Rheometry for Concrete 3D Printing: A Review and an Experimental Comparison

The rapid advancement of 3D concrete printing (3DCP) and the development of relevant cementitious material compositions can be seen in the last few decades. The commonly used 3DCP method is to build the structure layer by layer after extruding the material through a nozzle. Initially, the pumping and extrusion of the material should be done with considerable fluidity and workability. The extruded layers should retain their shape immediately after extruding and depositing. While constructing the structure in a layerwise manner, the bottom layers should have enough early age strength to support the layers at the top. Therefore, at different processes in 3DCP, the rheological requirement is contradictory. As the rheology of the material is the deterministic factor which decides the fluidity or workability of the mix, proper rheological characterization should be completed accurately. In some instances, due to the higher stiffness, and higher time and rate-dependent material behavior (thixotropic behavior) compared to the conventional concrete, standard rheology measurement techniques have many limitations when used for 3DCP material. Therefore, non-conventional and novel techniques can be implemented with suitable material models to characterize the rheology of 3DCP material. In this study, a comprehensive review was conducted on conventional and non-conventional methods used for characterizing the rheological parameters for 3DCP material. The previously conducted studies were highlighted with the targeted 3DCP processes in the study (if applicable), and rheological parameters achieved from the test (i.e., yield stress, viscosity, and thixotropy). In addition, some experimental studies were conducted to compare several selected testing methods. The rheological parameters achieved from different test methods were compared to identify the similarities, dissimilarities, pros, and cons between the test methods. Furthermore, the extrudability and buildability studies were conducted for the mixes to demonstrate the usage of the mixes in 3DCP applications and to correlate the achieved rheological parameters with these processes.

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