## 3 Results and Discussion
### The Characterization of Geopolymer Composites
#### 3.3.5 Compressive Strength  
For the estimation of mechanical properties, the compressive strength was determined only tentatively at 28 days for a ratio of 100 g of the geopolymer matrix and 40 g of the waste-glass fraction (see Sample Preparation). The results are shown in the graph (Figure 10). The pure geopolymer matrix serves as a blank sample (without aggregates). The results show that geopolymer composites with the addition of AGW have sufficient mechanical properties. The 28-day compressive-strength values reach up to 81.3 MPa and 82.8 MPa for the finest fractions (0.16-0.25 mm) of AGW1 and AGW2, respectively. There is a noticeable trend for both types of glass waste where the compressive strength decreases with the increasing particle size of the glass waste. A similar decrease in compressive strengths has been observed by several authors, but in their case, AGW particles were applied as a partial replacement for sand aggregate in geopolymer [43, 45]. It can be assumed that the filling for other fractions was not optimal, especially for the \begin{table}
\begin{tabular}{l c c} \hline \hline
**Fraction** & **AGW1-G (ng\(\cdot\)kg\({}^{-1}\))** & **AGW2-G (ng\(\cdot\)kg\({}^{-1}\))** \\ \hline
0.16–0.25 mm & \(3.1\pm 0.1\) & \(6.4\pm 0.2\) \\
0.4–0.63 mm & \(0.7\pm 0.1\) & \(0.6\pm 0.2\) \\
1.25–2 mm & \(1.9\pm 0.1\) & \(2.5\pm 0.4\) \\
2-5 mm & \(4.1\pm 0.2\) & \(0.0\pm 0.1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The results of the quantitative analysis of triethylene glycol bis(2-ethylhexanoate) in the fractions of AGW-G samples. larger fractions, where sedimentation of the particles occurred. On the other hand, for the fraction of 0.16 to 0.25 mm whose content in the geopolymer matrix is almost optimal, the compressive strengths slightly exceed the strength of the geopolymer matrix (80.6 MPa), which is in agreement with the work of [PERSON] et al. and [PERSON] et al. [42; 46]. By optimizing the AGW content or by using a combination of several AGW fractions, possibly in combination with another type of filler, it would probably be possible to achieve higher values of mechanical properties. The main aim of this paper was to verify the possibility of using AGW as an alternative aggregate in a geopolymer matrix. Due to the composition of AGW, which includes organic safety films and heating elements, it was first necessary to characterize the AGW materials (AGW1 and AGW2) and determine the effect of an alkaline environment. Furthermore, the influence of the fractions used, both of the AGW itself and of the AGW incorporated in the geopolymer matrix, was also investigated. Direct exposure to an alkaline solution partially degrades AGW particles. However, because of the setting time of the geopolymer matrix (from 2 to 12 h) [65], there is no long-term exposure of AGW particles to alkaline environments. Therefore, the deterioration of these particles is minor. It is possible to assume that this phenomenon is part of the glass particle dissolution process described by several authors [38; 39; 40; 42] but due to the larger particle size, only partial degradation occurred. AGW materials have been found to comprise mainly triethylene glycol bis(2-ethylhexanoate), originating from the contained safety films, which may be further released into the environment. GC/MS analysis has confirmed that the addition of AGW to the geopolymer matrix has lowered the release of triethylene glycol bis(2-ethylhexanoate). The decline in the concentration of triethylene glycol bis(2-ethylhexanoate) in geopolymer composites may stem from the incorporation of this organic substance into the structure of the geopolymer because geopolymers are able to form hybrid bonds with organic substances (hybrid organic-geopolymer materials), as described by [PERSON] et al. [66]. Another possibility is the degradation within the alkaline environment of the geopolymer matrix [67]. Nevertheless, no byproducts of this degradation have been identified.