We set out to make an organic free form shape cast only in different sizes of aggregate.
The result of the first test of aggregate and slurry mix. The straws helped the cement mix to go down in the aggregate and the slurry mix seamed to work so we went up in size for the final cast.
We used three different sizes of aggregate, very small which we sieved, middle size and quite large pieces for where we wanted the cement mix to go down.
We poured the cement mix in steps to make sure that it would go down in the aggregate, and built the shape in many layers.
We used the slurry mix we tested in the first experiment:
750 g cement
300 g water
15 g super plasticizer
The end result.
A piece fell of in the process of removing the cast from the bucket, we could have reinforced the shape with for example steel wire, or greased the bucket before we cast.
Otherwise the shape we got was what we set out do make. The different aggregate made it possible to make voids and the shape was quite easily controlled.
How to go forward.
The method of casting in only different aggregate is good since there is not much waste material, and you don’t need that much cement since it is such a large portion of aggregate.
We´re trying to cast without mould using only different sizes of aggregate and letting the concrete fill the void in the bigger aggregate.
Testing two different slurrys and two different sizes of aggregate to see how far the concrete mix would go in the aggregate. Using some super plasticizer made the slurry go down more easy than using only water and cement.
250 g cement
90 g water
10 g super plasticizer
250 g cement
100 g water
Larger aggregate in the core and finer aggregate surrounding. Making “branches” of larger aggregate from the core to see if they will be filled or not.
750 g cement
300 g water
15 g super plasicizer
We added a straw for the air in the bottom to be able to come upp when pouring in the slurry.
We worked with aluminium foil in free form. We needed to add an additional 200 g of water for the concrete mix to flow easily and get down to the bottom. The aggregate we used for the inside of the aluminium shape was perhaps to small, so the concrete didn’t get down in a good way. If we were to do it agin, we would use larger aggregate so that we wouldn’t have to use so much water.
The shape after we took it out of the form after 24 hours. There was some leakage on the top, but that rather made it more interesting. Overall the shape was kept intact.
When mixing the fabric-concrete, we needed to add an additional 290 g of water to a 1 kg mix in order for the concrete to flow easily.
We used the non-strechty fabric and placed nails on a board underneath the fabric. When adding the concrete, the load of the concrete hopefully creates a flowy landscape around the pikes of the nails.
Varying stretch 10×20.
We placed a non-stretchy fabric around a frame, made some holes and then added the strechty fabric on top. The weight of the concrete should then make deeper “valleys” of concrete where the holes in the non-stretchy fabric are.
Mix 1. with 8.5 parts sand falls apart when touching it.
Mix 2. with 1 part water got a very smooth surface.
Mixes 3-5. 4% pigment. We needed to add 60 g water to the mixes to make the concrete workable.
We used sliced baguettes in hopes that the fluid concrete would fill the air holes and cracks and pour out on the edges in spontaneous shapes. The breads holes were probably too small so the concrete didn´t sink so far into the bread. For the shape to be completely freed from the bread it will either have to dry more or be burnt off the concrete.
Honeycombs are actively built by bees, the bees could make just about any shape but over a long period of natural selection their behavior evolved to make shapes that minimize the area of wax needed and still be structurally functional for their needs. Perhaps the same structural principles could be used when trying to improve concrete casting and reducing the amount of material needed to make a variety of concrete shapes.
Image source: https://www.quora.com/Why-does-nature-prefer-hexagonal-shapes