Invented in 1942 by the Swedish company Byggförbättring, the slipform technique is based on a system of mechanical lock nut hydraulic jacks connected to a hydraulic power unit, which allows all the vertical walls of large-scale structures to be built simultaneously. This process means that no scaffolding is required.
During slipform construction, the formwork is slid upwards at a rate of of 15 to 25 cm per hour, in conjunction with continuous concreting. The movement is provided by hydraulic jacks. The forms, which are generally 1.20 m high, travel 4 m in 24 hours, meaning that the concrete emerging at the bottom is 4 to 6 hours old. It must be firm enough to be able to hold without forms but must not have set sufficiently to stick to the formwork, which would then pull off bits of concrete as it rose.
Regardless of the operating method (24-hour or 8-hour), slip forming represents the quickest, safest and most economical forming technique for reinforced concrete vertical structures. It is economically beneficial from a height of 15 - 20 m for narrow structures, but the scale of a project or the repetition of elements further increases its profitability.
Examples of applications:
- Lift shafts and stair enclosures
- Main sections of commercial buildings
- Silos and chimneys
- Bridge piers
- Jetty piles
- Caissons for ports and jetties
- Oil platform bases
- Vertical and sloping wells
- Water towers