Concrete Slipform Construction Advantages
Your project can benefit in numerous ways from using this method of construction for taller concrete structures.
Consider the following items:
This technology becomes very competitive starting at about 60 ft of height and continues to improve with increasing height thereafter.
The slipform setup is very compact and can be pre-assembled ahead of time. Once the foundation is ready, the slipform can quickly be placed on the foundation and construction can start almost immediately.
No cold-joints are necessary. Construction can be continuous and monolithic, resulting in maximum durability and a long service life for your structure.
Speed of Construction
Speeds of between 7 ft and 30 ft per 24 hours are possible. Many times, this speed allows reuse of formwork on repetitive elements without impacting the overall schedule, thus reducing your total formwork cost.
No Form Ties
No ties are required because the limited concrete pressure is taken by the slipform yoke directly. Without ties, there are also no form holes to fill, which reduces labor costs, improves appearance and makes for a water-tight structure. This is particularly important for offshore structures such as gravity oil and gas platforms.
No Rebar Bolsters
Unlike in standard wall construction with panel forms, slipforming does not require lost rebar bolsters in every pour to control the rebar cover. In slipform construction, sliding guides are mounted on top of the slipform. These guides push the rebar into position and accurately control the rebar cover as the slipform moves upwards.
Slipforming is a continuous extrusion process. There is no need to set and strip forms every few feet. You do not need to tie up a crane as for handling conventional formwork.
Slipforming provides a superior concrete finish with no form fins to clean up and without horizontal joints. A sponge finish and other surface treatments are easy to apply from the second work platform suspended from the slipform assembly.
The slipform setup provides a safe and protected work environment for your crew. Relatively little climbing is required, the work area is compact and unchanging and weather protection can easily be added to the formwork setup. Enclosed spaces can be heated during the cold weather periods.
Also, the slipform is never released from the structure during climbing, as is commonly done with other form systems. It only climbs in small increments and is continuously connected to the structure at multiple points, making it a very safe system.
A slipform is of low overall height and very compact. That makes it is easier to handle and modify for changing concrete cross-sections. Also, the extension past the hardened concrete line is very short, so very little wind force has to be considered in the formwork design.
Many times, a slipform setup does not need a tower crane to service the work point, which is a great cost savings. A winch connected to the slipform can be used to bring up material on the inside of the shaft, where it is protected from the wind. A tower crane may have to shut down during high winds, whereas the winch can keep going.
Easy To Stop
The slipform operation can be stopped and resumed at will, to suit the contractor’s schedule. Slipform operations can be suspended for the weekend or during parts of the day as dictated by external factors. This is done by climbing another 18 in. or so after the last concrete has been poured. This gives the concrete time to set and helps to break the form adhesion to the fresh concrete.
Standard Concrete Mix
No special concrete is needed for a typical slipform project. For certain offshore structures, advanced concrete mixes have been developed to improve the performance of the structure in the ocean environment. However, these types of structures are rare and the vast majority of buildings and towers can be slipformed with ordinary concrete mixes.