regular intervals.


Types of Slip form construction

1. Vertical slip form

Slip forming - Wikipedia

In vertical slip forming, The concrete form may be surrounded by a platform on which workers stand, placing steel reinforcing rods into the concrete and ensuring a smooth pour. Together, the concrete form and working platform are raised by means of hydraulic jacks. Generally, the slip form rises at a rate which permits the concrete to harden by the time it emerges from the bottom of the form.

2. Horizontal slip form

Slipform Techniques for Accelerated Construction

In horizontal slip form is used for horizontal structures like pavements, canals , tunnelings and traffic separation walls. The concrete is cast, vibrated, worked and settled in place while the form itself slowly moves ahead. This method was initially devised and utilized in interstate highway construction during 1950s.

3. Tapered slip form

Slip forming - Wikipedia

Tapered slip form is used for chimneys, cooling towers, Silos etc. which have a conical shaped structure. It involves the constant changing thickness in walls and diameters. A form is used with section which overlap so that one gradually slides over the other. This is commonly done in chimney construction but it is not satisfactory for architectural concrete because of the lap shows. While the tapered slip forming process is similar to that used on the standard slip forming, It requires greater attention.



Precautions for slip forming
  • Concrete is continuously protected against loss of moisture and rapid temperature changes for 7 days.
  • Unhardened concrete is protected from the rain and flowing water.
  • Need to prevent plastic shrinkage cracks.
  • Need to fill up plastic cracks by injection of epoxy or resin grouting.

Advantages of slip form
  • A major cost of concrete structure construction is the required formwork to retain the concrete till it can be safely de-shuttered and be able to support itself and other imposed loads.
  • The formwork can be used repeatedly and re-erected at other newer location.
  • Continuous use of man power and equipment like cranes reduces time and save money.
  • In case of slip form building, the formwork is erected only once and remains intact until the entire structure is completed.
  • Great reduction in cost of formwork as well as time saving for re-shuttering work.





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