Utilization of volcanic ashes for geopolymer based on alkaline activator and solid-liquid ratio

Abstract

The volcanic ashes are an abundant natural resource in Indonesia, but they are still little is used optimally, such as geopolymer raw material. Geopolymers are a class of inorganic polymer that be able by the reaction of an aluminosilicate material with an alkaline solution. The research aims to investigate the synthesis of geopolymers using two types of volcanic ash (Mt. Merapi and Mt. Sinabung). The synthesis of geopolymer was carried out at variation of solid/liquid ratio at 65% : 35% and 70% : 30%, with two alkaline solutions (NaOH and KOH) under different alkaline concentration (8, 9, and 12 M). A multi-analytical approach is proposed: chemical (XRF) and spectroscopic (FT-IR) analyses. The Results showed that geopolymer is influenced by volcanic ash-type and SiO2/Al2O3 ratio. Geopolymers are formed when volcanic ash of Sinabung mix with NaOH 10 NaOH with ratio of 65% : 35%, and the polymers are relatively stable. The FTIR spectra of the synthesized geopolymers showed broad absorbance bands, between wave 972-962 cm-1 and 931-976 cm-1 assigned to the internal vibrations of Si-O-Si, and Si-O-Al respectively. Both volcanic ash materials from the Merapi and Sinabung volcanoes can be utilized for making geopolymer, suitable for both engineering and agriculture applications.