Experimental Developments of the Squeeze Flow Test for Mortars

Squeeze flow rheological technique is based on the compression of a cylindrical sample between parallel plates and is used to determine the flow properties of food, pharmaceuticals, composites, suspensions, including cementitious materials. This work summarizes the main experimental developments on squeeze-flow for the evaluation of mortars that have been performed in Brazil for the last 15 years and supported the creation of the Brazilian standard test method applied to rendering and masonry mortars (ABNT NBR 15839:2010). The paper exemplifies possible test setups (configuration, geometry, velocity, roughness) for different types of mortars and situations, the use of porous substrate (ceramic or concrete blocks) as the bottom plate, and a method to measure phase separation induced by the. A complementary instrumentation (interfacial pressure mapping) for the assessment of pressure evolution during flow is also presented – forming the pressure mapped squeeze flow method (PMSF) – which allows for identification of transitions in flow type and localized pressure peaks resulting from microstructural changes like particle jamming. The technique was also employed to study and develop laboratory mixing methods for mortars, as the resulting flow curves are very sensitive to the material’s agglomeration state. Finally, rheological parameters of mortars by squeeze-flow and rotational rheometry were compared showing that yield stress have some degree of agreement, whereas viscosity values from these techniques are complex to be related.