Wednesday, 10 April 2019

TESTS ON CEMENT

A. Field Tests

Carried out to roughly ascertain the quality of cement.
1. Colour :
·       Should be uniform and in grey color with light greenish shade.
·       Gives an indication of excess lime or clay and the degree of burning.
2. Physical properties  :
·       Should feel smooth when rubbed between fingers.
·       It should sink, but not float when a small quantity of cement thrown in a bucket.
·       Should feel cool and not warm when the hand is inserted in a bag/heap of cement.
3. Presence of  Lumps :
·       Should be free from any hard lumps.

B. Laboratory Tests

1. Fineness
·       Carried out to check proper grinding of cement.
·       Determined either by sieve test or by permeability apparatus test.
·       In permeability test, 'specific surface area' is calculated as a measure of the frequency of the average size of particles, expressed in cm2/g.
·       It should not be less than 2250 cm2/g for OPC, 3250 cm2/g for rapid hardening and 3200 cm2/g for low heat cement.
2. Consistency : 
·       To determine the % of the water required for making workable cement paste.
·       Apparatus  used Vicat's apparatus with Vicat plunger of 1 cm diameter.
·       As per Vicat's test, the percentage of water added to cement at which the needle penetration is in between 5 - 7 mm ( from the bottom of the mold) is called ''Consistency".
·       For OPC, consistency is around 30%.
3. Setting Time : 
Initial setting time :
·       Determined by Vicat's apparatus using Vicat's needle of 1mm squared needle.
·       Water added to cement is added 0.85 times the water required for standard consistency. the weight of the cement taken is 300 g to carry out this test.
·       Period elapsing between the time when water is added to the cement and the time at which the needle fails to pierce the test block by 5 plus minus 0.5 mm is taken as the initial setting time.
·       For OPC, it should not be less than 30 minutes for low heat cementsit should not be less than 60 minutes.
Final setting time :
·       Determined by Vicat's apparatus using Vicat's needle with an annual collar of 5 mm diameter.
·       Time lapsed since the addition of water to time at which needle with an annual collar can only make a mark on the hard concrete surface, but not piercing is taken as final setting time.
·       It should not be more than 10 hours for OPC.
4. Soundness
·       Soundness refers to the ability of cement to maintain a constant volume.
·       Carried out to detect the presence of uncombined lime in the cement.
·       Determined by Le-chatelier's apparatus or autoclave test.
·       Lechatelier's method measures expansion due to lime and autoclave method measures expansion due to magnesia.
·       Expansion more than 10 mm indicates unsoundness of cement.
5. Heat Of Hydration
·       Hydration is the process of adding water to cement.
·       Determined by adiabatic calorimeter test or vacuum flask test.
·       For OPC. the heat of hydration at 7 days should not be more than 65 cal/g and at 28 days should not more than 75 cal/g.

6. Specific Gravity
·       Determined through a test conducted - using kerosene and specific gravity bottle at 27-degree temperature.

·       Specific gravity for OPC is about 3.1.


By : Dipali Pounikar


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