Different circles

There's much we still need to understand about where the greatest value of an obsolete concrete structure lies

We’re fully in the swing of event season, and it’s great to be out and about, meeting people in person and having lots of conversations about sustainability and concrete. This is undeniably a challenging time for construction, and many people I speak to are grappling with how to achieve carbon targets amid the uncertainties of the current market.

One solution is to make use of the materials we already have in our built environment. It certainly feels like there is a shift towards greater consideration of the potential of existing structures, partly driven by planning policy. For inspiration, check out our cover project: Richard Seifert’s Space House office tower, which has been renewed and expanded as a super-modern workplace.

But there are many factors in play that determine whether retention of an existing structure is viable. Concrete frames tend to be able to outlive other building components, but sometimes a building just isn’t useful enough in its current form, and it needs to come down.

Today, almost all concrete from demolished buildings is recycled, most commonly as unbound material for ground works, but also in new concrete. But these are not the only options, and the industry is exploring some very promising alternative strategies – finding ways to retain concrete’s value for as long as possible is one of the five pillars of the refreshed UK Concrete Sustainable Construction Strategy.

In recent issues of CQ, we’ve spoken to scientists and innovators who are developing new techniques for reprocessing and upcycling crushed concrete to make new products, and even new cement. Our Application feature in this issue (page 34) focuses on a different opportunity: reclaiming concrete elements and using them in new structures, in much the same way as precast components are used today.

There is something very exciting about the prospect of chopping up an existing structure and repurposing it, and there are already some brilliant examples. But there is also much we still need to understand about where the greatest value of an obsolete concrete structure actually lies. Is it always as a “donor structure” providing components for new buildings? Or might crushing it, as a source of new lower- carbon cementitious material, prove more effective?

Right now, the only thing we do know is that we need to use less of everything – we need to stop and think, “does this need to be new?” If you don’t want to waste food, you look in the fridge to see what you’ve already got before deciding what to have for dinner or heading to the shops. We could take the same approach to the built environment.

The default for many years has been to demolish and rebuild from scratch. In a decarbonised, circular world, that default will need to shift. We may not know how emerging technologies will evolve, but we do know that taking time to understand what we have will always be the right decision – as only then can we work out how to retain it at its highest value.

Elaine Toogood, Director, Architecture and Sustainable Design, The Concrete Centre