*3.2. Flexural Strength*

The results for flexural strength are shown in Figure 3. The test was carried out on three samples for each variant. The graph shows the mean value obtained from these measurements.

**Figure 3.** Results from the flexural strength test.

In the case of bending strength, samples with particle sizes of the raw material above 900 μm obtained a result below the reading sensitivity of the testing machine, hence no value was recorded for this type of sample. Again, the best strength was achieved with geopolymers with particle sizes below 200 μm, while this value was comparable to the result for geopolymers with grain sizes of 200–900 μm.

#### *3.3. SEM Observation*

Figure 4 shows a SEM image for sample G 200–900 μm.

The observed microstructure is typical for geopolymers. A significant number of pores ranging from 2 to 3 μm were observed. The EDS analysis identified compounds of silicon, aluminum, sodium, calcium, potassium, chlorine and iron in the selected areas 1–3 (Figure 5).

**Figure 4.** SEM image of geopolymer G 200–900 μm at 50× magnification.

**Figure 5.** Sample G 200–900 (**a**) with marked areas of measurements, (**b**) results of the EDS analysis.
