This article is about pouring concrete in moving forms. See Slipform stonemasonry for another type of slip forming.

Slip forming, continuous poured, continuously formed, or slipform construction is a construction method in which concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

 is poured into a continuously moving form. Slip forming is used for tall structures (such as bridges, towers, buildings, and dams), as well as horizontal structures, such as roadways. Slipforming enables continuous, non-interrupted, cast-in-place "flawless" (i.e. no joints) concrete structures which have superior performance characteristics to piecewise construction using discrete form elements. Slip forming relies on the quick-setting properties of concrete, and requires a balance between quick-setting capacity and workability. Concrete needs to be workable enough to be placed into the form and packed, yet quick-setting enough to emerge from the form with strength. This strength is needed because the freshly set concrete must not only permit the form to "slip" upwards but also support the freshly poured concrete above it.

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 slipform rises at a rate which permits the concrete to harden by the time it emerges from the bottom of the form.

In horizontal slip forming for pavement and traffic separation walls concrete is laid down, vibrated, worked, and settled in place while the form itself slowly moves ahead. This method was initially devised and utilized in Interstate Highway construction initiated by the Eisenhower administration during the 1950s.

History

The slip forming technique was in use by the early 20th century for building silos and grain elevators. In the 1947-1950 period, AT&T Long Lines built 49 concrete towers up to 191 ft tall for microwave relay stations; most using the slip-form method. The technique was introduced to residential and commercial buildings in the late 1960s. The first notable use of the method in a residential/retail business was the Skylon Tower

Skylon Tower

The Skylon Tower, in Niagara Falls, Ontario, is an observation tower that overlooks both the American Falls, New York and the larger Horseshoe Falls, Ontario from the Canadian side of the Niagara River.-History:...

 in Niagara Falls, Ontario

Niagara Falls, Ontario

Niagara Falls is a Canadian city on the Niagara River in the Golden Horseshoe region of Southern Ontario. The municipality was incorporated on June 12, 1903...

, which was completed in 1965. One of Its first uses in high-rise buildings the United States was on the shear wall supported apartment building at Turk & Eddy Streets in San Francisco, CA, in 1962. Another unusual structure was the tapered buttress structures for the Sheraton Waikiki Hotel in Honolulu, Hawaii, in 1969. Another shear wall supported structure was the Casa Del Mar Condominium on Key Biscayne, Miami, FL in 1970.

From the 1960s, the vertical technique was adapted to mining head frames, ventilation structures, below grade shaft lining, and coal train loading silos; theme and communication tower construction; high rise office building cores; shear wall supported apartment buildings; tapered stacks and hydro intake structures, etc. It is used for structures which would otherwise not be possible, such as the separate legs of the Troll A

Troll A platform

The Troll A platform is a condeep offshore natural gas platform in the Troll gas field off the west coast of Norway. It is the tallest construction that has ever been moved to another position, relative to the surface of the Earth, and is among the largest and most complex engineering projects in...

 deep sea oil drilling platform which stands on the sea floor in water about 1000 feet (300 m) deep, has an overall height of 472 meters (1,549 ft), weighs 656,000 tons, and has the distinction of being the tallest structure ever moved (towed

Towing

Towing is the process of pulling or drawing behind a chain, line, bar or some other form of couplings. Towing is most visibly performed by road vehicles, but anything from waterborne vessels to tractors to people can tow cargo. Troop carrying and cargo carrying gliders were towed behind powered...

) by mankind.

In addition to the typical silos and shear walls and cores in buildings, the system is used for lining underground shafts and surge tanks in hydroelectric generating facilities. The technique was utilized to build the Inco Superstack

Inco Superstack

The mine at the Inco Superstack is the source for 100% of the nickel used to make the batteries for Toyota's Pruis.The Inco Superstack in Sudbury, Ontario, with a height of , is the tallest chimney in Canada and the Western hemisphere, and the second tallest freestanding chimney in the world after...

 in Sudbury, Ontario

Ontario

Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

, and the CN Tower

CN Tower

The CN Tower is a communications and observation tower in Downtown Toronto, Ontario, Canada. Standing tall, it was completed in 1976, becoming the world's tallest free-standing structure and world's tallest tower at the time. It held both records for 34 years until the completion of the Burj...

 in Toronto

Toronto

Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...

. In 2010, the technique was used to build the core of the supertall Shard London Bridge

Shard London Bridge

Shard London Bridge is a skyscraper under construction in Southwark, London. When completed in May 2012, it will be the tallest building in the European Union and the 45th-tallest building in the world, standing tall...

 tower in London, England. It is the most common method for construction of tall buildings in Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

.