CMT

Normal Consistency of Cement

Procedure:

1. Mix 500 grams of cement with a measured quantity of clean water following the procedure of mixing for cement pastes and mortars of plastic consistency, as follows:

a) Place water in the mixing bowl.

b) Add cement to the water and allow 30 seconds for the absorption of the water

c) Mix for 30 seconds until cement paste is formed.

d) Stop mixing for 15 seconds and during this time scrape down into the batch any paste that may have collected on the sides of the bowl

e) Start mixing again for 1 minute

2. Quickly form the cement paste into a ball and toss six times from one hand to the other maintaining the distance between the hands 150 mm apart

3. Press the ball into the larger end of a conical ring, while the ring rests on the plate, filling the ring with paste completely. Remove the excess at the larger end by a single movement of the palm of the hand.

4. Place the ring on a glass plate resting on its larger end. Slice off the excess paste at the smaller end by a single oblique stroke of a sharp-edged trowel. Take care not to compress the paste during cutting or smoothing of excess patte

5. Center the paste under the plunger end of the Vicat apparatus which shall be brought in contact with the surface of the paste.

8. Set the moving indicator of the Vicat apparatus to the upper zero of the scale and release the plunger immediately which must not exceed 30 seconds after completion of mixing. The apparatus shall be free of vibration during the test

7. The paste shall be of normal consistency when the plunger settles to a point 10 mm +1 mm below the original surface in 30 seconds after being released.

8. Make trial pastes with varying percentage of water until the normal consistency is obtained. Use fresh cement for each trial

Setting Time of Cement

Procedure:

1. Using Gillmore Needle

1.1 Prepare a neat cement paste of normal consistency.

12. Place the paste into a 3 inches diameter pot 1/2 inch thick, tapering it at the edge

13. Apply the small Gillmore needies at intervals of 30 seconds Ioaded to weigh 1/4 pound

1.4. See to it that the tip of the needle touches the surface of the paste before it is released

1.5 Repeat step 4 subsequently until the pot fails to make any appreciable mark. At this point the initial set is said to have occurred. Start counting the time of setting at this point

1.6. Change to a large Gillmore needle loaded to weigh 1 pound and apply at intervals of 30 seconds.

1.7. Repeat step 4 subsequently until it fails to make any appreciable mark. At this point the final set is said to have occurred. Stop the counting of time at this point

1.8. Record the time from the initial to the final set.

2. Using Vicat Needle

2.1 Weigh 500g of cement.

22 Prepare amount of water as to that calculated in normal consistency test.

2.3. Prepare a cement paste following the same procedure in Lab Test No. 1. Place it in a Vicat conical ring

2.4. Allow the specimen to set for 30 minutes after molding without being disturbed. Determine the penetration of 1mm needle at this time and every 15 minutes until a penetration of 25mm or less is obtained. Allow the needle to settle for 30 seconds

2.5. Note that no penetration shall be made closer than 6mm from any previous penetration and no penetration shall be made closer than 9.5 mm inside the mold. The initial setting time is the time when a penetration of 25 mm is obtained.

2.6. The final setting time is when the needle does not sink visible into the cement paste

Strength Test of Cement

Procedure:

1. Mix 500 g of cement with the percentage of water required for normal consistency following the procedure of mixing cement paste

2. Place the paste in a thinly oiled plastic or glass container and shake until it is level with the diameter of the container with 1/2 inch thickness

3. Cover and stand to harden for 24 hours

4. After it hardened, remove the sample from the container and place it into a pot files with water with the plane surface of the sample on top

5. The cake should rest on a grill so that it will not touch the pot's surface when heated

6. The water is brought to a boil for 15 minutes and left boiling for 2 hours. See to it that the specimen is always fully submerged in water while boiling.

7. The test should be repeated with cement that has been exposed for at least 24 hours

8. After boiling remove from heat and let cool

9. Try to break the hardened cement with the bare hands. A good cement will not break