It is very important that the cement shall not undergo any appreciable change of volume. The change in volume causes disruption of the set and hardened mass of concrete. This will seriously affect the durability of concrete. The soundness test of cement is done to ensure that the cement does not show any appreciable change in volume.
The unsoundness in cement is due to the presence of the excess of Lime than that could be combined with acidic oxide at the kiln. It could also be due to the high proportion of magnesium or calcium sulphate.
Unsoundness in cement does not come to surface for a considerable period of time. Therefore, accelerated tests are required to detect it.
The Le-Chatelier test detects unsoundness due to the excess Lime ONLY.
The unsoundness in cement is due to the presence of the excess of Lime than that could be combined with acidic oxide at the kiln. It could also be due to the high proportion of magnesium or calcium sulphate.
Unsoundness in cement does not come to surface for a considerable period of time. Therefore, accelerated tests are required to detect it.
Le-Chatelier Method to detect unsoundness as per IS:4031-Part 3:
The Le-Chatelier test detects unsoundness due to the excess Lime ONLY.
The test apparatus shall conform to IS 5514:1996.
The variation on balance in use shall be +/- 1.0 gram per 1000 gram. The permissible value of a new balance shall be half of this value.
The permissible value on weight are given below:
Weight (g)
Permissible variation on weight (g)
Weight (g)
Permissible variation on weight (g)
500
0.35
20
0.05
300
0.30
10
0.04
250
0.25
5
0.03
200
0.20
2
0.02
100
0.15
1
0.01
50
0.10
Water Bath capable of containing immersed Le-Chatelier moulds with specimens and of raising their temperature from $27\pm 2^\circ C$ to boiling in $27 \pm 3$ minutes.
Procedure:
- Prepare the cement paste by gauging cement with 0.78 the water required to give a paste of standard consistency.
- Place the lightly oiled mould on a lightly oiled glass sheet and fill it with cement paste.
- Cover the mould with another piece of a lightly oiled glass sheet and place a small weight on the covering glass sheet.
- Submerge the whole assembly in water at temperature $27 \pm 2^\circ C$ immediately and keep it there for 24 hours.
- Measure the distance separating the indicator points to the nearest of 0.5 mm.
- Submerge the assembly again at the temperature as specified above and bring the water to boiling, while the assembly is submerged, in 25 to 30 minutes and kept it boiling for 3 hours.
- Remove the assembly from the water and allow it to cool and measure the distance between the indicator points.
- The difference between the two reading indicates the expansion of the cement
Retest: If the cement fails to meet the test for soundness, a retest may be made after aeration. For this purpose, spread out the cement in a layer of 75 mm thickness and store it for 7 days in an atmosphere maintained at a temperature of $27 \pm 2^\circ C$ and relative humidity of 50 to 80 %.
| Weight (g) | Permissible variation on weight (g) | Weight (g) | Permissible variation on weight (g) |
|---|---|---|---|
| 500 | 0.35 | 20 | 0.05 |
| 300 | 0.30 | 10 | 0.04 |
| 250 | 0.25 | 5 | 0.03 |
| 200 | 0.20 | 2 | 0.02 |
| 100 | 0.15 | 1 | 0.01 |
| 50 | 0.10 |
Le-Chatelier soundness limits for different types of cement
| Cement | Soundness (mm) Max | Cement | Soundness (mm) Max |
|---|---|---|---|
| 33 Grade OPC | 10 | Slag Cement | 10 |
| 43 Grade OPC | 10 | High Alumina Cement | 5 |
| 53 Grade OPC | 10 | Super Sulphated Cement | 5 |
| Sulphate Resisting Cement | 10 | Low Heat Cement | 10 |
| Portland Pozzolana Cement | 10 | Masonry Cement | 10 |
| Rapid Hardening Cement | 10 | OPC Grade 53 S [IRS-T-40] | 5 |
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