Date: 5/01/2018 15:08:56
From: mollwollfumble
ID: 1169823
Subject: Good Scientist Cartoon 472 to 482
I’ve slowed down producing these.
Date: 6/01/2018 08:50:50
From: mollwollfumble
ID: 1170126
Subject: re: Good Scientist Cartoon 472 to 482
mollwollfumble said:
The Rev Dodgson said:
No 482:Sorry to be a pedant, but I can’t help it:
1. Strength – high strength concrete compressive strength would be about as high as the minimum tensile strength of aluminium, true, unfortunately its tensile strength is only about 10% of that.
2. Elastic modulus – the short term elastic modulus of high strength concrete is approaching that of aluminium, true, unfortunately when you add in the effects of creep and shrinkage its long term elastic modulus is around 30% of that.
On the other hand, if we look at ultra-high strength concrete with added steel fibre reinforcement, what you say is true for both tensile strength and long term elastic modulus.
Yep. Tensile strength is a killer, so strong reinforcement is needed, preferably prestressing. If the reinforcement is not corrosion-proof then a very thick cover is needed.
I just find it totally amusing that very-high-strength concrete can be used as a 1:1 replacement for general-purpose aluminium when tensile strength and electrical conductivity are not the deciding factors. We normally think of concrete and aluminium as so different.
Question for Rev Dodgson, could you use cloth woven (or knitted) from a plastic such as polyester, nylon or kevlar as reinforcement for concrete? Some plastics have a tensile strength above 310 MPa.
Aluminium can be made 0.016 mm thick. Could very-high-strength concrete be made 1.6 mm thick? I think it could, not with big aggregate of course. Two ways could generate the same result. The batch method would be to lay down tensioned shirt-fabric on a metal slab with slots, then put down a uniform layer of very-high-strength concrete, then a final layer of tensioned shirt fabric. When the concrete is the right consistency, sew the opposite layers together with a heavy-duty sewing machine, through the slots in the metal slab. When dry, remove from the metal slab.
A more subtle method that can produce the same result would be to use the techniques of plastic/aluminium extrusion. Have a billet of slightly wet concrete extruded through a slot-like die and feed tensioned shirt-fabric down the sides. Here a custom-made sewing machine just past the die would sew the edges together. This way you could make a concrete I-beam with a 1.6 mm web, or a concrete pipe with a 2 mm wall thickness, as well as a flat slab.
This picture is of concrete extrusion already used for making hollow-core concrete bricks and slabs.
The following picture is of a table made of concrete.
