Field Tests for Cement
The Following are the Field Tests for Cement that are carried out inorder to ascertain the quality of Cement,
(1) Colour
(2) Physical properties
(3) Presence of lumps
(4) Strength.
(1) Colour: The colour of cement should be uniform. It should be typical cement colour i.e., grey colour with a light greenish shade. This is not always a reliable test. But it gives an indication of excess lime or clay and the degree of burning.
(2) Physical properties: The cement should feel smooth when touched or rubbed in between fingers. If it is felt rough, it indicates adulteration with sand. If hand is inserted in a bag or heap of cement, it should feel cool and not warm. If a small quantity of cement is thrown in a bucket of water, it should sink and should not float on the surface. A thin paste of cement with water should feel sticky between the fingers. If the cement contains too much of pounded clay and it as an adulterant, the paste will give an earthy smell.
(3) Presence of lumps: The cement should be free from any hard lumps. The lumps are formed by the absorption of moisture from the atmosphere. Any bag of cement containing such lumps should be rejected. This Field tests for cement are carried out to check lumps.
(4) Strength: This Field tests for cement is to check strength of cement and can be roughly ascertained in the following ways:
(i) The briquettes with a lean or weak mortar are made. The size of briquette may be about 75 mm x 25 mm x 12 mm. The proportion of cement and sand may be 1:6. The briquettes are immersed in water for a period of 3 days. If cement is of sound quality, such briquettes will not be broken easily and it will be difficult to convert them into powder form.
(ii) A block of cement 25 mm x 25 mm and 200 mm long is prepared and it is immersed for 7 days in water. It is then placed on supports 150 mm apart and it is loaded with a weight of 340 N. The block should not show signs of failure.
(iii) A thick paste of cement with water is made on a piece of thick glass and it is kept under water for 24 hours. It should set and not crack.