Comparison between yield stress measurements for fiber-reinforced 3D concrete printing

Advancements achieved in the field of 3D concrete printing (3DCP) have required a more detailed understanding of its rheological behavior during the manufacturing process. Development and validation of new control techniques are essential to enable the extensive use of 3DCP. Yield stress of concrete is quite important in the 3D printing process as it is directly linked to the buildability performance, as well as it is also related to its structural integrity over time. Incorporation of microfibers is a popular strategy to enhance the mechanical performance of the material, reducing autogenous shrinkage, and, thus affecting its rheological properties. This study assessed the yield stress of fiber-reinforced 3DCP through rotational rheometry, slug tests, and buildability tests. Additionally, flow tests were performed. Concrete mixtures with different types (rock and steel) and percentages (0%, 0.5%, and 1.0%) of microfibers were evaluated. Results demonstrated an increase in the material’s yield stress proportional to the increase in fiber content. When comparing the two types of fiber, rock wool had a greater impact on the yield stress due to its higher surface adhesion compared to steel wool.