Title:
X-Ray Tomography and Impedance Spectroscopy to Elucidate Anisotropy in 3D Printed Concrete
Author(s):
Sahil Surehali
Publication:
Web Session
Volume:
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
11/3/2024
Abstract:
Extrusion-based 3D concrete printing (3DCP), in which printable cementitious materials are deposited as a continuous filament from a nozzle in a layer-wise manner, results in two different interfaces – the interfilament interface between the adjacent layers and the interlayer interface between the layers printed on the top. The printing parameters, including the layer height, width, and print velocity, dictate the number and quality of interfaces, rendering direction dependence on the mechanical and transport properties in 3D printed elements. In addition to interface quality and numbers, microstructure in the interfacial regions, including porosity content and pore morphology, present a physical basis for the anisotropic behavior. This work focuses on the impact of layer heights (6, 13, and 20 mm), test directions (along the direction of printing, along the direction of layer build-up, and in the direction perpendicular to the above two directions), and fiber-reinforcements on the compressive strengths and non-steady state chloride migration coefficients of 3D printed concretes. Interface-parallel cracking is found to be the primary failure mechanism under compression loading. The inter-filament interfaces are shown to be more detrimental from an ionic transport standpoint. A thorough investigation of the porosity parameters in the bulk and interface regions via mercury intrusion porosimetry and X-ray computed tomography, respectively, compiled with electrical impedance spectroscopy, indicates higher porosity at interfacial regions. Overall, the work provides guidelines on furthering the use of 3D-printed concrete elements via simple process changes (choosing appropriate layer height and print direction or appropriately orienting weaker interfaces) and material modifications (such as fiber reinforcement) for desired end applications.