Objective: To determine the initial and final setting time of a given sample of cement.
Apparatus: Vicat apparatus conforming to IS : 5513-1976, Balance, Gauging Trowel, Stop Watch, etc.
Theory : For convenience, initial setting time is regarded as the time elapsed between the moments that the water isadded to the cement, to the time that the paste starts losing its plasticity. The final setting time is the timeelapsed 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 firmness to resist certain definitepressure
- Preparation of Test Block – Prepare a neat 300 gms cement paste by gauging the cement with 0.85 times the water required to give a paste of standard consistency. Potable or distilled water shall be used in preparing the paste.
- Start a stop-watch at the instant when water is added to the cement. Fill the Vicat mould with a cement paste gauged as above, 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.
- Immediatel after moulding, place the test block in the moist closet or moist room and allow it to remain there except when determinations of time of setting are being made.
- Determination of Initial Setting Time – Place the test block confined in the mould and resting on the non-porous plate, under the rod bearing the needle ( C ); lower the needle gently until it comes in contact with the surface of the test block and quickly release, allowing it to penetrate into the testblock.
- Repeat this procedure until the needle, when brought in contact with the test block and released as described above, fails to pierce the block beyond 5.0 ± 0.5 mm measured from the bottom of the mould shall be the initial setting time.
- Determination of Final Setting Time – Replace the needle (C) of the Vicat apparatus by the needle with an annular attachment(F).
- The cement shall be considered as finally set when, upon applying the needle gently to the surface of the test block, the needle makes an impression thereon, while the attachment fails to do so.
- The period elapsing 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 to do so shall be the final setting time.
- Weight of given sample ofcement is____ gms
- The normal consistency of a given sample of cement is____ %
- Volume of water addend (0.85 times the water required to give a paste of standard consistency) for preparation of test block_____ ml
Result: i) The initial setting time of the cement sample is found to be …..
ii) The final setting time of the cement sample is found to be …..