Refractory Bricks Characterization Manufactured from Geopolymers Based on Volcanic Ash

The aim of this study is to analyze the mechanical and physical properties of refractory bricks produced via geopolymerization using volcanic ash. Volcanic ash was combined with 12 M sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) as activators, with a liquid-to-solid ratio of 0.2. Two brick prototypes were produced: a cylindrical specimen for testing compressive strength and water absorption, and a rectangular prism for analyzing thermal conductivity. The bricks were calcined at 600°C and 800°C, showing favorable performance compared to well-known commercial refractory bricks. Cylindrical specimens calcined at 600°C reached an average compressive strength of 5.51 MPa, while those calcined at 800°C averaged 6.60 MPa—more than double the 2.80 MPa of commercial bricks. The average density of the specimens at both temperatures was similar, around 1.58 g/cm³, significantly higher than the 0.95 g/cm³ of commercial counterparts. Moreover, the average thermal conductivity of the geopolymer bricks was 0.008 W/m·K, indicating superior insulating properties compared to the 0.39 W/m·K of commercial refractory bricks. These results demonstrate optimal properties in refractory bricks made from geopolymer-based volcanic ash.