Product category:
Concrete, Cement, Admixtures
News Release from: The Concrete Centre
Edited by the Buildingtalk Editorial
Team on 06 November 2007
Recycled materials usage sets benchmark
Arup collected first prize in The Concrete Centre's Award for Sustainability 2007 for high percentage of recycled materials used at Number 1 Coleman Street, London.
Arup design team's decision to use a high percentage of recycled materials has set a new environmental benchmark for construction The Award was presented at The Concrete Society awards dinner in London
This article was originally published on Buildingtalk on 31 Jul 2007 at 8.00am (UK)
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Developed by Stanhope and designed by architects Swanke Hayden Connell Architects, the nine-storey, 18,000m2 office demonstrates sustainability as an integral part of the construction process.
The engineer, Arup, chose to use china clay stent as a natural coarse aggregate to replace the use of primary quarried Croft granite.
In addition, the project used a secondary cementitious material - fly ash.
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Although the use of secondary cementitiouos materials such as fly ash is well established, the difference in 1 Coleman Street is that rather than the commonly employed level of 30% fly ash by mass of cement, Arup used a higher content of up to 40% as standard.
The use of china stent and fly ash plus the use of reinforcement manufactured from 100% scrap metal increased the recycled/secondary value of the concrete to as much as 77% depending on the amount of reinforcement in an element.
Stent is the term used to describe the waste granite rock material that has been separated from kaolin (china clay) by high-pressure water jets.
For every tonne of china clay, approximately 4.5 tonnes of stent is produced along with other waste, which is usually tipped onto ever-growing surface spoil heaps.
Conventional wisdom has been that stent was not of a sufficiently high quality to enable it to be used as a concrete aggregate.
Evidence to refute this comes from the long history of stent's use in ready-mix concrete in Cornwall and Devon.
1 Coleman Street is the first major use of stent outside the South-West.
The stent was supplied by Bardon Aggregates from the Littlejohn Quarry near St Austell was selected in order to meet the requirements of BS EN 12620 and PD 6682-1 for concrete aggregate.
Despite sourcing the stent from a quarry 250 miles away there were no additional lorry journeys.
Instead, a total of five 1,200 tonne train loads travelled from the quarry site to the rail head at Bardon Concrete's ready-mix plant in Bow, London.
The use of the stent meant that 6,000 fewer tonnes of china clay waste were deposited onto the spoil heaps and equally, 6,000 fewer tonnes of primary aggregates were quarried.
Another environmentally sensitive decision was to use 40% fly ash by mass of cement in the structure's C32/40 pile caps and 35% in the C28/35 and C32/40 superstructure elements.
In the watertight concrete ground slab, the fly ash content was restricted to 30% simply to meet the specification requirements of the admixture producer.
Because of the innovative nature of the concrete, discussions between the parties involved commenced well in advance of construction to allow time to obtain test data, develop mix designs and perform trials.
Full test data for the aggregate's physical properties, petrographic characteristics and alkali-silica reactivity were obtained to ensure that no risks were taken and that the material could fully meet the project procurement requirements.
It was realised at the specification stage that the stent aggregate concrete would cost a little more per cubic metre than its conventional equivalent.
This was largely due to the transportation and testing costs.
However, these extra costs were partially offset by the fact that stent is exempt from the UK aggregates levy and if used more often for future projects there would be less need for extensive testing.
Presenting the winning award to Arup, Ian Cox, chief executive of The Concrete Centre said: "The level of recycled/secondary content in this commercial project is extraordinary".
"Furthermore, the design has been beautifully executed".
"Equally impressive is the commitment demonstrated by the project team to build upon the knowledge gained and to take it further on other projects".
He continued; "1 Coleman Street has proved the feasibility of using 100 per cent secondary coarse aggregate in a large scale project remote from the source of the material and has demonstrated the scope for using above average fly ash cement combinations".
"Moreover, the project has not encountered problems with specification, supply or quality control of the concrete".
"It is truly worthy winner of our 2007 Sustainability Award".
Project team.
Client: Stanhope.
Architect: Swanke Hayden Connell Architects, David Walker Architects.
Engineer: Arup.
Construction Manager: Bovis Lend Lease.
Main contractor John Doyle.
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