A new methodology for characterizing segregation of cement grouts during rheological tests

• A new methodology for characterizing the segregation of cement grouts under shearing is proposed.
• The segregated grout presents particular rheological behavior which is not observed in case of stable grout.
• The reliability of rheological testing of grouts can be verified.

This work proposes a new methodology for characterizing the segregation of cement grouts under shearing during rheological tests. This methodology uses a rotational rheometer with coaxial-cylinder geometry (Couette type) and a specific protocol composed of two shearing cycles with various steps of shear rate and two values of bottom gap. Density measurement of the upper and the lower part of the grout’s sheared volume in the rheometer were carried out at different characteristic times of the protocol and compared with rheological behavior of grout during shearing. The methodology was validated on (i) a stable grout with low water/cement ratio, (ii) an unstable grout with high water/cement ratio and high amount of superplasticizer. It has been shown that the segregation of the unstable grout, characterized by the density decreasing in the upper part of the sheared volume, leads to a characteristic rheological behavior depending on the bottom gap of the rheometer and the shear rate. This specific rheological behavior is not observed in the case of stable grout or when viscosity modifying agent was added for stabilizing unstable grout.