Concrete

[Kitsune]

I am asking this hear because it has to do mostly with science fiction.

First, will conventional concrete harden in space?
Second, if not, could a special concrete be developed which would?

The reason why I am asking is that I am considering the idea of concrete merchant starships, probably in-system craft for transporting various bulk cargo assuming some sort of thrust-less science fiction drive system.

[Darth Raptor]

Cement hardening is a hydration reaction, which should work in space, unless it's exposed to inordinate amounts of cosmic radiation or something.

[Gil Hamilton]

Once you actually mix the water and the concrete, it should harden. The chemistry of concrete, as DR noted, is hydration. The calcium and various other chemicals in concrete break down the water and become things like Ca(OH)2 and such, producing a bunch of heat in the process. You don't need air for that.

However, what I'd be concerned about is the chemistry of the reaction in a lack of pressure and what effects that would have. It would certainly make liquid water harder to add to the mix, since it's going to want to boil in vacuum rather than being a nice polite reactant.

The lack of gravity might be interesting too, but it might be a boon. It would take considerably effort to make the aggregate, cement, and water to become a homogeneous mixture in microgravity. However, it will still need to be stirred until pouring, of course, to prevent it from setting in the vessel.

I'm curious about the use of concrete as a building material for a spaceship though. Sure, it's literally cheap as dirt, but at the same time, what you really want is something to keep air in and space out. You might as well use aluminum for that or bake up some ceramic tiling.

[Stormbringer]

First, will conventional concrete harden in space?
Second, if not, could a special concrete be developed which would?

The answer to both questions is, not in any sort of useful form. The hydration reaction can theoretically occur but concrete is sensitive to even terrestrial temperature differences. You have to pay attention to a bunch of factors like temperature, water content, and the mixture of the ingredients in the concrete. It's far more sensitive than one would first think when you're talking about serious structural applications. Trying to do it with all the difficulties that come with working in space would be practically impossible.

The reason why I am asking is that I am considering the idea of concrete merchant starships, probably in-system craft for transporting various bulk cargo assuming some sort of thrust-less science fiction drive system.

It's in no way remotely practical for use in such applications. Concrete is only really good in compression, is always and inevitably going to crack, and is heavy for it's weight. On top of that, the dire difficulty with quality control of the finished product is going to wipe out any potential savings from using concrete.

[Shroom Man 777]

Just call it "duracrete" or Space Concrete, which is concrete in name only. "Constructing" a starship with duracrete or Space Concrete would involve pouring thick liquid duracement or Space Cement, but the actual chemical composition of the substance would be nothing like normal concrete. Space Concrete's composition would be thousands of lightyears ahead of anything humanity can conceive of in this day and age.

[Kitsune]

It's in no way remotely practical for use in such applications. Concrete is only really good in compression, is always and inevitably going to crack, and is heavy for it's weight. On top of that, the dire difficulty with quality control of the finished product is going to wipe out any potential savings from using concrete.

You do know that concrete was used in both World War I and World War II for limited scale shipbuilding?

Also, I thought I remember hearing a discussion of using moon materials in construction of structures and I thought it was something concrete like....

[Darth Raptor]

Naturally, there will be a difference between moon dust adobe buildings and spaceship hulls. The latter will be subject to stresses beyond anything you'd find in a wet navy. And if you have mass/inertia dampeners or balls-out reactionless drives, why make ships out of concrete? Anachronisms for their own sake are stupid.

[RedImperator]

A major problem with using concrete is that the primary ingredient in cement is limestone, which is found only on Earth, as it's composed of the shells of marine organisms. So to make these cheap spaceships, you have to haul millions of tons of limestone out of a gravity well.

[Gil Hamilton]

I don't think it necessarily has to be "concrete" as we think of it. Technically, a concrete is made of an aggregate, a cement, and water. It doesn't have to be limestone. Limestone is just a really available source of calcite, which provides the calcium for the various chemical reactions that happen in concrete. Admittedly, you aren't going to find much limestone in space, since even the inorganic version of calcium carbonate formation requires seawater as part of its crystallization, but there are no doubt other sources of calcium out there.

Or you might have the cement part made of something else that isn't clay and limestone. If it is made of the three above things and is poured into molds for construction, it could be reasonable called cement even if you use different chemistry and materials to make it. In future material science, they could have a poured concrete that isn't subject to Earth Concretes sensitivity to temperatures (doesn't expand and contract with temperature, leading to cracking, so easily) and doesn't have such a god awful mass-to-volume. Of course, that kind of defeats this thread, but it's a possibility.

[RedImperator]

I don't think it necessarily has to be "concrete" as we think of it. Technically, a concrete is made of an aggregate, a cement, and water. It doesn't have to be limestone. Limestone is just a really available source of calcite, which provides the calcium for the various chemical reactions that happen in concrete. Admittedly, you aren't going to find much limestone in space, since even the inorganic version of calcium carbonate formation requires seawater as part of its crystallization, but there are no doubt other sources of calcium out there.

Or you might have the cement part made of something else that isn't clay and limestone. If it is made of the three above things and is poured into molds for construction, it could be reasonable called cement even if you use different chemistry and materials to make it. In future material science, they could have a poured concrete that isn't subject to Earth Concretes sensitivity to temperatures (doesn't expand and contract with temperature, leading to cracking, so easily) and doesn't have such a god awful mass-to-volume. Of course, that kind of defeats this thread, but it's a possibility.

True. Another possibility might be Pykrete. There's certainly plenty of water in the solar system, and if you could substitute some kind of synthetic fiber manufactured out of hydrocarbons available in space for wood pulp, all the raw materials are readily available. Of course, keeping it insulated would be critical, and I don't know how to deal with waste heat, but I'm sure some clever engineer could figure it out. Self Promotion Alert: In The Humanist Inheritance, I had the outer solar system colonists use Pykrete extensively in construction, though of course a colony buried under the surface of Oberon does not face the same engineering challenges a spacecraft does (a spaceship designer, for example, does not have the luxury of using 1.8 billion cubic kilometers of water ice as a heat sink).

The deeper problem, though, is that no matter what you use, there are better materials available in space for hull construction. Aluminum, for example, is everywhere, and a society that has advanced to the point of reactionless drives should have more than enough energy available to refine it in mass quantities. I'm hard pressed to think of a single reason to use a concrete hull in space when aluminum is available, let alone whatever advanced alloys a spacefaring society ought to be able to create.

[Surlethe]

Radiation protection is the only reason I can think of to build a concrete spaceship, and that is accomplished more easily by lead. In any case, concrete is not homogeneous; I'm guessing that's why, as Stormbringer pointed out, it always and inevitably cracks. Imagine a concrete spaceship orbiting the Earth; every forty-five minutes, it suddenly expands (or contracts) as it passes out of (or into) the Earth's shadow. You can't predict how it will respond to thermal variation, so you can't control for the expansions and contractions like you can with a homogeneous metal like aluminum (which is also a conductor, so it gets rid of heat better and more uniformly).

[Fingolfin_Noldor]

There's another thing to thing about Concrete; it's porous. Because it is porous, water leaks in unless you coat it with some coating that prevents water or some other liquid from leaking in, you are in trouble.

Plus, this means that water can condense on its surface, and freeze in the pores while you ascend into space. That itself will weaken the concrete over time. Pretty much why you would see concrete crack over time as well, due to erosion when it is exposed to the elements, without the coating.

[Darmalus]

If you want a cheap, plentiful material for the hull, would the slag left over from space based refining of asteroids work?

[Stormbringer]

You do know that concrete was used in both World War I and World War II for limited scale shipbuilding?

Yes, I do as a matter of fact. But most of those applications were intended for extremely short use and never for anything truly long term. There's a reason we build ships out of steel, not concrete. Simply because something is possible doesn't make it any thing like practical.

As I was saying, though flubbing it because of the late hour, concrete poses a pretty significant challenge just to get a properly cured structure. The cement in the concrete is sensitive to even relatively small changes in temperature; the difference between a cold day and a sunny day can affect some mixtures. What to do think's going to happen to the hydration reaction in sub-zero temperatue or direct unfiltered sunlight? Another big factor is evaporation; you'll lose a tremendous amount of moisture to the vacumn, making hydration extremely difficult to sustain for the month or more it will take to cure.

It may be possible to overcome these, provided you spend enough money and time and have sufficient manpower. But on top of disadvantages, one of which is the cracking which will be problematic for keeping in atmosphere and another being the serious mass to strength issue, you're basically expending a lot of work to get a sub-par product. It's not likely to be remotely worth it to build a space-going vessel out of structural concrete.

[Sea Skimmer]

Concrete could be quite useful for low cost impact and radiation protection on a steel hulled ship (screw aluminum, its fatigue life is undesirable for a star ship that might otherwise last centuries), but you could also just use liquid loading and it would do pretty much the same job. If you actually want to build a ship out of concrete the only remotely decent way to do it would be to assemble the ship out of prestressed concrete slabs and other pieces manufactured in some kind of space dock or even the surface of a moon.

[Gil Hamilton]

True. Another possibility might be Pykrete. There's certainly plenty of water in the solar system, and if you could substitute some kind of synthetic fiber manufactured out of hydrocarbons available in space for wood pulp, all the raw materials are readily available. Of course, keeping it insulated would be critical, and I don't know how to deal with waste heat, but I'm sure some clever engineer could figure it out. Self Promotion Alert: In The Humanist Inheritance, I had the outer solar system colonists use Pykrete extensively in construction, though of course a colony buried under the surface of Oberon does not face the same engineering challenges a spacecraft does (a spaceship designer, for example, does not have the luxury of using 1.8 billion cubic kilometers of water ice as a heat sink).

I can see that. Pykrete is an interesting idea and I don't see any reason why you can't still use regular cellulose for it, if your spacemen have access to vats of engineered algae that happen to use it to make cell walls.

The deeper problem, though, is that no matter what you use, there are better materials available in space for hull construction. Aluminum, for example, is everywhere, and a society that has advanced to the point of reactionless drives should have more than enough energy available to refine it in mass quantities. I'm hard pressed to think of a single reason to use a concrete hull in space when aluminum is available, let alone whatever advanced alloys a spacefaring society ought to be able to create.

Aluminum, titanium, and iron should all be available in quantities out in space and there is no reason you can't make good quality ceramics out their either. Even if we are relatively modern with our material science, we can make much better hulls with such things than concrete. The problem in space is that gathering sufficient volatiles is an issue depending on where you settle, rather than metal and silicates. When you live on a dusty asteroid, you are more worried where you are going to get your organics rather than building materials. That's what makes lunar colonization such a bitch, since it has to be largely supported by Earth unless your astronauts want to hoard every molecule in the system and live very frugally.

I've been batting a story around about a collection of lunar colonies that were abandoned when Earth largely went to pot and could no longer support them and their society evolving to a state that makes the Fremen in Dune seem wasteful in order to survive.

[RedImperator]

There are plenty of volatiles in carbonaceous asteroids, so that won't be a problem. You're right about the moon, though: that place just sucks.

[Kitsune]

Just a quick response that most of your arguments are quite persuasive as far as using concrete (or something like it) as a starship material being mostly not effective.

[Sikon]

The usual space analogy of concrete would tend to be cast basalt and other remelted rock. For example, it is suitable for pavement and roads around a lunar station like concrete might be used on earth. If one has cheap energy available, melting rock and cooling it at the right slow rate can produce an inexpensive material suitable for some applications, whether using lunar material or a rocky asteriod.

Example:

Green (1980a, unpublished Summer Study document) has discussed the properties of lunar basalt at length. Raw lunar soil may be fused at about 1550 K, then allowed to cool and solidify into a very, hard, exceptionally strong material. If cooling is virtually immediate - minutes or tens of minutes - the liquid basalt is quickly quenched and becomes a polymeric glassy substance. The material is very strong but also moderately brittle, permitting cracks to propagate rather easily. [...] However, if the liquid basalt is permitted to cool more slowly - allowing perhaps several hours for the melt to pass from full liquidity at 1570 K to hard solid below about 1370 K - the material anneals into a crystalline form. This method of platform construction takes much longer and requires more energy, but would produce a far less brittle foundation. Such a basalt crystal platform could be prepared as one continuous surface, whereas the glassy basalt platform must be made in slab-sized sections. [...]

According to Nichols, concrete pavements for highways are generally about 15-25-cm thick, 30 cm and higher for airport runways. Adjusting for the 0.17-g lunar gravity and the attendant reduced forces to be sustained, the equivalent load bearing strength on the Moon would require a thickness of perhaps 2.6-4.3 cm for highways. Both highways and encounter heavier use than the LMF platform is expected to receive in normal use, so a choice near the lower end of this range appears justified especially since basalt appears to be stronger than concrete in compression and shear (Baumeister and Marks, 1967; Zwikker, 1954). Consequently, a thickness of 3 cm (Green, 1980b, private communication) was tentatively selected.

From here

Technically one could make concrete with ice from comets as a water source for hydrating the minerals. It's just that such doesn't tend to compare as favorably to alternatives as on earth.

As suggested above, some applications like pavement subject mostly just to compressive loading could be suitably fulfilled by cast basalt extraterrestrially. Aside from usage in bases on moons, it is one of the options for radiation shielding around a spacestation, although nickel-iron asteroid material or even just bags of asteroid or lunar dirt stuffed into a metal shell could work for that too.

Another structural material that might be often almost as inexpensive for a space civilization would be melting and processing nickel-iron asteriod material since such is metal instead, almost like a giant block of stainless steel. Such has much greater tensile and bending strength, a ductile metal more appropriate for general structure in space colonies and spaceships, just like we don't make cars with concrete roofs today since such would have to be undesirably thick and heavy, brittle and weak compared to metal.

concrete (or something like it) as a starship material being mostly not effective.

Indeed. High-performance high-velocity spacecraft where extra mass is a concern would tend to use metal alloys or composites, way beyond the strength to weight performance of concrete or even cast basalt. Such could use aluminum, titanium, different types of steels, carbon-fiber composites, maybe some future diamondoid composites in some applications, and/or other fancy materials as appropriate.