Friday, 28 September 2018

7 Cement Test To Check Quality of Cement

7 Cement Test To Check Quality of cement

Cement Test
Testing of cement Can be categorized as follows:
1) Field Testing.
2) Laboratory Testing.
CEMENT TEST

1) Field Testing Of Cement

The Purity and quality of cement can be judged by applying the following rough and ready field tests:

⇰ The color of the cement should normally be greenish grey.

⇰ When hand is inserted into a bag of cement ,It should feel cool and not warm.

⇰ Any lump found in the cement bag should be powdered by pressing between the thumb and the fore finger.If it does not turn into powder form , the cement is considered to be spoiled by air setting.


⇰ It should give smooth feeling when rubbed in between fingers.


⇰ A handful of cement thrown into a bucket of water ,should float for some time.


⇰ It should not feel oily when touched.

2) Physical / Laboratory Testing Of Cement

The following 7 tests of cement are usually conducted in the laboratory:

7 Cement Test To Check Quality of Cement

a) Fineness Test
b) Normal consistency test 
c) Initial and final setting time test 
d) Soundness test
e) compressive Strength Test
f) Heat of hydration test
g) Chemical composition test.

a) Fineness Test of Cement

The object of this test is to check the proper grinding of cement.
Fineness of cement is tested in two ways:
i) By Sieving 
ii) By Determining the specific surface

i) Sieving

Weight correctly 100 grams of cement and take it on a standard IS sieve no 9 (90 microns) .Break down the air set lumps in the sample with fingers.  

Continuously sieve the sample manually or mechanically for 15 minutes, Weigh the residue left on the sieve. This weigh shall not exceed 10% for ordinary cement & 5% for rapid hardening or low heat cement. 

b) Normal Consistency Test of Cement

This test is conducted to determine the quantity of water required to produce a cement paste of standard  or normal consistency for use in  other tests.

This test is perform with the help of Vicat's apparatus Standard or normal consistency of a cement paste is that consistency which will permit the Vicat plunger (10 mm in diameter & 40-50 mm in length) to penetrate to a point 5 to 7 mm from the bottom of the Vicat mould.

To perform this test about 400 gm sieved cement is taken & 100 gm of water is added and mixed thoroughly for about 3 minutes.The paste is then filled in to the Vicat mould,Making it level with the top of the mould. 

The filled up mould is placed centrally below the movable rod fitted with plunger.The bottom surface of the plunger is brought in contact with the surface of the cement paste and the reading of the scale is taken.The rod is then quickly released and the penetration is noted.

If the rod penetrates 5 to 7 mm from bottom,the paste is said to be of normal consistency . Otherwise trial paste should be made with varying quantity of water and the test is repeated as above till the desired penetration is obtained.
Let W = Weight of cement taken.
W
1 = Weight of water for desired penetration.
Then the percentage of water for normal consistency P = (W
/ W)× 100

c)Initial and Final Setting Time Test Of Cement

When cement is mixed with water is stiff and sticky paste is formed. This cement paste remains plastic for short period. As the time lapses , the plasticity gradually disappears and the paste changes into a solid mass.

This phenomenon by virtue of which the cement paste changes from plastic state to solid state is known as setting of cement. The time to reach this stage is known as setting time .

The time is reckoned from the instant when water is added to the cement .The setting time is divided into two parts namely initial setting time and final setting time .

The time at which the cement paste loses its plasticity is termed the initial setting time. the time taken to reach the stage when the paste becomes a hard mass is known as the final setting time.

The initial and final setting time test is performed with the help of Vicat apparatus. The initial setting time of cement shall be the time from the period elapsing between the time when the water is added to the cement and the time at which the needle (1 mm square or 1.13 mm in dia and 40 to 50 mm in length) penetrate to a point 5 mm from the bottom of the Vicat mould.

To perform this test about 400 gm sieved cement is taken and water is added to it @ 0.85 P by weight of cement. Where, P is the percentage of water required for normal consistency paste. 


At the instant of adding water, the stop watch is started. Water is mixed thoroughly for about 3 minutes. The paste is then filled in to the Vicat mould, making it level with the top of the mould.  

The filled up mould is placed centrally below the movable rod fitted with needle.The bottom surface of the needle is brought in contact with the surface of the cement paste and the reading of the scale is taken.The rod is then quickly released and the penetration is noted. 

The procedure is repeated until the needle fails to penetrate the flock for about 5 mm measured from the bottom of the mould. The time from the stop watch is recorded which gives the initial setting time.

The cement shall be considered it finally set while applying final setting time needle gently, only an impression is marked on the top surface.

d) Soundness Test Of Cement

This test is performed to identify the presence of excess free lime and magnesia in the cement. This test is performed with the help of  Le-Chatelier apparatus.

e) Compressive Strength Test Of Cement

To perform this test 200 gm of cement and 600 gm of standard sand are taken and mixed thoroughly.To this, water is added @ P/4 + 3% when standard sand is used and @ P/4 + 3.5 % when ordinary sand is used.Where, P is the percentage of water required for a paste of normal consistency. 

It is mixed thoroughly to an even colour. The cube mould of size 7.06 cm is placed on a non porous base plate and is oiled inside. The above mortar is put into the cube mould and is compacted for two minutes by the vibration machine. The top surface is smoothened off by trowel.  

Like this mould ,six moulds are filled. The prepared cubes are kept at a temperature of 27° ± 2° C  for 24 hours. After this period, mortar cubes are taken out of the moulds and submerged in clean and fresh water for curing .
Compressive strength test is performed at the period mentioned below.
For ordinary cement, after 3 days and 7 days
For rapid hardening cement, after 1 day and 3 days
For low heat cement, after 3,7 and 28 days.


The cube is tested by placing it under the Jaws of compressive testing machine. The load is steadily and uniformly applied. The load at which the cube is fractured is noted in each case. The compressive strength is calculated by dividing this load by the cross sectional area of the cube.
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