Reducing the cement content in 3D concrete printing (3DCP) mixtures through porcelain polishing residue incorporation

The fresh-state requirements of 3D concrete printing (3DCP) often lead to high cement consumption. Polishing porcelain residue (PPR) is a fine material with pozzolanic activity, being a potential candidate for replacing cement in 3DCP. In this work, we produced 3DCP formulations with 0-40% replacement of cement with PPR; a commercially available 3DCP mixture was also assessed for comparison. Paste rheological tests demonstrated that PPR incorporation led to higher structural build-up rates ( A struct ), with the flocculation contribution ( A thix ) being dominant over the chemical contribution ( A chem ) for the highest PPR content. 3D printing tests showed that replacing cement with PPR did not affect the yield stress and buildability of the mixtures, while it progressively increased the A struct , allowing for a 135% higher layer deposition time. Replacing cement with PPR reduced the 28-day compressive strength of the 3D-printed elements by 11.4% (20% PPR) and 21.1% (40% PPR). Nonetheless, the CO 2 intensity index decreased from 15.4 kg CO 2-eq /m 3 .MPa (0% PPR) to 12.7 kg CO 2-eq /m 3 .MPa (40% PPR), matched values reported in the literature for conventional concrete. The 28-day flexural tests conducted in printed elements yielded strengths of 6.8-9.4 MPa, and SEM-EDS revealed a homogeneous distribution of the chemical elements across the bulk layer and joint region. • PPR replaced up to 40% of cement in 3DCP mixtures without impairing buildability or initial yield stress. • PPR incorporation increased structural build-up of 3DCP, enabling faster layer deposition and higher vertical printing productivity. • Cement replacement with PPR lowered the CO 2 intensity of 3DCP to values comparable with conventional concrete.