WFT-based assessment of the rheological characteristics, particle packing, and buildability of Pcc-FA-GGBFS composite materials for 3D printing

The extrudability and constructability of fresh cement paste were investigated after Portland cement clinker (Pcc) was changed with industrial solid waste fly ash (FA) and granulated blast furnace slag (GGBFS) to adjust the water film thickness (WFT) and rheological characteristics of cement slurry. The effects of FA/GGBFS on the bulk density and WFT of clinker-based composites were basically the same. Compared with GGBFS, FA had a stronger and more obvious effect on bulk density and WFT. The addition of appropriate amounts of FA /GGBFS enhanced the particle packing density and WFT of the slurry, enhancing its fluidity and rheology. The larger the WFT was, the lower the apparent viscosity of the slurry, and the shear stress increased with increasing shear rate. When the FA concentration was 20 %, the slurry's bulk density and WFT achieved their maximum values of 0.757 and 0.742 μm, respectively. Compared with the blank sample, the bulk density and WFT increased by 0.93 % and 0.6 %, respectively. The sample of the slurry was used to print 10 layers, the height of each layer is 9.9 mm, and the extrusion length reached a maximum of 140 mm. SEM examination revealed that the hydration products were predominantly C-S-H, CH, and ettringite. The amount of hydration products increased when the oxidation time was increased. The free water and WFT in the slurry were the key factors affecting the hydration rate and heat release. It enables the use of industrial solid waste FA and GGBFS in the field of 3D printing construction.