Initial and Final Setting Time are two very important properties of cement which are required in estimating free time for transporting, placing, compaction and shaping of cement paste.
Initial setting time is the time from mixing dry cement with water till the beginning of interlocking of the gel.
Final setting time is the time from mixing dry cement with water till the end of interlocking of the gel
AIM
To determine the initial and the final setting time of cement as per IS: 4031 (Part 5) - 1988.
APPARATUS
i) VICAT Apparatus.
ii) Digital weighing scale, used to measure the weight of dry cement.
iii) Glass graduates, used to measure the volume of water.
iv) Trowel.
v) Mixing bowl.
vi) Stop-watch.
vii) Portland Pozzolna Cement.
viii) Water.
PROCEDURE
i) Prepare a cement paste by gauging the cement with 0.85 times the water required to give a paste of standard consistency.
ii) Start a stop-watch, the moment water is added to the cement.
iii) Fill the Vicat mould completely with the cement paste gauged as above, the mould resting on a non-porous plate and smooth off the surface of the paste making it level with the top of the mould. The cement block thus prepared in the mould is the test block.
A) INITIAL SETTING TIME
Place the test block under the rod bearing the needle.Lower the needle gently in order to make contact with the surface of the cement paste and release quickly, allowing it to penetrate the test block. Repeat the procedure till the needle fails to pierce the test block to a point 5.0 ± 0.5mm measured from the bottom of the mould.The time period elapsing between the time, water is added to the cement and the time, the needle fails to pierce the test block by 5.0 ± 0.5mm measured from the bottom of the mould, is the initial setting time.
B) FINAL SETTING TIME
Replace the above needle by the one with an annular attachment. The cement should be considered as finally set when, upon applying the needle gently to the surface of the test block, the needle makes an impression therein, while the attachment fails to do so. The period elapsing between the time, water is added to the cement and the time, the needle makes an impression on the surface of the test block, while the attachment fails to do so, is the final setting time.
REPORTING OF RESULTS
The results of the initial and the final setting time should be reported to the nearest five minutes.
CONCLUSION:
To measure the setting times of cement, we have to do our tests on cement of standard consistency. Normal consistency of standard cement can be gained by using the W \ C ratio and depending on 26%- 33%. The higher rate of water the more initial setting time needed.
