# Rheological Properties of Lunar Mortars
## 5 Additional Considerations in the Context of Cement-Based Lunar Materials  
Lunar outpost construction would require innovative solutions on almost all levels. With extreme external conditions on the Moon, namely, lack of atmosphere and high cyclic temperature changes, the continuous supply of thermal energy and power is a crucial issue as they are necessary to create and maintain conditions in which any building object could be constructed. For most locations on the lunar surface, darkness lasts for periods of about 350 h; thus, it is a great challenge for the solar photovoltaic cells and radioisotope thermoelectric generators to provide enough energy [33]. The lack of atmosphere on the Moon has an additional crucial impact on the design of any lunar structure--ionizing radiation--which impacts both future residents of the constructed buildings and the durability of used construction materials. Due to the missing magnetosphere and atmosphere, particles of galactic and solar origin reach the surface of the Moon unattenuated. Any construction on the Moon, including the ones built from regolith, is required to reduce the exposure to safe levels for prolonged human presence on the Moon [34] as well as protect  
Figure 8: Compressive strength and flexural strength of tested mortars, including standard mortar with CEMI 42.5R and mortars containing 20% of quartz powder (QP) or lunar regolith simulant (LRS) in the total mass of aggregate. Figure 7: The consistency of lunar micro-mortars of w/c = 0.50 expressed by flow diameter (test performed acc. to the modified test procedure and standard test procedure in conformity with EN 1015-3). it against meteoroids impacts with velocities that vary from 2.4 km/s to 72 km/s and weighing from less than 1 kg to over 5 tons [35]. When designing the lunar construction, one needs to take into consideration all the abovementioned factors. The lunar regolith morphology resulted from the continuous impact of meteoroids and the bombardment of the lunar surface by charged particles from the Sun [8]. It has low thermal conductivity, and therefore, the thicker its layer is, the larger the reduction in the temperature variations is [35]. Additionally, from the perspective of radiation health, a regolith layer of 2-3 m thickness provides radiation shielding of about 40 g/cm\({}^{2}\), whereas Earth's atmosphere provides a shielding equivalent of 100 g/cm\({}^{2}\). Rare, large solar flares require shelters with shielding of at least 700 g/cm\({}^{2}\)[35]. By using lunar regolith as an aggregate for mortars or concretes, it is possible to take advantage of those properties and increase the shielding properties of the new construction composites. While the impact of the lunar environment on the solidification of cement and its properties is nascent, a great deal can be learned from studies conducted on Earth utilizing JSC-1A regolith simulant. JSC-1A can be a feasible precursor for alkali activation, the resulting product of which has been termed Lunamer [36]. It achieved 16 MPa in compressive strength when cast with conventional methods and provides good radiation shielding and thermal insulation [37]. Alkali-activated materials present a relatively new group of construction materials and therefore require an additional significant amount of research in both terrestrial and extraterrestrial settings [38]. The microgravity conditions present on the Moon result in an increase in porosity and pore sizes in hydrated cement pastes [39]. Admittedly, using OPC (and certainly manufacturing it) on the lunar surface is nontrivial; the hurdle is the environment. Despite the high cost associated with transporting cargo to space, shipping small amounts of OPC to the Moon could be an alternative to initiate the construction of a lunar outpost until the crew is ready to process the in situ resources to manufacture materials.