Contents
Soundness Test Of Cement
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 their 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.
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