Steel fibres reinforced 3D printed concrete: Influence of fibre sizes on mechanical performance

Mechanical properties of high-performance printing concrete reinforced with steel fibres with different lengths (3 and 6 mm) at different fibre volume contents (0.25%, 0.5%, 0.75% and 1%) are investigated. The experimental results substantiate that critical length and volume fraction of fibres, particularly 0.75% and 1% steel fibres of 6 mm length, in conjunction with fibre alignment, are of major importance for generating fibre bridging mechanism to improve flexural performance. As a result, enhanced load-carrying capacity, deflection hardening behaviour and less brittle failure can be achieved in printed specimens tested in a specific direction. Compressive and flexural strengths of printed concrete are in a range of 70-111 MPa and 6-15 MPa compared with the cast control of 90-113 MPa and 11-14 MPa, respectively. Results from micro-computed tomography scanning on hardened concrete without fibres reveal that the high-quality printed concrete has lower pore content, which is 8.8% compared with 9.8% and 11.4% in the cast and low-quality printed samples, respectively. It also shows that more than 90% of extruded fibres align within 0 degrees-30 degrees from the filament orientation. (C) 2020 Elsevier Ltd. All rights reserved.