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Concrete

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Re: Concrete
Post by Weird Harold   » Tue May 09, 2017 8:57 am

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Keith_w wrote:Rebar is usually steel is it not?


20th century rebar was commonly steel, but almost anything will work to one degree or another. you just need more cotton twine than you do steel. :D
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Re: Concrete
Post by Hildum   » Tue May 09, 2017 2:11 pm

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Concrete, when prepared correctly, meaning not too much water in the mix, has fantastic compressive strength. You can pile bricks on it all day without problems. Unfortunately, the moment you start stretching it, it will crack and fail due to having low tensile strength.

If you design your buildings with only domes, arches, buttresses (and get the angles correct) you can do a lot with unreinforced concrete. The moment you want a flat roof or a spanning beam, you have a problem; the top of a beam is in compression, while the bottom is in tension. Thus you cannot use pure concrete for this. The only material that could be used was wood, which is okay (but not great) in both compression and tension but has other problems (it rots, for example, and weathers quickly if not maintained properly).

By adding reinforcing to concrete, the tensile strength of concrete can be improved significantly, thus allowing for spanning beams of concrete. This, plus careful shaping of the concrete elements, allows the construction of (relatively) lightweight, high load bearing structures. Think of the typical freeway overpass - a concrete box in tension below and compression above, bearing the load of dozens of cars and trucks over spans of 20 meters or more. While you could build a bridge that supports the same load out of wood, you could not have an unobstructed road beneath it.

Steel is a good material for rebar as it has high tensile strength and wears well, but as the previous poster mentions, you can use anything that a) binds to the concrete, and b) has good tensile strength. They probably used iron reinforcing on Safehold, which while not as good as steel, would allow at least some flexibility in design.

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Re: Concrete
Post by Maldorian   » Wed May 10, 2017 6:07 am

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Steel is the only Metal you can use for reinforced concrete, because of the linear Expansion coefficient.

If the temperature changes, material expand with different rates. Concrete and steel expand with nearby the same rate, so that you can mix it.

Other materials would blow up the concrete if the temperature changes.
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Re: Concrete
Post by Keith_w   » Wed May 10, 2017 7:18 am

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Maldorian wrote:Steel is the only Metal you can use for reinforced concrete, because of the linear Expansion coefficient.

If the temperature changes, material expand with different rates. Concrete and steel expand with nearby the same rate, so that you can mix it.

Other materials would blow up the concrete if the temperature changes.


That's what I thought. Thanks to Hildum and Weird Harold (hey, hey, hey) for their responses.
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Re: Concrete
Post by Hildum   » Wed May 10, 2017 2:47 pm

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Maldorian wrote:Steel is the only Metal you can use for reinforced concrete, because of the linear Expansion coefficient.

If the temperature changes, material expand with different rates. Concrete and steel expand with nearby the same rate, so that you can mix it.

Other materials would blow up the concrete if the temperature changes.


Actually, I think forged iron would work well, but clearly steel is better due to better tensile strength. See the following for example coefficients of expansion:

http://www.engineeringtoolbox.com/linea ... -d_95.html
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Re: Concrete
Post by ZVar   » Thu May 11, 2017 1:04 am

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Maldorian wrote:Steel is the only Metal you can use for reinforced concrete, because of the linear Expansion coefficient.

If the temperature changes, material expand with different rates. Concrete and steel expand with nearby the same rate, so that you can mix it.

Other materials would blow up the concrete if the temperature changes.


I was going to say the same thing, thank you.
One thing I wonder though, is since Iron and Steel are basically the same metal do they expand and contract at the same rate?
Or is the higher carbon in steel what causes the expansion/contraction to match concrete?
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Re: Concrete
Post by Maldorian   » Thu May 11, 2017 5:28 pm

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I was going to say the same thing, thank you.
One thing I wonder though, is since Iron and Steel are basically the same metal do they expand and contract at the same rate?
Or is the higher carbon in steel what causes the expansion/contraction to match concrete?


I think Iron and Steel would both work. The difference isn´t that much if it has a difference.

Only question is, will Iron make a noticeble Change than pure concrete? Or let´s say, it could be that the difference between pure concrete and Iron reinforced concrete is too low that it would calculate.

Is someone still produce Iron in the Empire? Would be a waste of material.
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Re: Concrete
Post by Keith_w   » Sat May 13, 2017 7:44 am

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I don't think the question is "Is someone still produce Iron in the Empire? Would be a waste of material." The question is, when they built or repaired canals before the war, what did they use to reinforce the concrete?
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Re: Concrete
Post by WeberFan   » Sat May 13, 2017 10:56 am

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Keith_w wrote:I don't think the question is "Is someone still produce Iron in the Empire? Would be a waste of material." The question is, when they built or repaired canals before the war, what did they use to reinforce the concrete?

I'm not an expert by any stretch, but two solutions come to mind right away:
- They poured the walls without using any reinforcement / rebar at all. From one of the previous posters - concrete has good compressive strength. So long as the walls are properly backfilled, and the lock walls thick enough, I think they could have gotten away with it.
- They didn't pour the walls at all. Instead, they used concrete as a parge coat over a substrate, most likely dressed stone - like stucco I suppose. In this case, the stone would provide all the strength and the concrete / cement would only be a thick coat used for waterproofing.

This presupposes that ironmaking wasn't advanced enough, and that there wasn't any understanding about reinforcement being required. Given the Proscriptions, I can't see any civil engineering "research" going on. What they did probably came through the Writ and was mandated by the Archangels: "In God's Holy Canals, thou shalt always incorporate iron bars lest Shan Wei destroy thine efforts..." :lol:
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Re: Concrete
Post by Castenea   » Sat May 13, 2017 4:23 pm

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WeberFan wrote:
Keith_w wrote:I don't think the question is "Is someone still produce Iron in the Empire? Would be a waste of material." The question is, when they built or repaired canals before the war, what did they use to reinforce the concrete?

I'm not an expert by any stretch, but two solutions come to mind right away:
- They poured the walls without using any reinforcement / rebar at all. From one of the previous posters - concrete has good compressive strength. So long as the walls are properly backfilled, and the lock walls thick enough, I think they could have gotten away with it.
- They didn't pour the walls at all. Instead, they used concrete as a parge coat over a substrate, most likely dressed stone - like stucco I suppose. In this case, the stone would provide all the strength and the concrete / cement would only be a thick coat used for waterproofing.

This presupposes that ironmaking wasn't advanced enough, and that there wasn't any understanding about reinforcement being required. Given the Proscriptions, I can't see any civil engineering "research" going on. What they did probably came through the Writ and was mandated by the Archangels: "In God's Holy Canals, thou shalt always incorporate iron bars lest Shan Wei destroy thine efforts..." :lol:
Cement is relatively expensive, I would expect that much as today they used a mixture of cheaper materials for bulk. Primarily sand, but I have seen gravel and heard of fly ash being used. It is probable that some form of wrought iron has been used on Safehold for applications where the concrete would be put in tension. I remember an episode of Modern Marvels where they mention that a dome has an iron chain embedded in the concrete.
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