Making greener concrete

30 April 2018

Interview with 

Dimitar Dimov, University of Exeter

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The world’s worried about carbon emissions, and the manufacture of cement to make concrete is one of the largest single contributors - at between 5 and 10% - of the world’s total carbon dioxide output every year. So can this be cut down? Well, researchers from the University of Exeter think they’ve found a way to do it by adding graphene - the stuff that makes up graphite: the carbon in a pencil lead - to the mix. Georgia Mills heard more from discoverer Dimitar Dimov…

Dimitar - We need to reduce the carbon emissions, and we need to make the construction industry a more environmentally friendly one. One way to do it is to reduce the amount of concrete used per cubic metre: if you can reduce the amount of concrete you decrease the amount of materials used on site and, therefore, there's less need for cement. But how do we do that? We need to change something fundamentally in order to make concrete stronger and more durable to be able to withstand the current loading specifications around the world.

Georgia - How are you looking into this?

Dimitar - We are introducing the wonder nanomaterial graphene through cement and concrete, and this results in increased strength and, therefore, we can decrease the amount of material used per cubic metre.

Georgia - What is graphene and how does it have this effect?

Dimitar - Graphene comes from graphite.

Georgia - The stuff off pencils?

Dimitar - Yes, exactly. The graphite, or the pencil: it’s structure is composed of thousands of identical layers stuck to the top of each other; one of these layers is called graphene. You can stretch it, you can bend it and it will retain its original shape and size so it’s almost indestructible. And, therefore, I thought okay, so why don’t we combine the strongest nanomaterial ever discovered with concrete, wouldn’t that make it even stronger.

Georgia - What happens then when you add the graphene?

Dimitar - It increases the compressive strength by 140%, it increases the flexural strength by 80%, and probably the most fascinating property is that it increases the water impermeability by 400% so, basically, it makes that material less permeable to water. This is very important for two reasons: first around the world you have some areas subject to flooding and if you have material which is less water permeable that will increase it’s life, and also water is one of the main causes for concrete degradation. This means that internally the concrete degrades with time when it’s subject to rain basically. So if you have a material which is less permeable, that only increases its life cycle and it means less maintenance costs.

Georgia - I guess graphene: it’s a strong material so adding it to another material it increases the strength. That makes sense, but why on Earth should it affect how water resistant it is?

Dimitar - That’s a good question. When we add the graphene it bonds with the cement crystals. These crystals, they are various in terms of sizes and shapes and when they react with water they just grow together and form a matrix. What happens is the graphene comes in and it attaches to these crystals and leaves less air voids, leaves less cracks. The mechanical interlocking between these crystals is actually enhanced; it’s much better than before and this all happens on a nanoscale level; therefore, when you have a denser matrix it’s more difficult for the water to go through the material.

Georgia - Right. So when you have concrete you have all these different little lumps of it all about and this graphene and essentially, it’s like a tiny tiny nanospider went in and threaded a web through it all and this catches the larger water molecules before they can get in an do damage?

Dimitar - Yeah, exactly.

Georgia - So what’s the catch then? It sounds too good to be true.

Dimitar - There is always a catch. I just haven’t discovered it yet because I haven’t performed enough tests to find a catch but, from what I’ve seen, it’s very promising. More research has to be done on the this topic.

Georgia - How easy will this be to scale up and actually put into use around the world?

Dimitar - Well, all my samples are tested according to British Standards for constructions so it’s readily applicable on site. And the method that we use currently produces more than 100 litres per hour because you literally take the graphene in powder form, you put it in water, you blend it, and there you go you have your graphene solution. You have your graphene in water and you mix it with cement and sands to make concrete.

If you can imagine if you take this to a factory, this could be easily scaled up. The method is very straightforward and you don’t use any expensive chemicals, so it’s very close to commercialisation I think.

 

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