# Rheological Properties of Lunar Mortars
## 6 Conclusions  
In the conducted research, the influence of powder simulating the granulometry and morphology of lunar regolith on the rheology of lunar micro-mortars and mortars was tested. The microscopic observations confirmed the sharp-edged morphology of LRS particles, characteristic of the lunar soil, which unfortunately affects negatively the consistency of mixes of cementitious composites with these fillers. The determining particle size distribution of LRS showed strong similarities with the real lunar regolith data. The used LRS characterized by a density of 2.641 g/cm\({}^{3}\), i.e., a very similar to that of quartz (2.650 g/cm\({}^{3}\)), which allowed for the mass substitution of quartz aggregate in mortars; however, due to the much finer granulation in comparison to standard sand, it was decided that the substitution would be considered for a composite containing both quartz sand and quartz micro-filler similar to the LRS in terms of PSD. As presented in the Results Section, very fine LRS of much more developed specific surface area (thus also much higher water demand ratio) than standard sand had a negative impact on the rheological properties of cementitious composites; therefore, it required the use of a very effective superplasticizer. Ultimately, it was possible to obtain a mortar mix in which 20% (by weight) of the aggregate was replaced with LRS, which is characterized by very similar (or even slightly better) plasticity in comparison to the standard mortar. Moreover, the tests of the mechanical properties carried out after 28 days showed that the mortar modified in this way was characterized by identical values of flexural strength and compressive strength as the standard mortar (respectively 7 MPa and 50 MPa). Taking into consideration the lunar environment, characterized by much lower gravitational pull than Earth's, those results confirm that mechanical properties of regolith-based cement composites are sufficient for lunar construction purposes [37]. In order to better investigate the relation between the cement paste phase and LRS, and considering the need to create cement composites using only LRS as fillers, based on the results of two series of lunar micro-mortars with a w/c ratio that differs almost twice (0.265 and 0.500), the dependencies were developed in the form of very well fitted to empiric data functions describing the LRS/Cement-mix consistency relation. Taking into account that nonstandard concreting of the mortar mixture by 3D printing is a potential solution in the Moon conditions, it was shown that it was possible to obtain a micro-mortar consistency suitable for this technology. Considering that the flow values obtained by the standard method on the flow table (see Figure 8) were within the range recommended by scientists working on 3D printing technology (compared to the recommended ranges described in the last part of Section 3, i.e., from 180 to 240 mm), it can be concluded that the developed micro-mortars meet those requirements. However, the next stage of optimization research should include buildability time. The appropriate consistency of cementitious composites enables the easier production of cement-based products. Performed research showed that in order to consider the use of cement composites on the Moon, the issue of regolith's impact on its consistency needs to be addressed. The obtained results allowed to formulate a conclusion that the use of the lunar regolith in mortars and micro-mortars has potential, but their qualitative and quantitative compositions should be very precisely selected, especially when trying to develop compositions of lunar mortars with much lower water contents. The new generation superplasticizers (e.g., with hyperbranched polymers [45; 46] or polyphosphate comb polymers [47]) of highly improved efficiency in fluidizing could prove useful in increasing lunar regolith content in cementitious composites while maintaining consistency and w/c at reasonable levels. Conceptualization, J.J.S. and P.W. ; resources, J.J.S.