Rheology‐driven material design of sustainable cementitious composites for extrusion‐based additive manufacturing via particle packing optimization

The development of extrusion‐based cementitious materials for additive manufacturing requires precise control of rheological behavior and particle‐scale interactions governing flow and structural build‐up. This study investigates the role of particle packing and supplementary cementitious material (SCM) distribution on the rheological and mechanical response of sustainable cementitious composites incorporating recycled fine aggregate (RFA). A particle packing approach based on the Elkem Material Mixture Analyzer (EMMA) was employed to design a dense granular skeleton, enabling systematic variation of binder composition within a constrained packing domain. The effects of SCMs (fly ash, silica fume, and ground granulated blast‐furnace slag) and RFA content on flowability, yield stress evolution, and thixotropic behavior were evaluated through rheological characterization and extrusion‐based printability assessment. Results indicate that optimized particle packing significantly enhances shear‐thinning behavior and promotes rapid structural build‐up after deposition, enabling stable filament formation and multi‐layer stacking. The incorporation of SCMs modifies interparticle interactions and paste rheology, contributing to improved cohesion and reduced segregation tendency. The optimized composite exhibited a balanced response, achieving controlled flow (165 mm slump), stable extrusion, and sustained layer deposition, while maintaining a compressive strength of 39.8 MPa and flexural strength of 5.72 MPa at 28 days. The findings demonstrate that particle‐scale material design governs the coupling between rheological response and structural performance in extrusion‐based cementitious systems. This study provides insight into the fundamental role of packing density and binder composition in tailoring sustainable materials for additive manufacturing applications.