Design Note on Post-Tensioned Cast Basalt

Construction of permanent settlements on the Moon will be greatly facilitated by the use of local building materials. The structural materials normally employed in Terrestrial construction (steel, Portland Cement concrete, wood and masonry) are to a great extent unavailable on the Moon. (Steel and Lunar-style masonry may eventually be fully available — but concrete requires large quantities of water, and wood will not be an option.) The Lunar surface does, however, feature large quantities of basaltic rock, which is already employed on Earth as an industrial material. Cast Basalt has many desirable structural properties — yet its ultimate failure mode is brittle fracture, especially under bending loads, which is highly undesirable. This design note will discuss one option for scaling up Terrestrial experience with Cast Basalt as an industrial material, to use in larger castings for structural construction on the Moon. Post-tensioning of the basaltic castings, based on Terrestrial experience with reinforced concrete structures, will be outlined. Post-tensioning will enhance the use of these elements for building crewed habitations. Using a tensile material to compress the more brittle basaltic casting will transform the combined structural element from a brittle into a ductile material, for purposes of structural design and risk evaluation. In the Lunar environment, with internal air pressure being the dominant loading for inhabited structures, ductility of the structural elements will be a vital need.