Anisotropic chloride transport in 3D printed concrete and its dependence on layer height and interface types

Layered concrete systems, such as those obtained using 3D printing, demonstrates inter-layer and inter-filament defects, which influence transport of moisture and ionic species through the structural element, thus impacting its durability. The printing parameters, including the layer height and width, and printing rate, dictates the number and quality of the interfaces, rendering a directional dependence to the transport of moisture and deleterious ions. This work focuses on the impact of layer heights (6, 13, and 20 mm) and transport directions (along the direction of printing, along the direction of layer build-up, and in the direction perpendicular to the above two directions), on the non-steady state chloride migration coefficients (D_nssm) of 3D printed concretes. The direction-dependent D_nssm values of the printed samples are 10–30% higher than those of companion cast samples. Interrogation of the microstructure of the printed samples through porosity and electrical conductivity, along with the transport quantification, establishes the influence of anisotropy on the transport properties. The inter-filament interfaces are shown to be more detrimental from an ionic transport standpoint, thereby providing guidelines on choosing the printing direction with respect to the direction of ionic ingress.