# Rheological Properties of Lunar Mortars
## 2 Research and Scope  
It was very difficult to design the research program determining the potential use of lunar regolith. The research aim was to find a composition with the highest accepted lunar regolith simulant content in the mass of the composite while not worsening composite rheological properties. Therefore, the most difficult task was to decide on the initial quantitative composition of the tested composites so that the results could be interpreted and assessed. Considering the very fine particle size distribution of lunar regolith and  
Figure 3: Particle size distribution (PSD) of the lunar regolith simulants—American “Chenobi” of uniformity coefficient, Cu = 3.68 (dashed line) and Polish “AGK-2010” of uniformity coefficient, Cu = 3.54 (solid line). Reprinted from [28]. therefore very high water demand ratio, when replacing aggregate with lunar regolith in mortar, it was not possible to perform a simple substitution of sand with regolith simulant. If the substitution were to be carried out directly, the aggregate of comparable grain size should be replaced. For this reason, mortars containing both sand (aggregate up to 2 mm) and quartz powder were tested. However, in order to have any known and recognized reference point described in the standards, it was necessary to prepare a classic standard mortar (meeting the requirements of EN 196-1 standard), which then began to be modified. Therefore, the adopted sequence of experimental stages began with the determination of material characteristics of Polish lunar regolith simulant (LRS) but also the selection of similarly graded quartz powder. The next stage was the experimental initial determination of the possible grade of filling the standard mortar with very fine filler (the so-called micro-filler: quartz powder or lunar regolith simulant) keeping the water/cement ratio identical to that of the standard mortar (i.e., w/c = 0.50) and with constant consistency (not to introduce additional variables apart from the aggregate composition). At the next stage, apart from the remaining sand, the interaction between the cement paste (water + cement in a constant proportion) phase and the LRS micro-filler phase was tested. At that stage, the micro-mortars with regolith simulant were tested and the influence of LRS on the rheological characteristics of such mixes was assessed. The important task was to obtain compositions of a possibly high content of LRS and good workability of the mixes (necessary to enable efficient filling of the molds with the lunar mortar mix) and on the other hand, reduce water content. At this stage, the analyzed input variable was the content of LRS in relation to cement mass, and the output data were the consistency of lunar micro-mortars tested with various methods. Additionally, the compressive strength and flexural strength of selected lunar mortars were tested after 28 days and compared to the properties of reference standard mortar. The subsequent stages of the experimental program are presented in Table 2.  
Given the environmental \"circumstances\" on the Moon, it can be assumed that traditional concreting methods could not be applicable. However, 3D concrete printing technology presents an interesting option for lunar concrete construction [29]. From this point of view, consistency was considered one of the main properties that could affect the technological process of producing elements of cementitious composites.