# Preliminary Investigation of Geopolymer Foams as Coating Materials
## 3 Results and Discussion
[PERSON] et al. focused in their work on testing different variants of fly ash-based foamed geopolymers. After performing thermal conductivity tests for the above materials, they obtained results in the range of 0.15 (W/(m \(\times\) K)) to 0.48 (W/(m \(\times\) K)) [49]. It is important to strive for such parameters with spraying application, so any trials and achievements in this area are very important. Figure 5 shows the average compressive strength results for the foamed geopolymers obtained (Mix 1 and Mix 2) by using mold casting technology. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **Mean Temp. (K)** & **Delta Temp. (K)** & **Thermal Conductivity (W/(m\(\cdot\)K))** & **Load Pressure (kPa)** \\ \hline Cardboard & 283.15 & 20.0 & 0.04169 & 2.0 \\ \hline Geopolymer layer (Mix 2) on the cardboard & 283.15 & 20.0 & 0.15545 & 0.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Thermal conductivity and thermal resistance of the manufactured sample. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Material** & **Mean Temp. (K)** & **Delta Temp. (K)** & **Thermal Conductivity (W/(m\(\cdot\)K))** & **Load Pressure (kPa)** \\ \hline Mix 1 & 283.15 & 20.0 & 0.12493 & 2.2 \\ Mix 2 & 283.15 & 20.0 & 0.12581 & 2.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Thermal conductivity of the manufactured sample. A geopolymer based on fly ash and river sand foamed with H\({}_{2}\)O\({}_{2}\) (Mix 1) achieved an average compressive strength of 1.1 MPa. The average compressive strength for the geopolymer foamed with aluminum powder (Mix 2) was approximately 0.7 MPa. This is a decrease in compressive strength of approximately 36% compared with the geopolymer foamed with H\({}_{2}\)O\({}_{2}\). In their study, [PERSON] et al. investigated the compressive strength of geopolymer foams based on fly ash and metkaolin, cured at different temperatures. H\({}_{2}\)O\({}_{2}\) was used as a foaming additive in this case. The materials obtained in their work had compressive strengths ranging from 1.14 to 1.78 MPa [50]. [PERSON] and [PERSON] investigated the strength parameters of foamed geopolymer reinforced with GFRP mesh in their study. The results obtained for foamed geopolymers reinforced with GFRP mesh oscillated between 0.68 MPa and 9.14 MPa [51]. [PERSON] et al. obtained compressive strength results for ultra-lightweight Portland cement-based foam concrete of 0.8-1.1 MPa [52]. Scanning electron microscopy (SEM) allows for the visual examination of a material to obtain information about its surface topography. In addition, it allows for the identification of the structures formed that cannot be revealed by other examination methods [53; 54]. Figure 6 shows the microstructure of the foamed geopolymers based on fly ash and sand after the compressive strength test. Figure 6(a) shows the microstructure of fly ash and the sand-based geopolymer material foamed with H\({}_{2}\)O\({}_{2}\). In addition to the macropores, which ranged in size from 2 to 3 mm, smaller pores could also be observed, which ranged in size from 10 to 300 \(\upmu\)m. Figure 6(b) shows the microstructure of the geopolymer material based on fly ash and sand, foamed with aluminum powder. Compared with the material foamed with H\({}_{2}\)O\({}_{2}\), this geopolymer foam had a more uniform pore size in its structure, which oscillated around 500 \(\upmu\)m. We obtained a very similar microstructure to the geopolymers studied by another group of scientists [55; 56]. Figure 5: Average compressive strength for geopolymer material obtained via mold casting method. Figure 6: SEM images of foamed geopolymer materials at 50\(\times\) magnification: (**a**) Mix 1; (**b**) Mix 2.