Novel binder material in geopolymer mortar production: Obsidian stone powder.

This paper presents the results of mechanical and micro‐structural properties of geopolymer mortars with obsidian, ground granulated blast furnace slag, and metakaolin. In this study, 13 different combinations were created using 25% by weight of obsidian, blast furnace slag, and metakaolin. Geopolymer mortars were poured at 0.45 water/binder ratio, 12M NaOH concentration, and exposed to thermal cure at 75°C, 90°C, 105°C, and 120°C for 72 h. The flexural and compressive strengths of the mortars were measured and their microstructural properties were analyzed. As a result of the study, the maximum compressive strength was obtained as 93.7 MPa, and the maximum flexural strength was 21.4 MPa. From the results obtained when different combinations are used, it has been observed that the materials work in harmony with each other and the optimum curing temperature is 90°C. Also, scanning electron microscopy (SEM) and EDS analyses indicated that the compact structure of the geopolymer matrix and the Ca/Si ratio are directly proportional to the mechanical strength of the sample. The high wavelength value formed in the main band as a result of Fourier‐transformed infrared spectroscopy (FTIR) analysis shows that the mortars have high mechanical properties. [ABSTRACT FROM AUTHOR]