Soundness of Cement
The soundness of cement is an ability of hardened paste after setting to retain its volume and it is very important that the cement shall not undergo any appreciable change of volume after setting.
Certain types of cement after setting have been found to undergo a large expansion causing disruption of hardened mass and the set. So, the soundness of cement is an ability to retain its volume after it gets hardened.
In soundness of cement test a specimen of hardened cement paste is boiled for a fixed time and by doing this any tendency to expand is speeded up and can be detected and most used test for the soundness of cement is “Le Chatelier Apparatus Test”.
On the setting of cement, it is understood that, its capacity to form a non-disintegrating, hard uniform strong mass by the soundness of cement test.
As we know that cement consists of eight micro-ingredients such as;
- Iron oxide
- Calcium sulfate
- Sulfur Trioxide
In order to make cement perfect, each has its own set of properties and characteristics like lime are the main product which contributes almost 70 percent.
The excessive amount of lime makes the cement unsound while deficiency of lime makes the cement set quicker.
As unsoundness of cement makes the work saggy as shown in fig below;
That’s why before using we test the soundness of cement and this test ensures that the cement will not go any subsequent expansions.
Methods of Soundness of Cement:
There are two methods for the soundness of cement such as;
- Le Chatelier Apparatus Test
- Autoclave Method
Le Chatelier Apparatus Test:
The Le Chatelier Apparatus Test is used for the soundness of cement.
Having an internal diameter of 30 mm it consists of a small, split, metallic cylinder and it has 30 mm in height, with the thickness of being 0.5 mm of the wall.
With two indicators it is fixed and 165 mm is the distance from the end of the indicator to the center of the cylinder.
There are also some other apparatus used in Le Chatelier Apparatus Test;
- Measuring box
- Water bath
- Le Chatelier apparatus
- Glass sheets
- Enamel tray &
The cement to be tested is made into a paste of specified consistency and 100 gm of cement is mixed with water calculated at 0.72 p in common practice. Where ‘p’ is the percentage of water required for making a paste.
To give the past normal consistency do the consistency test to obtain the water required before the cement setting-time test.
- By adding 0.78 times the water, prepare a paste to give a paste standard consistency and lightly oil the Le Chatelier mold and on lightly oiled glass sheet place it.
- In the cylindrical mold, the paste of unknown consistency is filled and covered with a glass sheet and for 24 hours kept under the water at 27 degrees to 32-degrees centigrade.
- Then the cylinder is taken out and between the two indicators distance is measured as the name it as x and the in the water it is again immersed.
- Then the water is brought to the boiling point in 15 to 30 minutes and kept boiling for one hour. Then the distance between the two indicators is again measured as the name it as y.
- In the setting, the difference of x-y gives the expansion of cement specimen.
- For the cement to qualify as soundness cement, it is specified that this distance shall not exceed 10 mm.
Keep in mind that the test should be done again from the same sample if the sample does not comply with the specified requirements.
There are several precautions in this test such as;
- While taking the measurements, good care should be taken.
- On the mold, while filling it, do not apply more pressure.
- During boiling the water level should not fall below the height of the mold.
- The determined expansion should not exceed 10 mm.
Observation and Recording:
The soundness of cement is equal to L1 – L2.
L1 is the measurement taken after 24 hours of immersion at a temperature of 27 ± 20C in water.
L2 is the measurement taken after 3 hours of immersion at boiling temperature in water.
For ordinary or OPC, rapid, low heat, PPC, and high alumina cement this value must not exceed 10 mm.
||100 C (min)
Enamel tray and trowel is also used.
- With mineral oil thinly cover the mold and then attach the reference points to get 250 mm of effective length.
- To give a paste standard consistency take 500 g of cement and mix with sufficient water and then by pressing the paste into corners by thumb after mixing fill the mold in one or two layers.
- Then store it in a moist room for a period of 24 hours after completion of preparation of the mold and remove the specimen from the moist atmosphere, measure its length L1 and place it in the autoclave at room temperature.
- Left the vent valve open until steam begins to escape to permit air to escape from the autoclave during the early portion of the heating period.
- From the time, heat turned on to make the gauge pressure less than 0.1 N/mm2 in 1 to 1.5 hours and for 3 hrs this pressure is maintained.
- Switch off the autoclave after 3 hours and let it be closed to make the pressure less than 0.1 N/mm2 in one hour and by opening the vent valve bring it to the atmospheric pressure.
- Then from autoclave remove the specimen and place it in water maintained at a 900C temperature and in 15 minutes cool the water to 27±20C.
- Dry the specimen surface and measure its length L2.
There are some important points to know such as;
- The volume expands due to the unburnt lime and magnesia in cement mortar and cement concrete.
- To determine the presence of unburnt lime (CaO) Le Chatelier Apparatus Test is used.
- Due to unburnt lime, the cracks develop in the structure because it increases the cement volume.
- The other reason for cracks in structure is that lime and magnesia react with water and in the cement increase in volume occurs.