Evaluation of printing performance of cementitious pastes with alternative powders

The adoption of 3D concrete printing presents a promising pathway toward automation and sustainability in the construction industry. However, the high dependence on Portland cement in 3D printable materials raises environmental concerns. This study investigates the fresh-state behaviour, specifically extrudability and buildability, of cementitious pastes for 3D printable compositions, where Portland cement was replaced by alternative powders, including supplementary cementitious materials and powders derived from industrial and construction waste. Through flow table and 3D printing tests, this research evaluates pastes made with different Portland cements and powders. Each paste was tested in a range of water-to-powder ratios, from the minimum required for extrusion through the nozzle to the point where the excessive water causes the printed layers to collapse. Materials tested include limestone filler, quartz powder, metakaolin, silica fume, fly ash, waste marble, granite and slate powder, clay brick powder, bottom ashes from municipal incineration and sugarcane bagasse ashes. The results reveal that metakaolin provided the best balance between extrudability and buildability, while some waste-derived powders, such as marble powder, showed poor performance, highlighting the good performance of slate powder. The findings underscore the need for tailored mix design strategies and particle refinement to optimise 3D concrete printing mixtures for sustainability and performance. The study demonstrated that flow table tests alone are insufficient to determine a material's suitability for 3D concrete printing, they must be complemented by extrusion tests to fully assess its 3D printing performance. • Metakaolin provided the most favourable balance of extrudability and buildability. • Flow table tests alone did not reliably predict 3D printability performance. • A practical printability window was defined using extrusion and deformation metrics. • Some waste powders (e.g., slate, clay brick) showed promising printability potential. • Particle characteristics and w/p ratio critically influenced fresh-state behaviour.