Soundness Test on Cement: Le Chatelier method

Soundness Test on Cement

It is very essential that the cement after setting shall not undergo any appreciable change in volume, because change in volume after setting of cement causes

• cracks, 
• undue expansion,and as a result 
• disintegration of concrete.

Soundness of cement is determined using the Le Chatelier apparatus. This apparatus consists of a split  cylinder made of spring brass or other suitable metal.

The cylinder is 30 mm in diameter and 30 mm high. The cylinder has two indicator arms 165 mm long (measured from the center of the cylinder)  with pointed ends on either side of the split.

The procedure for test is explained in the following reference links:

http://www.theconstructioncivil.com/2009/11/soundness-test-on-cement.html

http://www.engineeringcivil.com/test-to-check-soundness-of-cement.html

And the following video shows how the test is conducted.

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

The unsoundness in cement is due to the following reasons:

• 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 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 C3A content.  

What happens if gypsum is more in cement?

If  gypsum is more than that could be combined with C3A, excess quantity of this gypsum will remain in the cement in free state.  This excess of gypsum causes expansion in cement when mixed with water and leads to disruption of the set cement paste.