Influence of supplementary cementitious materials on rheological properties of 3D printed fly ash based geopolymer

3D printed fly ash based geopolymer was prepared with fly ash and quartz sand as main raw materials while slag powder and silica fume as supplementary cementitious materials. In this paper, anhydrous sodium silicate powder was used as activator and ATTAGEL-50 thixotropic thickener was used as 3D printing additive. The effect of slag powder and silica fume on the rheological properties of 3D printed fly ash based geopolymer was studied. The results show that the apparent viscosity, thixotropic property, plastic viscosity and yield stress of geopolymer first increased and then decreased with the increase of slag powder and silica fume respectively. Compared with the Bingham (BH) model, the Herschel-Bulkley (H-B) model is more accurate and more suitable for characterizing the rheological model of fly ash based 3D printed geopolymer. The suitable content for slag powder is 10%. On the basis of adding slag powder, silica fume was also used to replace the fly ash, the suitable content for silica fume is 10% in this fly ash-slag powder based 3D printing geopolymer. According to the SEM observations, it is found that the interior of the printing layer of the 3D printing block is more conducive to the production of the geopolymer gel than the interlaminar surface of the printing layers. It is found that the printing layers are connected with each other through bridges.