So you want to pave the road for your electrified trucking route on the Moon. What are you going to pave it with? Concrete is the obvious choice, with roads being one use among many. Unfortunately Concrete on Earth is made from limestone (technically a fossil product in that it’s a stone made from the compressed shells of ancient lifeforms). I have an idea that might or might not make sense that I want to put out there.
The purpose of concrete is to be a kind of cast-able rock. Terran concrete is strong in compression but weak in tension (sometimes steel is added in to form rebar, a composite material with improved tensile properties).
Concrete is a mixture of cement and aggregate, aggregate being sand and gravel and fly ash and stuff. Cement is the active ingredient, which itself contains a lot of ingredients, but the core reaction is that calcium oxide is mixed into water, and as the calcium oxide absorbs water to form calcium hydroxide cross-links form in the material which hardens into a solid. Here’s the reaction:
CaO + H2O -> Ca(OH)2
This stuff is mostly available on the Moon though not in concentrated form (thanks to early life forms, Earth has an abundance of Calcium Carbonate, better known as limestone). While water has been discovered in reasonably large quantities, it might be rare enough to be worth conserving. Totally possible this concept isn’t with using anywhere but I think it might work so I’m going to post it.
Anyway, the concept is to replace the cross-linking generated by the calcium oxide-water reaction with cross-linking generated by a reaction between sodium metal and iron oxide. The core reaction looks something like this:
2 Na + Fe2O3 -> Na2O + 2 FeO
(most of the iron on the moon is likely FeO and not Fe2O3, so oxidation may be an additional process step. There are possible alternatives which I’ll discuss later)
I choose sodium specifically for three reasons: First, it’s very reactive, and will gladly steal oxygen from almost any other element. Secondly, it’s got a convenient melting point, at 97C: Solid at room temperature but liquid during the lunar day. This can be modified to below 0C by adding Potassium, which is similarly reactive. Sodium or Sodium and Potassium together also have very low vapor pressure, meaning they can exist as a liquid under vacuum conditions without a significant loss of material.
So the process looks something like this:
- Produce sodium metal and Fe2O3 (probably more Fe2O3 than sodium)
- Combine Fe2O3 with other materials (silica, alumina, etc, appropriate forms and proportions to be determined by experiment)
- Mix with liquid Sodium metal under vacuum conditions (ideally a very minimal amount of sodium, like a few percent)
- Pour, probably during the lunar day; once the reaction starts it should generate enough heat to sustain itself
- Even once the reaction is mostly complete, any remaining sodium will continue to slowly react during the lunar day, so that (like terran concrete) the material gains strength over time
In fact, since sodium and Fe2O3 will likely be small portions of the whole, even if well-mixed, the reactions won’t be iron and sodium right away. This is fine, even better: Sodium will reduce any other common oxide material in lunar regolith (Calcium, Magnesium, Titanium, Silicon, Aluminum, Iron, etc). Over time, those oxygen atoms will continue to be swapped until it’s at its minimum energy state. This is important, because it amplifies the cross-linking (more cross-linking=stronger) initiated by the sodium. Strictly speaking, the Fe2O3 may not be necessary at all, but it’s a dial you can turn to tune the reaction rate and final properties.
The reason this is poorly suited to Mars (or Earth) is that the raw sodium will react aggressively with water or carbon dioxide to poison the reaction.
Gamma Factor 