It is very important that the cement after setting shall not undergo any appreciable change of volume. Certain cements have been found to undergo a large expansion after setting causing disruption of the set and hardened mass.This will cause serious difficulties for the durability of structures when such cement is used.This test is to ensure that cement does not show any appreciable subsequent expansion is of prime importance.
The unsoundness in cement is due to the presence of excess of lime than that could be combined with acidic oxide at the kiln.This is also due to inadequate burning of insufficiency in fineness of grinding or through mixing of raw materials.It is also likely that too high a proportion of magnesium content or calcium sulphate content may cause unsoundness in cement. For this reason the magnesia content allowed in cement is limited to 6%.
APPARATUS
i) The apparatus for conducting the Le-Chatelier test should conform to IS: 5514 - 1969
ii) Balance, whose permissible variation at a load of 1000g should be +1.0g
iii) Water bath
PROCEDURE
i) The mould is placed on a glass sheet and it is filled with the cement paste formed by gauging cement with 0.78 times the water required to give a paste of standard consistency.
ii) Then the mould is covered with another piece of glass sheet, a small weight is placed on its covering glass sheet and immediately the whole assembly is submerged in water at a temperature of 27 ± 2oC and kept it there for 24hrs.
iii) The distance separating the indicator points to the nearest 0.5mm is measured (say d l ).
iv) The mould is submerged again in water at the temperature prescribed above.The water is bought to boiling point in 25 to 30 minutes and it is boiled for 3hrs.
v) Then the mould is removed from the water, allowed to cool.The distance between the indicator points is measured (say d 2 ).
vi) (d 2 – d l) represents the expansion of cement.
REPORTING OF RESULTS
The mean of the two values to the nearest 0.5mm to represents the expansion of cement.
