Work began in March to demolish St Helen鈥檚 Tower at 1 Undershaft in the City of London to make way for a taller replacement.
At 118 metres, St Helen鈥檚 Tower is the tallest building to be demolished in the capital to date. Switzerland-based concrete recycling specialist Neustark has been studying the planning documents published by the City of London Corporation. It calculates that there will be 49,000 tonnes of concrete aggregate removed from the site.
The opportunity to reuse some, if not all, of the 49,000 tonnes of concrete aggregate from the demolition of St Helen鈥檚 Tower would allow it to be returned to the same site at 1 Undershaft, and聽permanently store at least 490 tonnes of CO鈧� in recycled concrete aggregate (RCA).
The replacement skyscraper, known as One Undershaft, will be 309.6 meters tall, making it the same height as The Shard and the tallest building in the Square Mile.聽According to details published, One Undershaft will require 170,000 tonnes of concrete. Assuming building contractors use the full 20% substitution of gravel with RCA allowed by UK standards (BS 8500-2), roughly 14,000 tonnes of carbonated recycled concrete aggregate (cRCA) could be reused at the same site 鈥� equating to 140 tonnes of CO鈧� being permanently stored. Under the current UK limit of 20% aggregate, this would leave a surplus of approximately 35,000 tonnes of RCA left over from the demolition of St Helen鈥檚 Tower, and a further opportunity to sink a further 350 tonnes of CO鈧� on other local building projects.
Answering the call of London鈥檚 circular economy are projects such as 100 Leadenhall Street and 50 Fenchurch Street. Both projects are in pre-construction phase and have been recognised for their green credentials. These projects have architects, owners, and operators who are likely to welcome the opportunity to reduce embodied carbon, a key metric used by green certification bodies such as RIBA and BREEAM. Neustark says that there will never be a shortage of building projects willing to support all avenues of green construction, but UK legislation is holding back construction businesses from reaching the potential for carbon removal and building green supply chains.聽
Neustark says that the restriction imposed by British Standard BS 8500-2, limiting RCA use to 20% in reinforced concrete, is a significant constraint on greener building solutions. By contrast, countries within the EU and Switzerland are allowed to use 80% or more (depending on use cases) in commercial buildings.
The Bellis project, near Z眉rich, is a mixed-use residential and commercial development with 44 apartments, office and commercial space, and business apartments. Except for prefabricated elements, all concrete structures 鈥� including walls, floors, floor slabs, and ceilings 鈥� were built using cRCA. In total, 7,500鈥痬鲁 of concrete incorporating cRCA was used, allowing for approximately 75 tonnes of CO鈧� to be stored within the structure.
Neustark argues that raising the limits of RCA use in line with the rest of Europe will allow London鈥檚 high-profile regeneration projects such as One Undershaft to reuse all of the demolished concrete from the incumbent building, St Helens Tower. Other landmark developments, such as Canary Wharf Group鈥檚 Wood Wharf, are already demonstrating this approach, where concrete from a decommissioned, 100-year-old quay nearby has been broken down and repurposed for the foundations of new residential buildings.
Valentin Gutknecht, founder and joint chief executive of Neustark, said: 鈥淭he UK is one of the leading countries within Europe for its efforts towards decarbonisation. However, within the construction industry, regulation and green standards are lagging behind countries such as Switzerland and Netherlands.鈥�
He added: 鈥淯pdating guidelines, in line with Europe, for the use of recycled concrete for commercial construction will enable London construction firms to utilise existing waste stream, like demolition concrete, as a tool for climate action. Carbonated recycled concrete aggregate will indeed present an opportunity to turn a problem into a solution by taking one of the most essential materials for commercial construction and turning it into a carbon sink.
"Investing in local supply chains and carbonated recycled concrete aggregate is one of the most efficient ways for London to reduce emissions from commercial construction projects. The environmental benefits are clear, and the cost-effective nature of this solution should be a significant factor in its adoption."
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