|Compressive strength||39–75.7 N/mm2 (MPa)|
|Young's modulus||21.4 kN/m2|
|Temperature coefficient||5.4 × 10−6 K−1|
Lunarcrete, also known as "mooncrete", an idea first proposed by Larry A. Beyer of the University of Pittsburgh in 1985, is a hypothetical aggregate building material, similar to concrete, formed from lunar regolith, that would cut the construction costs of building on the Moon.
Only comparatively small amounts of moon rock have been transported to Earth, so in 1988 researchers at the University of North Dakota proposed simulating the construction of such a material by using lignite coal ash. Other researchers have used the subsequently developed lunar regolith simulant materials, such as JSC-1 (developed in 1994 and as used by Toutanji et al.). Some small-scale testing, with actual regolith, has been performed in laboratories, however.
The basic ingredients for lunarcrete would be the same as those for terrestrial concrete: aggregate, water, and cement. In the case of lunarcrete, the aggregate would be lunar regolith. The cement would be manufactured by beneficiating lunar rock that had a high calcium content. Water would either be supplied from off the moon, or by combining oxygen with hydrogen produced from lunar soil.
Lin et al. used 40g of the lunar regolith samples obtained by Apollo 16 to produce lunarcrete in 1986. The lunarcrete was cured by using steam on a dry aggregate/cement mixture. Lin proposed that the water for such steam could be produced by mixing hydrogen with lunar ilmenite at 800°C, to produce titanium oxide, iron, and water. It was capable of withstanding compressive pressures of 75 MPa, and lost only 20% of that strength after repeated exposure to vacuum.
In 2008, Houssam Toutanji, of the University of Alabama in Huntsville, and Richard Grugel, of the Marshall Space Flight Center, used a lunar soil simulant to determine whether lunarcrete could be made without water, using sulfur (obtainable from lunar dust) as the binding agent. The process to create this sulfur concrete required heating the sulfur to 130–140°C. After exposure to 50 cycles of temperature changes, from -27°C to room temperature, the simulant lunarcrete was found to be capable of withstanding compressive pressures of 17MPa, which Toutanji and Grugel believed could be raised to 20MPa if the material were reinforced with silica (also obtainable from lunar dust).
Casting and production
There would need to be significant infrastructure in place before industrial scale production of lunarcrete could be possible.
The casting of lunarcrete would require a pressurized environment, because attempting to cast in a vacuum would simply result in the water, required for the chemical reaction that forms the curing process, evaporating, and the lunarcrete failing to harden. Two solutions to this problem have been proposed: premixing the aggregate and the cement and then using a steam injection process to add the water, or the use of a pressurized concrete fabrication plant that produces pre-cast concrete blocks.
Lunarcrete shares the same lack of tensile strength as terrestrial concrete. One suggested lunar equivalent tensioning material for creating pre-stressed concrete is lunar glass, also formed from regolith, much as fibreglass is already sometimes used as a terrestrial concrete reinforcement material. Another tensioning material, suggested by David Bennett, is Kevlar, imported from Earth (which would be cheaper, in terms of mass, to import from Earth than conventional steel).
David Bennett, of the British Cement Association, argues that lunarcrete has the following advantages as a construction material for lunar bases:
- Lunarcrete production would require less energy than lunar production of steel, aluminium, or brick.
- It is unaffected by temperature variations of +120°C to −150°C.
- It will absorb gamma rays.
- Material integrity is not affected by prolonged exposure to vacuum. Although free water will evaporate from the material, the water that is chemically bound as a result of the curing process will not.
Bennett suggests that hypothetical lunar buildings made of lunarcrete would most likely use a low-grade concrete block for interior compartments and rooms, and a high-grade Dense Silica Particle cement-based concrete for exterior skins.
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