What’s stopping us from reusing concrete?

Throughout the construction industry we are starting to consider the circularity of the materials we are using more frequently. We’re putting in place processes to allow for the reuse of steel sections and we’re considering ways to reuse lots of other elements including bricks, raised access floors, ductwork and glazing units. But there’s one material where we’re still usually talking about recycling rather than reusing — concrete.

Versatile, cheap and readily available, concrete can be used to build almost anything and as an industry we’ve really taken advantage of that. We’ve poured so much concrete that it’s now the most widely used material on earth after water. And while that’s a somewhat terrifying fact, it does suggest that there might be quite a lot of opportunity for reuse if we can figure out how to do it.

By far the best way to reuse concrete elements is to keep them in place in an existing building. Concrete structures are relatively durable and, if they are maintained, are often able to exceed their original design life. Structural defects tend to be evident during inspection or can be tested for, and therefore these structures can be reused with a reasonable level of confidence. Plus, a lot of the concrete is below the ground in the foundations and infrastructure that supports our buildings, and therefore it’s much easier to leave it where it is.

But if you’ve decided that you’re going to demolish, for whatever reason, it’s rare that reuse of concrete structural elements is considered. Most likely, the concrete elements will be broken up; the steel reinforcement will be recycled and used to make more reinforcement and the concrete will be broken down to be used as aggregate or fill material. Whilst this is obviously better than putting the materials into landfill, there’s still a huge amount of energy and carbon required to reprocess these materials.

So what’s stopping us from extracting and re-using the elements? Perhaps the most obvious answer is that in situ concrete structures are monolithic. They’re not made up from smaller elements in the same way as steel structures so they’re difficult to take apart. But actually, when steel beams are extracted for reuse they’re often still cut out, so couldn’t we cut out a concrete beam and re-use it as it is?

With such a huge amount of concrete out there, it seems like a reuse opportunity that’s too good to be missed!

Well, there are a lot of challenges that would need to be overcome; concrete reinforcement typically isn’t detailed to allow this to happen, and there’s a risk that cutting the concrete might cause damage during demolition. The element itself would be bulky and difficult to deal with structurally and someone would need to take responsibility for the integrity of the beam. But maybe there’s an opportunity to create units that are more similar to precast units, that could be sold and reused in a more standardised way. And if we’ve figured out how to overcome issues such as extraction, testing and responsibility for steelwork, can’t we do it for concrete too?

For existing pre-cast structures the situation is a little different. Pre-cast concrete elements are formed off site and whilst they are designed so that they can be “stitched” together the individual elements are separate and could theoretically be taken apart. If we’re considering ways to reuse concrete structures then pre-cast elements offer the best opportunity if we can figure out who takes responsibility for the elements and how they could be stored.

And if we can’t re-use elements structurally perhaps we could find other ways to reuse concrete without breaking it down. Maybe slabs could be cut into blocks to use as part of internal partition walls or in a similar way to void formers within foundations? Some contractors have also found ways to re-use concrete as kentledge in temporary works or to help provide access routes within sites.

As we start to take a more circular approach to the materials we’re using, it’s vital that we don’t overlook the opportunities that concrete could offer. Perhaps it’s a little more difficult than other materials and there are definitely risks to be overcome, but as we try to reduce the carbon of our structures isn’t it worth considering? And with such a huge amount of concrete out there, it seems like a reuse opportunity that’s too good to be missed!

>> Also read: How the creative reuse of ordinary buildings is revolutionising approaches to regeneration