Rheological and Fresh-State Characterization for 3D-Printable Concrete: Evaluating Printability across Different Binder Systems

This study establishes rheological criteria to achieve optimal printability for concrete mixes incorporating various binder systems. The mixtures were evaluated based on critical design parameters for three-dimensional (3D) concrete printing, including pumpability, extrudability, buildability, and open time. The objective of the study is to define desired performance parameters with acceptable limits, such as flow spread value, flow retention, open time, and both static and dynamic yield stress measurements (including their evolution over time) and phase separation assessment. Fresh-state and rheological characterization studies were conducted on mixes with various supplementary cementitious materials (SCMs) including fly ash (FA), slag, limestone calcined clay (LC), alkali-activated materials, and calcium sulfoaluminate–based systems. Findings indicated that initial performance parameters defining printability, such as initial static and initial dynamic yield stresses, remain unaffected by the reactivity of binder systems. On the other hand, the static structuration rate is dependent on reactivity of binder systems, unlike the dynamic structuration rate. The study also showed that the range of desirable rheological properties for 3D-printable concrete include an initial flow spread of 165 to 180 mm, an initial static yield stress within the range of 1.5 to 1.8 kPa, and an initial dynamic yield stress falling between 0.4 and 0.5 kPa, independent of binder type.