Optimization of Fast Penetration Tests for Rheology Control in 3D Printing Concrete

3D printing concrete must meet demanding requirements in terms of its rheology, which also needs to evolve to adapt to each stage of the printing process. As a result, a thorough control of the rheology during printing is essential for its success. However, the rheological characteristics of 3D-printed con-crete (particularly its yield stress) differ significantly from those displayed by conventional ones. Thus, conventional laboratory tools are generally not suitable for the measurement range required by 3D-printed concretes. Also, for a test method to be applicable for the monitoring of 3D printing, extra requirements must be met, such as being fast, simple and with little sample preparation.
This work presents the use of fast penetration tests as a simple method for in situ control of the yield stress of 3D-printed concrete. The study is initially focused on the identification of parameters that may affect the robustness and repeatability of the test for various penetration probe geometries. For this purpose, several tests were carried out on non-aging pure plastic materials (i.e. clays) using penetration probes of different geometries and sizes and varying the test conditions (penetration speed, user and sample shape). The results indicate that the robustness and dispersion of the results are closely related to the geometry of the penetration probe. In that sense, probe geometries that minimize the user dependence and present an adequate size compared to the sample and aggregate size provided optimal results. The clays were tested by additional methods (squeeze test and pocket vane) to obtain equivalence between penetration forces and yield stress. Finally, the method feasibility was tested on 3D printed samples and compared with the results obtained by pocket vane tests.