Rheological Properties Analysis of Recycled Powder‐Modified 3D Printing Mortar

ABSTRACT Recycled concrete powder can substitute for part of the cement in 3D‐printable mortar, but the accompanying changes in fresh‐state resistance must be assessed together with deposition behavior and hardened performance. Mortar containing fully recycled fine aggregate and recycled powder (RP) was investigated. Cement was replaced by RP at 0%–50% by mass, with a nominal net‐water‐to‐total‐powder ratio of 0.42 and a fixed additional water dose for recycled fine aggregate. This batching ratio does not imply constant free‐water availability because RP water demand was not independently measured. Static and dynamic yield responses, plastic viscosity, shear‐history‐dependent hysteresis, and five‐layer deposition were examined over 0%–50%; compressive response and reported CT pore fractions were assessed over 0%–30%. From 0% to 50% RP, the reported equivalent dynamic yield stress increased from 434.16 to 825.65 Pa (+90.2%) and plastic viscosity increased from 8.52 to 18.41 Pa·s (+116.1%). Peak compressive stress decreased from 13.187 to 8.452 MPa at 30% RP (−35.9%), while the segmented CT pore‐volume fraction increased from 9.19% to 20.14% in the examined specimens. Representative CT images at 0% and 20% RP indicated more clustered pore features at 20%. These associations are consistent with combined cement dilution, changing water availability, and deposition‐related defect retention; their individual contributions were not isolated. The empirical relations describe the investigated mixtures and do not establish recovery kinetics, pore connectivity, interlayer strength, or a universal printing threshold. At 30% replacement, 185.63 kg/m 3 of cement was displaced, demonstrating a resource‐substitution benefit that must be balanced against the measured strength loss.