# Rheological Properties of Lunar Mortars
## 1 Introduction
### Conditions of Concrete Preparation and Performance on the Moon  
The conditions on the Moon differ significantly from those on Earth, which largely determines the choice of components and technology of execution and use of elements and structures made of lunar concrete. The most important differences are the lack of an atmosphere, less gravity, and scarce water resources. A very important issue is the large temperature fluctuations on the surface of the Moon in the circadian cycle (which lasts 656 h). The temperature on the surface of the Moon varies greatly--at the equator, it ranges from \(-180\)\({}^{\circ}\)C to \(+123\)\({}^{\circ}\)C [23]. Locations from the side of the Earth (on the bright side) and closer to the equator are indicated as optimal due to the temperature criterion (and the possibility of obtaining energy from photovoltaic panels). Based on the trajectories of flights from Earth's previous missions, including manned missions, landed there (Figure 1), the poles and the other side of the Moon are excluded as habitat locations as the conditions there are extremely unsuitable for humans. The scarcity of liquid water on the Moon adds difficulty in carrying out construction work, especially in terms of the potential use of cement concrete. This applies to both the use of water as a component of concrete and for its subsequent maintenance, as well as in  
Figure 2: Morphology, particle size distribution (PSD) plot, and chemical composition of the lunar regolith (based on [16; 19; 20; 22]). work related to the cleaning and maintenance of equipment and molds. Therefore, concrete-like composites with water-free organic synthetic polymer binders or sulfur binders are also considered types of lunar concrete [13; 23]. Considering the aforementioned low temperatures at poles and the fact that the vicinity of poles is not destined for the landing of terrestrial landers, as well as for the construction of the base itself, the search for water (in the form of ice) requires the use of complex technical solutions, reliable at very low temperatures and water/ice transport over relatively long distances. The cost of carrying out such a water extraction process is currently disproportionate to its efficiency. However, NASA plans to search for water ice with the aforementioned VIPER rover so that it would not be necessary to transport water from Earth. The gravity on the Moon is six times smaller than on Earth (i.e., 1.62 m/s\({}^{2}\)) [19]; thus, the technology of performing construction work on the Moon requires adaptation to the reduced gravity. Horizontal and vertical transport can be performed with less energy, while obtaining tight piles of crumb aggregate and proper mixing and compaction of the mixture may be difficult. As a result of such low gravity, segregation of the concrete mix may occur. Heat treatment with a closed-circuit heating factor might be a feasible method for developing concrete on the Moon, which has significant advantages over conventional concreting (faster and more intense hydration, resulting in shorter curing time). Additionally, the autoclaving method prevents the material from being exposed to a lunar vacuum and thus avoids rapid water evaporation [24]. The impact of the practical lack of atmosphere (atmospheric pressure on the Moon is approx. \(3\cdot 10^{-13}\) kPa) [19] on the maintenance and subsequent exploitation of composites should also be considered--both in the context of the absence of oxides that react with concrete components (e.g., carbon dioxide activity leading to concrete carbonation) [25] and in the context of exposure of concrete to solar radiation unfiltered by the atmosphere, including ionizing radiation and UV radiation, which are the cause of intense aging, especially for concrete containing polymers [12].