TESTING OF CEMENT - NORMAL CONSISTENCY, INITIAL AND FINAL SETTING TIMES, SOUNDNESS, FINENESS, COMPRESSIVE STRENGTH, SPECIFIC GRAVITY OF CEMENT,

CONTENT

SLNO	TEST DESCRIPTION
1	DETERMINATION OF NORMAL CONSISTENCY
2	DETERMINATION OF INITIAL AND FINAL SETTING TIMES OF CEMENT
3	DETERMINATION OF SOUNDNESS OF CEMENT BY THE LE- CHATELIER METHOD
4	DETERMINATION OF FINENESS OF CEMENT
5	DETERMINATION OF COMPRESSIVE STRENGTH OF CEMENT.
6	DETERMINATION OF SPECIFIC GRAVITY OF CEMENT.

1. 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.

  

2.DETERMINATION OF INITIAL AND FINAL SETTING TIMES OF CEMENT.

( IS : 4031 – part – 5 )

Object:

 Determination of the Initial and Final setting times of cement.

 Apparatus:

 The vicat apparatus ( conforming to IS : 5513 – 1968 ).

  

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, andthe 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.

  3. DETERMINATION OF SOUNDNESS OF CEMENT BY THE LE CHATELIER METHOD.

( IS : 4031 – part – 3 )

Object:

 Determination of the Soundness of cement by the Le Chatelier method.

 Apparatus:

 The apparatus for conducting the test consists of small split cylinder of spring brass or other suitable metal of 0.5 mm thickness, forming a mould 30 mm internal diameter and 30 mm high. On either side of the split mould are attached two indicators with pointed ends, the distance from these ends to the center of the cylinder being 165 mm. The mould shall be kept in good condition with the Jaws not more than 0.50 mm apart.

 

 Procedure:

Place the mould on a glass sheet and fill it with cement paste formed by gauging cement with 0.78 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, taking care to keep the edges of the mould gently together while this operation is being performed. Cover the mould with another piece of glass sheet, place a small weight on this covering glass sheet and immediately submerge the whole assembly in water at a temperature of 270C +/- 20C and keep there for 24 hours.

 Measure the distance separating the indicator points. Submerge the moulds again in water at the temperature prescribed above. Bring the water to boiling, with the mould kept submerge, in 25 to 30 minutes, and keep it boiling for three hours. Remove the mould from the water, allow it to cool and measure the distance between the indicator points.

 The difference between these two measurements represents the expansion of the cement.

 Limits:

 Expansion should not be more than 10 mm.

  

4. DETERMINATION OF FINENESS OF CEMENT.

( IS : 4031 – part – 3 )

 Object:

 To determine the fineness of cement by dry sieving.

 Apparatus:

 a) Standard balance with 100 gm. weighing capacity.

 b) IS : 90 micron sieve confirming to IS : 460 – 1962 and a Brush.

 Procedure:

 a) Break down any air-set lumps in the cement sample with fingers.

 b) Weigh accurately 100 gms of the cement and place it on a standard 90 micron IS.sieve.

 c) Continuously sieve the sample for 15 minutes.

 d) Weigh the residue left after 15 minutes of sieving. This completes the test.

 Result:

 The percentage weight of residue over the total sample is reported.

 

Wt.of Sample Retained on the Sieve

% Weight of Residue =       ------------------------------------------------

       Total Weight of the Sample

 

 Limits:

The percentage residue should not exceed 10%.

 Precautions:

Sieving shall be done holding the sieve in both hands and gentle wrist motion, this will involve no danger of spilling the cement, which shall be kept well spread out on the screen. More or less continuous rotation of the sieve shall be carried out throughout sieving.

Washers, shots and slugs shall not be used on the sieve. The underside of the sieve shall be lightly brushed with a 25 or 40 mm bristle brush after every five minutes of sieving.

Mechanical sieving devices may be used, but the cement shall not be rejected if it meets the fineness requirement when tested by the hand method.

 

5.DETERMINATION OF COMPRESSIVE STRENGTH OF CEMENT.

( IS : 4031 – Part – 6 )

 Object:

Determination of the compressive strength of standard cement mortar cubes compacted

by means of a standard vibration machine.

 Apparatus:

 1. Vibration machine, cube moulds of size 7.06 cms(confirming to IS : 4031 – 1968), and

   

Fig. Cement Cube mould & Vibrating Machine for Casting of Cement Mortar Cubes

2. Standard Sand to be used in the test shall be confirm to IS : 650 – 1966.

 

Fig.Standard Sand

Procedure: 

Mix Proportions and Mixing: Clean appliances shall be used for mixing and the temperature of the water and that of the test room at the time when the above operations are being performed shall be 270 +/- 20C.

Place in a container a mixture of cement and standard sand in the proportion of 1 : 3 by weight; mix it dry, with a trowel for one minute and then with water until the mixture is of uniform colour. The quantity of water to be used shall be as specified below. In any event, it should not take more than 4 minutes to obtain uniform coloured mix. If it exceeds 4 minutes, the mixture shall be rejected and the operation repeated with a fresh quantity of cement, sand and water.

The material for each cube shall be mixed separately and the quantity of cement, standard sand and water shall be as follows:

Percentage of water to be added to the cement and sand in ( 1:3 ) cm (P/4 + 3) X %

combined weight of cement and sand = (P/4 + 3) X 800/100.

Cement 200 gms, standard sand 600 gms, water (P/4 + 3) per cent of combined weight of cement and sand, where P is the percentage of water required to produce a paste of standard consistency.

 Moulding Specimens:

In assembling the moulds ready for use, cover the joints between the halves of the mould with a thin film of petroleum jelly and apply a similar coating of petroleum jelly between the contact surfaces of the bottom of the mould and its base plate in order to ensure that no water escapes during vibration. Treat the interior faces of the mould with a thin coating of mould oil.

 Place the assembled mould on the table of the vibration machine and firmly hold it in position by means of suitable clamps.

Securely attach a hooper of suitable size and shape at the top of the mould to facilitate filling and this hooper shall not be removed until completion of the vibration.

Immediately after mixing the mortar, place the mortar in the cube mould and rod with a rod. The mortar shall be rodded 20 times in about 8 seconds to ensure elimination of entrained air and honey combing. Place the remaining quantity of mortar in the hooper of the cube mould and rod again as specified for the first layer and then compact the mortar by vibration.

The period of vibration shall be two minutes at the specified speed of 12000 +/- 400vibrations per minutes.

At the end of vibration remove the mould together with the base plate from the machine and finish the top surface of the cube in the mould by smoothing surface with the blade of a trowel.

 

Curing Specimens:

Keep the filled moulds at a temperature of 270C +/- 20C in an atmosphere of atleast 90% relative humidity for about 24 hours after completion of vibration. At the end of that period remove them from the moulds immediately submerge in clean fresh water and keep them under water until testing. The water in which the cubes are submerged shall be renewed every 7 days and shall be maintained at a temperature of 270C +/- 20C. After they have been taken out and until they are tested, the cubes shall not be allowed to become dry.

Testing:

Test three cubes for compressive strength at the periods mentioned under the relevant specifications for different hydraulic cements, the periods being reckoned from the completion of vibration. The compressive strength shall be the average of the strengths of the three cubes for each period of curing.

The cubes shall be tested on their sides without any packing between the cube and the steel platens of the testing machine. One of the platens shall be carried base and shall be self-adjusting and the load shall be steadily and uniformly applied, starting from zero at a rate of 350 kgs/cm2/min.

 Calculation:

Calculate the compressive strength from the crushing load and the average area over which the load is applied. Express the results in kgs/cm2 to the nearest 0.5 kg/cm2.

Compressive strength, kg/cm2 = P/A, where ‘P’is the crushing load in kg, and ‘A’ is thearea in cm2.

  

6. DETERMINATION OF SPECIFIC GRAVITY OF CEMENT.

( IS : 2720 – Part – 3 )

Object: To determine the specific gravity of cement using Le Chatelier Flask or Spcefic

Gravity Bottle.

 Apparatus:

a) Le Chatelier Flask or Specific Gravity Bottle – 100 ml capacity.

b) Balance capable of weighing accurately upto 0.1gm.

 

Procedure:

Weigh a clean and dry Le Chatelier Flask or Specific Gravity Bottle with its stopper (W1). Place a sample of cement upto half of the flask (about 50 gm) and weight with its stopper (W2). Add kerosene (polar liquid) to cement in flask till it is about half full. Mix thoroughly with glass rod to remove entrapped air. Continue stirring and add more kerosene till it is flush with the graduated mark. Dry the outside and weigh (W3).

Entrapped air may be removed by vacuum pump, if available. Empty the flask, clean it refills with clean kerosene flush with the graduated mark wipe dry the outside and weigh (W4).

 Calculations:

( W2 – W1)

Specific gravity =      -------------------------------------------

( W2 – W1) – ( W3 – W4) X 0.79

 Where           W1 = weight of empty flask.

W2 = weight of flask + cement.

W3 = weight of flask + cement + kerosene.

W4 = weight of flask + kerosene.

0.79= specific gravity of kerosene.

 Limit: Specific gravity of cement = 3.15 g/cc .