Measuring the rheological properties of fresh building materials such as cement paste, mortar or concrete is a very challenging task. In contrast to many other substances, building materials consist of a very wide particle size distribution, with particles ranging from the sub-micron range to the double-digit millimeter range. In (standard) rheological measurements, this results in the formation of slippage layers and segregation, which spoil the rheological measurement. Further, concrete, mortar and paste are chemically highly reactive systems, which leads to sometime pronounced problems in carrying out rheological measurements on such systems.
Working Group Rheometry in SPP 2005 addresses these questions by investigating and comparing the different measurement techniques available for cementitious systems. In detail, WG Rheometry has the following goals:
A major achievement of the working group resulted in a paper dealing with an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The main goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using various rheometers and measurement geometries. The procedures for both in preparing the cement paste and performing the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.
Currently, a new test series on in-situ measurement techniques is being evaluated. Here, a focus is set on analytical studies of granulometry and chemical composition during rheological measurements. For this purpose, results of the Focused Beam Reflectance Measurement (FBRM), Electrosonic Amplitude (ESA), Rheomicroscopy, Rheo-Raman, Rheo-NMR and other measurement methods of cement suspensions are combined and correlated. The objective is to gain a deeper understanding of changes of the particulate state within a cement suspension during applied shear load.
Materials and Structures 53 (2020)