Initial and Final Setting time of Cement
Testing of Cement- Click Here3-Setting time test-
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| Testing of Cement |
A-Initial setting time test-
Initial setting time is define as the time that is measured form the instant water is added into the cement up to the time it starts losing its plasticity.
In order to perform this test, 500gm of cement sample is taken and graded with 0.85P [85% of the water required to prepare the cement paste of standard consistency is added in it] & the paste prepared is filled in the mould.
Initial setting time is referred as the time in which the square needle of size of 1mm shows the penetration of 33 to 35 mm into the mould from the top.
For OPC, initial setting time is approximately 30 minute.
B-Final setting time test-
Final setting time is define as the time, which is measured from the instant ,water is added into the cement up to the time, it completely losses its plasticity and attains sufficient firmness so as to resist definite pressure.
In order to find final setting time ,mould is prepared as above & Final setting time is referred as the time in which needle at the center of the annular ring [5mm annular ring] is able to make the impression over the mould but annular collar fails to do so.
For OPC, final setting time is approximately 10 hrs.
4-Soundness test-
No significant change in the volume of the cement takes place after its setting as it affects the durability of the structure in which it is used for construction. Unsoundness of the cement is due the presence of lime, magnesia, & sulphure in it.
A- Unsoundness due to lime-
Unsoundness due to lime is measured by le-chatelier test, that consist of split cylinder of dia & height of 30mm & indicator arms of length of 165mm.
In order to perform this test 100 gm. of the cement is graded with 0.78P [78% of the water required to prepare the cement paste of standard consistency is added] & the paste form is fill in the split cylinder ,which is covered from top and bottom with the help of glass plates & the entire assembly is immersed in the water having the temp. in the range of 27 to 32 for 24 hr.
The cylinder is removed from the water & the distance between the indicator arm is noted [x]. The entire assembly is again immersed in the water, temp. of which is increased up to its boiling point in 25 to 30 minute & is maintain for next 3 hrs. The assembly is removed from the water allow to pull off & distance between the indicator arms is again noted [y].
For OPC, difference between the two readings must not exceed 10mm. [Y-X] ≯ 10 mm.
B-Unsoundness due to magnesia-
[If mgo >3%] unsoundness due to magnesia is determine using Auto clave test. This test is sensitive to both unsoundness due to lime & magnesia.
In order to perform this test mould of size 25mm x 25mm x 250 mm from the given sample of cement is placed into the Auto clave. Steam pressure in the auto clave is increased such that gauge pressure of 21kg/cm2 is attain in 1 hour & is maintain for next 3 hours. The mould is removed from auto clave allowed to pull off & is tested for its size.
For OPC, increase in size of any side should not exceed 0.8%.
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