## 2 Materials and Methods  
### Materials  
For the cement mortar studies, Portland cement CEM I 42.5R was used, meeting the requirements of the PN-EN 197-1 standard [66], along with standardized quartz sand with a 0-2 mm fraction in accordance with PN-EN 196-1 [67], and tap water from Czestochowa compliant with PN-EN 1008: 2004 [68]. The water contained an average of 37.0 mg/dm\({}^{3}\) of nitrates, 31.5 mg/dm\({}^{3}\) of chlorides, and 53.8 mg/dm\({}^{3}\) of sulfates. Two waste materials were also used: fly ash generated from municipal waste incineration (code 19 01 13*) and dust from rotary kiln dedusting (CKD) used in cement production (code 10 13 80). Both materials were sourced from the local market in Poland (Figure 1). MSWI waste was collected from a municipal solid waste thermal treatment plant located in the Malopolskie Voivodeship (Poland). The waste was collected over a three-month period at the turn of 2023/2024, and the sample for testing was homogenized. The chemical composition of these waste materials (Table 1) was determined using SpectroXEPOS X-ray fluorescence spectroscopy (SPECTRO, Jozefow, Poland), and their specific density was measured in accordance with PN-EN 196-6 [69]: 2.32 g/cm\({}^{3}\) for fly ash (MSWI-FA) and 2.63 g/cm\({}^{3}\) for kiln dust (CKD). The chemical composition determines the suitability of waste for use in cement composites. MSWI-FA was used as a sand substitute because it does not have binding properties at a level that would allow it to replace cement, and CKD (containing over 60% CaO and SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\)) is a cement substitute. A thermal analysis (TGA-DTA) was performed for the waste materials used in the study using an SDT 650 thermoanalyzer from TA Instruments (New Castle, DE, USA). Thermograms were recorded in a synthetic air atmosphere with a heating rate of 10 \({}^{\circ}\)C/min up to 1000 \({}^{\circ}\)C. The results include thermogravimetry (TG), differential thermogravimetry (DTG), and differential thermal analysis (DTA). Based on the TG/DTA curves for the MSWI-FA sample (Figure 2), a slight mass loss was observed in the temperature range of 300-400 \({}^{\circ}\)C, which may be associated with the loss of physically and chemically bound water. In this temperature range (approximately 300-400 \({}^{\circ}\)C), the decomposition of magnesium carbonate (MgCO\({}_{3}\)) may also occur, as it is reported in the literature to decompose in the range of 170-330 \({}^{\circ}\)C. A minor endothermic peak on the DTA curve confirms the carbonate decomposition reaction. Additionally, an endothermic peak observed in the 600-800 \({}^{\circ}\)C range on the DTA curve corresponds to the decomposition of calcium carbonates, aligning with the mass loss observed on the TG curve in the same temperature range. According to literature data, calcium carbonate decomposition occurs between 550 \({}^{\circ}\)C and 825 \({}^{\circ}\)C. For the CKD sample (Figure 3), mass losses were observed in two temperature ranges: approximately 500-600 \({}^{\circ}\)C and 700-800 \({}^{\circ}\)C. These ranges coincide with two endothermic peaks on the DTA curve, likely associated with the decomposition of calcium carbonates. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Waste** & **SiO\({}_{2}\)** & **CaO** & **MgO** & **Al\({}_{2}\)O\({}_{3}\)** & **F\({}_{2}\)O\({}_{3}\)** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** & **P\({}_{2}\)O\({}_{5}\)** & **S** & **Cl** \\ \hline MSWI- & 17.22 & 37.22 & 4.31 & 9.62 & 2.91 & 9.02 & 1.45 & 1.13 & 3.14 & 4.51 \\ CKD ** & 8.87 & 62.15 & 1.51 & 5.45 & 1.05 & 6.7 & 0.87 & - & - & 0.29 \\ \hline
**Waste** & **Mn** & **Zn** & **Ti** & **Pb** & **Sn** & **Cu** & **Cr** & **Ba** & **Sr** & **Br** \\ \hline MSWI- & 0.09 & 0.83 & 1.31 & 0.93 & 0.03 & 0.05 & 0.01 & 0.14 & 0.05 & 0.02 \\ CKD & 0.05 & 0.01 & 0.08 & 0.01 & - & - & - & 0.01 & 0.04 & 0.02 \\ \hline \end{tabular}  
* fly ash-MSWI-FA; ** cement kiln dust-CKD.  
\end{table} 
Table 1: Chemical composition of investigated MSWI-FA and CKD waste, [%].