[z64555]

I was looking at one of my sketches of a installtion defense turret, and somehow got to wondering if it could be made out of something like concrete.

I mean, just about every space Sci-Fi I've come across has suggested that the large structures floating about in space are almost entirely made of metals and plastics. But what if said structure was quite remote from supply chains, and it was more efficient to mine raw materials out of asteroids and nearby planetoids?

Metal of course is fairly easy to work with once you've smelted it to a desired purity, but you have to dig fairly deep for it. Asteroids are something of a gamble, they could be made up of just about anything... iron, nickle, slag, platinum, volcanic glass.

Significance this is probably only limited to the look of installations in games and media, but it may also provide a plot device or two (a burgeoning space-faring civilization needs to find raw materials to build their new home, etc.)

[Achillion]

I don't know much about construction, but I do know that it's rather difficult to expand and patch up concrete structures. It's relatively easy (is it? not sure) to bolt on an extra module when a station is made of something metallic, but it's really hard to attach one concrete structure to another. In fact, I believe the best (only?) way to expand a concrete structure is if it has those metallic rods sticking out. If it's a military installation, it'll be hell if it's taking damage and you need to be patching it up all the time.

There's also the matter of the actual construction of the station. As far as I know, building something out of concrete isn't as simple as just moulding it into place and waiting for it to try. Reading http://en.wikipedia.org/wiki/Concrete#Curing I get the impression that there's a required procedure that appears to depend on quite specific atmospheric conditions.

That all said, this http://www.nss.org/settlement/nasa/spaceresvol3/cpmss1.htm suggests that people who know more about it than I do, have considered the possibility

[Black Wolf]

I would think permeability would be the biggest issue there. To be entirely honest I've not looked into it for concrete, but my suspicion is that it wouldn't hold hard vacuum at bay for particularly long. Of course, there could be sealant layers and stuff in the structure...

[FUBAR-BDHR]

Seems like any use of concrete to try to build in the freezing cold of space would be difficult at least.  Unlike metals concrete has water in it that needs to dry. 

[Black Wolf]

Space is supposed to be a very good dessicant, but I suspect that dessicating and drying would result in very different fine structures, and very different emergent properties as a result.

Also, Relevant Link.

[Nuke]

you know you could possibly do something with inflatable concrete forms. they can be launched from earth, inflated, then you can inject lunacrete or whatever into the form and control the atmosphere to facilitate rapid drying. for cylindrical forms you could apply a little bit of rotation to allow even hardening. of course if you are launching lunacrete from the moon you might as well just build prefab parts there and launch those instead.

[z64555]

I would think permeability would be the biggest issue there. To be entirely honest I've not looked into it for concrete, but my suspicion is that it wouldn't hold hard vacuum at bay for particularly long. Of course, there could be sealant layers and stuff in the structure...

Iirc, concrete isn't by itself water-tight due to it being fairly pourous. It'll prevent any rapid flow of fluid but it may leak. It is entirely possible to paint air-tight layers on top of the concrete to condition it to maintain positive pressure inside the structure.

I don't know much about construction, but I do know that it's rather difficult to expand and patch up concrete structures. It's relatively easy (is it? not sure) to bolt on an extra module when a station is made of something metallic, but it's really hard to attach one concrete structure to another. In fact, I believe the best (only?) way to expand a concrete structure is if it has those metallic rods sticking out. If it's a military installation, it'll be hell if it's taking damage and you need to be patching it up all the time.

Not necessarily, you can always drill into an existing concrete structure and stick some steel connecting rods in it, wet the contact surface and then paste the new concrete right on it. If done right, the bond will be just about the same strength as solid concrete.

Speaking of damage, there has been some breakthroughs in "self-healing" concretes that will eventually mend cracks and fissures, so long as the forces that caused said cracks and fissures have been removed.

There's also the matter of the actual construction of the station. As far as I know, building something out of concrete isn't as simple as just moulding it into place and waiting for it to try. Reading http://en.wikipedia.org/wiki/Concrete#Curing I get the impression that there's a required procedure that appears to depend on quite specific atmospheric conditions.

 It depends on the type of cement used. There's hydraulic (which most are familiar with) and then there's non-hydraulic. From what I've read, non-hydraulic cements so far have been inferior to that of hyraulic in terms of strength, but offer the ability to be cured using a CO2 rich atmosphere.

Unlike metals concrete has water in it that needs to dry. 

As far as I know, concrete doesn't need to dry, per se, but it does need to cure. Concrete has been known to form stronger bonds when in a still-moving aquatic environment

[redsniper]

Concrete, and ceramics in general, tend to perform much better in compression than in tension. So it's great for stuff that has to bear a lot of weight, pillars, foundations, walls, etc., but not so much for things that will be pressurized from the inside (like space stations). You can do stuff to help alleviate this, like using reinforced or prestressed concrete, but I think for a pressure vessel shell you're going to get better strength to weight with metals. Though having said that, I looked briefly on google and apparently concrete pressure vessels exist.

But anyways, consider how we make boats out of steel all the time, but making a concrete boat is rather difficult. Concrete is just so damn heavy. The tradeoff is that it's cheap though, good for when you need metric ****-tons (literally) of building material.

Now for something built in space that doesn't have to go anywhere, weight obviously won't matter as much. So in that case I could maybe see using concrete to make some kind of man-made asteroid base: Just a big solid block you can bolt stuff to and have rooms and tunnels cast in. Then it could just be so thick that holding one atmosphere of pressure is no problem.

[FUBAR-BDHR]

First the original post was about building a station remote from supply lines.  In this situation concrete is a bad choice for many reasons.

1.  The before mentioned need for water and drying/curing which can take years (Hoover dam still isn't cured last time I heard). 
2.  The need for forms.  You would need to ship these to the site.  Yes they could be reused from area to area but that would slow down construction.
3.  The need for reinforcement.  Your going to need to manufacture on site some kind of reinforcement like rebar. 
4.  The need for an energy source.  While this is true of metals as well you need a lot of heat to make cement.  Can't make concrete without making cement.  Can't make cement without making clinker.  Clinker requires a lot of heat to make.  If you need to make rebar as well then you are needing quite a bit more energy to produce 2 products.
5.  Flexibility.  Concrete doesn't like to expand and contract or flex like metals and plastics will.  Depending on how near to stars/planets the structure is built you need to take into account temperature and gravitational changes.  Looking at our own solar system building an installation around someplace like mars would cause a good deal of heating and cooling every day.  Anywhere near Jupiter and you have to deal with either the planet and possibly all of those moons as well.  Even things as small collisions could cause cracks instead of dents. 
6.  Mining resources.  Unless everything is being shipped in (which kind of kills the idea of not using a lighter, more durable material) you are going to need to mine resources.  Mining usually involves some kind of drilling either for tunnels or small holes for blasting.  If you have an asteroid stable enough for mining it would seem to be a more logical path to use the asteroid itself for the base of the installation.  Why make concrete when you have ready made rock?  Drill into it (by whatever means the current tech allows, mechanical drills, phasers, BFGreens) to mine the resources and seal the tunnels you make.  Yes you would still need to line the tunnels and seal the environment but that could be initially done with light weight materials you brought with you and later with metals that were mined.

I had a few more but forgot what they were.  Anyway would it be possible to build out of concrete?  Probably.  Would it be practical probably not.