In order that the concrete may be placed in position conveniently, it is necessary that the initial setting time of cement is not too quick and after it is laid, hardening should be rapid so that the structure can be made use of as early as possible. The initial set is a stage in the process of hardening after which any crack that may appear will not reunite. The cement paste or concrete is said to be finally set when it has obtained sufficient strength and hardness.
Initial setting time is defined 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 firmness to resist certain definite pressure.
APPARATUS:
- Vicat apparatus
- Needle for initial and final setting time
- Cement and water
- Stopwatch
PROCEDURE FOR INITIAL SETTING TIME:
1) Take 400 gm of cement in a pan. Prepare a neat cement paste by adding 0.85 times the water required to give a paste of standard consistency by the previous test.
2) Start a stop watch at the instant when water is added to the cement. Keep the Vicat mould on a non porous plate and fill the cement paste in it.
3) After completely filling the mould, it should be shaken slightly to expel the air. Smooth off the surface of the paste making it level with the top of the mould.
4) Place the test block and the non porous plate under the rod bearing the needle having 1sq.mm.cross section.
5) Lower the needle gently till in contact with the surface of the test block and quickly release allowing it to penetrate in to the test block. 6) In the beginning the needle will completely pierce the block. Repeat the procedure until the needle fails to pierce block for 5+-0.5mm measured from the bottom of the mould.
PROCEDURE FOR FINAL SETTING TIME:
1) Take 400 gm of cement in a pan. Prepare a neat cement paste by adding 0.85 times the water required to give a paste of standard consistency by the previous test.
2) Start a stop watch at the instant when water is added to the cement. Keep the Vicat mould on a non porous plate and fill the cement paste in it.
3) After completely filling the mould, it should be shaken slightly to expel the air. Smooth off the surface of the paste making it level with the top of the mould.
4) Place the test block and the non porous plate under the rod bearing the needle with the annular attachment for final setting time.
5) Lower the needle gently till the needle makes an impression there on, while the attachment fails to do so.
6) In the beginning the needle will completely pierce the block. Repeat the procedure.
7) The period elapsing between the time when water is added to the cement and the time at which the needle fails to make an impression on the surface of the test block shall be the final setting time.
OBSERVATIONS:
- Weight of cement taken = _________gms
- Qty of water added to cement = 0.85 X Quantity of water required for standard consistency = _______ ml
NOTE : Minimum Setting time of Cement should not be less than 30 minutes and Maximum setting time should not be more than 600 minutes.
RESULT:
1)Initial Setting time of cement = ———– minutes
2) Final Setting time of cement = ———– minutes
