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Foamed concrete reaches the Pinnacle

Some 380m3 of foamed concrete from Propump Engineering has been used to fill three Victorian arched sub-pavement vaults as part of the foundation works at the £575 million Pinnacle Tower. Set to spiral 288 metres skyward from its base, the tower will become the tallest building in the City of London and the second highest in both the United Kingdom and the European Union.

Once complete it will form the apex of an emerging cluster of tall buildings in the centre of London’s main financial district. But before construction of the Pinnacle Tower could begin essential site strengthening works had to be carried out.

Having used Propump in the past, the UK’s leading demolition and civil engineering company, Keltbray Ltd, specified foamed concrete for the job. “We can trust Propump to do a good job,” explained Andy McClafferty of Keltbray. “Plus, if in the future the vaults need to be accessed, the foamed concrete is easily excavated unlike conventional concrete mixes.”

Typical of streets built in Victorian and Georgian times, the corner of Greater St. Helens – part of the Pinnacle Tower’s footprint – was home to a number of pavement vaults originally built as coal cellars. Accessed via external stairwells, Propump placed the lightweight, self compacting foamed concrete in 1 metre lifts. Each layer was set before applying the next to ensure the material did not consolidate under its own weight.

Manufactured on site via a Propump In-line Foamed Concrete System (IFCS), the foamed concrete was pumped into the vaults using hoses. Designed and built exclusively by Propump, the IFCS drives base material (sand, cement, water) through a specially designed squeeze pump to an injection chamber housed on the rig. From here, the preformed foam is injected into the base material and forced through a series of in-line mixers. The two are then blended together to produce the foamed concrete.

Reducing both truck movements and the time on site, the system provides an extremely efficient method of making foamed concrete. As well as being significantly more economic and environmentally friendly in comparison to other methods of foamed concrete production, it’s also safer than traditional concrete pumps due to its reduced operational pressures.

Designed to make substantial contribution to the public realm, the prestigious 63-storey skyscraper at Crosby Court, Bishopsgate, will contain 88,000 square metres (950,000 square feet) of office space and accommodation for over 8,000 workers. Completion for the Pinnacle Tower is scheduled in 2012 and the building is expected to open in 2013.

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