Challenges in Rheological Characterization of Cement Pastes using a Parallel-Plates Geometry

Cement-based materials are characterized as complex suspensions that may experience a thixotropic behavior caused by physical and chemical phenomena. The characterization and understanding of the rheological properties of cement-based materials have become essential with the introduction of 3D printing in field of civil engineering. Therefore, there is a need to accurately measure such properties to obtain repeatable and consistent results. To measure the rheological properties, different geometries are available, such as vane, parallel-plates, or coaxial cylinders: These are the most used for cement-based materials. Although, there are no specific guidelines on how to select the appropriate geometry for the material that will be tested. Proper understanding of the advantages and disadvantages as well as the limitations of each geometry should be taken into account. Since parallel-plates is a common tool used to evaluate fresh cement-based materials, due to its simplicity, the small sample volume required and the variable gap that can simulate the distance between the aggregates. This paper discusses the major challenges and issues encountered when using parallel-plates geometry to measure the rheological properties of cement-based suspensions under shear. Some issues such as wall slip, sample spill, dryness, particles sedimentation, non-uniform shear rate applied, etc. can be prevented but the user should be aware of these problems