Calcium Carbide Method

• This is a field method used in the quick determination of water content for the purpose of proper field control such as in the case of compaction of an embankment. This method is also known as the Rapid Moisture Method.

Procedure

• A wet soil sample of 6 g is collected in an air-tight container aka moisture tester.

• It is now mixed with a sufficient quantity of fresh Calcium Carbide Powder.

• The mixture is thoroughly mixed by shaking it vigorously.

• The moisture present in the soil and the calcium carbide produces acetylene gas during the shaking of the mixture.

Reaction

• The gas thus produce exerts pressure on the sensitive diaphragm is placed at the end of the container.

• At the diaphragm, a dial gauge is located which reads the water content directly.

• However, the dial gauge is calibrated to give water content (w’) based on the wet of the soil sample, which can be converted using the relation between w & w’. 

w=w'1-w'
or 
w=w'100-w' 

Note: In order to check that no balls are formed, having wet soil inside and dry soil outside during the reaction with calcium carbide, the soil may be mixed with perfectly dry soil.
Also: Sometimes a big container is also used, which permits the use of 26 grams of soil sample containing clay. In this container, 2-30 mm diameter metal balls are used for proper pulverisation of clay soil during the shaking process.

Advantages

• This is a very quick method -  the results can be obtained in 5-10 mins.

• It contains a small kit of moisture tester, a small single-pan weighing balance, a bottle containing calcium carbide and a brush. No need of carrying heating equipment and a desiccator to the field.