A Comprehensive Analysis of Buildability of 3D Printed Concrete and the Use of Bi-Linear Stress-Strain Criterion-Based Failure Curves Towards Their Prediction (2022-01)¶

The buildability of cementitious materials, along with its extrudability, determines the printability of the concrete mixtures used in 3D printing of concrete. Buildability, defined as the critical height to failure during printing, is a function of the material properties (time-dependent), filament dimensions, and print geometry. This study employs a novel approach to evaluate the buildability of 3D printed concrete using a combination of: (i) modified green compression test (GCT) carried out on cylinders extracted from 3D printed prisms (in lieu of cast cylinders) at different times from mixing to extract a bi-linear stress-strain response until the yield point, from which material properties are deduced, and (ii) models considering material failure (e.g., plastic collapse) or instability (e.g., buckling/crippling) that employ refined material parameters (elastic and initial plastic yield stresses and moduli) from GCT. Failure curves are developed for different 3D printable mortar mixtures using the lower bounds of failure heights at different times predicted by the different failure models. Laboratory-scale printing of wall and hollow cylinder elements showed that the models can adequately predict failure heights. The ability to accurately predict critical (failure) height enables enhanced control in optimizing the material design and printing process.