Different Types of Cement Tests
The quality of concrete depends on the quality of the cement. There are several types of cement available in the market. Therefore, it is very important to check the quality of cement before using it. Various tests on cement are conducted to ensure its quality. Cement tests Can be classified as follows:
a) Field Test.
b) Laboratory Test.
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a) Field Test
The Purity and quality of cement can be judged by applying the following rough and ready field test of cement:
⇰ The color of the cement should normally be greenish-grey.
⇰ When the 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 a 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.
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b) Physical / Laboratory Test
The following 8 Types of cement tests are usually conducted in the laboratory, this is also known as a physical test of cement:
1. Fineness Test.
2. Normal consistency test.
3. Initial and final setting time test.
4. Soundness test.
5. Compressive Strength Test.
6. Chemical composition test.
7. The heat of hydration test.
8. Tensile Strenght Test
1. Fineness Test
The object of this cement test is to check the proper grinding of cement. The fineness of cement is tested in two ways:
i) By Sieving.
ii) By Determining the specific surface.
i) Sieving
First of all, 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.
2. Normal Consistency Test
Normal Consistency test of cement 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 performed 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 into 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 a 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 the bottom, the paste is said to be of normal consistency. Otherwise, the trial paste should be made with a varying quantity of water and the test is repeated as above till the desired penetration is obtained.
Let, W = Weight of cement taken.
W1 = Weight of water for desired penetration.
Then, the percentage of water for normal consistency P = (W1 / W)× 100
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3. Initial and Final Setting Time Test
When cement is mixed with water is stiff and sticky paste is formed. This cement paste remains plastic for a short period. As the time lapses, the plasticity gradually disappears and the paste changes into a solid mass.
The phenomenon by virtue of which the cement paste changes from a plastic state to a solid-state is known as the 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 is 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 on cement 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 stopwatch is started. Water is mixed thoroughly for about 3 minutes. The paste is then filled into 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 a 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 stopwatch 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.
4. Soundness Test Of Cement
Soundness test of cement is performed to identify the presence of excess free lime and magnesia in the cement. This test is performed with the help of the Le-Chatelier apparatus.
Statement Of Problem: Two samples of cement are given, find out:
- Which cement is unsound? and
- Which cement is sound?
Theory
It is very important that the cement concrete is not so much as the change in its volume when it will be hardened. So it is necessary to control or reduce the quantity of the presence of free lime (CaO) and magnesia (MgO) in cement. So, the soundness test of cement is done to determine the quantity presence in cement.
During the manufacture of cement, free lime is produced. Free lime reacts with water and increases in volume considerably. Magnesia also has the same effect but its rate of reaction is slow.
A larger percentage of free lime and magnesia, if present, therefore, tends to increase the volume of the hardened concrete, thus causing disintegration. The cement is, therefore, said to be unsound when the percentage of free lime and magnesia is more than that specified by ISI (Table I). Unsoundness is measured with the help of the Le-Chatelier mould as explained in the procedure.
It must be specially mentioned here that in the event of the cement failing to comply with the above requirement, a further test should be made by the “Le-Chatelier Method” from another portion of the sample after aeration by spreading it out to a depth of 75 mm at relative humidity.
Test Procedure
Following are the procedure for Soundness Test of Cement:
a) Weigh accurately 100 gm of cement and place it on a standard IS Sieve 90 microns.
b) Break down any air set lumps in the sample with fingers, but do not rub on the sieve.
c) Continuously sieve the sample by holding the sieve in both hands and giving a gentle wrist motion or automatic sieve shaker may be used for this purpose. The sieving should be continuous for 15 minutes.
d) Weigh the residue left after 15 minutes sieving. This residue shall not exceed the specified limits.
e) For recording observations, use plate 4, in Part IV.
Precautions
a) The cleaning of the sieve should be done very gently with the help of a brush i.e. 25 mm or 40 mm bristle brush with 25 cm handle.
b) After sieving the cement must be removed from the bottom surface of the sieve gently.
c) Weighing machine should be checked before use.
d) Sieving must be carried out continuously.
5. Compressive Strength Test
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 a 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 of cement 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 the 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.
6. Chemical Composition Test.
As per IS: 269 – 1975 the chemical requirements of ordinary cement should be as follows
1. The ratio of the percentage of alumina to that of iron oxide should not be less than 0.66
2. The ratio of the percentage of lime to those of alumina, iron oxide and silica calculated with the following formula should not be less than 0.66 and it should not be greater than 1.02.
➤ The loss on ignition should not exceed 4 %.
➤ Total sulphur content as SO3 should not exceed 2.75 %.
➤ Weight of insoluble residue should not exceed 1.5 %.
➤ Weight of magnesia should not exceed 5 %.
7. The Heat of Hydration Test
The heat of hydration is defined as the chemical reaction between cement and water. during hydration of cement, sufficient heat is generated. The process of heat generation is quite rapid in the initial stage of the setting but its rate diminishes with the passage of time.
For mass concrete low heat cement should be used. As per IS: 4031 – 1968, the heat of hydration for low heat cement should be as follows:
After 7 days not more than 65 calories per gram and after 28 days not more than 75 calories per gram of cement.
8. Tensile Strenght Test
For evaluate the tensile strength of the cement, at first, six numbers of standard briquettes are made from cement mortar. All these briquettes are broken after 1 day, 3 days and 7 days of curing. The average strength of briquettes after 1, 3 and 7 days should be as follows:
| Time of immersion( Curing period) | Ordinary cement | Rapid hardening cement |
| After 1 day | ———— | 20 kg/cm2 (2 N/mm2) |
| After 3 days | 20 kg/cm2 (2 N/mm2) | 30 kg/cm2 (3 N/mm2) |
| After 7 days | 25 kg/cm2 (2.5 N/mm2 ) | ———- |
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