2.2.2. Strength Tests

Compressive strength tests were carried out by EN 12390-3 ("Testing of hardened concrete. Compressive strength of specimens") on cubic specimens (50 × 50 × 50 mm) using a Matest 3000 kN universal testing machine (Matest, Treviolo, Italy). The test speed was set at 0.05 MPa/s. The test was carried out using a load cell designed for lower loads— 300 kN. Strength tests were conducted after 28 days of conditioning of the specimens. For the compressive strength tests, 10 samples of each type of geopolymer were used to calculate the average of the results.

#### 2.2.3. Microstructure

The geopolymer materials were microscopically observed to characterize the shaped structure. The study was carried out using a JEOL JSN5510LV scanning electron microscope (JEOL Ltd., Tokyo, Japan). Samples were used for the study after mechanical property tests. Before the examination, the surface of the sample was coated with a conductive gold layer on a JOEL JEE-4X vacuum evaporator (JEOL Ltd., Tokyo, Japan).
