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#76 2019-12-12 12:05:10

tahanson43206
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Registered: 2018-04-27
Posts: 12,668

Re: Construction technology for Mars?

For JoshNH4H re #75

Thanks for the great news of your Construction project.

May I ask if you would permit post #75 to be reproduced on the new luf.org blog.  It is a curated blog, but I am hopeful your announcement will be considered of potential interest to the readership there.

Second: Recently I had a chance to read your post from the start of a topic on 3D Printers.  At the time, you were asking for recommendations, but (as I recall the discussion) the offerings were slim.  Have you selected a 3D Printer?  if you have, and if you are willing, please update the 3D printer topic with your observations.

Third: I admit to being stunned when you pointed out the blind spot in my understanding of chemistry.  We were discussing confinement of iron atoms without electrons.  These are produced in great numbers by supernovae events (I gather) and in any case, they are present in abundance in the rain of particles in the open Solar System.

However, and this is the follow up question for you ... would you agree that a stream of these particles would make a useful tool for cutting rock, as Elon Musk needs to do for his Hyperloop system, or as Mars settlers might have to do to build underground habitats.

Setting aside the practical considerations of how such a beam might be created, my question is a simple one ... in your estimation would the electron stripping capability of electron free iron atoms achieve an effective cleavage of molecular bonds in rock?

Thanks, and best wishes for success with the new blog.

(th)

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#77 2019-12-12 13:54:01

louis
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From: UK
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Posts: 7,208

Re: Construction technology for Mars?

Hi Josh,

Very interesting presentation.

Here's one alternative which meets your list of requirements I think: cut and cover. Dig a trench in the regolith. That means you have radiation protection on all sides. Line with a suitable material e.g. basalt tiles, or cement/concrete. Cover with steel arches and steel segments.  Load on regolith - that gives you radiation protection on top. You could incorporate light wells to bring in natural light.

Cut and cover seems a viable construction technology for the early stages of settlement.

JoshNH4H wrote:

Hey All,

Much of the articles should be familiar if you follow this thread, but I'm doing a series on my blog about construction architectures on Mars.  So far parts one and two are up:

Construction on Mars, Part One: General Principles and Design Assessment Criteria: In this post I give a broad overview of design constraints and produce the following six criteria for evaluation:

  1. The structure sustains a pressurized atmosphere

  2. The structure provides protection from radiation

  3. The structure is failure resistant

  4. The structure is failure tolerant

  5. The structure can be constructed in an affordable way

  6. The structure is useful as such

Construction on Mars, Part Two: Design, Details, and Evaluation: In this post I go into the details of my design (familiar to you all from this thread) and discuss how it meets the criteria described in Part One. 

The next posts are going to discuss materials and specifications (IE dimensions), Construction technology and methods, setups for different functions, building entire settlements using these structures as units, and more!

Interested in hearing your comments and thoughts.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#78 2019-12-12 14:43:28

JoshNH4H
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From: Pullman, WA
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Posts: 2,526
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Re: Construction technology for Mars?

Hey Tahanson,

Absolutely feel free to share that post wherever you like.

As far as using stripped ions for digging:

You asked me to disregard practicability, so I will: Yes, it could be done.

I maintain that it is not practical.  These things are hard to create and even harder to store.  It's basically impossible for that to be the cheapest or easiest way to deliver energy into rock.


-Josh

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#79 2019-12-12 15:12:18

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,526
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Re: Construction technology for Mars?

Hey Louis,

Cut and cover goes back to what I have described, here and elsewhere (including repeatedly in both blog posts), as the First Rule of Space Construction

Here's what I had to say about a similar idea in the Covered Craters, Tented Towns thread.

As far as your "gorges" go: I'm not opposed to the idea per se but I don't think you've fully thought it through.  You can correct me if you disagree, but the effective difference between a "domed crater" and a "gorge" is that, per square meter of roof, the gorge has more internal volume because you've dug down inside the enclosure.

I have no problem with this (in fact I think it's a good idea) but many of the design constraints for a roofed trench and a domed crater are the same:

  • The fundamental law of space construction still applies: The key design criteria is how you contain the pressure

  • Assuming the pressure is the same (and why would it be different?) there's just as much upwards force on the roof of the gorge per unit area as the roof of a dome

  • No matter how you're containing the pressure, the exterior walls of the gorge need to be sealed against leakage.  Rock and regolith are not airtight and shouldn't be used for this purpose, not just to prevent air loss but also because pressure can, over time, cleave rocks apart and cause a catastrophic blowout.

  • Rock and regolith are poor structural members and probably can't be used for wall or floor support without modification (read: a construction project)

Again, the key consideration for a roofed trench or a domed crater is how you're going to keep the roof and walls on against the internal pressure.  If you'd like the roof to be transparent, the answer is probably one of the ways I described, or a different method that I didn't think of that deals with that force in a different way.  If not, piling regolith on top is probably the best way to get vertical pressure containment and radiation protection at the same time.

To restate the point here, which I made at length at the beginning of the first blog post as well as at other points (including the quoted post and earlier in this thread), pressure containment is key and is *not* the same thing as leak prevention.  Your cut and cover design depends on the structural integrity of raw earth in the horizontal direction (even if it's covered in masonry) to avoid explosive decompression, and I don't think that is an adequate pressure containment method.


-Josh

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#80 2019-12-12 18:09:07

SpaceNut
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From: New Hampshire
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Posts: 27,155

Re: Construction technology for Mars?

Nice to see you come back to post Josh...

Ultimately simple methods will allow less mass brought to mars to have more useable mass to make use of for other things.
What you trench will not all be used in the cover and that allows for other uses as you have already expended energy to remove it from mars. Testing of it would allow for some of the work to already be done that when we get down to mining we will set up markers to tell what we would want to do with it.

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#81 2019-12-12 18:54:24

tahanson43206
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Registered: 2018-04-27
Posts: 12,668

Re: Construction technology for Mars?

For JoshNH4H re #75

Thanks for your approval.  Post #75 is now at the top of the page on luf.org.

My hope is that positive exposure of NewMars forum there and elsewhere will increase the number of contributing members.

***
Thank you for your reply regarding iron atoms without electrons.  It would appear that it takes a supernova to create these in any numbers.

I agree that a way of producing them for use as a tool seems outside present human competency.

(th)

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#82 2019-12-12 22:51:11

SpaceNut
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From: New Hampshire
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Posts: 27,155

Re: Construction technology for Mars?

The world's first 3D-printed neighborhood is being built in Mexico for families living on $3 a day

AAK4uVy.img?h=450&w=799&m=6&q=60&o=f&l=f

The printer is named Vulcan II

The 33-foot printer pipes out a concrete mix that hardens when it dries, building the walls one layer at a time. It takes 24 hours over several days to build two houses at the same time -- that's about two times faster than it takes New Story to build a home with regular construction. "We think part of what 3D printing allows us to do is to deliver a much higher-quality product to the housing market at a speed and price that's typically not available for people in" low-income housing,

About 1.6 billion people in the world don't have adequate housing, according to a 2015 Habitat for Humanity study.

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#83 2019-12-13 07:09:34

RobertDyck
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Re: Construction technology for Mars?

We keep seeing this, again and again. This construction technology is not applicable to Canada, much less Mars. You realize there's no basement, and no insulation in walls. Canada has actual winter. The ground freezes. Foundation has to be sufficiently deep that ice will not form under the foundation. When water freezes, or moist soil, the ice expands. That's strong enough to lift a house. That lift is always uneven, it will break a house. I heard stories of post-war houses built on concrete pads here in Winnipeg. When the ground freezes in winter, it can lift and twist the house so much that a crack forms in the exterior wall large enough to see daylight. When the temperature is -40°C outside, real temperature not windchill, that causes cold to flood the house. It isn't just a draft, cold pours in. To ensure frozen ground doesn't break the house, foundations must be dug minimum 4 feet below grade. That's why every house built today has a full basement. In the late 1970s and 1980s there was a trend to build houses with larger basement windows. The excuse was so finished basements would have better windows to look through, but it also meant basements didn't have to be dug so deep. They still dug foundations below the 4 foot minimum, but not quite as deep. These 3D printed houses are all built on a pad, no basement.

As an example, in the winter of 2013 Winnipeg had an unusual winter. It didn't set any record low temperature, but it set a record of the number of days below -20°C (-4°F). We normally get a cold snap 2 weeks at a stretch when the daytime high does not rise above -20°C. However, in 2013 we had 90 days like that. This froze the ground to an unusual depth. Snow adds insulation, the ground doesn't get so cold, but streets are cleared of snow, so ground beneath streets froze to a greater depth. Water mains that crossed beneath a street often froze, depending on depth of the pipe. For neighbourhoods without water the city brought in a truck with a tank of water, and a truck with a pump powered by a diesel engine. The hose was connected to a house garden/yard tap. Water actually flowed backward from that house into the water main to supply neighbours.

The other issue is insulation. Walls must be insulated. Here are some examples of concrete walls made by 3D printers. Notice they all use flat walls with some sort of concrete interior structure for reinforcement. None have insulation; no fibreglass batt, no Styrofoam, no cellulose (flammable), no spray foam (ureaformaldehyde?). Insulation requires fine structures with thin walls and tiny air gaps, that's what these forms of insulation do. Rock wool insulation is made similar to fibreglass, but uses melted rock extruded as fibres. Rock wool has the advantage it doesn't require binder, so is not flammable. But these 3D printed houses don't have any wall insulation at all.

images?q=tbn:ANd9GcRljTfjG03tjOVmb9_wexYnnfu1xCTaSaTs8J-7cY3ZNqfIOncj&s
images?q=tbn:ANd9GcTP0ac1s8uVp2z_FktizHzxENynhhKNQwpM_wmWSkPSPBfSuySJ&s
images?q=tbn:ANd9GcTsTTIETxOt9L-ws56aaCjLqinWh-uWR538-tsRkaM99euM274o&s
images?q=tbn:ANd9GcSLeSNe9eri06giFu76_DUri_2VPHagWYwHtfQLIdrutcL_YYBG3Q&s

For Canada, houses could be pre-assembled as flatpacks. So pre-assembled walls with insulation, siding, and electrical wiring pre-installed. Assemble the walls on site. Some houses are built like that now.

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#84 2019-12-13 09:50:37

JoshNH4H
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From: Pullman, WA
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Re: Construction technology for Mars?

The idea of 3D Printing with concrete is a little weird because it's actually slower and harder than just pouring concrete down into a mold.

In my opinion the most interesting thing would be to start 3D Printing the molds (rather than framing them out with wood per current practice) and then pouring the structural concrete in to save labor.

Concrete is also extremely poorly suited for being a structural wall material for Mars because it has virtually no tensile strength.

I think a good design for insulation would be modular "insulation panels" that can be bolted onto the structure and onto each other.  Probably best for them to remain unpressurized: Insulation filled with gas at Martian ambient pressure is an even better insulator than insulation filled with gas at Earth ambient pressure.

I haven't done the numbers, but it would come as no surprise at all to me if air at 1 atmosphere and -20 C carried away more heat through convection than air at 0.007 atmospheres and -70 C.

Mars is also a lot drier than Canada (it basically never rains or snows) and never thaws.  This has downsides from a settlement perspective but also upsides in that the freeze-thaw cycle can be extremely damaging.


-Josh

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#85 2019-12-13 13:02:06

GW Johnson
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Re: Construction technology for Mars?

We do not have a concrete that will work on Mars.  It is too cold,  and the water in it will boil off in that thin air before it can do the cure chemistry.  The cold temperatures also stop the cure chemistry. That same water boiloff will induce voids where the water vapor bubbles formed,  so even the compressive strength of such concrete will be compromised.

You can get the equivalent of tensile strength in bending applications with steel rebar,  especially if you pre-stress the beam in compression.  That's a well-known technique here in bridge-building.  It's not the cheapest or lowest-effort way to go,  though.  You do it because you are forced to.

Foundations are subject to bending,  especially slab-type foundations.  That's why steel rebar is required,  period.  Usually not pre-stressing,  but that has been used occasionally.  Same is true of beams that support roofs,  even roofs dead-loaded with regolith to counter internal pressure:  rebar,  or even pre-stressing.  There will be no pressure to counter the dead load during construction.  You must support the deadload,  and that is definitely a bending application.  Longer roof beam spans get into the pre-stressing requirement very quickly.

Columns that hold up the roof are subject to compression,  yes,  but with a pressurized building,  they must also support pressure-panel walls.  That puts those columns into bending.  Inherently.  Taller columns get into the pre-stressing regime in the same way as roof beams. 

Not to mention the wall pressure-panels themselves,  which suffer not only tension,  but also very significant bending,  and rather high levels of stress concentration at the fastener points.  I would NOT recommend concrete for them. Glass or plexiglass would be better if transparencies are required,  but you need about 3 layers of them,  with different pressures in between.  Otherwise,  metal is best.

It ain't just a hoop stress equation,  either,  guys! 

I've got a building design concept that will work at Mars conditions.  It's on my "exrocketman" site,  titled "Aboveground Mars Houses",  and dated 26 January,  2013.  I was able to show the essential infeasibility of the classic sci-fi dome structures in an article titled "Pressurizable Domed Habitat Structures",  dated 9 June 2012,  same site. We have no material that will work for that.

GW

Last edited by GW Johnson (2019-12-13 13:11:34)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#86 2019-12-13 15:59:04

tahanson43206
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Re: Construction technology for Mars?

For GW Johnson re #85

As so often happens (to me at least) when someone delivers a thought provoking post such as yours to the forum, I went looking to see if anyone had been working on this problem.  Sure enough, it appears that a "concrete" made with sulfur may help.

http://www.cv.titech.ac.jp/~anil-lab/ot … ncrete.pdf

(th)

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#87 2019-12-13 17:15:03

GW Johnson
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Re: Construction technology for Mars?

My comments about water-based concrete are based on the vapor pressure of water at its triple point:  6.1 mbar and 0 degrees C.  At 0 C,  for atmospheric pressures below this,  you get violent boiling,  because the vapor pressure exceeds local atmospheric pressure. 

For higher water temperatures than 0 C,  the critical atmospheric pressure is even higher.  That's just steam chart stuff.  For pressures exceeding the water vapor pressure,  you just get rapid evaporation,  not violent boiling.  That's by no means "stable",  but at least it doesn't produce fatal porosity from violent boiling.

The paper Tahanson43206 linked seems to indicate using molten sulfur instead of water as the liquid for the concrete.  Correct me if I misunderstood. 

But if I am right,  then if the vapor pressure of sulfur at molten sulfur temperatures exceeds Martian atmospheric pressure (usually near 6-7 mbar,  lower on the highlands,  higher in the valleys and basins,  but not by all that much),  then you will get exactly the same violent boiling,  and the same fatal porosity once cooled and solidified.  Plus,  there is a huge energy expenditure required to melt the sulfur. 

Where will that energy come from,  especially if you go with Louis's ideas of solar,  or with NASA'a nonsensical only-10-MWe kilopower?  It only need be heat not electricity,  but there is still a requirement for a whale of a lot of it. 

So unless I misunderstood,  I stand by what I said:  we as yet have no concrete or concrete substitute that is ready for application on Mars. 

The closest thing would be WW2-vintage "icecrete" as used in the "Habbakuk" experiment in Canada,  but even that would have to be processed at atmospheric pressures high enough to prevent water boiling violently,  even at only 0 C.  And the resulting "icecrete" would have to be protected from surprisingly-rapid sublimation at pressures under 6.1 mbar,  unless chilled very far below 0 C.  Very far indeed.  It's just not ready,  either. 

We sure as hell need a concrete,  or a concrete substitute,  for Mars.  And there just is not not one ready to use!  That's the state of things,  near as I can tell. 

GW

Last edited by GW Johnson (2019-12-13 17:20:08)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#88 2019-12-13 17:38:44

Terraformer
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Re: Construction technology for Mars?

As far as pressure is concerned, it can't be all that difficult to erect a tent that can hold ~20mb over the building area, can it? To hold a 10mb pressure difference, we'd need 1000 N weighing it down for each square meter covered. A 20m diameter circle would require 84 tonnes filling the edge, and regular re-pressurisation, but if it makes construction much easier it might be worth doing.


"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony

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#89 2019-12-13 17:54:46

SpaceNut
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Posts: 27,155

Re: Construction technology for Mars?

The temporary dome that would have a building within it can be a plastic balloon where we just leave the balloon around the structure as its built and remove it once cured. Leave enough room inside so that a crew can seal the outside with an epoxy like coating while doing the same to the inside of the structure. Once the internal sturcture is cured we can lay an insulation up to the wall and make the heat isolated internal wall to keep the pressure in and cold out.
Sulfur would oxide over time and the home with its moisture would make it stink like crazy.

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#90 2019-12-13 18:37:57

tahanson43206
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Re: Construction technology for Mars?

For SpaceNut re #89 .... Your caution about use of sulphur in the "concrete" is interesting.

That concern deserves investigation.

For GW Johnson ... Your observations about working with sulphur on Mars should inspire further investigation as well.

(th)

Last edited by tahanson43206 (2019-12-13 18:40:24)

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#91 2019-12-13 19:30:37

SpaceNut
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Re: Construction technology for Mars?

Sulfur brick via compression has been talked of here and as a binder of the mars insitu materials for wall making.
will locate and post here....
i also forgot that we did do the icecrete discusion also with GW back several years ago.

No bake brick

Habitat Design on Mars

"Underground vs Above Ground" (Both actually).

Material Choices for Mars

Mars Colony Cement & Concrete

Concrete made with sulfur binder - article says Moon but why not Mars?

Mars Colony "Vacuum welding, Sintering".

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#92 2019-12-13 21:16:07

tahanson43206
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Re: Construction technology for Mars?

For SpaceNut re #91

Thanks for the links to previous discussions!  It is interesting to see the suggestion of sulfur for concrete on Mars has been batted around for a number of years.

For GW Johnson ... Inspired by your discussion, I went back to the study and read more of it and read more carefully.

Regarding the question of atmospheric pressure ... The Moon is cited as being unsuitable due to the (relatively) pure vacuum.  However, Mars was apparently found to be suitable, despite the low atmospheric pressure.

4. Summary and conclusions
In conclusion, the developed sulfur based Martian Concrete is
feasible for construction on Mars for its easy handling, fast curing,
high strength, recyclability, and adaptability in dry and cold environments. Sulfur is abundant on Martian surface and Martian regolith simulant is found to have well graded particle size distribution
to ensure high strength mix. Both the atmospheric pressure and
temperature range on Mars are adequate for hosting sulfur concrete structures. Based upon the experimental and numerical
results presented in this paper, the following conclusions can be
drawn:

However, beyond the conclusion that sulfur-concrete would bind on Mars at local atmospheric pressure, it seems reasonable to suppose that settlers might pressurize a work space where concrete is to be poured, which ought to reduce concerns about pressure.  For example, if a tunnel is being bored for a habitat, it would (presumably) be possible to pressurize the workspace, and then to pour concrete for walls or posts or whatever else is needed.

For SpaceNut ... You've been concerned about sublimation of sulfur for a number of years, so I looked for mention of that problem as well.

In the case of the Moon, the authors of the paper cited were explicit about that problem, although I'm not clear on whether they were concerned about the process occurring during curing or afterward.  They did mention the sulfur forming compounds during curing, so I would assume energy is released in that process, and therefore the sulfur should be resistant to dislodging later on, but I'd like to see confirmation of that.

In the case of concrete on Earth, where water is used to cure the concrete, I am under the impression that after water is properly cured, it is no longer available for sublimation.  If the same is true of sulfur in concrete made with it, then sublimation should not be a problem, but I would like to see confirmation of that expectation.

A Google search for "durability of sulfur concrete in various aggressive environments" yielded a number of citations, the most recent of which is from 2019.

The author of a 2013 study reported extensive testing of sulfur concrete on Earth, with a view to reducing the amount of sulfur waste accumulating in the environment.  The various mixes were compared to equivalent mixes which used Portland cement.

https://core.ac.uk/download/pdf/50565441.pdf

(th)

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#93 2019-12-13 22:51:11

Oldfart1939
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Registered: 2016-11-26
Posts: 2,311

Re: Construction technology for Mars?

I'm not particularly keen on using Sulfur as a building material, since it IS an oxidizer chemically. It happens to be a component of black gunpowder, along with Potassium Nitrate; both oxidizers.

I don't know what happened to one of my earlier suggestions of using polymer resins as a "solvent" or perhaps better stated as a "matrix" for making a polymeric "Marscrete." I'm aware that making a suitable fluid monomer, hereinafter referred to as "resin" would possibly consist of a mixture of Styrene and Divinylbenzene. Both of these compounds are theoretically possible to manufacture from carbon dioxide Martian atmosphere with some hydrogen obtained from in situ water after hydrolysis. This resin could be stirred with Mars regolith and added initiator making a thick slurry and packed into brick type moulds; and heated to polymerization initiation.

I would suggest an initiator be AIBN, Azo-bis-IsoButyroNitrile, or an analog thereof. This is a free radical polymerization initiator used in a concentration of about 0.5 % relative to the bulk of the monomers being polymerized. If we are using 100 kg of monomers, for example, we add 500 grams of this initiator to the liquids before adding the regolith in a mixer before pouring into the forms. It simply needs to be enough to make a thick slurry for this to work; if I still had a laboratory we could do a demonstration of this process pretty easily. Using heated forms, the "bricks" need to be heated to 64 degrees C for initiation, and kept at that temperature for curing of the product. The actual heat input decreases as the reaction proceeds, as styrene polymerization is strongly exothermic. The heating process needs about 4-8 hours for completion of this reaction. This would make a great project for a Grad student; make polystyrene-regolith bricks, then build a structure from them.

AIBN would need to be imported from Earth.

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#94 2019-12-13 23:40:01

RobertDyck
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From: Winnipeg, Canada
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Re: Construction technology for Mars?

Cold weather concreting

All concrete must be protected from freezing until it has reached a minimum strength of 500 pounds per square inch (psi), which typically happens within the first 24 hours. If concrete freezes while it is still fresh or before it has developed sufficient strength to resist the expansive forces associated with the freezing water, ice formation results in the disruption of the cement paste matrix causing an irreparable loss in strength. Early freezing can result in a reduction of up to 50 percent in the ultimate strength. Once concrete has attained a compressive strength of around 500 psi, it is generally considered to have sufficient strength to resist significant expansion and damage if frozen. Whenever air temperature at the time of concrete placement is below 40 degrees Fahrenheit and freezing temperatures within the first 24 hours after placement are expected, the following general issues should be considered:

Initial concrete temperature as delivered
During cold weather, it may be necessary to heat one or more of the concrete materials (water and/or aggregates) to provide the proper concrete temperature as delivered. Due to the quantities and heat capacity of cement, using hot cement is not an effective method in raising the initial concrete temperature.

Protection while the concrete is placed, consolidated, and finished
...windbreaks, enclosures, or supplementary heat...

Curing to produce quality concrete
Curing not only requires adequate moisture, but also appropriate temperature. The temperature of the concrete as placed should be above 40 degrees Fahrenheit using methods described above, however the duration of heating is dependent on the type of service for the concrete, ranging from one day for high-early strength concrete that is not exposed to freeze-thaw events during service to 20 days or more for a concrete element that would carry large loads at an early age. In structures that will carry large loads at an early age, concrete must be maintained at a minimum of 50 degrees Fahrenheit to accommodate stripping of forms and shoring and to permit loading of the structure.

In no case should concrete be allowed to freeze during the first 24 hours after it has been placed. Since cement hydration is an exothermic reaction, the concrete mixture produces some heat on its own. Protecting that heat from escaping the system using polyethylene sheeting or insulating blankets may be all that is required for good concrete quality. More severe temperatures may require supplemental heat.
...
It is also important to prevent rapid cooling of the concrete upon termination of the heating period. Sudden cooling of the concrete surface while the interior is warm may cause thermal cracking.

50°F = 10°C, triple point of water at that temperature is 12.5 mbar pressure

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#95 2019-12-14 07:50:01

tahanson43206
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Re: Construction technology for Mars?

For oldfart1939 re #93

Your post today inspired me to create a new topic for Best Practices.

You may be (probably are) among the small group of members of this forum who could put substantial content in the new topic, if you have the time and the energy. 

In the case of post #93, you would be "competing" with other ideas for mind share in young people who are now planning either their educations or their careers in space development, and specifically in development of infrastructure on Mars.

Among other possible outcomes, it is reasonable to suppose that one or more organizations might want to build a test system to deploy to Mars to test the validity of your idea, at the same time as others are testing their preferred solutions.

Writing at a level that would persuade/entice the substantial funding needed is what I am looking for.

(th)

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#96 2019-12-14 11:01:12

JoshNH4H
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From: Pullman, WA
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Re: Construction technology for Mars?

Hey GW,

I think the design I discuss in the second blog post (very similar to the one I discuss earlier in this thread) deals with the tension well with separate tension and compression elements.

As far as concrete goes you make a good point, but a bit of googling suggests an option, for Mars at least.

On Earth our concretes are typically made from Portland cement, which is a "Hydraulic" cement because it does not need to lose its water to harden.  These cements work, as you've said, by forming hydrates and hydroxides from their internal water.

There are also non-hydraulic cements.  These aren't used much these days, but typically they're made from "Slaked lime", IE CaO in water.  They work by first losing all their water to the environment, then absorbing atmospheric CO2 to form carbonates, IE CaCO3. 

Non-hydraulic cements are almost never used these days because they're slow to dry out and also slow to absorb CO2 due to its low concentrations, so it takes a long time for them to reach their full strength.

I believe the rates for both of these reactions will be increased on Mars.  Because of the very low ambient pressure, vaporization of water will be much quicker, and the CO2 partial pressure on Mars is actually higher than Earth by about a factor of 20.

Neither of these observations themselves solves the issues raised by RobertDyck or GW.

The low-temperature problem is the easier of the two to solve, as it can be fixed by heating.

The low-pressure problem is harder.  The boiling temperature of water at 7 mb is a bit above 0°C.  One solution is mild pressurization.  The boiling point of pure water is 9 mb at 5°C, 12 mb at 10°C, 17 mb at 15°C.  It's worth mentioning that at Mars gravity and assuming a density of 2000 kg/m^3 and an ambient pressure of 6 mb these pressures will be generated by the action of gravity at a depth of 4 cm, 8 cm, and 15 cm respectively.  This means the boiling problem is mostly a problem for the top surface.  A plate of steel 2 cm thick would generate enough pressure beneath it to raise the boiling point to 10°C.

So for the rapid boiling problem we're really talking mostly about the upper layer.  Not to say that makes it not a problem, because it definitely is a problem.

I do wonder whether the vapor pressure of pure water is relevant here.  Cement and concrete are mixtures, and while the components of cement are not highly soluble in water there’s a lot of “stuff” there, and it seems reasonable to me that you would see meaningful freezing point depression and boiling point elevation.  You might be able to further encourage this by doping the cement with salt or for a non-hydraulic cement mixing water with another liquid.

I’d be interested in looking more into the properties of non-hydraulic cements but don’t see many useful references online and I would definitely appreciate if anyone has any useful links.

Follow-Up: I found this PhD thesis PROPERTIES OF HYDRAULIC AND NONHYDRAULIC LIMES FOR USE IN CONSTRUCTION by Andrew J Edwards at the Napier University in Edinburgh, Scotland.  Looks like I've got some reading to do!


-Josh

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#97 2019-12-14 11:23:36

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 27,155

Re: Construction technology for Mars?

Oldfart1939 wrote:

earlier suggestions of using polymer resins as a "solvent" or perhaps better stated as a "matrix" for making a polymeric "Marscrete."

Nice a new term to make consistant for use in making mars construction from regolith and a binder. Yes I recall the discusion we had and will search out that post and link or add it in here.
edit:
Found the content in this same topic posts by oldfart1939
http://newmars.com/forums/viewtopic.php … 97#p144797
http://newmars.com/forums/viewtopic.php … 58#p144758
http://newmars.com/forums/viewtopic.php … 54#p144754
edit another place
http://newmars.com/forums/viewtopic.php … 88#p139388

The issue of any binder which contains water in any amount is problematic for the temperature and mars atmospheric pressure. Which is why we need to tent anything being built to aid in controlling the curing enviroment and time that it will need. which means temporary structure as well as the permanent need to be made as a shell in a shell to all for the structures to produce the desired effect of control which we need for the permanent one being made.

Structure shape and size is important when building on mars under the methods we can use. The other limit is the mass required to be taken from earth to be able to reuse it over and over again in the building process when using insitu materials.

The low temperature of mars and water sublimation are coupled to each other in that if you raise the temperature it will accelerate the water lose. Making the temperature colder does the oposite for the curing and further delays when it will set up.

Edit:
Thinking about the binder in which you mix and build under a canopy one can use a UV curing layer for a shell and then build inside it. One could also make a brick that is made inside a chamber and brought to the site to build the shell out of.

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#98 2019-12-14 11:45:29

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,992
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Re: Construction technology for Mars?

It sounds like a concrete equivalent for Mars might be developed.  If so,  it will need steel rebar.  On Earth,  it was possible to build unreinforced concrete masonry structures with the concrete loaded only in compression (ancient Rome did a lot of that).  That was because the buildings had no net pressure differences across their walls and roofs. 

That approach will NOT be useful on Mars for human habitations,  which will require about 0.5 to 1 atm pressure difference,  if synthetic air is to be used (and I think it will be).  You are looking at reinforced "concrete" beams,  and pre-stressed ones for the longer spans.  Rebar will have to be shipped from Earth for a long time on Mars.  That's steel mill stuff.  The rods for prestressing are an even tougher alloy than what is used in rebar.  They are also typically threaded on their ends,  too.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#99 2019-12-14 13:09:50

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 7,383
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Re: Construction technology for Mars?

Air-supported structure

The interior air pressure required for air-supported structures is not as much as most people expect and certainly not discernible when inside. The amount of pressure required is a function of the weight of the material - and the building systems suspended on it (lighting, ventilation, etc.) - and wind pressure. Yet it only amounts to a small fraction of atmospheric pressure. Internal pressure is commonly measured in inches of water, inAq, and varies fractionally from 0.3 inAq for minimal inflation to 3 inAq for maximum, with 1 inAq being a standard pressurization level for normal operating conditions. In terms of the more common pounds per square inch, 1 inAq equates to a mere 0.037 psi (2.54 mBar, 254 Pa).

300px-Air-supported_dome.jpg
So pressure varies from 0.762 mbar to 7.62 mbar. Since we need 12.5 mbar absolute, and Mars ambient can vary from 6.77 measured by Mars Pathfinder to 8.25 measured by Curiosity, then 6 mbar relative pressure (gauge pressure) is sufficient. So a construction site needs equivalent to one of these to pour cement and while concrete sets.

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#100 2019-12-14 14:33:50

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,526
Website

Re: Construction technology for Mars?

Gotta divide by ~2.5 for lower Martian gravity, but making things heavier than they need to be presents no difficulty at all.


-Josh

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