Initial and final setting time of cement

 Initial and Final setting time of cement|Settings time of cement

Setting Time Test:- 

An arbitraty division has been made for the setting time of cement as initial setting time and final setting time. It is difficult to draw a rigid line between these two arbitrary divisions.

For convenience, 

• Initial setting time is regarded as the time elapsed between the moment that the water is added to the cement, to the time that the paste starts losing its plasticity.

•  The Final setting time is the time elapsed between the moment the water is added to the cement, and the time when the paste has completely lost its plasticity and has attained sufficient firmnesst toresist certain definite pressure.

• In actual construction dealing with cement paste, mortar or concrete certain time is required for mixing, transporting, placing, compacting and finishing. During this time cement paste mortar, or concrete should be in plastic condition.

• The time interval for which the cement products remain in plastic condition is known as the initial setting time. 

• Normally a minimum of 30 minutes is given for mixing and handling operations. The constituents and fineness of cement is maintained in such a way that the concrete remains in plastic condition for certain minimum time. 

• Once the concrete is placed in the final position, compacted and finished it should lose its plasticity in the earliest possible time so that it is least vulnerable to damages from external destructive agencies. 
• This time should not be more than 10 hours.

*Apparatus Required:-

Vicat apparatus –

Vicat Apparatus

•  Vicat Apparatus consists of a plunger with a needle, which used to penetrate the cement specimen up to the depth of 5mm to 7mm and above.

• Weighing balance – Up to measure 1000g with 1g accuracy.
• Stop Watch.
• Measuring Cylinder 200 ml.
• Glass Plate.
• Vicat Mould.
• Tray.
• Trowel.

*Procedure:-

The Vicat Appartus shown in above  Fig.  is used for setting time test also. 

The following procedure is adopted -

•  Take 500 gm. of cement sample and guage it with 0.85 times the water required to produce cement paste of standard consistency (0.85 P). 

• The paste shall be guaged and filled into the Vicat mould in specified manner within 3-5 minutes.

•  Start the stop watch the moment water is added to the cement.

•  The temperature of water and that of the test room, at the time of gauging shall be within 27°C ± 2°C.

*Intial Setting Time :- 

• Lower the needle (C) gently and bring it in contact with the surface of the test block and quickly release. 

• Allow it to penetrate into the test block. 

• In the beginning, the needle will completely pierce through the test block. But after some time when the paste starts losing its plasticity.

• The needle  may penetrate only to a depth of 33-35 mm from the top.

•  The period elapsing between the time when water is added to the cement and the time at which the needle penetrates the test block to a depth equal to 33-35 mm from the top is taken as initial setting time.

Final Setting Time:- 

• Replace the needle (C) of the Vicat appartus by a circular attachment (F) shown in the Fig above fig.

•  The cement shall be considered as finally set when, upon, lowering the attachment gently cover the surface of the test block, the centre needle makes an impression, while the circular cutting edge of the attachment fails to do so. 

• In other words the paste has attained such hardness that the centre needle does not pierce through the paste more than 0.5 mm.