Is spaceship made of precast reinforced concrete tougher than those malleable alloy?

Question

Set in the mid 22nd century AD, a major construction work is being carried out in the orbit of Uranus. The military is developing a cheaper fleets using precast reinforced concrete(PRC) hoping to extend its influence across the outer planets within the solar system, they are betting on the strength and durability as compared to metal which is prone to fail at high temperature. The contract is to deliver 1000 battleships in one year, if PRC is superior in term of cost and toughness how can it be mass produced to sustain the construction project?

Answer 1

Could it be done? Probably. Does it make sense? Probably not.¹

It's certainly true that PRC could take the proverbial bullet better than what we would consider hull material today.² However, there are some problems with the use of PRC.

• Concrete is porous. That means you can't cast it in space as space would freeze/suck-out all the water before the concrete cured. It could also pose problems with high/warm humidity on the inside and cold/vacuum on the outside — but city-sized water storage tanks are built out of reinforced concrete, so maybe this isn't as important as I think it is. Note that the cold vacuum of space will make the concrete brittle, meaning it'll shatter from outside impact more readily.

• As a consequence of being porous (and the fact that cement isn't very hard, you can scrape dust off 100-year-old cement and dig small holes with the point of a knife), concrete isn't easy to hermetically seal under pressure. Yes, you can do it, but those connection points will be serious weak spots. Your hulls will want as few openings as possible.³

• PRC is heavy. That means using extra fuel to move it, turn it, anything-with-it. It might be the most economical material to build with, but it will not be the most economical material to fly with.

• Last, but not least, PRC can withstand a lot of force, if your only measure of success doesn't include cracking. Cement is brittle, which is why we add aggregate to form concrete. Concrete is also brittle, which is why we reinforce it with rebar to get reinforced concrete (RC). RC is also brittle, which is why places like Texas require foundation slabs to use tensioned rebar — which is still brittle. The reinforcement is what keeps buildings from falling over, but the moment the PRC cracks, everybody dies.⁴ Your ships might not be capable of fast acceleration (speeding up/down, turning) without cracking the concrete.

However, none of this completely exempts the use of PRC for spaceship hulls.

OK, so how can it be mass produced?

Herein is a big problem. As Shekhar Shah, Ph.D Chemistry, Veer Narmad South Gujarat University, explains, cement (the basis of concrete) is actually a complex little process. It requires:

• Lime or calcium oxide, CaO: from limestone, chalk, shells, shale or calcareous rock
• Silica, SiO₂: from sand, old bottles, clay or argillaceous rock
• Alumina, Al₂O₃: from bauxite, recycled aluminum, clay
• Iron, Fe₂O₃: from from clay, iron ore, scrap iron and fly ash
• Gypsum, CaSO₄.2H₂0: found together with limestone

The materials, without the gypsum, are proportioned to produce a mixture with the desired chemical composition and then ground and blended by one of two processes - dry process or wet process. The materials are then fed through a kiln at 2,600º F to produce grayish-black pellets known as clinker. The alumina and iron act as fluxing agents which lower the melting point of silica from 3,000 to 2600º F. After this stage, the clinker is cooled, pulverized and gypsum added to regulate setting time. It is then ground extremely fine to produce cement.

The problem isn't that you couldn't have a starbase or some other enclosed cement-manufacturing facility. The problem is whether or not Uranus' rings have all the constituent materials and whether or not it's practical to gather those materials.

I can't find a listing of whether or not all the components of cement can be found in Uranus' rings, but I'm going to go out on a limb and say they are not (big problem!). Let's take limestone, for example:

Limestone is a sedimentary rock, which means it was formed from small particles of rock or stone that have been compacted by pressure. Sedimentary rock is important because it often contains fossils and gives clues about what type of rock was on the Earth long ago. Just like a tree's rings tell a lot about its environment, layers found in sedimentary rock can tell about important changes in the environment.

How is it formed?

Limestone is formed in two ways. It can be formed with the help of living organisms and by evaporation.

Ocean-dwelling organisms such as oysters, clams, mussels and coral use calcium carbonate (CaCO3) found in seawater to create their shells and bones. As these organisms die, their shells and bones are broken down by waves and settle on the ocean floor where they are compacted over millions of years, creating limestone from the sediments and the pressure of the ocean water.

The second way limestone is formed is when water containing particles of calcium carbonate evaporate, leaving behind the sediment deposit. The water pressure compacts the sediment, creating limestone. (Source)

When you boil that all down, limestone requires pressure and water — and while those rings might have come from something that was under pressure, it's unlikely they came from something that had sufficient water to complete the process.⁵ Bauxite and gypsum are low contenders, too.

Add to this the problem that most of Uranus' rings are dust, which would be a whomping pain in the neck to collect at the volumes you need, and the process of using PRC for spaceship hulls becomes impractical.⁶

Conclusion

While PRC could be used to build a spaceship, I do not believe it is an any way a practical solution to the problem — especially where combat is concerned. Just the cost in fuel to compensate for the mass of the PRC is enough to justify not doing it. Add to this the low likelihood of mineral access in Uranus' rings, then the effort needed to mine and process it, and this doesn't sound like a winner.

At the tech levels you're talking about it might be easier to collect the silica from the rings and make artificial diamond, which is also brittle, but not like concrete.

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_{¹ This is officially a frame challenge. I do not believe it's possible to manufacture 1,000 warships a year in a practical way for practical purposes and therefore am not answering the OP's specific question.}

_{² It's worth noting that a combat-grade warship using future technology we haven't invented yet will probably use laminate materials (not unlike today's tanks) that would always be a better solution — in combat — than PRC. Let's ignore this for now.}

_{³ E.G., no portholes like you find in Star Trek or B5. Think "General Products Hull #2" as you would find in various Larry Niven novels.}

_{⁴ Yes, you could build a fluid/goo layer that auto-seals the crack when it forms, etc., but if you're going to go to all that effort just to use PRC, why use PRC in the first place? Keep in mind that PRC will be (not might be, will be) thicker than an alloy laminate, which means it needs more fluid to solve the problem (it's not enough to say, "yeah, but the metal hull needs that, too").}

_{⁵ Not that it wouldn't be UBER-COOL to find limestone in any planetary ring. That's proof of non-terrestrial life. Oh yeah, that would be cool! Regrettably, that's basically why no ring is expected to have it. You might find calcium, but you're using precious life-giving necessary-to-breathe oxygen to make Calcium oxide.}

_{⁶ As you might imagine, creating a vacuum in the vacuum of space is challenging. That means you're scooping the dust or using some form of electrostatic gathering process. Complex, power-hungry, and messy.}

Answer 2

You might be interested to know that this has been looked at, and it has been deemed feasible.

In 1981, Construction Technology Laboratories, a division of the Portland Cement Association, initiated a study of the feasibility of using concrete for structural components of a space station. The idea of using concrete in space may seem absurd to many scientists and engineers. Nevertheless, the study shows that concrete is not only suitable but also economical for space station construction.

Concrete: Potential Material for Space Station

Answer 3

JBH has provided an answer as to why concrete isn't the ideal material for spacecraft. While I agree with him that concrete isn't the way to go, I will expand on the OP's idea a bit.

Reading between the lines, the Uranus Space Navy (USN) is looking for a means of rapidly producing spacecraft hulls. Reasoning that using some sort of precast material will allow for faster spacecraft production than alternatives such as traditional metal construction or some form of 3D printing, we might be able to meet the desire of the USN in a number of ways:

1. Cast basalt.This basically takes lunar slag or similar materials and melts them. The molten material is injected into a mold to produce standard shapes, which can then be linked together. While cast basalt might not have much material advantage over concrete, a thick enough layer will provide radiation shielding and thermal mass to absorb incoming laser or particle beam fire, and even some resistance to kinetic energy from projectiles. This might work best layered over a metal, composite or ceramic hull.
2. Water. Remarkable as it sounds, a ship can be "built" simply and cheaply by essentially having one balloon of reinforced fabric placed inside a larger balloon and the inter-space filled with water. A layer of water 5m thick will provide radiation protection and thermal mass, and should be allowed to freeze into shape to provide structural strength. Mixing reinforcing material like fibre into the water will improve the strength, Project Habakkuk in WWII mixed wood pulp with water to create a reinforced ice which took three years to melt.

http://www.neofuel.com/iceship/iceship_isru_1998.html

3. Sintered regolith. Sintering is a less energy intensive manipulation which presses grains of material together with heat and pressure. The resulting material is strong but porous, providing a cheap shielding material to layer over existing hulls or installations, much like cast basalt.

So while the use of cast materials like regolith or ice might not provide an elegant solution, it is fast and inexpensive. Using these materials for their shielding properties and thermal mass is likely the best possible way of exploiting their properties, and if used as the basis of mass produced sacrificial "drone" ships, the USN could conceivably overwhelm their enemies with massive fleets of drones backed by a few manned ships with diplomats and Space Navy officers.