Evaluation and optimization of 3D-printed concrete based on flowability considering printability and micro-pore characteristics

Flowability significantly impacts the performance of 3D printed concrete (3DPC). However, reconciling the conflicting demands of printability (extrudability and buildability) remains a challenge, and a comprehensive framework for quantitative evaluation and optimization remains underexplored. This study addresses the conflicting requirements of extrudability and buildability in 3DPC by developing two novel quantitative indices: the extrudability impact factor (D) and the buildability impact factor (I), both based on flowability measurements. A multi-objective optimization approach integrating the non-dominated sorting genetic algorithm (NSGA-II) and the analytic hierarchy process (AHP)-entropy method was employed to determine the ideal balance between these properties. The ideal solution on the Pareto frontier was further refined using the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS). Microstructural X-ray computed tomography (XCT) was further used to explore the impact of flowability on pore characteristics, including interlayer and intralayer porosity. Furthermore, a porosity impact factor (P) was proposed to quantify the microstructural characteristics of interlayer and intralayer pores, enabling the establishment of a cubic fitting curve between flowability and P. This curve served to correct the optimal flowability range determined by dual-objective optimization. The results showed that an optimal flowability range (175.8–180.4 mm) minimizes pore-related defects while ensuring high extrusion quality and structural stability. The proposed framework provides a robust, quantitative methodology for optimizing 3DPC material performance, offering theoretical and practical insights for advanced 3D printing applications. • Novel indices are introduced to evaluate extrudability and buildability. • A multi-objective optimization framework for printed concrete is employed. • The impact of flowability on the pore structure of printed concrete is analyzed. • The optimal flowability range of printed concrete is identified.