# Lightweight Insulating Geopolymer/Phase-Change Materials Applied Using an Innovative Spray Method
## 2 Materials, Methods, and Developed Technological Setup  
The research on developing the innovative technological line was conducted for a geopolymer mixture based on fly ash originating from the Skawina Power Plant. Table 1 shows the oxide chemical composition of the fly ash, while Table 2 presents the particle size analysis results. The chemical analysis (Table 1) indicated that the main mineral components were silicon dioxide (SiO\({}_{2}\)) and aluminium oxide (Al\({}_{2}\)O\({}_{3}\)), with contents of 59.41% and 30.15%, respectively. The calculated molar ratio of SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) was approximately 1.97, which falls within the optimal range (1.5-2.5) conducive to efficient geopolymerisation. The presence of additional oxides, such as Fe\({}_{2}\)O\({}_{3}\) (3.48%), CaO (2.21%), K\({}_{2}\)O (2.11%), TiO\({}_{2}\) (0.74%), and SO\({}_{3}\) (0.56%), can further affect the rheology, reaction kinetics, and physicochemical properties of the material, including durability and resistance to environmental factors. Particle size analysis (Table 2) showed that the material had a relatively fine grain size, as evidenced by characteristic values of D\({}_{10}\) = 2.44 \(\upmu\)m, D\({}_{50}\) = 12.86 \(\upmu\)m, and D\({}_{90}\) = 32.23 \(\upmu\)m, with an average particle size of 16.23 \(\upmu\)m and a very low standard deviation (0.03 \(\upmu\)m). Such parameters testify to a homogeneous distribution of grains, which translates into a large specific surface area and promotes high reactivity of the raw material in alkaline environments. The appropriate chemical composition and grain size of fly ash indicate its high suitability as a component for manufacturing durable and homogeneous geopolymer materials. The geopolymer mixture contained 10 wt.% of phase-change material (PCM), a commercial product called GR42 from Rubitherm. The additive was introduced to further enhance the thermal properties of the coatings. Hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) with a concentration of 36% was used as the foaming agent and was continuously dosed during the spray application of the geopolymer, ensuring that its proportion in the geopolymer mixture ranged between 2 and 4 wt.%. The geopolymers were produced using an alkaline solution composed of sodium hydroxide (10M) and a sodium silicate solution (water glass R-145). Foamed geopolymer was sprayed onto plasterboard panels mounted on walls. Thus, removing these panels after spraying enabled further testing of the resulting coatings. The trials described in this paper primarily focused on the liquid geopolymer spraying process, using a specially designed technological line. The following description details the construction and operation of the devices and elements that are part of this system. The technological line developed for the production of foamed geopolymer coatings by spraying directly onto construction surfaces consisted of a mixing and spraying unit (optionally \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Precursor**} & \multicolumn{6}{c}{**Oxide Composition (wt.\%)**} \\ \cline{2-7}  & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **K\({}_{2}\)O** & **TiO\({}_{2}\)** & **SO\({}_{3}\)** \\ \hline
**Fly ash** & 59.41 & 30.15 & 3.48 & 2.21 & 2.11 & 0.74 & 0.56 \\ \hline \end{tabular}
\end{table} 
Table 1: Fly ash oxide analysis. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Material**} & **D\({}_{10}\) [\(\upmu\)m]** & **D\({}_{50}\) [\(\upmu\)m]** & **D\({}_{90}\) [\(\upmu\)m]** & **Average Value [\(\upmu\)m]** & **Standard Deviation [\(\upmu\)m]** \\ \hline
**Fly ash** & 2.44 & 12.86 & 32.23 & 16.23 & 0.03 \\ \hline \end{tabular}
\end{table} 
Table 2: Fly ash-particle size analysis. including a flow mixer, from which the geopolymer mass was fed to the unit), a manipulator equipped with a spray nozzle (to which a hose supplying liquid geopolymer was attached), and an infrared heater.