Kiacrete: concrete that can weather the storm

Things like our ageing housing stock and our built environment - pose a huge problem when it comes to climate change. In a bid to redress some of the problems that concrete causes, Alalea Kia - a materials scientist and engineer at Imperial College London - has developed a version of it that tackles one of the other challenges predicted to come with climate change: altered rainfall patterns, and more extreme weather. This all adds up to requiring better stewardship of our water: At the moment, as cities expand and we concrete over the countryside, we render the ground impervious to rainfall, which all hits the sewers in a giant rush and causes flooding and is then lost out to sea. The earth below is also progressively deprived of water that would previously have soaked in and preserved groundwater stocks. Alalea’s eponymous product, developed with the help of the UK Research and Innovation and the Royal Academy of Engineering, is called ‘Kiacreate’. It’s concrete created with holes through it that allows water to run through so it can be captured and used, and also soak into the ground like a sponge so a deluge doesn’t turn into a flood…

Alalea - There are a number of different challenges that the engineers are facing today, including decarbonisation, ensuring that the UK hits its national carbon targets. And also another problem is flooding. So we need to not only ensure that we reduce our carbon footprint of our flood management interventions to contribute to net zero targets, but also we need to ensure that our infrastructure are capable of coping with more extreme weather events.

Chris - Is there anything we can do about that problem of the fact that concrete is largely impervious and the water that lands on it runs straight off and goes down the drain? Is there a better way of doing that?

Alalea - So one of the ways is to ensure that pavement infrastructure is permeable, is able to allow the water to go through it and to prevent that nuisance to the society. And also that water is then used in a more clever way rather than the way it is now, which just ends up into the drainage network and causes more problems down the line.

Chris - And how can we do that? Because isn't one of the major things about concrete, the wonderful aspect of it, that it's incredibly strong. You can put massive loads on it, but in order to achieve that, you have to have something which effectively is solid rock.

Alalea - To achieve a high strength, you don't necessarily have to be completely impermeable. So what we have been trying to do is to come up with a pavement structure that essentially has a lot of channels in it that would allow that water to drain through it. So it still will have the same strength as your traditional impermeable concrete surfaces, but it has the added benefit that it has a really high permeability or drainage ability that eliminates flooding and stormwater runoff and also improves the splash and display related visibility issues. And it reduces weather related accidents so it eventually enhances societal safety.

Chris - How does it work?

Alalea - Essentially you have a form work that a load of these channels inside it. You pour your cementitious materials around that form work, and then that gives you a concrete surface that gives you a lot of holes inside it. Once you have that extreme weather event, the water goes through those wholes, and down into the ground.

Chris - I'm just picturing this in my mind. So is it effectively a mould with lots of holes and you put concrete into that mould and that means that you get concrete with holes in it, which then allow the water to go vertically through the concrete layer. But because the concrete is still all connected together, it's still strong, but it's got channels in it.

Alalea - That's essentially it. You are essentially picturing a solid concrete that has a lot of holes in it. As you mentioned earlier. The form work has all of these interconnected channels that would allow the water to go down vertically, but also the material has a really high strength that can sustain the loads of an aircraft or vehicular loads or pedestrian loads or cyclist loads.

Chris - And when you say you can capture and therefore repurpose the water that goes down those holes, is that because there's some way or some system of collecting what's come through the holes underneath? So would you lay the concrete on something that's capable of acting as a conduit for that water, which is how you grab it?

Alalea - Yes. So essentially the pavement surfaces are typically built on what we call a forest substructure. So we are talking about just stones and the water would go through those stones and then it goes into what is called a storage tank. So this storage tank would first of all delay the water and prevent the water from going into the drainage network and causing flooding downstream. But also that water that is within that tank could be used for irrigation purposes or it could even depending on the area that is built in, it could go into the ground and recharge the groundwater table.

Chris - What about in countries like ours in winter where it's incredibly cold and you can get frost because one of the biggest problems with concrete and water is frost shattering.

Alalea - So the benefits of the system that we have developed is that it's very efficient in absorbing water as quickly as possible. So we've had a number of field trials and also laboratory testing where we exposed this solution to extreme temperature. So extreme heat, extreme like freezing temperature and then heating it. And we've shown that it actually doesn't allow the frost to build up on the top surface because it has a lot of holes, it's very efficient in allowing the water to go through it as quickly as possible and not leading to that layer of frost to be built up on the surface.

Chris - And the cost implication? Because the one thing that developers are always going to look at is the bottom line. Because you're using less concrete because you've got the holes in the way, does that actually translate into a saving?

Alalea - So when you look at the cost, we need to look at the whole life cost of the pavement structure. So the initial cost in terms of the labour cost is similar to the traditional pavement surfaces. But when you look at the whole life cost is actually much cheaper than the traditional pavement surfaces because not only you are reducing the challenges that you would be facing with the impermeable surfaces because of this rainfall and runoff issues, but you are also reusing that water and it's a pavement that has much more reduced maintenance in comparison to traditional pavement surfaces. So essentially you are saving on that front and as you said, you are also saving in terms of material because you are using less material in comparison to the traditional surfaces. So if you'd considered the whole life of the pavement structure, it has lower cost than the traditional surfaces.