3D printing of cementitious mortar with milled recycled carbon fibres: Influences of filament offset on mechanical properties

This study investigates the effects of layer offset on the mechanical strengths of 3D-printed mortar containing milled recycled carbon fibres (rCF). Compared to previous works, the printing scale of carbon-fibre reinforced mortar is increased to move closer to the stage of practical engineering application. For different fibre content, 1.5 vol% is recommended as the optimum fibre dosage for the mortar printing. Three degrees of layer offset are designed for the unidirectional printing pattern, including 0%, 25% and 50% of the filament width as the nozzle drifting distance. X-ray micro-computed tomography analysis demonstrates the internal pore structures in printed specimens consist of channel pores between filaments and micro pores within filaments. The channel pores are generally less geometrically regular than micro pores. Increasing the offset degree leads to improved compressive and flexural strengths along different loading directions. The increase in the compressive strength is more substantial along the direction of layer deposition and lateral expansion compared to the printing direction. Printed specimens with 25% and 50% layer offset also exhibit a much lower level of anisotropy in compression than those without offset. As the degree of layer offset rises, the total porosity decreases and the volume percentage of micro pores in total pores increases, thereby rendering less severe stress concentration around defects and strengthening the mechanical performance of printed specimens. The experiment results show the 3D-printed mortar containing milled rCF with layer offset, normally serving for self-sensing purpose, has the potential to achieve decent mechanical properties for large-scale industrial printing.