Methodology for the design and optimization of potassium silicate-activated slag used as the binder of 3D printable materials

This study explores the development of potassium silicate-activated ground granulated blast furnace slag (GGBFS) as a binder for 3D printable construction materials. The initial mix design was guided by slump tests to meet basic printability requirements. To further define the workable time frame, which referred to as the printing window, ultrasonic pulse velocity (UPV) testing was employed to monitor the setting behavior of the mixtures in real time. To address key challenges such as rapid setting and poor extrudability, the study implemented targeted mix design optimizations. These included the incorporation of pure silica, adjustments to sand content and grading, and fine-tuning of water dosage during the final mixing phase. These strategies successfully extended the printing window and improved the rheological behavior of the fresh mixtures. The optimized printable mixtures achieved compressive strengths up to 100 MPa at 90 days and a limited shrinkage below 0.8% at 300 days. These findings offer practical insights into improving the printability and performance of alkali-activated slag (AAS) systems, supporting their potential as sustainable binders for 3D concrete printing.