Nozzle-Integrated Slump Scanner Test : Development of an Automated Shape Stability and Instantaneous Yield Stress Measurement Method for the Set-on-demand 3D Concrete Printing

In the process of set-on-demand 3D Concrete Printing (3DCP) construction, maintaining consistent extrusion quality and ensuring that the extruded concrete layers possess sufficient yield stress to support their self-weight is critical. This shape retention capability is a fundamental requirement for the stability of the printed geometry and adherence to the intended print design. Prevalent methods for assessing the shape stability of stiff printed layers, such as comparing the shape of extruded layer with the dimensions of the nozzle, may have limited applicability for the set-on-demand mixtures. With the advancing research and growing interest in 3DCP for set-on-demand mixtures, there is an increasing demand for swift, inline, automated testing methods to assess extruded concrete’s quality, yield stress and shape stability in real-time. In this context, the globally recognized slump test, a standard test for evaluating concrete’s shape retention under self-weight, offers a promising foundation. Leveraging the concrete industry’s familiarity with this test and its well-established correlations with concrete rheology, this study introduces a novel testing system based on the slump test. This system utilizes a customized nozzle to extrude concrete into layers that mimic the geometry of concrete specimens used in the slump test. This study uses depth sensors for generating 3D images of the concrete slump flow and calculates the instantaneous yield stress. The developed system’s performance is validated though real-time printing and monitoring of the slump and shape stability of the concrete printed layers. The developed test is an economical, inline, and automated quality control system.