Rational utilization of volcanic ashes based on factors affecting their alkaline activation

The present study evaluates the criteria that affect the characteristics of both volcanic ashes and their alkaline activated products, hence their rational utilization. To that end, five samples of volcanic ash were examined chemically, mineralogically and physically whereas certain characteristics of their alkaline activated products were determined. In order to elucidate the relationship between the characteristics of volcanic ashes and the products of their alkaline activation, mechanical strength, Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) of geopolymer specimens aged 14 days were examined. Volcanic ashes with large amount of amorphous phase (18.2-42.5% by mass) led to geopolymers with compressive strengths of 3.1-12.6 MPa. As for volcanic ashes with small amount of amorphous phase (10.2-12.5% by mass), alkaline activation at 80 °C led to geopolymers with compressive strength of 1.0-4.1 MPa. The results obtained showed that volcanic ashes could be used either for geopolymer synthesis or as filler. The classification depended mostly on the amount and the SiO2/Al2O3 molar ratio of amorphous phase.