## 3 Results and Discussion
The porosity of MOC cement composites containing EPP aggregate increased compared to R-MOC. Similar behavior can be found in literature regarding the incorporation of different kind of plastics into a matrix based on Portland cement [32; 44]. The lightening of high-density structure by the use of the EPP aggregate resulted in lightweight composites with high porosity which extended their application potential in the construction sector. The used hydrophobic admixtures had almost no effect on structural characteristics of composites with EPP. The comparison of strength characteristics of examined composites is given in Table 7.  
Mechanical parameters of MOC composites are mainly dependent on used molar ratios of MgO/MgCl\({}_{2}\) and H\({}_{2}\)O/MgCl\({}_{2}\), which governs the formation of binding phases and amount of unreacted raw materials [45]. For mortars, the parameters of filler and ratio of filler/b \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **Specific Density (kg\(\cdot\)m\({}^{-3}\))** & **Bulk Density (kg\(\cdot\)m\({}^{-3}\))** & **Porosity (\%)** \\ \hline R-MOC & 2460 \(\pm\) 25 & 2130 \(\pm\) 51 & 13.4 \(\pm\) 0.5 \\ EPP-MOC & 1420 \(\pm\) 14 & 908 \(\pm\) 22 & 36.1 \(\pm\) 1.2 \\ EPP-MOC-IH & 1413 \(\pm\) 14 & 926 \(\pm\) 22 & 34.5 \(\pm\) 1.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Basic structural characteristics of lightweight MOC cement composites. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **R-MOC** & **EPP-MOC** & **EPP-MOC-IH** \\ \hline Flow diameter (mm) & 229 & 145 & 142 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Diameter of fresh mixtures. considered. The replacement of sand with EPP aggregate led to the significant reduction in all strength parameters. The compressive strength reductions of EPP-MOC and EPP-MOC-IH were 90% and 88%, respectively, as compared to control material R-MOC. This strength decrease is in accordance with the density and porosity data (Table 6). Similarly as in our case, many researchers stated that the incorporation of plastics aggregate of varying shape, kind, and amount causes the loss of mechanical resistance in the composites based on the Portland cement [30; 32; 45]. Accordingly, the decrease of compressive strength of MOC cements containing different additives was reported by [PERSON] [33]. The typically higher flexural/compressive strength ratio of MOC composites compared to that based on the Portland cement was observed for all developed MOC samples. It can be anticipated that the use of smaller EPP particles would increase the mechanical resistance of the final composites. The improvement in strength parameters might by possible also by vibrating the fresh casted specimens. The decrease in the thermal transport and storage parameters of MOC composites with EPP aggregate content is obvious from Table 8.  
The great drop in the thermal conductivity values noticed for materials EPP-MOC and EPP-MOC-IH were 83.7% and 83.3%, respectively, compared to R-MOC. In the case of the volumetric heat capacity, a decrease of ~12% was observed for MOC composites containing EPP. [PERSON] et al. [12] reported on the reduction of thermal conductivity of MOC-based composites with addition of cenospheres derived from fly ash. For cenospheres, addition in the amount of 5, 15, and 25% by weight of the magnesia powder, they observed the thermal conductivity values reduced by 16, 21 and 32%, respectively, as compared to the reference sample without cenospheres. In our case, the deceleration of heat transport by the use of the substitution of silica sand with crushed EPP was much higher. In summary, the main parameters that affect the resulted thermal properties of developed MOC composites were the amount and type of used aggregates, thermal parameters of the aggregates themselves, and the porosity of the composites which significantly increased because of the use of EPP particles.