DETERMINATION OF NORMAL CONSISTENCY


DETERMINATION OF NORMAL CONSISTENCY

(IS: 4031 – part – 4)
Object:
Determination of the quantity of water required to produce a cement paste of standard consistency.
Apparatus:
Vicat apparatus (confirming to IS : 5513 – 1968) with plunger ( 10mm in dia ).
Theory:
The standard consistency of a cement paste is defined as that consistency which will permit the vicat plunger to penerate to a point 5 to 7 mm from the bottom of the vicat mould, when the cement paste is tested as described in the following procedure.
Procedure:
Prepare a paste of weighted quantity of cement ( 350 gms) with a weighted quantity of water, start with 30% water of 350 gms of cement taking care that the time of gauging is not less than 3 minutes and not more than 5 minutes and the gauging shall be completed before any sign of setting occurs. The gauging time shall be counted from the time of adding the water to the dry cement until commencing to fill the mould. Fill the vicat mould with this paste, the mould resting upon a non-porous plate. After completely filling the mould, trim off the surface of the paste, making it in level with the top of the mould. The mould may slightly be shaken to expel the air. Place the test block with the mould, together with the non-porous resting plate, under the rod bearing the plunger ( 10mm dia ) lower the plunger gently to touch the surface of the test block and quickly release, allowing it to penetrate into the paste. This operation shall carried out immediately after filling the mould. Prepare trial pastes with varying percentages of water and test as described above until the amount of water necessary for making the standard consistency as defined above is obtained. Express the amount of water as a percentage by weight of the dry cement.
Precautions:
Use clean appliances for gauging. The temperature of cement and water and that of test room, at the time when the above operations are being performed, shall be  270C +/- 20C.  the room temperature shall be maintained at  270C +/- 20C.

DETERMINATION OF INITIAL AND FINAL SETTING TIMES OF CEMENT.
( IS : 4031 – part – 5 )
Sample: 350 gms of cement is taken.

Procedure:
Preparation of Test Block
Prepare a neat cement paste by gauging 350 gms of cement with 0.85 times the water required to give a paste of standard consistency. The paste shall be gauged in the manner and under the conditions prescribed in determination of consistency of standard cement paste. Start a stopwatch at the instant when water is added to the cement. Fill the mould with the cement paste gauged as above, the mould resting on a non-porous plate, fill the mould completely 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. Use clean appliances for gauging. The temperature of water and that of the test room, and the time gauging, shall be 270C +/- 20C. During the test, the block shall be kept at a temperature of 270C +/- 20C and at not less than 90% relative humidity.
Determination of Initial Setting Time:
Place the test block confined in the mould and resting on the non-porous plate, under the rod bearing initial setting needle, lower the needle gently in contact  with the surface of the test block and quickly release, allowing it to penetrate into the test block. In the beginning the needle will completely pierce the test block. Repeat this procedure until the needle, when brought in contact with the test block and released as described above, fails to pierce the block for 5 +/- 0.5 mm measured from the bottom of the mould. The period lapsing between the time water is added to the cement and the time at which the needle fails to pierce the test block by 5 +/- 0.5 mm  shall be the initial setting time.
Determination of Final Setting Time:
Replace the needle of the vicat apparatus by the needle with an annular ring. 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 outer ring 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 the test block while the attachment fails to do so, shall be the final setting time.

Limits: Initial Setting Time, minimum = 30 minutes & Final Setting Time, maximum = 600 minutes.



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