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Tuesday29 July 2014

Spun concrete columns

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Technology once used for drains is now producing concrete columns with the smallest footprint ever.

The practice of spinning concrete and using centrifugal force for internal compaction began in the 1950s when large diameter concrete pipes were spun with spigot and socket ends to supply the main drains for many new industrial and housing estates across Germany.

Europoles, based in Neumarkt, Germany, saw the possibilities in adapting the technology for architectural uses, and developed it to make smooth faced, circular columns for building structures, as well as for supporting high tension electrical transmission lines for the national grid, for the German railway and for tall telecommunication masts.

The company has become a leading producer of spun concrete columns, which it supplies in single- or multiple-storey lengths of up to 38m, with various profiles – circular, oval, square and tapered.

It offers architectural columns in a choice of surface textures, colours, and profiles. It can also create innovative column arrangements for all types of frames and floors – in situ, precast or steel composite decks.

For a given loading, these slender columns result in the smallest footprint of any concrete column type, increasing net lettable and useable floor space. This is achieved because of the high-strength concrete that is specified – from 90 Mpa (megapascals, which are units of pressure) to 120Mpa – and the high percentage of reinforcement – up to 15%.

Manufacturing spun concrete columns

Fully engineered, slender, circular, architectural spun columns provide a blemish-free finish in a range of lengths.

These photographs, taken in one of Europoles’ factories, show the process used to make a communications tower – a slightly different production process from making architectural columns. Telecommunications towers are often made in two or three sections because of their overall length (often 40m tall) and are enclosed in steel flange plates which allow the tower to be connected on site.

These flange plates are retained once the tower is in place, whereas architectural columns, being shorter, do not require the flange plates and the concrete is left exposed.

Spun concrete columns

Filling the mould

The columns are cast in circular steel moulds, built in two halves. The bottom half of the mould is positioned on the spinning bed, to receive the reinforcement cage and the concrete mix. High-strength concrete is placed in the mould by an overhead hopper.

Spun concrete columns

Spinning the column

The top half of the mould is then closed and clamped tight and the column box spun at about 900 revolutions per minute for 15 to 20 minutes. The spinning creates a centrifugal force of 20 gravity which compresses and compacts the fresh concrete against the steel mould face, eliminating any air voids and producing a dense, durable surface finish.

Spun concrete columns

Revealing the hollow shell

The hollow column shell created by the spinning process not only reduces the weight of the column, but it also offers a hidden conduit for services, for ducted air and for rainwater disposal. It is fast to erect, speeds up the floor construction cycle, it is self finished and has a good fire rating.

UK case study: Liberty building, Leeds University school of law

Leeds University’s new Law School, the Liberty building by Broadway Malyan, features a colonnade of slender spun concrete columns to support a louvred brise-soleil – the first time the technique has been used in the UK.

Completed last autumn, the £8.2 million Law School occupies the north-west corner of the university’s western campus.

Leeds University school of law

Source: Martine Hamilton Knight

Broadway Malyan’s Liberty Building uses spun concrete columns to support a louvred brise soleil

The four-storey flat slab concrete frame offers flexibility and openness for services and for access provision; while the exposed concrete soffit provides a smooth, clean, light reflective ceiling.

The spun columns are 300mm in diameter and 14m in length with a bolted base plate connection to the foundation and a steel top hat connection for carrying the brise-soleil canopy.

The building was designed with a natural ventilation system and used the exposed concrete frame’s thermal mass. The ventilation stacks in the heart of the building allow fresh air to be drawn into the offices and discharged via the central atrium, through external louvres.

The inclusion of a biomass boiler, the use of natural ventilation, plus airtight construction and the concrete’s thermal mass, has produced a Part L carbon emission rating of 9.82kgCO2/m2, which is low for an office building.

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