The effect of adding alumina-oxide to metakaolin and volcanic ash on geopolymer products: A comparative study

This research compares the properties of geopolymers made from metakaolin and volcanic ash and investigates the effect of addition Al2O3 to metakaolin and volcanic ash-based geopolymers and synthesis at ambient temperature (24 ± 3 °C). FTIR, XRD, mechanical testing and SEM were used to characterize the geopolymer pastes. The results show that both metakaolin and volcanic ash can be utilized as source materials for the production of geopolymers. Metakaolin is a good source of Al2O3 and SiO2 and it is highly reactive with alkaline activators and produces a higher degree of geopolymerization in comparison with volcanic ash. The properties of volcanic ash-based geopolymer can be improved when alumina is used to compensate the deficiencies in Al2O3 content in the volcanic ash. Addition of appropriate amount of Al2O3 (such as 20% of Al2O3 to MK and 40% of Al2O3 to Vol) increased the geopolymerization extent resulting in the increase of the compressive strengths. It was typically found that 20% and 40% Al2O3 lead to 18.1% and 32.4% increases of the compressive strengths respectively for the metakaolin and volcanic ash-based geopolymers.