Extraordinary Possibilities for Concrete

Why?

So, ask yourself, why on earth we need to have an extraordinary change in the way that we deal with concrete structures, such as present?

The answer is all to do with carbon emissions.

Background

By 2025, developed countries have to reduce their carbon emissions by 50% and by 2050, 80%, compared with 1990 levels, and you might still be wondering, what does this have to do with these concrete structures? Well, here are some of the statistics that may astound you.

First of all, the cement which is an ingredient of concrete, accounts for over 5% of the planet’s carbon dioxide emissions.

Secondly, we make 4,000 kilograms of concrete every year. These two little bits of information are sufficient to surprise everyone. But the most astonishing statistic is that 60% of this concrete serves absolutely no structural purpose.

Example

So, if we look at the concrete building above, have a look at the suspended concrete slab. That is just one example of slabs which we see all over construction sites, all over buildings, all over the world. Now, always of those concrete slabs that we see, the concrete is flat, which means that we have the same amount of concrete everywhere. But we know, of course, through common sense that the load on the entire beam is not the same. Some parts are heavily loaded, and some parts are lightly stressed. So, by definition, we are wasting concrete as we are not putting concrete in varying amounts where the stresses vary, and that’s terribly important to us too. If we are wasting 60% of our concrete, and we have this amount of carbon emission coming, we have to do something about it.

Key points for Design

One should keep the basic two key points before designing these structures.

• The first one is only to put material where we need it.
• Second to remember that concrete is a fluid and we can shape it any shape we want.

Why do we always mould concrete rectangular?

Why don’t we do like this? This is a concrete beam, supported at those two points, and it might carry some load across the top of it. Now that, as it turns out, structurally, is the perfect shape for that concrete beam, because the stresses are high where we have large amounts of concrete. And where the stresses are low, we do not have very much concrete at all. And that gives us that perfect structural shape. It also looks more beautiful and natural.

That is how things work in life. We know that airplanes are beautiful because they are very efficient. Well, that is a very efficient concrete structure, and therefore is also rather beautiful.

How to make such concrete beams?

How do you make such a concrete beam, which will save material compared with a rectangular beam? Using fabric, we can cast these kinds of structures.

This is an image of fabric which we use.

So, what do we do with this fabric?

We place it in a mould, which can stretch longitudinally and transversally, to produce any shapes that we want for architectural and/or structural reasons, and then we pour concrete into that mould and then we can end up with structures which look a bit like this.

This is a wonderful example of a fabric-formed concrete structure. Thus, it is got all the attributes that we require. It saves concrete, because if you look carefully, it is tapering towards its ends, where the stresses are low, and it’s nice and deep in the middle, where the stresses are high.

Another place in a concrete structure where we can remove material is in the centre. Stresses are really rather low in the centre of a concrete structure — along the centre so we can remove holes. We can take great big chunks of concrete out of a concrete structure, without affecting the strength. And what you are looking at here is concrete. You are not looking at fabric. The fabric has been removed, and that is the texture that you get at the end of casting concrete into the fabric. It is texturally attractive. Now you need to ask yourself, how many times have you ever walked up to a concrete structure and felt it? And we can play further. We can make those holes bigger, and we can create architectural and structural shapes that are entirely appropriate, which save enormous amounts of concrete, and which are very simple to build, using a single piece of fabric.

How do we make columns?

Equally easy — we take the fabric, as shown in this image, and we drape the fabric, and we clamp the fabric — in this case, using two pieces of timber. Then we pour wet concrete into the resulting tube, and that tube is formed. After that, as the wet concrete rises up in that tube, it’s formed into a circular shape by the forces of nature. So, the forces of nature — those hydrostatic forces — give us that circular shape, which we require.

We can make concrete columns which taper, which splay out, which do all kinds of things, by playing around with the amount of fabric that we either release or constrain at certain parts of these sorts of structure, by using, again, a single piece of fabric. And the final aspect of fabric formwork, which I think is exciting, deals with durability.

When we cast wet concrete into the fabric, air and water escape through the fabric, and that is a perfectly natural process. And the benefit which that has is that the concrete which is close to the surface becomes cement-rich and a very durable and powerful concrete — usually about a centimeter deep — in exactly the correct position to protect the reinforcement.

Results

• Improves Carbonation Characteristics.
• Improves resistance to chloride (salts) ingress.
• Make concrete Harder by 20%.
• Enhances Architecture.
• Enhances Structural Engineering.
• Enhances Durability.
• Efficient Use of Concrete.
• Prevention of needless waste which we see at present.

Article by & Cover Graphic by: Nasratullah