Unveiling fibre alignment in 3D-printed FRCC using particle cleansing considering combined effects of nozzle size, fibre length, and volume fraction

Fibre alignment strongly influences the mechanical behaviour of 3D-printed fibre-reinforced cementitious composites (FRCC). However, conventional characterisation methods such as μCT, BSE imaging, and mechanical testing require long preparation time and cannot support rapid evaluation. This study proposes a particle cleansing method that enables fibre orientation to be assessed within approximately 1 h. By dissolving the fresh cementitious matrix using an ethanol–water solution at a flow rate of 50 mL/min, fibre networks were exposed with minimal disturbance and captured. The method successfully differentiated randomly distributed fibres in mould-cast FRCC samples (average angle at 45.8°) from aligned fibres in 3D-printed FRCC samples (average angle at 11.1°). Furthermore, the combined effects of fibre volume fraction and length on fibre alignment under nozzle extrusion were investigated. Specifically, under the constraint of a narrower nozzle, higher fibre volume fractions (up to 2.0%) and increased fibre lengths (up to 18 mm) collectively enhanced fibre alignment along the extrusion direction, which potentially contributed to the improvements in ultimate tensile strength and strain capacity. This study not only provides a fast and practical tool for fresh-state fibre orientation characterisation but also offers novel mechanistic insights into enhancing fibre alignment in 3D-printed FRCC.HighlightsNovel particle cleansing rapidly assesses fibre alignment in 3D-printed FRCC.Cleansing results are highly consistent with cross-sectional BSE imaging analysis.Higher fibre volume fractions significantly enhance fibre alignment during extrusion.Extending fibre length also yields superior alignment along the printing direction.Narrower nozzles amplify combined fibre alignment driven by fibre length and dosage.