A new look at the measurement of cementitious paste setting by Vicat test

The Vicat test is a standard test for measuring the setting times of cement paste and mortar. The physical background of the test is based on the resistance of a paste to dynamic penetration by a rod with a certain weight and shape (shear strain). The information obtained (initial and final set time) is very useful to compare cement setting properties. This study shows that it is possible to obtain more fundamental information about the setting property kinetics with only one modification of the testing procedure. The apparent mass of the static full immersed needle is measured. Due to the deformation of the cement paste at rest, the needle apparent mass varies with time. We show that the variation of the stress mobilized at the plate surface is related to the increase of yield stress during the setting period. The results of these experiments are discussed and compared with the traditional Vicat test for cement paste.