Information Civil

OBJECTIVE:

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

APPARATUS:

Vicat apparatus (conforming to IS: 5513-1976) with attachments, balance, weights, gauging trowel.

THEORY AND SCOPE:

In actual construction dealing with cement, mortar or concrete, certain time is required for mixing, transporting and placing. 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 setting time. Initial setting time is regarded as the time elapsed between the moments 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 pressure. 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 which is referred to as final setting time. Initial setting time should not be less than 30 minutes.

PROCEDURE:

Preparation of Test Block:

1. Prepare a neat cement paste by gauging 300 gram of cement with 0.85 times the water required to give a paste of standard consistency.

2. Potable or distilled water shall be used in preparing the paste.

3. The paste shall be gauged in the manner and under the conditions prescribed in determination of consistency of standard cement paste.

4. Start a stop-watch at the instant when water is added to the cement.

5. Fill the mould with the cement paste gauged as above the mould resting on a nonporous plate.

6. 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.

DETERMINATION OF INITIAL SETTING TIME:

1. Place the test blocks confined in the mould and rests it 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.

2. In the beginning, the needle will completely pierce the test block.

3. Repeat this procedure until the needle, when brought in contact with the test block and released as described above, fails to pierce the block to a point 5 to 7 mm measured from the bottom of the mould shall be the initial setting time.

DETERMINATION OF FINAL SETTING TIME:

1. Replace the needle of the Vicat apparatus by the needle with an annular attachment.

2. 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 there on, while the attachment fails to do so.

3. The period elapsed 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.