Linking Oscillatory Rheology and Buildability in Direct Ink Writing of Ceramic Pastes Containing Recycled Waste

The effect of replacing clay with recycled foundry waste (FW) namely ceramic shell mould waste (CSMW) foundry waste material on the rheological properties and printability of ceramic pastes for Direct Ink Writing (DIW) was investigated. To isolate the influence of structural stability from flow behaviour, the water content of each formulation was adjusted to achieve comparable shear-thinning characteristics. Structural stability was evaluated using oscillatory rheology through the parameters G′ and τ_LVR and validated by DIW printing experiments. Although all mixtures exhibited similar flow behaviour, significant differences in buildability were observed. A moderate waste addition (20 wt.%) resulted in a slight increase in G′ and improved paste processability, homogeneity, and printing reproducibility. In contrast, increasing waste content above 40 wt.% led to a progressive decrease in τ_LVR, reduced structural stability, lower stable printing heights, and increased susceptibility to deformation and collapse. The mixture containing the highest waste content could not be printed under the selected conditions. The results demonstrate that comparable flow behaviour does not necessarily ensure comparable buildability and identify τ_LVR as a practical indicator of structural stability and printing performance in ceramic DIW systems containing recycled materials.