A comparative study of two methods to produce geopolymer composites from volcanic scoria and the role of structural water contained in the volcanic scoria on its reactivity

Volcanic scoria (ZG, ZK) and kaolin (MY38) were applied for producing geopolymer mortars using two methods such as fusion and conventional methods. Kaolin was transformed (700 °C, 1°/min, 4 h) into metakaolin and used to consume the excess alkali needed for the fusion and also to increase the amount of amorphous phase in volcanic scoria. In order to investigate the effect of structural water contained in volcanic scoria on their reactivity, only volcanic scoria were used to produce geopolymer pastes using conventional method. X-ray pattern of volcanic scoria ZG shows the presence of muscovite and TG curves indicate that ZG and ZK content approximately 6 wt% and 0 wt% of water respectively. Geopolymer pastes from ZK (ZKG) obtained only with volcanic scoria were handled easily after 7 days at ambient temperature. Whereas geopolymer pastes from ZG (ZGG) at the same curing condition were handled after 24 h. The compressive strength of GZK (geopolymer mortars from ZK using conventional method), GfZK (geopolymer mortars from ZK using fusion method), GZG (geopolymer mortars from ZG using conventional method), GfZG (geopolymer mortars from ZG using fusion method), ZGG and ZKG are 25, 15, 39, 17, 33 and 10 MPa respectively. It can be concluded that the conventional method is a good process to synthesize geopolymers using volcanic scoria. The structural water from muscovite (clayey mineral) influences positively the properties of volcanic scoria based-geopolymers.