4.2.1.1 C ement Test by Sieve No. 170
The fineness of cement affects the quality of the concrete industry in general. A big
cement particle cannot completely react with water as water cannot reach a remaining
core in the cement particle. The water propagates through the cement particles and
they start to dehydrate, which causes an increase in temperature, which is the main
reason for the forming of hair cracks and preventing stabilization of cement volume.
As a result, an increase in the cement particle size reduces the strength of the same
cement content and increasing the fineness of the cement will improve the workability,
cohesion, and durability with time and decrease the water moving upward to the
concrete surface.本文来自辣.文,论-文·网原文请找腾讯3249.114
Figure 4.1, from Neville’s book (1983), presents the relation between concrete
strength and the concrete fineness at different ages. To perform this test, take a sample
of 50 g of cement and shake it in a closed glass bottle for two minutes and then
revolve the sample gently using dry bar. Put the sample in a closed bottle and leave
it for two minutes. Put the sample in 170 sieve (90 microns) and move it, shaking
the sieve horizontally and rotationally, then confirm finishing the sieve test when the
rate of passing cement particles is not more than 0.5 g/min during the sieve process.
Remove the fines carefully from the bottom of the sieve using a smooth brush. Then,
collect and weigh the remaining particles on the sieve (W1).
Repeat the same test with another sample. Then the residual weight for the second
test is obtained (W2). Calculate the values of the remaining samples through
R1 = (W1/50) × 100
R2 = (W2/50) × 100
The ratio (R) is calculated by taking the average of R1 and R2 to the nearest 0.1%
and, in the case of deviating results of the two samples, more than 1%. Do the test a
third ti论文范文http://www.chuibin.com/ me and take the average of the three results.
You can accept or refuse the cement based on the following condition:
For Portland cement t • he R must not exceed than 10%.
• For rapid hardening Portland cement the R must not exceed 5%.
4.2.1.2 Initial and Final Setting Times of Cement
Paste Using Vicat Apparatus
The objective of this test is to define the time for initial and final setting of the paste
of water and cement with standard consistency by using a Vicat apparatus and determine
whether the cement is expired or can be used.2512