Title: Buildability, Rheological Properties, and Early-age Deformations of 3D-Printed Cement-based Materials

Author(s): Mohamadreza Moini

Publication: Web Session

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Date: 3/28/2021

Abstract:
Ability to extrude and to achieve shape stability of layer-wise additively manufactured cement-based elements depends upon the early-age rheological properties (shear moduli, yield stress, viscosity) of the deposited materials. Upon successful extrusion, buildability challenges can originate from two common failure mechanisms: yielding of the material in lower layers and buckling of the element. However, it is yet unclear which among various rheological properties controls the early-age materials’ deformation during printing processes and thus contributes to the resulting buildability of the elements. This presentation focuses on how buildability is dependent upon rheological properties as well on predicting the buildability using a buckling theoretical framework. Specifically, the relationship between early age rheological properties of various cement pastes and the buildability of hollow cylinders dominated by buckling failure mechanism was investigated. It was found that certain shear moduli of the fresh pastes (G, G*, and G’) obtained from oscillatory shear stress sweep tests performed within the first 30 minutes after combining water and cement showed better correlation with buildability of hollow elements than some other rheological properties (i.e., loss modulus G”, yield stress s yield , yield strain yield, and complex viscosity ?*). Measured shear modulus (G) was used to calculate elastic modulus (E) of the pastes using the assumed value of the 0.5 for Poisson’s ratio () for fresh cement paste. Euler’s buckling theory was used to predict buildability (i.e., ultimate height) of hollow cylinders. It was found that Euler’s theory overestimates the buildability from 93% to 194%, mainly due to assumption of ideal geometry (i.e., no initial or printing imperfections) and linear elasticity. An isosceles triangle was also developed and used as a support structure for assessment of early-age deformation of individual cement paste filaments over varied.