Grading depends on when the needle stops penetrating or after 30 seconds, whichever
is earlier, and indicates the distance between the mold base and the end of the
needle, as well as the time start from the zero level measurement.
Repeat the process of immersing the needle in the same paste in different locations
with the distance between the immersing point and the edge of the mold or
between two immersing points not less 10 mm after about 10 minutes, and clean the
needle immediately after each test.
Record time is measured from zero up to 5 ± 1 mm from the base of the mold as
the initial setting time to the nearest 5 minutes. Ensuring the accuracy of measurement
of time between tests reduces embedment and the fluctuation of successive
tests. The needle is used to identify the final time of setting; follow the same steps
as in determining time of initial setting and increase the period between embedment
tests to 30 minutes.
Record the time from zero measurement until embedment of the needle to a distance
of 0.5 mm, which will be the final setting time. Control the impact of the
needle on the surface of the sample so the final setting time presents the effect of
the needle. To enhance the test’s accuracy reduce the time between embedment tests
and examine the fluctuation of these successive tests. Record the final setting time
to the nearest 5 mm.
According to the Egyptian specifications the initial setting time must not be less
than 45 minutes for all types of cement except the low heat cement,
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initial setting time must not be less 60 minutes. The final setting time must be shorter
than 10 hours for all types of cement.
4.2.1.3 D ensity of Cement
The purpose of this test is to determine the density of cement by identifying the
weight and unit volume of the material by using the Le Chatelier density bottle. The
determination of the cement density is essential for concrete mix design and to control
its quality. This test follows specifications of the American Society for Testing
and Materials, ASTM C188-84.
The Le Chatelier device is a standard round bottle. Its shape and dimensions are
shown in Figure 4.3. This bottle must have all the required dimensions, lengths, and
uniform degradation and accuracy.本文来自辣.文,论-文·网原文请找腾讯3249,114
The glass that is used in the Le Chatelier bottle must be of high quality and free
from any defects. It should not interact with chemicals and have high resistance to
heat and appropriate thickness to have a high resistance to crushing. Measurements
start at the bottle’s neck and go from zero to 1 mL and from 18 to 24 mL with accuracy
to 0.1 mL. Each bottle must have a number to distinguish it from any other.
Write on the bottle the standard temperature and the capacity in millimeters over the
highest point of grading.
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