Development and Optimisation of a Standardised Rheological Method for 3D Printing Cementitious Mixtures Using Rotational Rheometry: An Experimental and Statistical Approach

This study presents the development and optimisation of a standardised rheological test method based on rotational rheometry for the characterisation of cementitious mixtures designed for 3D printing. Tests were performed using a Discovery HR-20 rotational rheometer (TA Instruments, New Castle, DE, USA) equipped with a concentric-cylinder cup-and-paddle geometry. A high-early-strength Portland cement (ASTM C1157 Type HE) with a constant water-to-cement ratio (w/c) of 0.35 was employed. The methodological framework comprised five sequential stages: (i) assessment of the pre-conditioning effect; (ii) standardisation of the static shear test; (iii) optimisation of pre-conditioning parameters; (iv) standardisation of the dynamic shear test; and (v) evaluation of the influence of sample volume. Optimal conditions were determined as follows: for pre-conditioning, a shear rate of 50 s−1, holding time (Ht) of 30 s, and rest period of 180 s; for the static shear test, a shear rate range of 0.05–0.10 s−1 with a Ht of 60 s; for the dynamic shear test, a 30 s ramp up/down, maximum shear rate of 100 s−1, and Ht of 90 s. An optimal sample volume ranging between 150 and 175 mL was established. The proposed method represents a robust and reproducible experimental protocol for evaluating, comparing, and optimising the rheological behaviour of cementitious mixtures using rotational rheometry, providing a reliable tool for the formulation of mixtures tailored to additive manufacturing or 3D printing processes.