Lightweight structural concrete for composite metal deck floor extension

60 London Wall, City of London



Byrne Brothers Formwork Limited



Location type

Office & Retail


October 2020

The challenge

A complete rework of a postmodern office building (60 London Wall), situated in the heart of the City of London. The project aim was to extensively refurbish, reconfigure, reinvent and reposition the building. The objective was to strip back the building to its frame and re-core to provide efficient high quality modern workplace accommodation with a prime retail offering at ground floor level.

Our solution

Due to the addition of a composite metal deck floor extension and additional steel frame for the top floors, Tarmac’s Toplight C lightweight structural concrete was seen as the perfect solution as it could be pumped and ensured a weight loss of 30% at no jeopardy to the structural concrete performance.

Results and benefits

The lightweight concrete mix design LC30/33 D2.0 at a density of 1850kg/m3, containing structural lightweight aggregates was pumped 60 metres (12 storeys) vertically on to the new composite deck floors. The use of lightweight concrete reduced the load by 30% which minimised the need for under pinning the existing frame and structures. The construction programme time was significantly reduced by using Toplight C which insured completion of the work was done in the shortest time possible for this 32,000m2 prime City of London office space.

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Additional info

Toplight C can be used in any application where normal weight concrete is specified as follows:

To create lighter concrete slabs, foundations, floors and walls to reduce loads on structures.

For reinforced concrete slabs

Using Toplight C, Designers can not only look to reduce the thickness of the slab, columns and foundations but also reduce the amount of steel mesh required resulting in a quicker more cost-effective greener building

On composite metal decking

Toplight C is ideal for composite metal decking. As spans increase the deflection becomes the defining factor. The use of Toplight C minimises the weight by up to 30% therefore reducing the deflection.

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TOPLIGHT C case studies