Size effect on flexural and fracture behaviors of 3D printed engineered cementitious composites: Experimental and numerical studies

One of major problems in 3D concrete printing (3DCP) is the integration of steel reinforcement. Engineered cementitious composites (ECC) with superior tensile properties have the potential to remove steel reinforcement in 3DCP. Interlayer interfaces may affect the size effect and fracture behaviors of printed ECC, which are important for structural design. Nevertheless, the related study is lacking. To fill the research gap, three-point bending test and finite element modeling (FEM) were conducted on printed ECC notched beams with depths from 60 mm to 500 mm. Results reveal that the printed ECC beams exhibit multiple fine cracks and display a branched critical crack. Size effect behavior is found in flexural strength, which decreases from 16.92 MPa to 10.89 MPa with the increase of depth from 60 mm to 500 mm. The fracture toughness ranges from 3.71 MPa·m^1/2 to 6.38 MPa·m^1/2, comparable to natural timber materials. Parametric analysis reveals that the flexural strength and fracture toughness of FEM model with a depth of 100 mm and bond strength higher than 2.5 MPa are similar to that of mold-cast ECC. The fracture toughness indicates the possibility to construct structural components with ECC in 3DCP, and the findings on size effect can facilitate the structural design.