GGBFS –silica fume blended cementitious composite for extrusion‐based 3D concrete printing

The utilization of supplementary cementitious materials (SCMs) to reduce the Portland‐cement fraction is of growing interest in 3D concrete printing. This study investigates the fresh‐state, rheological, printability, buildability, and mechanical performance of a GGBFS–silica fume blended cementitious composite developed for extrusion‐based 3D concrete printing (3DCP). The printable mixture comprised 472.5 kg/m 3 ordinary Portland cement, 182.5 kg/m 3 ground granulated blast‐furnace slag (GGBFS), and 75 kg/m 3 silica fume, with SCMs constituting 35.27% of the total binder. Fresh‐state characterization showed an initial flow diameter of 172 mm and a flow‐based practical open time of approximately 45 min. Stable extrusion was achieved with an average filament width of 21.2 mm and an extrudability index of 1.06. Rheological characterization using the Herschel–Bulkley model showed good agreement with the experimental data ( R 2 = 0.97), while penetration‐derived static yield stress increased from 0.48 to 3.21 kPa over 75 min, consistent with progressive time‐dependent structural build‐up under the adopted test arrangement. The mixture successfully produced a 50‐layer wall element without collapse, with a height deviation of 2.72% under the investigated printing conditions. After 28 days of curing, the printed composite achieved an average compressive strength of 41.8 MPa and an average flexural strength of 6.0 MPa, with modest numerical variation among the investigated loading orientations. The findings indicate that the selected formulation containing 35.27% supplementary cementitious materials exhibited continuous extrusion, successful 50‐layer wall fabrication, and the measured mechanical performance under the investigated printing conditions. The 35.27% SCM incorporation represents a reduction in the Portland‐cement fraction.