Pelletization and properties of artificial lightweight geopolymer aggregates (GPA): One-part vs. two-part geopolymer techniques

Pelletization is currently the most-widely adopted method for the production of artificial geopolymer aggregates (GPA). However, as a newly-developed technology, there is still lack of fundamental research relevant to the influence of the pelletization techniques on the properties of the produced GPA. In this study, different alkalinity, precursor types and pelletization methods (i.e., one-part and two-part) for GPA production were investigated. Results showed that the pelletization efficiencies of almost all the mixes reached approximately 80%. In terms of GPA properties, the one-part GPA with the alkali concentration of 6% had lower oven-dried particle densities [1851 kg/m3 for highly-reactive fly ash (HRFA) and 1668 kg/m3 for lowly-reactive fly ash (LRFA)] than those of the corresponding two-part GPA (1905 kg/m3 for HRFA and 1705 kg/m3 for LRFA), and higher alkalinity (8%) would result in an even lower oven-dried particle density (1802 kg/m3 for HRFA) when one-part pelletization method was used. It was also found that the one-part GPA had a lower pellet strength than the two-part ones, due to the higher porosity observed in the XCT images. From the internal porosity of GPA in different XCT scanning layers, the two-part GPA showed a more uniform distribution of internal porosity compared with the one-part ones, indicating that the two-part pelletization process is more suitable for GPA production. Given the same alkali concentration (6%), the porosities of two-part GPA (1.0% for HRFA and 1.7% for LRFA) were lower than those of the one-part GPA (3.4% for HRFA and 3.2% for LRFA). The findings of this study can provide useful knowledge for the future industrialization of the pelletization technique in the GPA production.