## 4 Results
### Life Cycle Assessment of Crumb Rubber Use in Concrete
Some approaches allocate minimal or zero energy consumption to preparing recycled materials, especially when focusing on the primary product's life cycle. This perspective is often adopted to emphasize the environmental benefits of recycling by attributing the majority of energy consumption to the initial production phase. For instance, the report \"Modeling recycling in life cycle assessment\" discusses allocation problems in LCA due to material recycling and highlights that the method for modelling material recycling can significantly impact the environmental assessment of products with high recycled content [51]. Additionally, the article \"Assessing the Impact of Recycled Building Materials on...\" examines the potential of recycled construction materials to reduce greenhouse gas emissions \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **River Sand** & \multicolumn{2}{c}{**Crumb Rubber**} \\ \hline
**\%** & **Weight, kg** & **\%** & **Weight, kg** \\ \hline
100 & 1000.0 & 0 & 0.0 \\ \hline
90 & 870.1 & 10 & 45.6 \\ \hline
80 & 740.2 & 20 & 91.2 \\ \hline
50 & 435.0 & 50 & 228.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Substitution figures for replacing river sand with crumb rubber by volume. Figure 4: GWP100a for different crumb rubber substitution scenarios in concrete mixes replacing river sand. and energy usage, emphasizing the importance of adopting integrated approaches that combine LCA and Material Flow Analysis within the circular economy framework [52]. These sources provide insights into how energy inputs for recycled materials are considered in LCA studies, supporting the assumption of minimal or zero energy consumption in the preparation of crumb rubber. The LCA results obtained using OpenLCA software 2.0.2 indicate that the GWP100a of 1 ton of the reference cement mix is 288.2 kg CO2 Eq. Upon substituting 50% of the river sand with crumb rubber by volume, the GWP100a is reduced to 284.2 kg CO2 Eq, resulting in a reduction of 4 kg CO2 Eq, or approximately 1.39%. This modest reduction highlights the limited environmental advantage of using crumb rubber as a sustainable alternative to natural river sand. However, the key value of this approach lies in the superior functional properties offered by rubberized cement composites compared to traditional concrete. Rubberized cement composites demonstrate enhanced elasticity, shock absorption, and sound-dampening capabilities, making them ideal for applications such as highway noise barriers, railway sound protection walls, and flooring in impact-prone environments. Additionally, crumb rubber contributes to increased durability, particularly in freeze-thaw cycles, as the elasticity of the material helps reduce micro-cracking caused by thermal stresses. Furthermore, the reduced density of crumb rubber composites can offer advantages in lightweight construction, making these materials suitable for seismic-resistant structures and applications where weight reduction is critical. Furthermore, when considering the CO2 emissions associated with the recycling of end-of-life truck tires (36.1 kg CO2 Eq.) and car tires (122.9 kg CO2 Eq. ), the integration of crumb rubber derived from these sources into cement composites can lead to a negative carbon footprint in the range of \(-\)36.1 kg CO2 Eq. to \(-\)118.9 kg CO2 Eq. This underscores the dual environmental benefit of diverting waste tires from incineration and reducing the carbon emissions of cement composites. These findings emphasize the potential of crumb rubber to support circular economy initiatives by mitigating GHG emissions and promoting sustainable material usage in the construction industry.