## 4 Conclusions  
The research results show that:  
* Lightening of the concrete mixture was achieved by replacing aggregate with rubber granulate from waste tires in cement composites, which places this mixture in the category of lightweight concrete class LC 1.4 according to CSN EN 206-1 [50]. The workability of this mixture containing rubber granulate can be controlled using plasticizing or super-plasticizing additive. * Cement composites containing recycled rubber from waste tires show better sound insulation properties at a layer thickness of 10 mm--at frequencies of 125 and 2000 Hz, at a sample thickness of 30 mm--at frequencies of 125, 500 and 2000 Hz, and at a sample thickness of 50 mm--at frequencies of 125, 500 and 2000 Hz when compared to the comparative sample containing natural aggregate. * 100% replacement of natural aggregate with recycled rubber will significantly reduce the coefficient of thermal conductivity, which will significantly improve the thermal insulation properties of the cement composite. * 100% replacement of natural aggregate with recycled rubber results in a significant reduction in the strength characteristics of the prepared cement composites. This reduction is caused by the lower cohesion of the cementing compound with rubber particles and the high elasticity of the rubber compared to natural aggregates. * Based on the acoustic and thermal properties, mixture Z2 can be selected as the optimal mixture of cement composite based on recycled rubber. This mixture contains fr. 0/1 mm in the amount of 50% and fr. 1/3 in an amount of 50% as well. In this study, the authors were looking for a new type of sustainable material that will use a tire recycling product at the end of the life cycle in its structure. Natural aggregate as a clean source was replaced with a secondary raw material in the form of recycled rubber fraction 0/1 and 1/3 mm. Since natural aggregate was completely replaced with recycled rubber as the filler in cement composites within the scope of this research, a decrease in the strength characteristics of the prepared composites was expected due to the high elasticity of rubber and the different density of both materials. The potential of the newly developed material is not heading towards the segment of structural concrete, but the application of this material will be directed to the segment of lightweight concrete fillers, thermal and sound insulating concrete. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Measurement Mixtures**} & **Thermal Conductivity** & **Specific Volume Thermal** & **Thermal Conductivity** \\  & **Coefficient \(\lambda\) [W**-**m**\({}^{-1}\)**-**K**\({}^{-1}\)]** & **Capacity \(c_{p}\) 10\({}^{6}\) [J**-**m**\({}^{-3}\)**-**K**\({}^{-1}\)]** & \(a\)**\(\cdot\)10\({}^{-6}\) [m**\({}^{2}\)**-**s**\({}^{-1}\)]** \\ \hline Comparative & 2.9706 & 2.0568 & 1.4487 \\ Z2 & 0.3120 & 1.5079 & 0.2069 \\ Z3 & 0.3547 & 1.5508 & 0.2287 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Determination of thermal properties of comparative mixture. In the future, the expected focus of further research will be the use of this composite based on recycled rubber as part of a sandwich panel. The main supporting element of the panel will be designed from concrete based on natural aggregate and the sound-absorbing layer will be made of a cement composite based on recycled rubber. Based on the presented results, 30-50 mm seems to be the optimal thickness of the absorbing layer. This panel should find subsequent use in the construction of noise barriers in busy line structures. Conceptualization, J.S., T.D. and V.V. ; methodology, J.S., T.D., E.J. and V.V. ; validation, J.S., T.D. and V.V. ; formal analysis, J.S., E.J. and T.D. ; investigation, J.S., T.D., E.J. and V.V. ; resources, S.H., J.C., K.M. ; writing--original draft preparation, J.S., T.D. and V.V. ; writing--review and editing, J.S., T.D. and V.V. ; visualization, K.M. and J.C.; funding acquisition, S.H., J.C., V.V. and K.M.