Buildings Made with a Printer

Technology Review describes the work of Neri Oxman, an architect and professor at MIT's Media Lab, to 'print' complex structures using concrete, polymers and other materials.  Her work goes beyond initiatives such as "Robo-Brickie Builds a House in a Day" by varying the properties of the material, such as elasticity of a polymer or the porosity and strength of concrete.  Columns can be structured with dense concrete on the outside where stress is the greatest and lighter-weight concrete on the inside Porous or composite materials could be used in low-stress areas to allow additional light into buildings. 

(image credit: Steven Keating).  

She is also developing software that takes into account design constraints and stress analysis to optimize materials usage and incorporate new functions.  One of her works, a chaise lounge called Beast displayed at the Museum of Science (Boston) in 2010, "adjusts its shape, flexibility and softness to fit each person who sits in it. Made from eight materials of varying flexibility, it hugs your body, reacting to each movement".  The design takes into account the shape of a human body as well as the distribution of pressure points to develop a complex structure that provides both compliance and support.

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nhoeller's picture

Exchange Between Julian Vincent and Tom McKeag

Vincent: e-mail of 2011/04/07 at 10:18

The RP [rapid prototyping] approach to buildings has been around for several years, but I like the graded porosity approach. Most RP work uses homogeneous material, whereas the biological version would have interchangeable heads to give different structures and materials, graded to suit their place in the structure. But, very interesting. I shall be able to incorporate this in the 3rd edition of my book, which is approaching completion (phew!)

...

Cheers, and thanks
Julian

McKeag, e-mail of 2011/04/07 at 10:10

Thanks, Norbert,

I have been following Khoshnevis and other large scale printer technologies. As to the palm tree inspiration, I’d have to know more (aggregate, fiber additives, entrainment, etc.): mere density change is not much of the story, is it? Isn’t it really about the fibers and how they are arrayed?

Tom

Vincent, e-mail of 2011/04/07 at 10:37

Controlling density is a good trick and a useful one. It can account for a large part of the design of bamboo (graded structures). I don't know how you could incorporate fibres with a RP approach. You would either have to have a pretty fast-moving 'spinneret', or one which moved up and down drawing the fibres. But as far as I know nobody has analysed the structure of a bamboo stem taking the anisotropy into account. When we modelled a dandelion flowering stem we found we could do it based only on the distribution of cellulose (which is about 25 times denser on the outer part of the stem than the inside). I should think the challenge would be to see how steep a gradient of density one could have before the low density material ceased to be structural. Perhaps you could mix short fibres in with the cement, but the fibres have to be long enough to bridge any defects in the cement, and the longer the fibres get, the more difficult the cement is to handle. And remember that material distributed away from the centre gives a far higher degree of support that you'd think (second moment of area). I think that the cellular material is supporting the outer shell against buckling (see some of the work Lorne Gibson has done on porcupine quills and hedgehog spines!)

Julian

McKeag, e-mail of 2011/04/07 at 10:48

Thanks, Julian!
You're right about the problems with adding any internal tensile components to the mix, like fiberglass flakes, etc. My interest is in self organized alignment of these materials within such a mix. Any thoughts about that?

Tom

Vincent, e-mail of 2011/04/07 at 11:26

I have two examples from biology.

  1. It's fairly well known that ceramics (mollusk shells, egg shell) include a small (<1%) of protein or glycoprotein which forms some sort of molecular composite. The outcome is to change the fracture behaviour so that it becomes more like a sort of viscoplastic glass than a crystal. So somehow this small amount of polymer is pinning the crystal structure and/or controlling the distribution of strain energy.
  2. Phase separation. This is done with technical materials quite commonly, polymers and metals and ceramics. But as far as I know it's only in polymers that you can vary the volume fractions sufficiently to get a range of structures - which includes fibres and layers. I suspect that you need the polymer component to get the self-assembly. How does a sea-urchin tooth form (I'm supposed to writing about it in my book sometime early next week - if I can keep up the pace of writing!)? You get plates and fibres of dolomite in a calcite matrix. Perhaps the urchins have a polymer scaffold which controls precipitation of Mg or Ca.

Which brings the following thoughts . . .
What you need is a sock-knitting machine working in parallel with the RP machine! We have great skills in textiles, yet they are hardly used in structures. But if you had a prestrained network laid down together with the concrete (or whatever is used) then you'd be able to control the anisotropy a bit more. Or perhaps look at some of the latest techniques used in hospitals making support splints. A thermosetting plastic would support the concrete which it was setting. And going for porosity - Salmaan Craig did a thesis at Brunel university recently, putting granules of expanded polyurethane into concrete. He was more interested in insulation, but may have measured some mechanical properties as well (I can't remember). It would be interesting to have a component in the concrete which expanded after the concrete has been extruded; it could orientate fibres as a form of post-processing. I'm sure there are other post-extrusion ways of manipulating, and perhaps joining, short fibres if their primary orientation could be controlled.

Julian.

McKeag, e-mail of 2011/04/07 at 14:31

Thanks!!! For that, Julian, 'will follow all these great leads

I wonder: 'seems natural that your idea about the post extrusion material change be combined with the curing (dewatering) and use differentially layered fibers that automatically oriented (or linked) the way you wanted as they swelled to final shape. This fluid flow from cement to fiber would have to be delayed until after extrusion, or induced as a result of exposure, I suppose, and be balanced with the curing requirements of the cement. Reminds me in general of the sea cucumber properties.

Tom

 

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