Determination of Soundness of Cement by Le-Chatlier’s Principle

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Soundness of cement can be defined as its ability to retain its volume after it gets hardened. This means that a properly sound cement will undergo minimum volume change after it converts into the hardened state. In the soundness test of cement, we determine the amount of excess lime. This test can be conducted by Le-chatelier method and Autoclave Method. Here we will discuss Le-chatlier method of determining the soundness of cement.

Significance of Soundness Test on Cement

Cement is a composition of lime, silica, alumina, magnesia, alkaline, sulfur trioxide, iron oxide, and calcium sulfate. Among which, lime constitutes 60 to 70%. Hence, a cement deficient in lime will set quickly and will affect the property of the cement. Lime content in higher amount will make the cement unsound. An unsound cement will affect the quality of the cement work performed. This demands of soundness test of cement before using it. Through this test, it is ensured that the cement won’t undergo any sort of expansion due to the presence of excess amount of lime.

Le-Chatlier's Soundness Test on Cement

Apparatus

1. Le- chatelier mould
2. Cement
3. Glass sheets
4. Mixing pan
5. Trowel
6. Wight

The mould consists of a small split cylinder of spring brass or other suitable metal of 0.5mm thickness forming of a mould 30mm internal diameter and 30mm height. On either side of the split are attached to indicators with pointed ends A-A- the distance from these ends to the center of the cylinder being 165mm. The mould shall be kept in good condition with the jaws not more than 0.5mmapart.

Procedure For Soundness Test on Cement

1. The Le- chatlier mould and the glass plates are lightly oiled before conducting the test
2. Prepare a cement paste as in consistency test with 0. 78 times the water required to give a paste of standard consistency
3. Fill the cement paste in the Le- chatelier mould taking care to keep the edges of the mould gently together during the operation.
4. Cover the mould with another piece of a glass plate and place a small weight over the cover plate.
5. Submerge the whole assembly immediately in water at a temperature of 27o+-2oC and keep it there for 24 hours.
6. Take out the assembly again in water at 27+/- 2 deg C. The distance between the indicator points are measured as A.
7. Submerge assembly again in water at 27  +/- 2 deg C
8. Bring the water to boiling in 25 to 30 minutes and keep at boiling for 3 hours. The assembly should be immersed in water during this process.
9. Remove the mould from water and allow it to cool to 27 +/- 2 deg C
10. Measure the distance between the indicator points as B.

Calculations

Expansion= B- A = Here, A = The measurement taken after 24hours of immersion in water at 27 ± 2­­degree Celsius B = The measurement taken after 3hours of immersion in water at boiling temperature

Conclusion

The value of soundness of cement obtained for Ordinary Portland Cement (OPC), Low heat cement, high alumina cement and rapid hardening cement must not exceed 10mm. The Le-chatlier’s Method helps us to determine the lime present in the cement in excess. This is the excess lime that causes expansion of cement.

Precautions

1. The test is conducted with special care and guidance
2. Filling of moulds must not be done by applying extra pressure.
3. During the process of boiling, the water level must not go below the height of the mould