Microstructural evaluation of initial dissolution of aluminosilicate particles and formation of geopolymer material

The rheological behavior of microparticulate structures of geopolymers was studied. The materials were developed from alternative sources of aluminosilicate and were activated in different concentrations using 5, 10, and 15 M sodium hydroxide, and sodium silicate, which were added in a 2:1 ratio (by volume). The solid constituents used were bottom ash/metakaolin and neat metakaolin in a 2:1 blend. The rheological characteristics were determined after 5 min of homogenization and a subsequent curing of the pastes at room temperature for 28 days. The materials presented amorphous characteristics, which confirmed the formation of geopolymers. A thixotropic behavior was observed for all formulations, except for bottom ash/metakaolin activated at 5 M, which resulted in geopolymers with a lower intensity compared with those activated at 10 and 15 M. High activator concentrations exhibited a proportional relationship for geopolymer ring growth, which resulted in a reduced structure mobility and, consequently, an increased viscosity and yield stress. The effects are more evident in the metakaolin samples, and are associated with the water content that is required for reaction. Samples that were activated with 10 M sodium hydroxide presented a favorable workability and particle packing, in terms of the rheological and structural aspects. (C) 2018 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.