Comparative analysis of 3D printing of Portland cement mortars with hydroxypropyl methylcellulose and microfibrillated cellulose as viscosity modifying agents

[Display omitted] •Portland cement mortars containing microfibrillated cellulose or hydroxypropyl methylcellulose exhibit good extrudability and printability.•Adding microfibrillated cellulose to Portland cement increases the viscosity more than hydroxypropyl methylcellulose.•3D-printed mortars exhibit better shape stability with microfibrillated cellulose than with hydroxypropyl methylcellulose.•3D-printed mortars have lower mechanical strength than cast mortars due to a more porous structure. The most used viscosity-modifying agents (VMAs) in 3D concrete printing (3DCP) are typically in powder form, which may pose challenges in dispersion and handling due to their low concentration and dust generation. This study explores the viability of using microfibrillated cellulose (MFC) in suspension and paste forms as a VMA in 3D-printable Portland cement mortars. The performance of these developed mortars was compared to a cement mortar containing hydroxypropyl methylcellulose (HPMC) in powder form. The mortars containing MFC in suspension and paste forms showed slightly higher workability, mechanical strength, and denser microstructure than those with HPMC. The MFC samples showed a higher viscosity and yield stress than the ones containing HPMC. A large-scale concrete 3D printer was used for the printability test. The HPMC mortars showed slightly superior extrudability and printability; however, the shape stability was inferior to that of the MFC mortars. The compressive strength of the 3D-printed samples was 40% lower compressive strength than the mold-cast samples; however, the flexural strength was comparable. Overall, the MFC in paste form outperformed the other VMAs studied here, providing better shape stability, while maintaining acceptable printability.