Building with bamboo

19 November 2019

Interview with 

Darshil Shah, Centre for Natural Material Innovation, University of Cambridge

BAMBOO

Bamboo growing

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We’re always looking for ways to save the planet. One potential thing that might help is building houses from more sustainable materials to cut the massive carbon footprint imposed by concrete. One candidate, that’s fast growing and strong, is bamboo, which also turns out to have some interesting thermal properties too, as Darshil Shah, from Cambridge University’s Centre for Natural Material Innovation explains to Chris Smith...

Chris - First of all, why bamboo as a building material - what's exciting about it?

Darshil - Bamboo is a fantastic material; it grows really fast: there are over a thousand species of bamboo, some of these can grow at a rate of a metre a day, or one millimetre every 90 seconds! While it grows it captures carbon as well as stores it within the material, and it is also abundant in certain parts of the world.

Chris - Is that bamboo in front of you? That's like a cannon!

Darshil - Yes. 

Chris - And can I see that?

Darshil - Of course you can.

Chris - This is huge. Probably, what, 10 centimetres across, this bamboo. 

Darshil - It can grow substantially thicker as well, and the stems - the cell wall - maybe about 15 to 20 millimetres thick; and they can grow up to 20 to 30 metres tall! 

Chris - But you alluded to this just now when you were saying, you know, this is a tube; that's not ideal as a building material is it like that for all kinds of applications?

Darshil - No exactly. So engineers would like to convert it into some form of beam material or as panels which can be used as walls, floors and these are converted into those sorts of materials by cutting these columns into strips and then blending them into rectangular shapes and then thereafter gluing and. 

Chris - And is that what that is? Because you've got some it looks a bit like the size of a big house brick.

Darshil - Exactly and these can be substantially longer three metres and they can also be in board form as well.

Chris - So you've given me as I say something about the size of a big house brick and looking at it, I can see that it's made of lots of little pieces of wood which have all been glued together. So you've cut sort of they're about centimeter and half by half a centimetre wide chunks and then they've all been presumably glued together. How strong is that?

Darshil - So bamboo has the same stiffness as wood, but it is substantially stronger than wood. 

Chris - When I introduced you I said that you've discovered some interesting thermal properties about bamboo this week. So what was the motivation for doing that why were you even interested in that and how did you do it. 

Darshil - Well yeah Firstly there has been a lot of research on the cell structure of bamboo and its relation to mechanical properties and some of this we have done ourselves, but there has been little research into how the structure is related to thermal properties. The amount of heating or cooling that is required in a building is fundamentally related to the properties of the materials that are made from particularly how much heat they conduct and how much heat they store. Also a better understanding of the thermal properties of bamboo would provide insights into how to reduce the energy consumption of a building and the fire behaviour of a building. If we are to make fire safe buildings, we need to understand the thermal properties of these materials.

Chris - So how did you scrutinise your bit of bamboo. 

Darshil - What we did was we actually took shavings off the bamboo and then we look under an atomic force microscope and what it does, is it heats the probe and you touch the surface of the bamboo and as you move the probe across the heat is conducted or not. That gives you a visual image of variations in the thermal conductivity. 

Chris - And what did you find?

Darshil - We find that bamboo is a structure with fibres produced in a manner in which there are thick and thin adjacent cell wall layers; the thick ones, which are oriented along the fibre axis, provide stiffness and strength in that direction, and also conduct heat in that direction; whereas, the thin cell wall layers do not conduct as much heat in that direction.

Chris - May I infer from that then that, if I were to try to push heat through a piece of bamboo, it would go along the bamboo quite well but through the bamboo quite poorly?

Darhsil - That is correct. 

Chris - So how does that affect the way in which we are going to make more materials like this big brick you've made with little pieces of bamboo or whole buildings out of bamboo. How is this going to change the way we fundamentally use it?

Darshil - Firstly we realise because bamboo is a combustible material, we need to protect it in some form so that the properties in that direction do not soften so rapidly and this is commonly done either through an intermittent paint or using some form of protective layer like a gypsum board, but also looking at graphine and how coatings from graphine might be able to divert heat from the bamboo.

Chris - They were talking about how we're going to live on Mars this week and they were saying that they're going to grow bamboo on Mars. I think it's a great material to grow in the first human settlements on Mars for all the reasons you said it grows so quick, and the kids do stuff with it, and it's a little bit of home from home. So maybe you should too. But there is an opportunity there.

Darshil - That is very interesting because I was watching Avatar a while back and I saw bamboo forests on that as well. And it's definitely something we should do we need to look into more anyways!

Phil - I'm excited because that opens up the possibility for panda colonies on Mars!

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