| Lunar Cement In "The Case for Mars" Dr. Zubrin states that lime, CaO, and sand can be mixed together, some gypsum (calcium sulfate) added, and the result is Portland cement. Basically that's true, but there's a little more to it. From Linus Pauling's "General Chemistry" (Dover:1988) we read that: "Portland cement is an aluminosilicate powder that sets to a solid mass on treatment with water...Portland cement before treatment with water consists of a mixture of calcium silicates, mainly Ca2SiO4 and Ca3SiO5, and calcium aluminate, Ca3Al2O6. When treated with water the calcium aluminate hydrolyzes, forming calcium hydroxide and aluminum hydroxide, and these substances react further with the calcium silicates to produce calcium aluminosilicates, in the form of intermeshed crystals. Ordinary mortar for laying bricks is made by mixing sand with slaked lime [CaOH]. This mortar slowly becomes hard through reaction with carbon dioxide in the air, forming calcium carbonate. A stronger mortar is made by mixing sand with Portland cement. The amount of cement needed for a construction job is greatly reduced by mixing sand and crushed stone or gravel with the cement, forming the material called concrete. Concrete is a very valuable building material. It does not require carbon dioxide from the air in order to harden, and it will set under water and in very large masses." On Earth limestone and clay are mixed together and heated to 1500 C. to get clinker. The limestone breaks down into lime and the clay which is basically just feldspar or plagioclase like the Highland regolith then react to make the mixture of calcium silicates and calcium aluminates. On the Moon it will be possible to heat calcium rich Highland regolith with solar energy at 2000 deg. C + to boil off silica and enrich CaO compositions to make high alumina cement with a composition of about 40% CaO, 50% Al2O3 and 10% SiO2 (1). This does not mean that simple oxides are mixed together in these proportions, but that calcium silicates and calcium aluminates exist with these general elemental proportions. Water will be required to make cement and concrete. On the Moon, water will come from suspected polar ice, hydrogen from volatile harvesting combined with oxygen, and imported hydrogen combined with lunar oxygen. Since water is only 1/9 hydrogen importation could be practical. Sulfur might also be used in place of water to make sulfur cement. Concrete made by mixing cement with lunar regolith and gravel will be very useful for construction within lava tubes someday. On Mars, ordinary mortar will react with the CO2 in the martian atmosphere to harden and bond bricks made from martian regolith. On the Moon we will need to use mortar made from cement and sand which does not require CO2 to harden to bond bricks made of sintered basalt perhaps in lava tubes. We will not want mortar to absorb CO2 from the air of lava tube habitations because carbon is scarce on the Moon and we need it for supporting crops. Water on Mars will come from the soil and the southern polar ice cap. Building towns and cities in lava tubes will be a job for more advanced Moon communities. We will need quite a bit of industry there to do the job. The original "seed packages" of robotic devices will grow and grow using lunar materials to make more equipment until we are ready to seal, pressurize and inhabit lava tubes and build towns for several thousand people with concrete, bricks, plaster, glass and metals mainly iron and steel. There will be no intrusion by ground water on the Moon to erode or rust our structures. These underground towns will be more homey than the metal and inflatable plastic bases we build in the early days of lunar industrialization. They will have gardens and farm sections illuminated by light piped in from the surface during the long day and super efficient microwave sulfur lamps that mimic the spectrum of the Sun without the UV and IR by night. Portland cement contains about 5% CaSO4, to delay setting time. This could be made by leaching highland anorthite with sulfuic acid. We might also choose to make plaster, wetted CaSO4, by sulfuric acid leaching of highland regolith or by leaching the calcium oxide enriched cement powder produced by heating highland regolith with solar energy. Leaching the cement powder might be more productive than leaching anorthite, CaAl2Si2O8, the main constituent of highland regolith. Plaster can be wetted and applied between two layers of glass fiber cloth and allowed to harden to make a wallboard that resists moisture and mildew. We will not need precious paper for wallboard. Thus, we can put up drywall in lava tube cabins, paint the walls, pin up photos and put nails into the walls to hang heavier pictures. Drywall will be an alternative to metal bulkheads and brick walls. Sulfuric acid leaching can be done at "room temperature" or at ambient temperatures of the lunar day. Sulfuric acid boils at 340 C. at 1 ATM and water at 100 C. Leaching tanks could be made of high silicon alloy iron that resists H2SO4 and be lined with cast basalt that resists over 98% sulfuric acid (2). 1) T.D. Lin "Concrete for Lunar Base Construction" Lunar Bases and Space Activities of the 21st Century ed. W.W.Mendell Lunar and Planetary Institute, Houston pg. 381 <http://ads.harvard.edu/books/lbsa/toc.html> <http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1985lbsa.conf..381L> 2) Petrugia <http://www.bia-bg.com/Business/directory/petrurgia/> More Informantion: Cement and Concrete Gene Corley and Larry A. Haskin http://www.belmont.k12.ca.us/ralston/programs/itech/SpaceSettlement/spaceresvol3/cemncon1.htm Lunar Cement William N. Agosto http://www.belmont.k12.ca.us/ralston/programs/itech/SpaceSettlement/spaceresvol3/lunacem1.htm Concrete: Potential Material for Space Station T. D. Un http://www.belmont.k12.ca.us/ralston/programs/itech/SpaceSettlement/spaceresvol3/cpmss1.htm |
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| David A. Dietzler, 2007 |