Influence of Test-Protocol on Determining the Rheological Properties of Cement-Pastes-Mixtures for Concrete 3D Printing (2023-03)¶

The rheology of cement paste plays a decisive role in the buildability, extrudability, and pumpability of 3D printable concrete. In the context of the same, this research examines the effect of the test protocol on the rheological properties of cement paste. The experimental studies are conducted on cementitious paste with a w/c ratio of 0.30. Three testing protocols of triangular, trapezoidal, and step up – step down procedures are evaluated under shear rates of 50 and 100 s-1. The yield stress and plastic viscosity are further predicted with Hershel-Bulkley, Modified Bingham, and Bingham models. It is found that the yield stress, flow, and consistency index are highly dependent on the selection of rheology protocol. The yield stress increases with the rise of the shear rate. The hysteresis area is maximum for a step up - step down protocol followed by a triangle and trapezoidal protocols. The hysteresis area at a shear rate of 100 s1 is 24.36%, 14.64%, and 68.12%, higher than tests conducted at a shear rate of 50 s1 for test protocols of the triangle, trapezoidal, and step up - step down, respectively. The repeatability and reproducibility of prediction using the Hershel-Buckley model are better compared to other models.