Sustainability Segment | Part 2: How do you bring steel into a circular economy?

Recycling – or better still, reusing – steel structures could create major carbon savings – Words by Tom Webster, RIBAJ

Art Studio / Scalar Architecture

A holistic approach?

The urban mining of buildings is a true celebration of the circular economy and has the potential to go a long way to reduce the embodied carbon in the built environment. While at a smaller scale, raised access floors and ductwork being up-cycled and reused are increasingly common, does it make sense for this approach to be applied to the structure of a building? Of course, the answer is Yes.

The technical stuff...

A standard office building, which is founded on piles ad has a superstructure of a steel frame with composite slab, is likely to create around 1200 tonnes of CO2e during the construction of the superstructure alone. The original embodied carbon of this structure has been spent and has done its damage. If it cannot be refurbished we could mine this building to place the constituents materials back into the supply chain.

Steel is a woeful performer in terms of embodied carbon, but it is a great circular economy material, being recyclable without harm to its structural performance. This may come as a shock to some through – recycling virgin steel produces around just 50% of the original CO2e. If we take this principle further things start to get really interesting. If we recycle steel to get really interesting. If we recycle steel elements within a building and replace it with a new timber frame building, we could potentially sequester enough carbon from the atmosphere to start creating an embodied carbon deficit.

"Steel is a woeful performer in terms of embodied carbon, but it is a great circular economy material, being recyclable without harm to its structural performance"

A steel frame with composite slab is between 30-40% heavier than an equivalent timber frame. By leaving the original foundations in the ground and reusing them for a new timber building, it could be 30-40% taller. If we replaced an existing six storey steel frame building with an eight storey timber frame one, the embodied carbon in the frame would be: 540 tonnes CO2e to recycle the steel and 450 tonnes CO2e to build new timber building – but sequestered carbon in the timber amounts to – 1500t Co2e.

So working through the numbers you can improve 500t CO2e from the atmosphere and provide a bigger building, while placing materials back into the supply chain for use elsewhere. And other types of urban mining could be more appealing to those less comfortable with use of timber in buildings.

Case Study

There are a few projects under way where the superstructure is all or part formed using reclaimed structural steel from other sites. This as a concept is a very pure version of the circular economy and urban mining. In this form the embodied carbon is kept to a minimum and the additional embodied carbon would be associated with storing, cleaning, re-fabricating and painting the steelwork.

If the steelwork is reused rather than recycled, that embodied carbon figure potentially falls from 540t CO2e to 150t CO2e – presenting us with a staggering potential net 900 tonnes of CO2e benefit. Scaling up urban mining for the circular economy to make it feasible across the industry needs to be part of the design process at the start of the project, and needs the support of manufactures. There are three critical moves. First, when a building is demolished all its components need to be scheduled and sorted for re-use. This requires space and time. Secondly, assurance and warranties would be required to ensure the buildings can be required to ensure the buildings can be designed appropriately and insured so that all or some of these components can be tested and their properties verified/certificated. And finally, a database listing where the components for reuse can be found and bought would be needed.

It requires some joined up thinking, a little investment to get things off the ground and some willing client to apply these principles to their schemes. One such client is Ivan Navarro and Courtney Smith, in Brooklyn, NY and there is a promising model in RotorDC, a Brussels-based group that deconstructs, processes and trades salvaged construction materials. Perhaps it is a precursor to a giant construction-based eBay for the built environment.

Art Studio / Scalar Architecture

Ivan Navarro and Courtney Smith Art Studio / Scalar Architecture

Located on a former warehouse within the industrial neighbourhood of Sunset Park, the three-level 5000 sf studio for the artists Ivan Navarro and Courtney Smith is a diaphanous volume for art production. Courtney Smith is an artist working in sculpture and performance. Iván Navarro is a Chilean artist of global recognition who works with light, mirrors, and glowing glass tubes to craft socially and politically relevant sculptures and installations.

Art Studio / Scalar Architecture

In line with their conceptual and political stance, the architectural solution reimagines, inhabits, and expands the existing facility by means of articulating recycled steel -so prevalent in the industrial activities of the neighbourhood - both as structure and reflective skin. Structurally, the recycled steel structure afforded the possibility to perch over and maintain the existing masonry through a series of frames. Text description provided by the architects. Scalar works with a renowned artist who crafts socially and politically relevant sculptures and installations

Art Studio / Scalar Architecture

Architects: Scalar Architecture

Area: 5000 ft²

Year: 2021

Photographs: Imagen Subliminal

Construction Unit: GNS

General Engineering: BDM Engineer