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#101 2019-12-14 15:04:13

RobertDyck
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Re: Construction technology for Mars?

JoshNH4H wrote:

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

The pressure for the air-supported structure is so water doesn't boil at 10°C = 50°F. The article on cold weather concreting said that's necessary for concrete to set properly. Structures on Earth are sized to support the weight of the roof, but I'm calculating requirements to set concrete. I'm sure that will be far more pressure than necessary to support the roof.

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#102 2019-12-14 15:29:48

JoshNH4H
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Re: Construction technology for Mars?

Yes, that's exactly the point.  When you have too much more pressure than is needed to support the roof you start needing to build increasingly heavy or complex tiedowns.  The specified pressure for pressure-supported structures is mostly to counteract the weight of the structure.  If you are going to have an inflatable structure with a pressure of +6 mb on Mars, the canopy should have a mass 2.5 times as much as the canopy for a corresponding internal pressure as Earth.


-Josh

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#103 2019-12-14 18:03:07

GW Johnson
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Re: Construction technology for Mars?

There's a lot more to construction than the finished product.  It takes only a couple of dozen mbar to keep water in ordinary concrete from boiling away violently,  at any reasonable casting temperature.  But,  human occupation requires 0.5 to 1.0 atm air pressure,  if synthetic air is used.  The pressure is lower 0.2-0.3 atm if pure oxygen is used,  but there are very serious biological issues with long-term exposure to pure oxygen. We did not evolve in that atmosphere.

When you are building the edifice,  initially it will be unpressurized.  That will be true all the way through piling up the regolith ballast upon its roof.  Thus,  during construction,  you must be able to support the roof dead load unpressurized. Period.  Plus,  once pressurized,  there is always the risk of loss of internal air pressure.  You simply do NOT want the building to collapse,  just because you lost internal pressurization. 

Just some practical aspects.  Looking at the ballast required vs internal pressurization in the finished product is NOWHERE NEAR what has to be considered for construction purposes.  Not even here on Earth.

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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#104 2019-12-14 18:14:16

SpaceNut
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Re: Construction technology for Mars?

All this can be simulated in a mars jar chamber here on earth for temperature and even atmospheric content by nasa and contractors that have the facilities. All that is required is the equipment, materials to test and the cash to fund the experiments...

Found another topic with Oldfarts1939 post
http://newmars.com/forums/viewtopic.php … 98#p139398

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#105 2019-12-14 19:15:54

JoshNH4H
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Re: Construction technology for Mars?

Hey GW,

Yup, we were just talking about mild pressurization for the concrete to set. Understood on all sides here that pressure containment in the actual building is much harder.


-Josh

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#106 2019-12-14 19:25:30

Calliban
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From: Northern England, UK
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Posts: 3,282

Re: Construction technology for Mars?

GW Johnson wrote:

There's a lot more to construction than the finished product.  It takes only a couple of dozen mbar to keep water in ordinary concrete from boiling away violently,  at any reasonable casting temperature.  But,  human occupation requires 0.5 to 1.0 atm air pressure,  if synthetic air is used.  The pressure is lower 0.2-0.3 atm if pure oxygen is used,  but there are very serious biological issues with long-term exposure to pure oxygen. We did not evolve in that atmosphere.

GW

There is the serious biological issue of catching fire and burning to death.  Ignition energies go down and flame temperature increases in pure oxygen.  Given that fire spreads by radiated heat, which increases with the fourth power of temperature, a 40% increase flame temperature more than triples the rate of flame spread.  In a pure O2 atmosphere, even at the same partial pressure as Earth sea level, materials control would need to be stricter and fire risk assessment would need to receive a lot of attention.

That being said, a pure O2 atmosphere does make a lot of sense in space habitats.  Nitrogen is poorly abundant on the moon and asteroids and it would make sense to explore the possibility of building habitats with pure oxygen atmosphere at <1bar pressure.  Qu: in pure oxygen, at 1bar, human beings suffer health effects from increased arterial pressure.  Would the same effects remain problematic at reduced pressure, such that oxygen concentration in blood is no greater than at Earth sea level?

Last edited by Calliban (2019-12-14 19:30:34)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#107 2019-12-14 20:35:39

Oldfart1939
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Re: Construction technology for Mars?

Let me return to my polymer-based Marscrete. Unlike Calcium Carbonate based concrete, my polymeric substance would have significant tensile strength in addition to compressive strength. Additionally, if the correct initiator is selected, and a UV light initiated catalyst used, this stuff could be 3 D printed.

SpaceNut- There is absolutely NO water involved; this is strictly a hydrocarbon based polymer system. Since it's extremely Hydrogen rich, it would also serve to some extent, as radiation shielding from Solar flares. GW is correct, however, that some type of stabilizing structure made from steel, ala rebar, be added as a needed stabilizing component.

Styrene based polymers are highly water resistant, and would hold pressurization well with very low rate of diffusion into and through the polymer matrix.

My concept was the addition of regolith as a mass filler, to minimize the amounts of actual monomers required, as well as adding internal mass to the structure constructed from this material.

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#108 2019-12-14 20:51:00

JoshNH4H
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Re: Construction technology for Mars?

Hi Oldfart,

Three questions.

1) How does the compressive strength of your proposed substance compare to the compressive strength of cement or concrete?

2) What is the cost per tonne and cost per cubic meter of this substance on Earth and how does it compare to concrete?

3) Why is it desirable to 3D print concrete when 3D printing is expensive and slow while pouring concrete is cheap and fast?


-Josh

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#109 2019-12-14 21:14:14

Oldfart1939
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Re: Construction technology for Mars?

JoshNH4H-
I don't have any actual figures at my fingertips for Marscrete, since it's only a concept. The only cost estimates I can give you are hopelessly obsolete, but styrene on Earth is a very inexpensive industrial chemical sold in railway tanker loads. I routinely bought it in 55 gallon drums years ago, and it was around $200 per drum, but with substantial quantity discounts available. Considering how efficiently it was converted to polystyrene plastics, very cheap. Divinylbenzene is the crosslinking component added to give strength and rigidity to the resulting plastic matrix, but it's normally used in varying proportions, up to maybe 10 % of the monomer mixture. My products manufactured utilized something like 1-2 % DVB. Structural plastics would need at least 8%.
I only suggested 3D printing to build actual habitats in place. The Mars Society annual meeting had a competition this past fall, and most habitats were capable of being 3D printed, robotically.

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#110 2019-12-14 21:54:40

SpaceNut
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Re: Construction technology for Mars?

https://www.sciencedirect.com/science/a … 6514004901
Utilizing in-situ resources and 3D printing structures for a manned Mars mission

https://www.mdpi.com/2504-477X/3/3/89/htm
A new basalt fiber reinforced acrylonitrile butadiene styrene (ABS) filament has been developed for fused filament fabrication (FFF, 3D printing) to be used in Mars habitat construction. Building habitats on Mars will be expensive, especially if all material must be shipped from earth. However, if some materials can be used from Mars, costs will dramatically decrease.

http://inpressco.com/wp-content/uploads … 7-1783.pdf
One type of asphalt cement grade (40-50) used and polymer styrene butadiene styrene (SBS) with (3%, 4% and 5%) by weight of asphalt cement. Two types of tests were carried for asphalt mixtures (mix coating test and compaction of asphalt mixture test).

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#111 2019-12-14 23:27:21

Oldfart1939
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Re: Construction technology for Mars?

I earlier suggested using ABS as a construction material, probably a year ago, but didn't include the basalt filament in my product.

Just a statement here in the FWIW department: the final 12 years of my professional career, I became a self-taught polymer chemist. Out of necessity. I worked principally with styrene-divinylbenzene copolymers by the suspension polymerization technique. I manufactured very precise and accurately sized polymer beads for the pharmaceutical industry, and these incorporated reactive sites for what is referred to as solid phase organic chemistry. Many of the products are today used in metric tonne quantities for manufacture of peptide pharmaceuticals.

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#112 2019-12-15 07:25:11

tahanson43206
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Re: Construction technology for Mars?

For JoshNH4H re #108 ...

There is nothing in the laws of physics to preclude 3D printers being fast, huge and cheaper than any other form of production.

The imperatives of economics would (it seems to me) drive constant improvement in speed, capacity, reliability and cost of 3D Printers.

A unit of currency allocated to one or more competitors in the 3D printing industry seem (to me at least) likely to prove rewarding over the long term.

(th)

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#113 2019-12-15 11:25:02

GW Johnson
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Re: Construction technology for Mars?

I think there is a very good reason that the advent of 3-D printing technology has not changed road construction.  Those are still best built as vehicle-spread stone and gravel,  with vehicle poured-and-compacted concrete or asphalt surfaces. 

I think the same will prove true of masonry building construction. 

On Mars,  something you might consider is compressive-only piled-stone columns holding up a metal-beam grid that is close-set enough to pile big rocks atop it.  Then smaller stones atop that,  then loose regolith atop that.  That gets you a roof that is a shield against radiation and UV light.  The sides are wide open between the columns.  You put an insulated inflatable inside underneath it.  You do have to dig way down and place big rocks as the foundation for each column.

You could build a pretty big habitat with the electric-powered equivalent of a Bobcat loader,  plus metal beams and an inflatable brought from Earth.  It's not as efficient a use of materials as the "mushroom house" I posted so long ago at "exrocketman",  but there's no bending or tension in anything not made of metal,  discounting the hoop stress in the inflatable.  No concrete required.

GW

Last edited by GW Johnson (2019-12-15 11:27:51)


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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#114 2019-12-15 14:00:10

kbd512
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Re: Construction technology for Mars?

One of the more interesting uses of CNT tape has been to directly electrically heat composite wind turbine blades to cure them, consuming substantially less power than an autoclave or oven.  The goal of the project was a substantial reduction in fabrication time and costs by eliminating very large, heavy, power-intensive, and expensive autoclaves and ovens.  IIRC, I posted links in the thread that Louis started about using wind turbines.  In this case, the film / tape was bonded into the rest of the composite to create a smooth electrically conductive surface that added lightning strike protection and provided a way to electrically de-ice the blades while in operation.  Conductive electrical resistance heating seems like the only practical way to heat very large fiber reinforced plastic molds for foundations.

Portland cement has a compressive yield strength between 40MPa and 45MPa some number of months after pouring, which is not significantly different than pure ABS.  The low-grade steel reinforcement typically used is around 175MPa or so.  Using Oldfart1939's suggestion of basalt fiber reinforcement should improve the figures for ABS, though not remarkably more so than glass fiber.  My understanding is that basalt, a natural product of volcanic processes, is simply much cheaper and easier to come by than glass or carbon fibers, which require substantial energy inputs to form the fibers.  Here in the US, most of our plastic production comes from natural gas base stock rather than oil.  Since we already intend to make Methane rocket fuel on Mars, we should adapt plastic production methods to use that same base stock.

After reading some more about the practical issues involved with making steel-reinforced concrete on Mars, I doubt we'd see much of a meaningful mechanical property or energy input advantage after working out all of the technical issues.  There's not much of a fire or flooding hazard on Mars and the weight that a structure has to bear is only 38% of what it is on Earth.  The tonnage of materials that have to be moved or processed will most likely determine the fastest and most energy efficient to fabricate, so a fiber reinforced plastic made almost entirely from local materials will be pretty hard to beat.

These are rough figures, but a 30% GF reinforced ABS should have a compressive yield strength of 100 to 115 MPa, tensile strength of 90 and 110 MPa, and flexural strength of 115 to 130 MPa.  Tg is 100C to 110C and we need processing temperatures between 205C and 240C.  Ensinger Plastics has a site that lists mechanical properties with a range of different plastics.

So, how could we actually fabricate our slab?

1. Dig down to bedrock, wherever we happen to be.
2. Grind the surface of the rock flat.
3. Erect a temporary construction dome over the site.
4. Remove excess dust, sand, and other loose material.
5. Lay a conductive CNT mat on the bottom of the slab to form the out surface of the heated mold.  CNT tape is very light, so this material can be imported from Earth for initial foundation fabrication efforts.  Later on, it can be made from atmospheric CO2.
6. Inject a basalt fiber reinforced plastic onto the surface of the hot mold to form the out skin of the sandwich panel core.
7. Use a large scale 3D printer to print a honeycomb fiber reinforcement onto the surface of the hardened plastic.
8. Inject more of the basalt reinforced plastic into the honeycomb as filler material.  Alternatively, finely ground regolith collected from the construction site and mixed with plastic binder could serve as the filler material.
9. Inject another layer of plastic onto the top, placing another CNT blanket atop the sandwich panel mold to heat the top surface.
10. Repeat steps 5 through 9 of this process to produce a slab of whatever thickness is required to support the weight of the structure placed on top of it.

A variant of this process that uses different materials is already used to create honeycomb sandwich core panels for wings and tails in commercial aircraft and wind turbine blades.  I don't see any reason why we couldn't adapt some of these aerospace fabrication methods to fabricate slabs on Mars since the cost of materials imported from Earth, rather than the tooling and materials required to implement this fabrication method will be the overriding determinant of cost.

If all of that is too complicated to implement, then perhaps it would be easier still, and require less technology, to simply dig down to bedrock and place the structure on a rock slab.  That obviously won't be practical everywhere, but there must be more than a few places on Mars where we could simply grind out a depression in the rock and then place our structure directly on top of the rock, especially for our small starter colony.  Site selection and weight distribution matters more, but it also requires a lot less technology to achieve.  Just my $0.02.

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#115 2019-12-15 14:50:12

RobertDyck
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Re: Construction technology for Mars?

JoshNH4H wrote:

Yes, that's exactly the point.  When you have too much more pressure than is needed to support the roof you start needing to build increasingly heavy or complex tiedowns.  The specified pressure for pressure-supported structures is mostly to counteract the weight of the structure.  If you are going to have an inflatable structure with a pressure of +6 mb on Mars, the canopy should have a mass 2.5 times as much as the canopy for a corresponding internal pressure as Earth.

Tie-downs are needed on Earth to counter wind. Mars atmosphere has extremely low pressure resulting in extremely low density. That means hurricane speed wind produces less force than a light breeze. Your tie-downs could be quite modest. An inflatable greenhouse uses strong tie-downs to squash the inflatable from a cylinder. Is that called an elliptic cylinder? An inflatable greenhouse was proposed in "Case for Mars" studies before founding of the Mars Society. That design was included in Mars Direct proposals ever since. The idea was for greenhouse width to be twice height, just to provide a practical usable volume inside. For construction if the roof is excessively high, producing air to fill that volume may cost less than any fancy tie-down system.

Remember, we're talking +6 mbar pressure above Mars ambient, or something similar. If you want wet cement to be +20°C (68°F) then the triple point of water is 23.3 mbar. If you want the triple point a little higher than working temperature: 24 mbar triple point is 20.4°C, 25 mbar is 21°C. Pressure measured by Mars Pathfinder varied from 6.77 to 7.08 mbar; using the lower pressure you could make the gauge pressure 18 mbar. That would make absolute pressure 24.77 mbar at the coldest, lowest pressure point of night. Triple point is 20.8°C at that pressure.

If you keep cement, aggregate, and all working material for concrete at +10°C (+50°F) then you could keep gauge pressure to +6 mbar. Again at the lowest ambient pressure recorded by Mars Pathfinder, that makes absolute pressure 12.77 mbar. Triple point of water is 10.4°C (50.7°F). If you build at a low altitude location such as Gale Crater where Curiosity rover landed, then ambient pressure is 8.25 mbar. That makes it even easier. And if the inflatable structure is filled with pressurized Mars atmosphere, not breathable air, then it's very inexpensive in terms of energy. Just let the roof "balloon up".

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#116 2019-12-15 14:59:36

RobertDyck
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Re: Construction technology for Mars?

GW Johnson wrote:

You could build a pretty big habitat with the electric-powered equivalent of a Bobcat loader

This is a video from "Canadian Electric Vehicles Ltd". It's a Bobcat E530 converted to electric. AC drive system, lithium-ion batteries. It's not just equivalent to a Bobcat, it is a Bobcat.
mqdefault_6s.webp?du=3000&sqp=CO7L3O8F&rs=AOn4CLDpb2Zr2h4Oso0uKARRLXusShZxSQ

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#117 2019-12-15 16:29:47

SpaceNut
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Re: Construction technology for Mars?

This next post is not political and we will not do that, right..
We know that we will mine and process mars to make the materials that we want but that comes with a risk.
They built a Chinese boomtown. It left them dying of lung disease with nowhere to turn.

What they are talking about is the inhaling of dust as provide just "inadequacy of the $1.50 cotton masks they were given, or the irreversible harm of inhaling silica dust that caked their faces once their drills bit into granite-streaked crust."

We will mine for a time in suits but once the depth and a seal door is on the chamber we will be trying to get out of those suits which will make it slower to work and dawn shirt sleeves to work and that is when the risk will increase for the desease but there will always be some risk and we need to make sure that it does not stop our mars colonies from growing without deaths from something that we can do to stop it.

We would also want to mitigate any dust from being tracked back into habital spaces that we would not have a suit on for protection either.

https://www.hop-law.com/is-exposure-to- … my-health/

The mars workers who cut or grind materials such as concrete, brick, stone, or granite to wear respirators or other devices designed to protect them from breathing in these materials. These silica dust particles can cause scarring in the lungs, leading to a serious and irreversible lung condition known as silicosis. The first symptoms of accelerated silicosis can begin 5-10 years after exposure has occurred. The symptoms of silicosis can vary depending on whether a patient is diagnosed with the acute, accelerated, or chronic variety of the disease. Early symptoms that can be a sign of silicosis may include shortness of breath, cough, wheezing, and tightness of the chest. Exposure to airborne silica has also been linked to diseases such as tuberculosis, kidney disease, and lung cancer. Symptoms of these diseases may include fever, weight loss, or night sweats. Over time, these symptoms may become worse as the disease progresses, leading to death.

The most important way to prevent exposure to airborne silica dust is to keep this dust out of the air. Simple measure such as wetting down materials containing silica before they are used can have a tremendous impact on the amount of silica dust that becomes airborne. Preventing dust from becoming airborne during cleanup. This can include the use of water hoses or wet-wiping instead of air blowers, vacuums equipped with HEPA filters, and wet sweeping. Airborne silica dust cannot be kept below NIOSH-recommended exposure levels (0.05 mg/m³ as a 10-hour weighted average), workers should be provided with respiratory protection in order to limit the amount of dust they inhale.

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#118 2019-12-15 19:05:47

kbd512
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Re: Construction technology for Mars?

SpaceNut,

I'm not sure what politics has to do with fabricating a slab, but I would presume that all of our workers will arrive with appropriate PPE provided to them.  Spending the inordinate sums of money required to transport highly capable and intelligent people, some of the best our societies have to offer, millions of miles across space and time, only to kill them at work from inadequate PPE, seems indefensibly stupid.

The Chinese government have made a desperate gamble on the supposition that the money obtained from manufacturing things in very dirty but cheap ways could then be used to clean up the massive environmental damage done through unregulated heavy industry after everyone in their society achieved sufficient personal wealth to live off of the surplus generated.  That didn't work out very well at all for the Russians and it may not work well for the Chinese, either, but time will tell.  For the sake of their people, I hope they're able to reverse that damage by cleaning it all up.  Although we have plenty of superfund sites here in the US, I can't imagine living in a place where entire cities are essentially superfund sites.

That said, most economic development prior to very modern technology was essentially a desperate gambit to escape perpetual poverty cycles.  Hindsight's always 20/20 and modern technology is always "magic" compared to what came before.  They went from an agrarian subsistence farming economy in perpetual poverty to cities every bit as modern as any others in less than the span of a human lifetime.  That was never going to occur as an end result of pharmaceutically clean industrial activities, given the technology they started with.  But yes, here in the 2020's we can and should do much better than we did in the 1980's because the technology of today is quite unlike what was available 40 years ago and in stark contrast to the tech of the 1950's.  Most of what's present in the world of today, in terms of tools and technology and even people, simply didn't even exist in the 1950's- even though the ideas from the 1950's were clearly the genesis of our modern world.  There's been more real technological progress in the last 100 years than the sum total of the rest of human history, but not without a real cost attached to it.  I'm certain that our luddites would disagree on the definition of "real progress", but at least we can feed them now so we can have our academic arguments about the same.

Moving beyond our historical technological foibles...

I would expect that, at a bare minimum, a full head seal positive pressure powered respirator will be used in densified CO2 atmospheres providing sufficient pressure to work without wearing cumbersome pressure suits.  This type of equipment would be no different than that used by firefighters or personnel who handle hazardous chemicals.  I also expect that something like a chemical protective suit will be worn to protect workers from the chemical cocktail present in the Martian surface environment.  This would be about as comfortable as we can make people who are essentially working outside while still providing adequate protection.

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#119 2019-12-15 19:22:40

tahanson43206
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Re: Construction technology for Mars?

This is a follow up to #119

For kbd512 re suit for Mars pressurized environment ...

kbd512 wrote:

SpaceNut,

I would expect that, at a bare minimum, a full head seal positive pressure powered respirator will be used in densified CO2 atmospheres providing sufficient pressure to work without wearing cumbersome pressure suits.  This type of equipment would be no different than that used by firefighters or personnel who handle hazardous chemicals.  I also expect that something like a chemical protective suit will be worn to protect workers from the chemical cocktail present in the Martian surface environment.  This would be about as comfortable as we can make people who are essentially working outside while still providing adequate protection.

As time passes, the idea offered by kbd512 is looking better and better to me.

The application I have in mind is greenhouses.  Mining is an application that can be addressed separately, and I hope it will be.

For greenhouses, the application of kbd512's suggestion seems potentially advantageous in a number of ways.

Since this topic is dedicated to construction on Mars, I'll devote most of this post to that focus.

However, I'm considering starting a new topic in honor of kbd512's creativity, to be dedicated to agriculture on Mars using all-CO2 at normal (Earth normal) atmospheric pressure. 

The advantage of working in a construction space surrounded by a pressure envelope became apparent to me as I watched a Russian video of their 3D printer building a small home designed for the Russian winter.  The key for the reported success of the design (it seems to me) is the interesting combination of machine and human participation in a complex task.  It reminds me (to some extent) of modern automobile factories, which combine machinery and human capabilities in an otherwise unachievable level of productivity.

The humans would be wearing ordinary clothing for construction activity, with only a face mask to supply sweet air as an added encumbrance.

Temperature would be Earth-normal, and lighting would be abundant to insure a comfortable work environment.

What I am deducing from the Russian video is that humans attend the 3D printer, adding plastic rods to the still-damp extruded wall material to insure strong connection between the inner and outer walls.  Insulation (two kinds were shown) can be added after the walls have solidified.  That was shown being accomplished by human operators directing flows of material from flexible pipes.

(th)

Last edited by tahanson43206 (2019-12-17 07:59:46)

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#120 2019-12-15 22:18:23

SpaceNut
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Re: Construction technology for Mars?

Just trying to point out that we are not using anything like KBD512 paragraph even here on earth for mining and that we need new PPE for the hazards of mars which are on every corner of the soils of mars as it contains perchlorates.

The hazmat suits would only work in an near earth pressure location of a sealed air locked mine as indicated.

That we have not the cleaning process for the spacesuits which we will use on mars.

That we have not a lick of experience for mining in a non breathable atmosphere.

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#121 2019-12-16 11:05:39

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

Hey OldFart,

Here's what I've been able to find:

1) Compressive strengths are not often provided for polymers but the tensile strength for Polystyrene is cited in various places as 35-55 MPa.  You can correct me if you believe I'm wrong but it seems to me that the compressive strength should be in a similar range, thus roughly 50 MPa±25 MPa.  I was surprised to find that this is roughly also the compressive strength of both portland cement and typical concrete. One thing I am truly uncertain about is whether sand/aggregate will bond to a styrene matrix in the same way as it bonds to a cement matrix.  Both cement and sand/aggregate are sort of rocky materials with somewhat similar structures and similar mechanical properties (densities, hardnesses, etc).  Styrene has very different properties--would a styrene-sand composite be as well-matched as cement-aggregate?  Would it last as long? Would the components bond to each other? Or would their different thermal expansions and hardnesses cause it to shred itself from within over time?

2) As far as pricing goes, it looks like polystyrene goes for about $10/kg, which is about $9500/cubic meter.  By contrast, concrete costs around $113/cubic yard, which is about $150/cubic meter or about $0.11/kilogram--much less.  It makes sense that this would be the case, because concrete is made from lightly processed bulk materials whereas styrene monomers have to be produced via a somewhat complex process of chemical purification and synthesis.  On the one hand, the availability of CaO or CaCO3 deposits on Mars is something of a question mark.  On the other hand, Styrene monomers are ultimately produced from crude oil which is almost certainly not present on Mars. (Crude oil comes from fossilized life-forms; CaCO3 most often exists as limestone accreted from living organisms but can also form naturally in water depending on pH and Calcium availability).

3) I'll talk about 3D Printing in my next post.


-Josh

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#122 2019-12-16 18:43:42

SpaceNut
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Posts: 28,598

Re: Construction technology for Mars?

We will need to use what we have on mars when it comes to materials to manufacture from.
These three words are about the same in cement, concrete, and mortar for what we use on earth.

I have heard of Granite chips and dust being used with cement or as a cement, which means its possible to use basalt as a filler material as well.

https://www.graniteprecast.com/
https://www.granitmix.com/
https://concretegranite.com/

http://www.basaltpowder.com/home.htm

https://www.thespruce.com/stone-dust-gr … rs-2132528
http://www.therockyardinc.com/calculato … erials.php

https://www.sciencedirect.com/science/a … 3715300130
Experimental study of concrete made with granite and iron powders as partial replacement of sand

https://www.sciencedirect.com/science/a … 5813015178
The Effect of Basalt Powder on the Properties of Cement

http://article.sapub.org/10.5923.c.jce.201401.01.html
Strength and Durability Properties of Granite Powder Concrete

https://www.quora.com/What-are-the-adva … crete-work

http://www.ce.memphis.edu/1101/notes/co … Chap05.pdf
Aggregates for Concrete - Civil Engineering

I think the real point is you do not need any cement to make a dust that is glued together to form a wall.

options for not steel for rebar
https://basalt-rebar.com/

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#123 2019-12-16 20:03:47

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,257

Re: Construction technology for Mars?

Josh,

What about the Exelus process that produces styrene from toluene and methanol?

This is another one of those zeolite bed processes.  At least we wouldn't need any crude oil to make benzene, but I believe we already make most of the aromatic hydrocarbons from methanol synthesized from natural gas.  We're kinda of unique here because our natural gas is almost free and it's rather expensive nearly everywhere else.

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#124 2019-12-17 06:15:14

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 3,282

Re: Construction technology for Mars?

On Mars, the energy needed to make a material is a good proxy for its cost and we can gauge practicality by comparing energy costs.  The wiki list of embodied energy applies to commercial products on Earth, where mass production will reduce embodied energy compared to Mars and where the embodied energy of plastics is much lower because we start with hydrocarbons.
https://en.wikipedia.org/wiki/Embodied_energy

Standard concrete has embodied energy 1.1MJ/kg.  Standard cement mortar is 1.33MJ/kg.  By my reckoning that puts Portland cement at about 4MJ/kg.

What would be the embodied energy of polymers on Mars?  Standard polyethylene has heat of combustion of about 40MJ/kg.  That is the amount of energy released if you burn it to CO2 and condensed water.  It would be the amount of energy needed to make it in a perfectly reversible process.  But we know that the energy efficiency of a Sabatier reactor making methane and oxygen from hydrogen and CO2 is about 18%.  So the embodied energy of methane is roughly equal to its heat of combustion (50MJ/kg) divided by the efficiency of the process that makes it (0.18).  So the embodied energy of synthetic methane on Mars is 278MJ/kg.

Making more complex monomers for plastics like polystyrene (which contains benzene rings) would require more reaction steps, each of which would add inefficiency to the process.  So the embodied energy of polystyrene on Mars will be a long way north of 278MJ/kg – pushing for two orders of magnitude more than Portland cement.  As it has about the same strength as concrete, it would only be sensible in applications where concrete is unsuitable for some reason.

Fresh steel on Earth has embodied energy of 30MJ/kg.  On Mars, we would produce this in an electric furnace, using hydrogen or CO as a reducing agent for heated iron oxide.  If electrolytic hydrogen is used, which is produced from electricity at efficiency 70%, one might expect embodied energy only slightly higher than 30MJ/kg.  Steel is 10 times stronger than concrete, but about 3 times denser.  Per unit strength, it is about 10 times more expensive in energy terms.  So again, you would not use steel in circumstances where concrete will do.  And we would not use polymers in circumstances where steel can be used instead.

Clay bricks have an embodied of 3MJ/kg, but typically have lower compressive strength than concrete (3-10MPa, compared to 40MPa).  Again, concrete wins.

Raw stone on Mars could have extremely low embodied energy if it were to require minimal processing.  On Earth, slate has embodied energy 0.1-1MJ/kg, with the high end presumably related to finished roof products.  So we would probably choose to build with amorphous stone with cement mortar filling in situations where this is suitable.  Compressed soil and adobe products have poor compressive strength but low embodied energy on Earth, and they are still used in many applications.  Raw soil products may be less desirable on Mars due to the relatively high energy cost of water (1MJ/kg).

Glass has embodied energy of 15MJ/kg.  It is as strong as most plastics, but is brittle.  Due to its lower embodied energy and UV resistance it will generally beat plastics on Mars in the production of pressurised transparencies.  But pressurised structures should avoid large spans in favour of smaller panes in a steel lattice.

On Mars, with minimal ground water, pressurised habitats could be created by digging holes, putting in place a frame or concrete arch above or within the hole and then filling in and pressurising.  If the walls of the hole are stable, then part of the structure has no embodied energy at all, aside from the energy needed for excavation.

Just a few thoughts that will hopefully be useful in guiding what Mars construction will look like.  Lots of stone and concrete, with underground construction where practical and the use of steel and glass where we need to let light in.

Last edited by Calliban (2019-12-17 06:29:16)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#125 2019-12-17 07:39:36

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 28,598

Re: Construction technology for Mars?

I am electrical / electronics guy so understanding the Mj in terms of the power source has a bit  more meaning. The watt hours unit number 277.78 W·h converts to 1 MJ, one megajoule.

https://www.unitjuggler.com/convert-ene … to-Wh.html

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