Mars Colony Cement & Concrete

Midoshi · 2012-02-11 10:50:13

With regard to atmospheric pressure: it is true that much of the southern Martian highlands are well below the average surface pressure, but you don't need to go to very low regions like Valles Marineris or Hellas Planitia to experience pressures > 6 mbar. The Viking landers are situated in Chryse Planitia (V1) and Utopia Planitia (V2) in the planet's northern plains, and never recorded pressures much below 7 mbar (see below). The pressure oscillations are due to changes in season and distance from the Sun, while the offset between V1 and V2 is a 1.5 km elevation difference (V2 is lower).

SpaceNut · 2012-02-11 21:31:26

The minimum pressure under which a substance can exist as a liquid occurs at the substance's triple point.

The triple point http://en.wikipedia.org/wiki/Tripple_point
In the case of carbon dioxide, the triple point corresponds to a temperature of -56.6°C and a pressure of 5.1 atmospheres (518,000 Pa). Now, while Mars does get as cold as (or colder than) -56.6°C, the surface pressure on Mars (or on Earth, for that matter) certainly never reaches 5.1 atmospheres. Thus we can be absolutely certain that carbon dioxide cannot exist as a liquid on or anywhere near the surface on Mars.

In contrast, the triple point of water occurs at a mere 611.73 Pa (6.1173 millibars), a pressure that is frequently exceeded on the surface of Mars, in craters and other low-lying areas, according to measurements by Viking and other spacecraft.

http://mars.spherix.com/spie2/spie98.htm

But with the temperatures so low there is likely no liquid water just ice but a brine containing sample would have a lower freezing temperature.

http://www.aerospaceweb.org/question/as … 0230.shtml

JoshNH4H · 2012-02-13 16:46:34

GW- In addition to what Spacenut and Midoshi said, Martian atmospheric pressure is a matter of definition as much as anything else. The Martian "sea level" or datum as it is apparently called, is defined to be the altitude where the pressure is, on average, 6.105 mb. Google has come out with "Google Mars," which is analogous to Google Earth. It's really cool, plus it has a topographic map built in to kind of give an idea as to what the pressure will be at a given location. You can find it Here.

PVAc dissolved in water is apparently a type of glue. I was thinking that we could put it in water, then let it dry out to form a film which could be put on top of things. If it were warmed before being placed over the icecrete it would bond quite nicely.

SpaceNut · 2012-02-13 22:08:07

Wood glue such as Elmer's which is slow to dry, needs lots of air flow and warm temperatures....

JoshNH4H · 2012-02-13 22:59:57

I agree that it would not be particularly practical to use as a glue for things that are outside, but it can be allowed to dry inside and then placed on top of the icecrete. Since a film does not involve a large amount of polymer, we don't need much air or much heat.

SpaceNut · 2012-02-14 22:04:48

My fear for using it on icecrete would be that exposed to humidity, this usually white glue is which is not waterproof, so while it can seal air, dust, dirt, etc as long as it's dry, it soon as it makes contact with any trace of water becomes wet, soft, & sticky once more....

JoshNH4H · 2012-02-15 00:36:55

Well, the big worry for icecrete isn't water per se so much as water vapor which will naturally sublimeaway unless somehow prevented from doing so. I don't know for sure but I wouldn't think that water vapor would have the same effect as liquid water. When placing the film on the ice we might see some mixing between it and the thin film of water just below it (I'm assuming that the film will be above freezing when placed on the icecrete), but the film should cool quickly and once it does it will be fused to the icecrete, which is desirable because it will make a strong seal. I don't think the film will be dissolved quickly.

SpaceNut · 2012-02-20 05:37:46

I was reminded that Mars has another brick that could be made by Gyrpd

Spacenut one posibility for bricks is to use regolith and to artificially put a bit of Iron Oxide in the mix. (Actually Mars might not need to do this) and to superheat it in a solar furnace. This melts the Iron bonding the bricks and creating a solid structure depending on the mold. There is even ways you can do without mortar to join the bricks by magnetising the bricks into positive and negative ends.

So what is in Mars Soil...
http://chapters.marssociety.org/winnipeg/soil.html
http://en.wikipedia.org/wiki/Regolith
http://chapters.marssociety.org/winnipeg/materials.html

So from the mix we would process the regolith to blend the mixture that we want the bricks to contain...
http://www.moonminer.com/Regolith-Refining-Summary.html

Then we would heat the mixture to form the brick...
http://www.lunarpedia.org/index.php?tit … d_Regolith
http://www.authorstream.com/Presentatio … owerpoint/

This process with the Iron Oxide would liberate some quantity of Oxygen as a by-product...

Last edited by SpaceNut (2012-02-20 05:45:34)

GW Johnson · 2012-02-24 02:02:40

I'm still thinking about a coating for "icecrete" to prevent sublimation. If the local pressure is 6+ mbar, then a coating is not needed. But, if it is, then I am not sure PVA (polyvinyl acetate?) or any other organic plastic will be easily obtainable on Mars or the moon.

Re: Mars atmospheric pressure: I have my doubts as to northern lowland pressures really being 6-7 mbar per Viking 1 & 2. Why? Because the recent northern polar lander (Phoenix) saw ice that it exposed while digging sublimate, and fairly quickly. If the pressure really were 6+ mbar in the polar lowlands, that would not have happened. Basic physics.

So, I really think we need an anti-sublimation coating. I'd like the coating to be local materials, and I'd like to avoid the energy expenditure of melting local rock or dirt. This is going to be some sort of chemistry thing. If we find one, it would work at 0.00 mbar on the moon, too. "Icecrete" is a pretty nice thing to have, so the anti-sublimation coating for "icecrete" is really a very important item.

For reinforced "icecrete", any material with tensile strength would do for the rebar substitute. Basalt (or any other rock) fiber would do, braided into a coarse-textured rope. I dislike the energy expenditure of melting the rocks to do it, but it seems unavoidable, since no one has ever spotted an active volcano on Mars or the moon. Ideas?

Does anyone know the elastic modulus of a braided basalt-fiber rope? (It would not the same as the individual fibers, not by a long shot, no real composite material ever has the properties of the individual fibers.) If the rope's effective modulus is near that of steel (30 million psi = 207 MPa), such a rope might in some way be tensioned very hard, thus serving as the pre-stress member in a pre-stressed "icecrete" beam. Not worth dreaming up, if the modulus is too low, though.

Having pre-stressed beams available is nice for bridges and buildings. Good for resisting bending, such as in pressurized habitats. Very important.

GW

Midoshi · 2012-02-24 10:24:23

On the sublimation of ice at Phoenix:

It is not necessary for the atmospheric pressure to be below 6 mbar for water ice to sublimate. Ice sublimates on Earth frequently, and our atmospheric pressure is far higher than 6 mbar. The reason a condensed phase sublimates is because the partial pressure of its vapor phase in the ambient atmosphere is less than the vapor pressure just above the condensed phase. In other words the atmosphere at the Phoenix site only had to be dry for the ice to sublimate.

When the atmospheric pressure is less than the vapor pressure, (i.e. 6 mbar at 273K for water ice) the condensed phase can never be stable. Even if the local atmosphere is entirely displaced by the vapor phase it will remain "dry". In this case the high pressure vapor expands into the ambient atmosphere, causing more sublimation from the condense phase, followed by more expansion, until the condensed phase has been converted entirely to vapor.

This also means that having a +6 mbar atmosphere is necessary for ice stability only if your operating temperature is 273 K. At lower temperatures the vapor pressure of ice is reduced. For example, it is 1 mbar at 253 K, and only 0.04 mbar at 223 K. At each of these temperatures ice can be stable as long as the atmospheric pressure is above the corresponding vapor pressure and it is not too dry. Since Phoenix saw typical temperature highs of -30°C (243 K), that would mean the atmospheric pressure would have to have been a fraction of a millibar if the ice was destabilized by low atmospheric pressure.

I hope that this makes it clear that this is a matter of a dry atmosphere, not insufficient atmospheric pressure. I also hope it didn't come across as patronizing; I was aiming for pedagogy. This phase stability thing confused the heck out of me the first time I really thought about it in my graduate materials science course, so I know first hand how hard it can be to grasp.

Last edited by Midoshi (2012-02-24 10:25:09)

GW Johnson · 2012-02-25 09:59:15

Thanks, Midoshi. I had forgotten the distinction between the vapor pressure above the ice vs the "air" pressure above the ice. Had been thinking vacuum-only, as for spacesuit compression issues so long, I got stuck in that rut.

BTW, "hi". Long time no see, crash and all that.

So, since Mars's atmosphere is generally very dry, the water vapor pressure in that atmosphere would be pretty near zero, regardless of the atmospheric pressure. Summer temperatures in the equatorial regions will get close to the standard freezepoint (triple point), so we can't count on very-cold-ice vapor-pressure reduction. Yep, "icecrete" will need a tough sublimation coating. That material will not know Mars from the vacuum of the moon or space.

I was hoping for some sort of paint coating we could spray on and "cure" right in place on the dirty-but-not-wet cold ice surface. Maybe an evaporating solvent cure with linking residuals like some oil-based paints here on earth.

Hmmm, some sort of water-based latex paint might even work, if it could be kept from boiling before it dries.

Does any body have a bell jar and a vacuum pump? Two ice cubes, one painted at below-freezing conditions with latex house paint, the other not. Maybe three: try an oil-base hardware paint, too. (Maybe even Krylon clear sealer spray - ha ha.) Paints will take a long time to set-up in the kitchen freezer on a not-wet icecube surface, but that's what we need.

Here in central Texas it's never cold enough to do the painting successfully outside, although I have a couple of good freezers. Maybe somebody in snow country?

GW

SpaceNut · 2012-02-25 21:32:27

That is interesting for sure as experiments go but alas I do not have a vaccum chamber to do it. But in either case I believe we can How to Paint an Ice Rink just as long as the How to Clean Paint Booths With Dry Ice does not occur.
Then again we are doing the exact oposite when MIT Puts Chill on Anti-Icing Coatings

Last edited by SpaceNut (2012-02-25 21:52:10)

GW Johnson · 2012-02-26 10:13:27

Well, following Spacenut's links, it appears that water-based paints can be applied to ice, at least here on Earth. Hmmmmm.

Maybe the experiment is really to see what happens to a bucket of (water-based) wet paint in vacuum. If there is no bubble formation, then we can paint poured "icecrete" structures once they are frozen, in vacuo.

The second test is to see if that coat of paint stops the sublimation.

If both tests are successful, then we have a way to create structurally-useful materials and construction parts on Mars, on the moon, or on any other celestial object that has both ice and regolith.

As to color, I'd suggest a highly-reflective white or aluminum pigment, to reduce the absorption of solar energy that could melt the ice. Or, just keep the stuff in the shade. The paint might have to be an imported item, but the paint on a pre-stressed "icecrete" beam weighs a lot less than the beam.

GW

GW Johnson · 2012-03-11 17:46:37

I posted an article with illustrations on "icecrete", over at http://exrocketman.blogspot.com, dated 3-11-12. There are still serious questions, but I was able to pose a list of credible experiments needing to be done. I am still very enthusiastic about such a material.

GW

SpaceNut · 2012-03-12 19:43:51

By the way thanks for the post on Your blog and that is how true open source ideas work. In fact I am going to post about this over on MarsDrive....

John Creighton · 2012-03-13 12:03:06

GW Johnson wrote:

I posted an article with illustrations on "icecrete", over at http://exrocketman.blogspot.com, dated 3-11-12. There are still serious questions, but I was able to pose a list of credible experiments needing to be done. I am still very enthusiastic about such a material.
GW

I replied to this the other day. I’m not sure what happened to my post. Anyway, I think from an economic perspective the value of water is will drive how often this technique is used. I am sure it will be great for building cool structures but question if it will be as strong a material for warmer structures. I bet it would be used a lot for cool tunnels between buildings because I think it would be much faster to work with then brick and labor will not doubt be a valuable resource on mars.

JoshNH4H · 2012-03-13 14:08:35

That's a really good point, actually, John: This material might find some very good use as a construction material for pressurized tunnels if it's simple enough to make. It will probably be in the form of an icecrete structure covered in regolith. IMO its a lot simpler to make a structure airtight and cover it with regolith than to make it airtight and make it able to withstand the pressure forces exerted on it. It is perhaps worth noting, though, that icecrete is not "free" in the sense that water on earth is "free," meaning that you just need to pump it into a receptacle. It does need to be melted from its solid component, which will require a minimum energy input of 334 kJ/kg. This is a lot less than a material like cast basalt (~1.25 MJ/kg), but still at least a little bit significant. I suppose it would be possible to use heat to cut ice blocks straight out of the frozen underground reserves, which the colony will certainly be sited very close to.

louis · 2012-03-13 15:15:50

Yes, I think my post went missing as well as John's.

Anyway, this certainly needs investigating. The presentation on your site GW was v. interesting.

I have my doubts about using this as a construciton material for pressurised environments. HOwever, I can imagine some other uses e.g. a retaining wall used as a barrier to drifting sand, to keep a base area clear of dust. Also, it could be used to make flat roadways. Another use might be for unpressurised buildings.

JoshNH4H · 2012-03-13 16:20:54

Well, there would be nothing wrong with using it as a frame for a tunnel to get from one building to another, so long as the tunnel isn't heated, which there is really no reason to do. It wouldn't really be load bearing, as piles of regolith can mostly do that on their own. It would just help retain the pressure (Perhaps not even of oxygenated air, but just CO2, so that only a face-mask is needed?).

I think this is definitely a material with a lot of potential. Just, maybe not for roads At least, not without a layer of something else over it. I think that for a while simply clearing the roadway of rocks should be sufficient. I gather that, lacking liquid water, Mars is mostly flat.

John Creighton · 2012-03-13 20:06:38

JoshNH4H wrote:

Well, there would be nothing wrong with using it as a frame for a tunnel to get from one building to another, so long as the tunnel isn't heated, which there is really no reason to do. It wouldn't really be load bearing, as piles of regolith can mostly do that on their own. It would just help retain the pressure (Perhaps not even of oxygenated air, but just CO2, so that only a face-mask is needed?).
I think this is definitely a material with a lot of potential. Just, maybe not for roads At least, not without a layer of something else over it. I think that for a while simply clearing the roadway of rocks should be sufficient. I gather that, lacking liquid water, Mars is mostly flat.

I bet it still has a fair amount of strength at about 1/10th the compressive strength of concrete. I think the tunnels could be heated some. I think they should be kept around 0 degrees Celsius. That way one would avoid gettin too cold going from one building to another. It would also be a nice place to store vegetables. I don't think it would collapse if the tunnels were a little above zero. As long as the majority of the structural material is below zero. Perhaps some foam would help keep a better temperature differential.

Keep in mind you can build a tunnel out of wet sand, compressed dirt or simply a pile of stone rubble. Well, wet sand may not make a large enough tunnel for people, if most of the structure is held together by ice crystals then maybe the sand would be strong enough.

The structural question I suppose is the maximum radius the top of the roof could be at. If the material was layered with flat stones the friction force would be much greater and allow a much larger tunnel/vault radius. I think the biggest structural risk is thermal cycling. The melting and freezing of glaciers is enough to turn stone into dust.

JoshNH4H · 2012-03-13 22:55:28

I would definitely agree with that. At the least, for tunnels intended for people to walk though it should not be an issue.

GW Johnson · 2012-03-14 17:53:32

I quite agree that the experiments need to be run: that high aggregate content eliminates, or at least reduces, the creep behavior of "icecrete". And, that high Young's modulus reinforcement does exactly the same thing. Does anybody have a specific contact at NASA, ESA, or JAXA for proposing such experiments as a small business initiative? I think I could actually run these experiments here on the farm.

As for melting problems, I suggest you do not use this material inside actual human habitations. Outside the heated environs, it would be fine for building construction. That is, assuming my contentions about creep limitations are true. There are few, if any, places on Mars, the moon, or the NEO's, that a shaded location at ambient pressure (or the lack thereof) would not be below 0 degrees C.

Assuming creep is not an issue, I see no reason that pre-stressed "icecrete" beams cannot be used in conjunction with "icecrete" slabs to form the pressure shell of a habitat. Burial under regolith is even better, but I see the freedom not to rely on burial, given a proper coating. The trick is to stay outside the insulation for the heated spaces, not necessarily the pressure shell! Those are two completely different issues.

For roads, scraping the rocks aside from the sand-like fine regolith might do, up to a point, but what happens when your vehicles start to fall in the 100,000 lb local weight class? And what happens when you have a wash to cross (don't kid yourself, these exist on Mars)? In either case, you need a tough substrate underlying your regolith-fines surface, and, you need a "real bridge" to cross the gulley. That's the same pre-stressed "icecrete" bridge beam technology, as the pre-stressed concrete bridge beam technology here on Earth.

Concrete in the sense of Portland cement-bonded aggregate and reinforcement structures, are going to be rare on Mars (or the moon, or the NEO's). Yet the substitution of ice for Portland cement, makes sense on all of these bodies, since rocks, regolith fines, and ice, are present on nearly all of them. And, temperatures in the shade are very cold.

Given the experiments regarding creep and anti-sublimation coatings, I think we're onto something here. This is every bit as important as the mechanical-counterpressure spacesuit idea, and that idea is absolutely critical!

GW

John Creighton · 2012-03-14 21:19:20

For mechanical properties of frozen ice see the following link.
http://www.uaf.edu/esm/esmpoll/mechpro.pdf

From figure 1 it looks like the strength goes up significantly with increased sand.

As a random though flour is good as absorbing water but would not doubt be to expensive on mars to use as bulk material.

JoshNH4H · 2012-03-14 23:25:12

GW- I would actually see a transition to railroads relatively quickly, probably before we have land transport capable of conveying that kind of mass. The vast majority on Mars will tend to be limited to a fairly small number of paths, meaning that railroads are a very effective way to reduce the costs associated with transportation on Mars. Based on what I see on Earth it looks like gravel is an acceptable substitute for concrete in forming a railroad foundation, though I don't actually know much about railroads so I could be wrong.

Given how cold Mars is, structures could probably be heated a bit and still not get anywhere near the melting point of water. I would imagine that -20 or -25 C would be more than acceptable as a structural temperature. I think that Icecrete will be a very common material, especially later on (Later on meaning colonies the size of a suburban town).

GW Johnson · 2012-03-15 09:11:47

Railroads of one type or another would make very good sense for hauling large loads to specific destinations on Mars, just like they do here. It was rail that opened up the American west, not wagon roads. (Bit of history.)

Railroad construction as we know it here uses "gravel" as the roadbed, yes, but not the gravel you are thinking of (the rounded stuff we also use in concrete). It's an angular crushed stone, sieved to size. There's layers of this stuff in different sizes, capped by the half-inch stuff you typically see. The cross-ties are embedded in this stuff, those being (here on Earth) timbers almost a foot square in section.

Some railroads have used concrete ties (the high-speed 150 mph+ ones), but timbers are far cheaper and more cost-effective here on Earth, even considering periodic replacement for ordinary freight at ordinary speeds. (And don't kid yourself about speeds, I've seen freights moving 60-80 mph right here in Texas. All it takes is well-maintained track to make that safe.)

The rails are spiked to the ties with "nails" that are about 10 inches long, and about an inch thick steel, not round, either. These days, rails are welded, and about 6 or 7 inches tall. That's to hold the steady upward growth in railcar weights I've seen the last several years. I've seen hopper cars labeled as 245,000 lb loaded going by at crossings. A lot of these are using aluminum in their structure now, as evidenced by unloaded weights creeping down from around 62,000 lb to about 41,000 lb.

Not sure what a railroad might look like on Mars, given that steel will not be generally available for a long time after the first bases are established, except as an expensive import. Could be a guideway-modified roadway with pneumatic tires at first, although the rolling friction with that is orders of magnitude higher than steel wheel on steel rail. I'm afraid maglev will always be too expensive for routine freight, even here. It's just hard to beat that low-friction rail transport, even after 3 centuries.

The power source for the locomotive needs some serious thought, since the only "fuel" I know of that burns with carbon dioxide is magnesium. Nuclear? Electric? There's several possibilities. The electric train with a central power plant supply might make the most sense.

GW

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