Composition Analysis

The chemical elements and aspect of the developed concretes were analyzed through Scanning Electron Microscopy (SEM, VegaTescan LMH II, SE detector, 30 kV) coupled with Energy Dispersive X-Ray Spectrometer detector (EDS, Bruker XFlash 6I30, Automatic mode). A low vacuum mode was necessary to analyze the samples due to the fact that all samples gassed quite hard. Cubes samples (1 cm3 volume) were mechanically cut and used for analyses.

#### Mechanical and Durability Properties Analysis

In Table 2, the essential elements for the applied methods in performing tests are presented regarding the compressive strength, flexural tensile strength, splitting tensile strength, resistance to repeated freeze–thaw cycles, and resistance to hydrochloric acid action.

**Figure 2.** Resistance to the action of hydrochloric acid: (**a**) Specimens immersed in 18% HCl solution; (**b**) Specimens' aspect after 10 days of immersion in 18% HCl solution.



The specimens were prepared by casting in metal molds: cylinders with 100 mm diameter and 200 mm length, prisms of 100 × 100 × 550 mm, cubes with sides of 100 mm and 50 mm. The tests were performed at 28 days. In all tests, 3 specimens were used for each mixture and each test, according to the standards mentioned in Table 2, and the average value was calculated. Only for the freeze–thaw resistance test were six specimens used for each mix, as three specimens were the control samples, not subjected to the freeze–thaw cycles, and three specimens were subjected to the action of the freeze–thaw process.
