Comparison of Rheology Measurement Techniques Used in 3D Concrete Printing Applications

Abstract

3D Concrete Printing (3DCP) is a novel and emerging construction technique to build using digital technologies and additive manufacturing concepts. Some main advantages of 3DCP are reduced formwork wastage, the capability of constructing complex geometric shapes, higher precision, shorter construction time and increased safety. In the particular method, the structure is built layer by layer by extruding the material through a nozzle. Initially, the material should be pumped and extruded with considerable fluidity and workability. Immediately after the extrusion, the extruded layers should have enough strength and stiffness to retain the desired shape. Therefore, controlling the rheology of the material is of high importance in 3DCP. Due to the higher stiffness, and higher time and rate-dependent material behavior (thixotropic behavior) compared to the conventional concrete, conventional rheology measurement techniques have many limitations when used for 3DCP material. Therefore, non-conventional (direct shear test, orifice extrusion, vane shear test), as well as conventional rheology measurement techniques (rotational rheometer and slump test), were conducted to compare the results and to characterize the rheological parameters. The rheological parameters (i.e. yield stress, viscosity, and thixotropic build rate) of concrete were measured for three different mixes. The achieved values were compared to decide the most suitable and reliable test method. The pros and cons of each test method also were discussed. The achieved yield stress values are different according to the test method used. However, a similar trend can be seen in all the testing methods. Rotational rheometer gives the lowest yield stress values, while an orifice extrusion test gives the highest yield stress values. Finally, it can be predicted that the extrusion-based testing methods such as orifice extrusion technique used in the current study give reliable results on yield stress and viscosity measurements due to the similarities between the measurement technique and the actual 3D printing extrusion process.