Soundness of Cement
Soundness of cement can be defined as its ability to retain its volume after hardening. If cement change its volume at the time of setting or hardening then its not sound. This means sound cement doesn’t go or undergoes minimum volume change after hardening. Lime content in cement plays significance role in soundness.
- Cement contains composition of lime, silica, magnesia, sulfur trioxide, iron oxide, calcium sulphate etc. Out of this lime has maximum content (60-70%). If lime content is then cement will harden fast and if its more then cement will become unsound.
- Soundness or volume change in cement or concrete may lead to cracks formation members. Cracks weakens the structure. So cement must be sound enough to resist volume change.
- Therefor finding out the soundness of cement is very important to avoid cracks or to maintain structure strength.
Le-Chateliers Apparatus:- Consist of small split cylinder of brass to other noncorrodible metal of 0.5mm thickness forming a mould of 30mm internal diameter and 30mm high. On either side of the split, two indicators are brazed suitably with pointed ends made of 2mm diameter brass wire in such a way that the distance of these ends to the centre of the cylinder is 165mm. The split cylinder will be kept
between two glass plates.
Water Bath: – Water bath capable of containing immersed Le-Chatelier moulds with specimens and of raising their temperature from 27±2°C to boiling in 27±3 minute.
Vernier Caliper: –Vernier Caliper should be able to measure up to 30 mm with least count of 0.1 mm
Wight Scale: – On balance in use, the permissible variation at a load of 1000 g shall be ± 1.0 g. The permissible variation on new balance shall be one-half of this value. The sensibility reciprocal shall be not greater than twice the permissible variation.
Test Procedure: –
You must know standard consistency of cement. Add 0.78P (P-Standard Consistency of Cement) of water in Sample cement.
Prepare a paste. Lightly apply oil in Brass cylinder and place La-Chateliers apparatus on glass plate.
Now Por cement paste in cylinder. Place a Glass plate on top as well.
Then, submerge the whole assembly for 24Hrs in water bath at a temperature of 270C
Remove entire apparatus after 24 hours from water. Then calculate the distance separating the two rod. It is our L1 note.
Again submerge the assembly in water. Water must be at boiling temperature
Remove it after 3 hours and calculate the distance between separating Rod. It’s our L2 note.
Expansion of cement = L1-L2
L1=Measurement taken after 24 hours of immersion in water at a temp. of 27 ± 20C
L2=Measurement taken after 3 hours of immersion in water at boiling temperature. Calculate the mean of two values to the nearest 0.5 mm.
Expansion Limits: –
|Types of Cement||Expansion Limits|
|Ordinary Portland cement [OPC] 33 Grade, 43 Grade, 53 grade||10mm|
|Portland Pozzolona Cement [PPC]||10mm|
|Rapid Hardening cement||10mm|
|Low heat cement||10mm|
|Super sulphated cement||5mm|