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Item Exploring the role of metakaolin in binary and ternary blended 3D printable mortars: deep insights into printability(Taylor and Francis Ltd., 2025) Mishra, S.K.; Upadhyay, B.; Das, B.B.This study investigates the utilisation of metakaolin and GGBS as partial replacements for OPC, examining their impact on printability, mechanical properties, microstructure and hydration kinetics in binary and ternary mortars. The printability of the mixes was thoroughly assessed through measurements of flowability, extrudability, open time, yield stress, shape retention, and buildability. It is observed that shape retention improved by 46% in the OPC–GGBS–metakaolin mix and 56.25% in the OPC–metakaolin mix, while the OPC–GGBS mix showed minimal improvement. Mechanical properties were evaluated, including water absorption, porosity, compressive, and flexural strength. Printed specimens exhibited anisotropic strength, with the lowest on the ZX plane and highest on the YZ plane. The 70% OPC, 20% GGBS, and 10% metakaolin mix demonstrated superior printability and mechanical performance, supported by optimal particle packing via the modified Andreasen and Andersen model. Furthermore, the denser microstructure observed in SEM micrographs, the decrease in Ca/Si ratio from EDX measurements, the emergence of additional C–S–H and C–A–S–H peaks in X-ray diffraction, the pronounced Si–O–Si/Al stretching bands in FTIR and the increased WH% (with consumption of CH) in TGA collectively confirm that GGBS and metakaolin significantly contributed to the secondary hydration reactions. © 2025 Informa UK Limited, trading as Taylor & Francis Group.Item 3D printing aspects of fly ash and GGBS admixed binary and ternary blended cementitious mortar(Taylor and Francis Ltd., 2025) Mishra, S.K.; Upadhyay, B.; Das, B.B.This study investigates the integration of Ground Granulated Blast Furnace Slag (GGBS) and fly ash to sustainably reduce the usage of Ordinary Portland Cement (OPC) in 3D printable mortar to enhance printability and engineering performance. Four mortar mixes were developed, and their printability parameters, such as flowability, extrudability, open time, yield stress, shape retention, and buildability, were assessed. Among mixes, O70G30 (70% OPC, 30% GGBS) showed the best printability, with an 18.3% and 54.3% higher shape retention factor than the control and O70F30 mixes, respectively, which can be attributed to improved particle packing and 5.5% higher yield stress. However, its open time was 22.2% lower than the control. This reduction can be attributed to the finer particle size and higher specific surface area of GGBS, which increased water demand and accelerated the loss of workability. In the hardened state, O70G30 exhibited 24% lower water absorption and 18.5% reduced permeable porosity than the control, indicating a denser microstructure. Printed specimens exhibited anisotropic strength, with the highest values observed on the YZ plane and the lowest on the ZX plane. Depending on the loading direction and mix composition, their compressive strength was 9.4–35.6% lower than that of mould-cast samples, while the flexural strength improved by 16.19% to 40.18%. Microstructural analysis revealed a denser matrix with a lower Ca/Si ratio and enhanced secondary hydration, evidenced by stronger C–S–H peaks in XRD, pronounced Si–O–Si/Al bands in FTIR, and 41.22% higher bound water (WH) with reduced portlandite (CH) in TGA compared to O70F30. These promising results can be attributed to GGBS’s role in enhancing hydration, refining the microstructure, and improving the performance of 3D printable mortar, offering a sustainable and effective pathway for digital construction. Also, the Life Cycle Impact Analysis (LCIA) revealed that the incorporation of supplementary cementitious materials (SCMs) significantly reduces environmental impacts compared to the control mix. © 2025 Informa UK Limited, trading as Taylor & Francis Group.