Inter-Layer Bonding Strength and Pore Characteristics of 3D Printed Engineered Cementitious Composites (2024-01)¶

Engineered cementitious composites (ECC) have emerged as promising materials for 3D printed concrete. This study delves into the vertical interlayer bonding properties of layer-by-layer 3D printed ECC. Techniques such as X-ray computed tomography (X-CT) and scanning electron microscopy (SEM) were employed to examine the pore characteristics and micromorphology. Furthermore, the influences of various printing and material parameters, including single-layer printing height, recycled fine aggregate replacement ratio, and fiber volume fraction, were analyzed. The findings indicate that as the fiber volume fraction and single-layer printing height increased, the bonding strength of vertical interlayer interfaces first rose and then declined. Differently, the bonding strength of these interfaces was inversely related to the replacement ratio of recycled fine aggregate. Moreover, the matrix and interfacial pores in 3D printed ECC have the shape of flattened ellipsoids, and an increase in printing height contributed to a notable improvement in sphericity. The thickness of the interlayer interface reflects the development of interlayer bonding strength to some extent. A thinner interface region reduced interlayer interface porosity and was beneficial for the adhesive properties of interlayer hydration products. The study evidences that the characteristics of interlayer pores, influenced by different printing and material parameters, play a pivotal role in interlayer bonding capability, which is important for quality control in 3D printed concrete.