## 3 Results and Discussion
### Evaluation of Results in the Context of Practical Use  
The research showed that cement mortar samples containing municipal solid waste incineration fly ash (MSWI-FA), CKD, and a mixture of both wastes achieved the lowest strength parameters compared to the control series samples. In particular, a significant decrease in compressive strength was observed after 7 and 28 days of curing in mortars containing MSWI-FA, which may be caused by the lack of binding properties of this waste. MSWI-FA is characterized by a high chlorine content (4.51%) and alkaline oxides (Na\({}_{2}\)O + K\({}_{2}\)O), which may lead to unfavorable chemical reactions weakening the structure of the mortar. The analysis of changes in the mechanical properties of the mortars after 7 and 28 days indicates that MSWI-FA shows a greater reduction in strength in the early curing period than after a longer time. This may result from the slow hydration of components  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Mortar Series**} & \multirow{2}{*}{\
\begin{tabular}{c} **Average Reduction in** \\ **Compressive Strength (\%)** \\ \end{tabular} } & \multicolumn{2}{c}{**Average Reduction in**} & \multirow{2}{*}{
\begin{tabular}{c} **Average Mass Loss** \\ **(\%)** \\ \end{tabular} } \\ \hline
**MS** & \(-32.66\) & \(-47.7\) & \(0.82\) \\ \hline
**MSWI-FA-10** & \(-27.10\) & \(-15.1\) & \(0.15\) \\ \hline
**MSWI-FA-15** & \(-13.70\) & \(-7.4\) & \(0.18\) \\ \hline
**MSWI-FA-20** & \(-6.10\) & \(-0.7\) & \(0.28\) \\ \hline
**CKD-10** & \(-35.21\) & \(-77.9\) & \(0.15\) \\ \hline
**CKD-15** & \(-21.56\) & \(-73.7\) & \(0.21\) \\ \hline
**CKD-20** & \(-19.52\) & \(-77.3\) & \(0.15\) \\ \hline
**MSWI-FA-CKD/10-10** & \(-11.38\) & \(-76.6\) & \(0.05\) \\ \hline
**MSWI-A-CKD/10-20** & \(-8.63\) & \(-25.6\) & \(0.36\) \\ \hline
**MSWI-FA-CKD/20-10** & \(-15.67\) & \(-48.5\) & \(0.19\) \\ \hline
**MSWI-FA-CKD/20-20** & \(-1.72\) & \(-9.9\) & \(0.24\) \\ \hline
**MSWI-FA-CKD/3-3** & \(-5.95\) & \(-8.2\) & \(0.28\) \\ \hline
**MSWI-FA-CKD/3-17** & \(-13.22\) & \(-44.0\) & \(0.34\) \\ \hline
**MSWI-FA-CKD/17-17** & \(-19.95\) & \(-56.6\) & \(0.17\) \\ \hline
**MSWI-FA-CKD/17-3** & \(-3.66\) & \(-20.2\) & \(0.07\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Freeze–thaw resistance test results for individual mortar series.  
present in the ash and the secondary pozzolanic reaction, which partially compensates for the initial decrease in strength. It is worth noting that after frost resistance tests, mortar samples containing MSWI-FA in amounts of 10%, 20%, and 30% showed an improvement in mechanical parameters. This may be significant for their application in construction, especially in structures exposed to low temperatures. In the future, research should focus on improving the properties of mortars containing MSWI-FA by modifying their composition, both through the optimization of MSWI-FA itself and the addition of appropriate chemical activators. Combining the ash with other mineral additives, such as metakaolin or amorphous silica, may enhance its pozzolanic properties. Alternatively, the introduction of modifiers in the form of polymers or synthetic fibers could improve both cohesion and resistance to environmental factors. Despite the potential environmental benefits of using MSWI-FA and CKD, their practical adaptation in the construction industry may face barriers related to technical standards and material durability limitations. The optimization of composition and further research on the stability of these materials are crucial for their large-scale implementation.