Composition and technological properties of geopolymers based on metakaolin and red mud.

New geopolymer formulations were designed by sodium silicate/NaOH activation of metakaolin, iron oxide and red mud mixtures. The effects of source materials on the microstructure and mechanical properties were studied. Each formulation induces different degree of geopolymerization reaction as reflected by the phase composition where the amorphous phase is predominant. These vestiges are related to silica provided by sodium silicate more reactive in the geopolymerization than the silica of metakaolin. Moreover, the variation in strength between the geopolymers is attributed to the same factors, with higher porosity and nonreacted phases found in the red mud based geopolymer matrix. In function of curing time, the mechanical strength increased from day 1 to 28 for the samples with a low amount of red mud. In these two cases, longer curing time improves the geopolymerization state resulting in higher compressive load. The metakaolin and metakaolin/red mud products exhibited comparable water absorption and density.