INITIAL AND FINAL SETTING TIME OF CEMENT

The initial time of cement is time by which cement turns into paste by mixing with water and begins to lose its plasticity. The final time of cement is time by which cement turns into paste by mixing with water and lose its plasticity completely and have a certain structural strength.

The mixing, transporting and placing of mortar or concrete require a certain minimum time that should be within initial setting time. During this activity time cement paste, mortar, or concrete should be in plastic condition which make working with cement easy. After placing in the final position, compacting and finishing, Cement paste, mortar or concrete should lose its plasticity as early as possible such that there are least chances of damaging from external destructive agencies. This time should not be more than 10 hours which is referred to as final setting time. Initial setting time of cement should not be less than 30 minutes.

 AIM: To determine the initial and final setting times of given sample of cement.

APPARATUS: Vicat apparatus with attachments, balance, weights, gauging trowel.

Vicat Apparatus

THEORY: The initial setting time of cements is time interval during which the cement paste, mortar or concrete remain in plastic condition. The Initial setting time can be defined as the time taken by cement paste to start losing its plasticity from the moment of adding water to cement. The final setting time of cement paste can be defined as the time taken by cement paste to lose its plasticity and attain the firmness from the moment when water is added to cement.  

PROCEDURE:

Test Block Preparation:

• Mix 300 grams of cement with 0.85 times the water required to give a paste of standard consistency to prepare a cement paste.
• The water used in preparing the cement paste should either potable or distilled.
• The cement paste shall be gauged under the conditions prescribed in determination of consistency of standard cement paste.
• Note down the time by starting a stop-watch at the instant when water is added to the cement.
• Fill the mould with the cement paste gauged as above while the mould resting on a nonporous plate.
• Fill the mould completely and smooth off the surface of the paste making it level with the top of the mould.

DETERMINATION OF INTIAL SETTING TIME:

• Place the test blocks along with mould resting on the non-porous plate, under the rod bearing initial setting needle of vicat apparatus.
• Then gently lower the needle in contact with the surface of the test block and release the needle quickly, allowing the needle to penetrate into the test block.
• The needle will completely pierce the test block in beginning of the test.
• Repeat this procedure until the needle fails to pierce the block to a point 33 to 35 mm from top of mould (or 5 to 7 mm measured from the bottom of the mould) shall be the initial setting time.

DETERMINATION OF FINAL SETTING TIME:

• Insert the needle with an annular attachment in place of the needle of the Vicat apparatus.
• When on applying the needle gently to the surface of the test block, the needle makes an impression there on, while the attachment fails to do so. Then the cement shall be considered as set finally.
• The final setting time of cement paste is time gap between the time when water is added to the cement and the time at which the needle makes an impression on the surface of test block while the attachment fails.

 PRECAUTIONS: 

• The appliances should be clean before gauging. All the apparatus shall be free from vibration.
• The temperature of water and that of the test room, at the time of gauging shall be 27ᵒC ± 2ᵒC.
• Care shall be taken to keep the needle straight.

RESULT: Initial setting time for the given sample of cement =

Final setting time for the given sample of cement =