In-line rheology of cement grouts - Feasibility study of an ultrasound based non-invasive method

Abstract: Grouting is used in underground construction to reduce the water flow into tunnels and caverns and to limit the lowering of the surrounding groundwater table. Due to their wide availability and low cost relative to other materials, cement based materials are commonly used as grouts and, in this context, the rheology of the cement grout is an important factor. Rheological properties of cement grout such as viscosity and yield stress are commonly measured off-line using laboratory instruments, and some simple tools are available to make field measurements. However, these methods often lack accuracy and reliability. Although the rheological properties of the grout used play a fundamental role in design and execution, no method has yet been developed to measure these properties in-line in field work. In this work, for the first time, an in-line rheometry method combining the Ultrasound Velocity Profiling (UVP) technique with Pressure Difference (PD) measurements, known as “UVP+PD”, was successfully tested for continuous in-line measurements of concentrated micro cement based grouts. The feasibility of using the UVP+PD method depends on the in-line determination of the rheological properties and time dependent behaviour of the cement grouts. A test set-up consisting of a combination of an experimental “flow loop” and a conventional field grouting rig – UNIGROUT E22H – from AtlasCopco, was used to investigate the feasibility of determining the rheological properties of cement grout using the UVP+PD method under field conditions. A laboratory based test set-up was used to further investigate the rheological properties in a more controlled environment. The velocity profiles were measured directly in-line. The shape of the velocity profiles was visualized, and the change in the shape of the profiles with concentration and time was observed. The viscosity and yield stress of the grout were determined using rheological models, e.g. Bingham and Herschel-Bulkley. In addition, rheological properties were determined using the non-model approach (gradient method) and the tube viscometry concept and were compared with results obtained using the rheological models. In addition, the obtained rheological properties were subsequently compared with off-line measurements using a conventional rotational rheometer.  The UVP+PD method was found to be capable of determining the true rheological behavior of cement grout regardless of the rheological model, providing the opportunity to visualize the change in the shape of the velocity profiles. Furthermore, it was possible to make an accurate determination of the velocity by ultrasound velocity profiling at a very flow rate (i.e. 1liter/min). The ultrasound velocity profiling was also found to be a reliable tool for determining the characteristics of the grout pump. In conclusion, the UVP+PD method was demonstrated to be a promising new in-line tool for determining the rheological properties of commonly used cement based grouts and the changes with concentration and time.