Quantifying Constructability Performance of 3D Concrete Printing via Rheology-Based Analytical Models

Abstract

3D printing of concrete (3DPC) is a developing automation technology that can promote further industrialisation in the construction industry. 3DPC has complex rheological requirements, namely low material viscosity for ease of pumping but high viscosity for constructability. Greater emphasis is therefore placed on the rheology of cement-based composites used for 3DPC compared to conventional construction techniques. Thixotropic materials demonstrate the material performance required for 3DPC. This research presents the work of Kruger et al., who developed a bi-linear thixotropy model [1] specifically for 3DPC materials. This model demonstrates the degree of thixotropy of a material and the static yield shear stress evolution after it has been extruded. A buildability model [2] predicts the maximum number of filament/printing layers achievable, which is based on the bi-linear thixotropy model. Lastly, a rheology-based filament shape retention model [3] determines the maximum height of a filament layer where no plastic yielding at a material point will occur. The three aforementioned models are applied in this research in order to quantify the constructability of 3DPC by only conducting rheology tests and no mechanical tests. A circular hollow column is 3D printed that validates the models presented in this research. The buildability model predicted 52 filament layers whereas 54 layers were obtained experimentally before failure, yielding a conservative 3DPC construction height prediction of 3.7%.