Fabrication and characterization of hardened bodies from Japanese volcanic ash using geopolymerization

Hardened bodies were fabricated from Japanese volcanic ash after mixing with an alkali solution, molding, and curing. The volcanic ash was composed of approximately 70% crystalline anorthite sodium [(Ca, Na) (Si, Al)₄O₈] phase and ≤30% amorphous silicate phase. First, a starting mixture was prepared by mixing the ground volcanic ash with a sodium hydroxide solution. The mixture was placed in a plastic mold using a glass rod, and then cured at 50 °C and 80% relative humidity for 3 days. The compressive strength of the resulting hardened body increased with increasing concentration of sodium hydroxide solution. When a 13.5 mol/L sodium hydroxide solution was used, the average compressive strength of the hardened body reached 80.1 MPa. The hardening mechanism for the volcanic ash during curing is discussed.