It is very important that the cement after setting shall not undergo any appreciable change of volume. Certain cements have been found to undergo a large expansion after setting causing disruption of the set and hardened mass. This will cause serious difficulties for the durability of structures when such cement is used. The unsoundness in cement is due to the presence of excess of free lime than that could be combined with acidic oxide at the kiln. It is also likely that too high a proportion of magnesium content or calcium sulphate content may cause unsoundness in cement. Soundness of cement may be determined by two methods, namely Le-Chatelier method and autoclave method.
In the soundness test a specimen of hardened cement paste is boiled for a fixed time so that any tendency to expand is speeded up and can be detected. Soundness means the ability to resist volume expansion.
Fig. 1: Le-Chateliers Apparatus
Le- Chatelier apparatus conforming to IS : 5514-1969
Fig. 2: Schematic of Le-Chateliers Apparatus
Consist of a small split cylinder of spring brass to other non-corrodible 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. The temperature of the moulding room, dry materials and water shall be maintained at 27±2°C The relative humidity of the laboratory shall be 65 ± 5 percent. The moist closet or moist room shall be maintained at 27 ± 2°C and at a relative humidity of not less than 90 percent.
Fig. 3: 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 minutes.
Fig. 4: Vernier Calliper
Vernier Calliper should be able to measure upto 30 mm with least count of 0.1 mm
Fig. 5: Balance
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.
The permissible variations on weights in use in weighing the cement shall be as prescribed in Table 1.
Table 1 : Permissible Variations on Weights
|Weight (g)||Permissible Variation on Weights in use Plus or Minus (g)|
IS 4031(Part 3):1988 Methods of Physical Test for Hydraulic Cement: Determination of Soundness. Reaffirmed- May 2014
Soundness/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.