C0191_18a_14
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Quickly form the cement
paste-- prepared as described
in the section on
preparation of cement paste--
into a ball with gloved hands,
and toss six times, from one
hand to the other,
maintaining the hands
about 150 millimeters--
or 6 inches-- apart.
Press the ball, resting
in the palm of the hand,
into the larger end
of the conical ring--
as shown in Figure A1.1
of the written standard--
held in the other hand,
completely filling the ring
with paste.
Remove the excess at the
larger end by a single movement
of the palm of the hand.
Place the ring on its larger end
onto the non-absorptive plate,
and slice off the excess
paste at the smaller end
of the top of the ring by
a single oblique stroke
of the trowel, held at a slight
angle with the top of the ring.
Smooth the top of the specimen,
if necessary, with one
or two light touches of the
pointed end of the trowel.
During the operation of
cutting and smoothing,
take care not to
compress the paste.
Immediately after molding,
place the test specimen
in the moist cabinet
or moist room,
and allow it to remain there,
except when penetration
measurements are being made.
The specimen shall remain in
the conical mold, supported
by the non-absorptive plate,
throughout the test period.
Allow the time of
setting specimen
to remain in the moist cabinet
or moist room for 30 minutes
after molding without
being disturbed.
Determine the penetration
of the 1-millimeter needle
at this time, and
every 15 minutes
thereafter, every 10 minutes
for Type III cements,
until a penetration of
25 millimeters or less
is obtained.
Perform the test by lowering
the needle of the rod
until it rests on the
surface of the cement paste.
Tighten the set screw,
and set the indicator
at the upper end of the scale,
or take an initial reading.
Release the rod by quickly
releasing the set screw,
and allow the needle to
settle for 30 seconds.
Then take the reading to
determine the penetration.
At the option of the tester,
if the paste is obviously
quite soft on the
early readings,
retard the fall of the
rod to avoid bending
the 1-millimeter needle.
But when the actual
penetration measurements
to determine time
of setting are made,
release the rod only
by the set screw.
Make each penetration test
at least 5 millimeters away
from any previous penetration,
and at least 10 millimeters
away from the inner
side of the mold.
Record the results of
all penetration tests,
and, by interpolation,
determine the time
when a penetration of 25
millimeters is obtained.
The elapsed time between the
initial contact of cement
and water and the
penetration of 25 millimeters
is the Vicat time of setting, or
Vicat initial time of setting.
Determine the Vicat
final time of setting
endpoint to be the first
penetration measurement that
does not mark the
specimen surface
with a complete
circular impression.
Verify final set by performing
two additional penetration
measurements on different
areas of the specimen surface.
Obtain verification
measurements within 90 seconds
of the first final
set measurement.
The elapsed time between the
initial contact of cement
and water, and the
endpoint determination
above is the Vicat
final time of setting.
Keep all the apparatus
free from vibration
during the penetration test.
Keep the 1-millimeter
needle straight and clean.
The needle must be kept
clean to prevent cement
from adhering to the
sides of the needle
and decreasing
penetration, and to prevent
the cement from
adhering to the point
and increasing penetration.