[7] Main Test of cement | Explain types of Field and laboratory test of cement

The main type of Cement test

Test of cement is mandatory for every construction site. It is also two main types of test can be done at site (field) and in the laboratory to ascertain its quality and to have an idea about the physical properties. Its also in detail explained the following given below.

1. Field testing of cement
2. Laboratory Testing of Cement 

(1.) Field test of cement. 

In the absence of laboratory types of equipment, the following tests can be performed at the site to roughly assess the quality of cement. The field test is very important for every cement before the use and laboratory test. It's following the given below in proper explanation.

• The cement should be of uniform greenish-grey colour.
• When touched or rubbed between fingers it should feel smooth. Adulteration may be there if it is rough.
• It should not feel oily when touched the cement.
• There should not be any hard lumps. Lumps are formed when the cement has absorbed moisture.
• A handful of cement when thrown into a bucket of water, should float in case the cement is of good quality. Adulterated cement may sink.
• When heated on a hot plate for 20 minutes, the cement should not change its colour. 
• When the hand is thrust into a bag or heap of cement, it should also feel cool. 
• The properly check the packing date of the cement bags. It should not be used after the 3 months from the date of manufacturing of the cement bag.

(2.) Laboratory Testing of Cement (As per Indian Standard Specifications)

Various tests are performed on representative samples, to assess the quality and physical-chemical properties of cement. For examining the suitability of cement, the following laboratory tests are generally performed are during construction are the given below following the main six types of laboratory testing of cement.

1. Fineness test of cement 
2. Consistency test of cement 
3. Initial and final setting time of cement 
4. Chemical composition of cement 
5. Soundness test of cement 
6. Compressive strength test of cement 

1. Fineness of cement

The fineness test of cement is generally performed to check that proper grinding of cement has taken place. The fineness of cement plays an important role. Finer the cement more will be the surface area and hence quicker will be the reaction with water. Finer types of cement gain early strength.

The fineness of cement Procedure - 100 g of cement is taken in a sieve test. It is sieved for 15 minutes through IS Sieve number 9 (i.e., 90 microns or 90 X 10-3 mm) with wrist motion. The residue left on the sieve is then weighed. The residue should not be more than 10% of original weight (i.e., 10% of 100 g) of OPC.


2. Consistency test of cement 

The consistency test is also helpful in determining the percentage of water required for preparing cement pastes for other tests like setting time, soundness and compressive strength of cement. This test is performed on the Vicat apparatus. This apparatus is used to find out the percentage of water required to produce a cement paste of standard or normal consistency.

Vicat Apparatus - It consists of a metal (gunmetal or aluminium) frame having a movable rod with a cap at its top. The total weight of movable rod including cap is 300 gm. Releasing pin is provided with the movable rod to fix the rod or to make it slide down freely. The lower end of the movable rod has the provision of fixing any of the three attachments i.e., plunger, initial setting time of square needle and the needle with the annular collar.

An indicator is attached to the movable rod which moves on a vertical scale to give us penetration value. The mould used for placing the sample is in the form of a cylinder and it can be split into two halves, it is known as Vicat mould. 

Consistency test Procedure  - Following the procedure is adopted to find out the consistency of cement paste. 

• Take 400 g of cement and sieve it through IS Sieve No. 9. Add approximately 100 g of water (i.e. 25% by weight of cement).
• Water and cement are mixed on a non-porous surface. The mixing is done thoroughly for about 3 minutes (not less than 3 minutes and not more than 5 minutes).
• The Vicat apparatus is properly cleaned and fitted with the plunger. Apply lubricant to the inside of the Vicat mould.
• The mould is placed on a non-porous plate and is filled with cement paste. The filling should be accompanied by slight shaking and tapping so that air is expelled out. The top surface of the cement paste is made level with a trowel and excess cement paste is removed.
• The mould along with the non-porous is placed under the plunger.
• The bottom surface of the plunger is brought in contact with the top surface of the cement paste. The initial reading on the vertical graduated scale is noted.
• The movable rod is released without any jerk and the penetration is noted. The value of penetration is noted on the vertical scale. If the rod penetrates into the paste by 33 mm - 35 mm from the top of the mould (or 5 mm - 7 mm from bottom), then the paste is of normal consistency.
• If the penetration is not up to the desired mark, then trial pastes should be made with varying quantities of water and test is repeated till the desired penetration is obtained (i.e., 33 mm - 35 mm from the top of the mould).
• Thus, the percentage of water necessary for making a paste of normal consistency is found as under. Let

W1 = Weight of cement taken.
W2 = Weight of water added for desired penetration.
and P = Percentage of water required for normal consistency.

 

P = W2/W1×100 

 

The value of (P) commonly ranges from 25% to 35%.

Consistency test Precautions - The following precautions should be taken while conducting this test : 

• The apparatus should be cleaned.
• The sample should be free from air pockets.
• The temperature of the water as well as of room should be within 27 + 2 °C and relative humidity of 90%.
• The top surface of the sample should be levelled.
• The movable rod should fall freely.

3. Initial and final setting time of cement 

Cement when mixed with water forms paste which gradually becomes less plastic, and finally a hard mass is obtained. The time to reach this stage is known as setting time. The time is counted from the moment when water is added to the cement. The setting time is divided into two parts i.e. initial and final setting time. The test is carried out on the Vicat apparatus.

The procedure of initial setting time of cement

• Take 400 g of cement and sieve it through I.S. Sieve No. 9. The water is added at the rate of 0.85 P (i.e., 0.85 times the water required to produce cement paste of normal consistency) by weight of cement (i.e., the weight of water to be added = 0.85 P x 400/100).
• The moment at which water is added into the cement, the stopwatch is started.
• The cement paste is thoroughly mixed for at least 3 minutes and not more than 5 minutes.
• Clean the Vicat's mould properly and lubricate it from inside so that cement paste does not stick to it.
• Place the mould on a non-porous plate and fill it with cement paste.
• The attachment used below the movable rod is the square needle.
• Place the mould along with non-porous plate below the square needle just touching the top surface of cement paste.
• Note down the initial reading on the graduated vertical scale.
• The needle is quickly released and is allowed to penetrate into the cement paste. Note the time on the stopwatch.
• Initially, the needle will penetrate completely. Repeat this process at regular intervals until the needle does not penetrate completely.
• Note down the time from stopwatch when the needle penetrates 5 mm to 7 mm from the bottom of the mould. Thus, the time noted denotes the initial setting time of cement.

Therefore, the initial setting time may be defined as the time lapsed between the addition of water to cement and the stage when the square needle fails to penetrate about 5 mm - 7 mm from the bottom of the mould.


Procedure for Final Setting Time of cement

• The cement paste is made in a similar manner as in case of initial setting time test.
• The initial setting time needle is replaced with final setting time needle (i.e., the needle with annular collars). 
• The needle is released on the top surface of the prepared cement paste sample at regular intervals and the time is recorded.
• Initially, the needle and the collar will make an impression on the top surface of the cement paste sample.
• The time is noted when the needle makes an impression but the collar fails to do so. The time thus recorded is the final setting time of cement.

Therefore, the final setting time may be defined as the time lapsed between the addition of water to cement and the stage when the final setting needle makes an impression on cement paste but the collar fails to do so.

Important note

• For ordinary Portland cement, the initial setting time should not be less than 30 minutes and the final setting time is not more than 10 hours.
• The point of immersion of needle is varied every time.

4. Chemical composition of cement 

The Chemical composition of cement governs the properties of cement. Various tests are performed to determine the chemical constituents of cement. The chemical composition of cement should be strict as per the following guidelines are the given below

• The ratio of the percentage of lime to the percentage of silica, alumina and iron oxide, when calculated by the formula given below should not be greater than 1.02 and not less than 0-66. This ratio is called a cementation index of lime saturation factor percent.
• The ratio of the percentage of alumina to iron oxide should not be less than 0-66.
• The loss on ignition should not be more than 4%.
• The magnesia content should not exceed 5%.
• The total sulphur content, calculated as SO3 should not be more than 2.80%.
• The insoluble residue should not be more than 2%.

5. Soundness test (Expansion test) of cement

The soundness test of cement is very important that the cement after setting shall not undergo any appreciable change of volume. The unsoundness in cement is due to the presence of an excess of lime and magnesia. The mortar or concrete prepared from a cement (having free lime and magnesia) is liable to expand after the final setting is complete. This is one of the major reasons for cracking in cement concrete.

Le-Chatelier apparatus is used to perform this test. The Le-Chatelier test detects unsoundness due to free lime only. This method of testing does not indicate the presence and after effect of the excess of magnesia. Indian standard specifications indicate that a cement having a magnesium content of more than 3% shall be tested for soundness by Autoclave test which is sensitive for your free lime and magnesia.

Le-Chatelier's Apparatus - It consists of the brass mould of diameter 30 mm and height 30 mm. the thickness of the mould is 0-5 mm. There is a split in the mould not exceeding 0.5 mm. On either side of the split, two indicators (165 mm long) are attached having pointed ends as shown in Fig.

Procedure soundness test of cement

• Take 100 g of cement and sieve it through I.S. Sieve No. 9. To this, add water at the rate of 0.72 P (Where P = percentage of water required for the paste of standard consistency) by weight of cement.
• Thoroughly mix the cement water matrix.
• The prepared cement paste is filled into the mould, mounted on a glass plate.
• The mould is then covered with another glass plate and a small weight is placed on the top of the glass plate.
• The complete assembly is submerged in water for 24 hours. The temperature of the water should range from 27 °C to 32 °C.
• Take the mould out from the water and the distance between the points of indicators is noted.
• The mould is submerged again in water. The water is heated in such a manner that the boiling point of water is reached in about 25-30 minutes and keep it boiling for 3 hours.
• Remove the mould from the water, allow it to cool and measure the distance between the tips of indicators again.
• The difference between these two measurements represents the expansion of cement. This must not exceed 10 mm for ordinary, rapid hardening and low heat portland types of cement. 

Important note - In case the expansion is more than 10 mm, then the cement is said to be unsound.


6. Compressive Strength test of cement 

The compressive strength of hardened cement is the most important of all the properties. Therefore, cement is always tested for its strength at the laboratory before the cement is used in important work.
The compressive strength test is performed to determine the compressive strength of cement. This test is the final check on the quality of cement.

The procedure of compressive strength test

• Take cement and standard sand in the ratio of 1 : 3 (i.e., Take 200 g of cement and 600 g of standard sand). Mix the dry in a non-porous enamel tray with the help of a trowel. The Standard Sand (Ennore Sand) should conform to IS 650 - 1991 specifications.
• Add water at the rate of  P/4 + 3.0 percent of the combined weight of cement and sand, where P = percentage of water required for a paste of standard consistency. 
• Note - Add P/4 + 3.5 percent if ordinary sand is used.
• Mix the three ingredients thoroughly until the mixture is of uniform colour. Time of mixing should not be less than 3 minutes and not more than 4 minutes.
• The cube mould (of size 70-6 mm) are cleaned and oil is applied on the inner surface of the mould.
• Place the mould on a non-porous base plate and mortar is filled into the mould. The mould is compacted for 2 minutes on a vibrating machine.
• The top surface of the mould is made level. Similarly, six moulds are filled simultaneously.
• The cubes are kept at a temperature of 27 °C  +/-  2 °C and at least 90% relative humidity for 24 hours to set and harden.
• The specimens are removed from the moulds and are submerged in clean and freshwater for curing at a temperature of 27 °C  +/-  2 °C.
• Three cubes are tested in a compression testing machine at the end of 3 days and the remaining three cubes are tested after 7 days of curing. (ar) Compressive strength of ordinary Portland cement should not be less than the values specified

For more information about the types of the test of the cement watch this video