PORTLAND CEMENT - Materials for Civil and Construction Engineers - page 210

FIGURE 6.4 Vicat set time apparatus.

determined and recorded as the initial set time. The final set time is when
the needle does not penetrate visibly into the paste.
Similar to the Vicat test, the Gillmore test (Figure 6.5) requires that a
sample of cement paste of normal consistency be prepared. A pat with a flat
top is molded and the initial Gillmore needle is applied lightly to its surface.
The application process is repeated until the pat bears the force of the needle
without appreciable indentation, and the elapsed time is recorded as the ini-
tial set time. This process is then repeated with the final Gillmore needle and
the final set time is recorded. Due to the differences in the test apparatuses
and procedures, the Vicat and Gillmore tests produce different results for a
single sample of material.
The initial set time must allow for handling and placing the concrete be-
fore stiffening. The maximum final set time is specified and measured to en-
sure normal hydration. During cement manufacturing, gypsum is added to

FIGURE 6.5 Gillmore set time

apparatus.