Soundness Test Of Cement | Le Chatelier Apparatus | Soundness Test On Cement

What is Soundness of Cement ?

The soundness of cement means the change in the volume of Cement, during the process of setting & hardening.

Due to change in volume, the concrete element will crack, which can affect the quality of the structure or even cause serious accidents,

This can be known as poor dimensional stability.

This test determines the expansion of cement after it starts setting.

Some other kind of cement has been found to undergo a large expansion after setting causing disruption of the set & hardened mass.

This expansion of cement can cause serious problems for the durability of structures when such cement used in construction.

The soundness of cement can also be measured by two methods :

1. EN-196 (1995), which is based on the Le Chatelier test method

2. The autoclave test (ASTM-C151, 2015).

Significance of Soundness of Cement

The testing of the soundness of cement, to ensure that the cement does not show any appreciable amount of expansion.

The main reason for the unsoundness of cement, occurring mainly due to an excess lime that could be combined with acidic oxide at the kiln.

There is also another reason due to to inadequate burning, insufficient fineness of grinding or thorough mixing of raw materials.

As well as unsoundness in cement, may be also due to high a proportion of magnesium content/calcium sulphate content may cause

Due to these reason, the allowable magnesia content in cement was limited to 6%.

This done to prevent flash setting, calcium sulphate is added to the clinker while grinding. The quantity of gypsum added may vary from 3-5% depending upon C3A content.

If the addition of gypsum is more than could be combined with C3A, excess gypsum will remain in the cement in Free State.

This high % of gypsum leads to an expansion & consequent disruption of the set cement paste.

The unsoundness in cement majorly occurs due to excess lime, magnesia, or excessive proportion of sulphates. The unsoundness effect of cement does not observed to the surface for a considerable period of time.

Le Chatelier Test

The soundness of cement is tested with the help of Le – chatelier’s soundness method.

Soundness Test of Cement [ Le chatelier Test ]

IS Code for cement soundness Test is IS 4031-Part 3-1988

Soundness Test Apparatus

Le- chatelier mould
Cement
Glass sheets
Mixing pan
Trowel
Weight

It consists of a small split cylinder of brass or other sulfa metal. Le- Chatelier mould is 30 mm in diameter & 30 mm high.

Both sides of the mould are attached with two indicator arms 165 mm long with pointed ends.

After that, Water is added to cement as 0.78 P.

where, P - % of water for standard consistency of cement.

Then, paste is filled in mould & properly covered them with a glass plate on both faces of mould.

Procedure Of Soundness Test

First we have to do oiling properly to the mould & the glass plates before conducting the test.
After that Take 400 grams of cement sample.
For doing the soundness test, we have to first determine standard consistency of cement. For that Water is taken as 0.78P (Where P is water required for Standard consistency in percentage)
For example, we get the Standard consistency as 30% of water, then take water percentage for soundness is 0.78 x 30% = 23.4%.
So water mixed in 400 gm of cement will be 400 x (23.4/100) = 93.6ml.)
After calculations, we have to Make a well-mixed paste of cement & then fill in Le- Chatelier mould.
We have to take care that to keep the edges of the mould gently together during the operation.
After doing the above step, we have to just Clean the upper surface & make it smooth. Then just place a small weight over the cover plate.

Now we have to just, Put this assembly quickly in water at a temperature of 27º C +/- 2ºC and keep it for 24 hours.
After 24 hours, we have to Take out mould from water & measure the distance between the indicators points as Reading-1.(For example : it is 2 mm)
Now, again we have to put this assembly in boiling water for 25-30 minutes & keep at boiling for 3 hours. The mould should be in boiled water during this period
After completing 3 hours, we have to Remove the mould from the water. Keep allow it to cool at room temperature.
Finally, we have to Measure the distance between the indicator points as Reading-2. (Suppose it is 10mm)

The soundness of cement = (Reading-2) – (Reading-1)

= 10 mm – 2mm

= 8 mm

These result indicates the soundness of cement. The soundness limit must exceed 10 mm for ordinary, rapid hardening, as well as for low heat Portland cement.

If expansion is more than 10 mm as tested above, the cement is said to be unsound.

The Le Chatelier test has the drawback that it detects lime-caused unsoundness.

Also important thing in these test, that this method does not measure unsoundness caused by the presence of an excess of magnesia.

Indian Standard recommends that cement having a magnesia content of more than 3% shall be tested by Autoclave test, which is sensitive to both free magnesia and free lime.

For this test, a cement specimen 25 x 25 mm is placed in a standard autoclave & the steam pressure inside the autoclave is raised at such a rate as to bring the gauge pressure of the steam to 21 kg/sq cm in 1 — 1’/4 hour from the time the heat is turned on.

We have to maintain these pressure for 3 hours, after cooling the sample, the length is measured again.

The Stream pressure applied eventually accelerates the hydration of both magnesia and lime.

For determine the unsoundness due to excess calcium sulphate there is no satisfactory test is available.

But, we can easily determine the amount present in it by chemical analysis.

FAQs:

What is the purpose of the soundness test?

The testing of the soundness of cement, to ensure that the cement does not show any appreciable expansion. The unsoundness is occurring mainly due to an excess lime that could be combined with acidic oxide at the kiln.

What is Le Chatelier apparatus?

The simple & most popularly used instrument for measuring the Soundness Test of Cement is Le – chatelier’s soundness test.

IS code for soundness test of cement?

IS Code for soundness test of cement is IS:4031-Part 3-1988

Soundness Test

The soundness test of cement measured the expansion of cement after it starts setting. Common observation that cement has been found to undergo a large expansion after setting .

Which may causing disruption of the set & hardened mass.

The serious problems releated with durability occurs due to the expansion of cement.