Determination of Soundness of Cement by Le-Chatelier method

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. The unsoundness in cement is due to the presence of excess of lime than that could be combined with acidic oxide at the kiln. It is also likely that too high a proportion of magnesium content or calcium sulphate content may cause unsoundness in cement.

AIM:

To determine the soundness of a given sample of cement by Le-Chatelier method.

Apparatus:

·         Le- Chatelier test apparatus conform to IS : 5514-1969,

·         Balance,

·         Gauging Trowel,

·         Water Bath etc.

FIGURE:

Procedure:

1.   Before commencing test, do the consistency test to obtain the water required to give the paste normal consistency (P). 

2.   Prepare a paste by adding 0.78 times the water required to give a paste of standard consistency (i.e. 0.78P). 

3.   Lightly oil the Le-chatelier mould and place it on a lightly oiled glass sheet.

4.   Fill the mould with the prepared cement paste. In the process of filling the mould keep the edge of the mould gently together. 

5.   Cover the mould with another piece of lightly oiled glass sheet, place a small weight on this covering glass sheet. 

6.   Submerge the whole assembly in water at a temperature of 27 ± 20 C and keep there for 24 hours. 

7.   Remove the whole assembly from water bath and measure the distance separating the indicator points to the nearest 0.5 mm (L1). 

8.   Again submerge the whole assembly in water bath and bring the temperature of water bath to boiling temperature in 25 to 30 minutes. Keep it at boiling temperature for a period of 3 hours. 

9.   After completion of 3 hours, allow the temperature of the water bath to cool down to room temperature and remove the whole assembly from the water bath. 

10.                Measure the distance between the two indicator points to the nearest 0.5 mm (L2).

Observation:

Express the amount of water as a percentage by mass of the dry cement to the first place of decimal.

Sr. No.	Distance separating the indicator submerge in normal temp water for 24 hours	Distances separating the indicator submerge in boiling for three hours.	The difference between these two measurements	Remark
1.
2.
3.
4.

Conclusion:

The given cement is said to be sound / unsound.

Why soundness test is required to be carried out on cement?

Quality control during the manufacturing of cement influences its soundness. The unsoundness in cement is due to the following factors during its production:

·         If there is an excess of lime present in the cement. 

·         If the cement would have undergone inadequate burning. 

·         Insufficiency in fineness of grinding or non-uniform mixing of raw materials. 

·         If there is too high a proportion of magnesium content in the cement. 

·         If there is too high calcium sulphate content in the cement.

As unsoundness in cement does not show up for a considarable period of time, accelerated tests are required to detect it before using the cement in the work.

How to achieve better soundness of cement?

To achieve better soundness properties of cement,

·         The magnesia content allowed in cement is limited to not more than 6 per cent. 

·         Calcium sulphate (CaSO4) ie gypsum is added to the clinker while grinding to prevent flash set of cement. 

·         The quantity of gypsum in cement manufacturing varies from 3 to 5 per cent depending upon Tricalcium Silicate (C3A) content.

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