Rheology and printability control of low-carbon 3D-printed cementitious materials via circular use of recycled concrete powder

Although interest in incorporating recycled concrete powder (RCP) into 3D-printed concrete has increased, challenges in regulating the rheological properties continue to hinder printing accuracy and overall printability, limiting its practical and sustainable application. This study investigates the mix design of 3D-printed cementitious materials (CM) containing RCP and applies response surface methodology (RSM) to achieve precise rheological control, targeting controllable rheology and stable structural application. The results demonstrate that RCP significantly enhances the static yield stress and elastic modulus of the 3D-printed CM. Furthermore, a synergistic optimization, reducing the water-to-cement (W/C) ratio while adjusting the dosage of water-reducing agent (WRA), effectively regulates hydration kinetics, ultimately improves resistance to deformation during multi-layer deposition, and enhances stable structure formation. RSM analysis reveals critical interactions among variables, establishes a predictive model for printability optimization, and identifies optimal ranges: RCP content (15–25 %), W/C ratio (0.4–0.45 %), and WRA dosage (0–0.30 %). Importantly, the incorporation of RCP achieves dual benefits by reducing carbon emissions and cutting raw resource consumption. This approach enables a cleaner production pathway that converts solid waste into high-value construction materials and advances low-carbon 3D printing technology.