water content determination by calcium carbide method / moisture content determination

water content determination by calcium carbide method / moisture content determination 

Determination of Moisture Content of Soil by Calcium Carbide Method           Calcium carbide method is one of the commonly used laboratory test for determination of water or moisture content. This test also called as Speedy moisture tester. this test is conducted as per IS2720 (Part-II) - 1973 Materials and Apparatus for Calcium Carbide Method            The soil samples used for these tests are taken in 6, 26 and 200 gram sizes. The basic apparatus include: 1.      Moisture Tester 2.      Scale for weighing the soil sample 3.      Scoop for measuring the reagent 4.      A sturdy Carrying case 5.      Steel Balls 6.      Calcium Carbide Reagent   Sample Preparation for Calcium Carbide Method            If the soil sample is 26 gm, the three scoops of calcium carbide reagent and two balls are placed in large chamber of the tester. These steel balls are used for breaking down the cohesive materials in the case of 26 gm grain sample. When a 6 gm sample tester is used, a level scoopful of calcium carbide is placed in the chamber without the addition of steel balls. The calcium carbide reagent is available in cans in finely pulverised material form. This reagent produces 2.25 cu.ft of acetylene gas per pound of calcium carbide. Procedure The following procedure is to flowed to conduct calcium carbide test, 1.      The test sample is weighed for weights 6, 26 and 200 grams on a weighing machine. 2.      After weight the soil sample is placed on the cap of the testing cap. Then maintain the pressure vessel in a horizontal position, insert the cap in the pressure vessel. After that seal and tight with the help of clamp. The sample does not contact with calcium carbide, 3.      Now, the pressure vessel is raised in the vertical position that the soil in the cap falls into the pressure vessel. 4.      In order to break the lumps present in it, the tester is vigorously shaken. This helps calcium carbide to react with all the free moisture present. 5.      If steel balls are used in the tester, the shaking must be performed with the help of rotating motion. This is to avoid any damage to the instrument and to avoid the possibility of soil particles to get embedded with the orifice reading ( Used to make pressure diagram). 6.      For granular soils, shaking is performed for 1 minute and for other soils, the shaking is performed for 3 minutes. This shaking helps to perform the complete reaction of the calcium carbide reagent and the free moisture. This reaction is exothermic, hence time must be provided to allow dissipation of the heat generated. 7.      The dial reading when stops to move, the instrument is kept in a horizontal position at the eye level and the reading is taken. 8.      Now the weight of the sample and the dial reading is recorded. 9.      Slowly release the gas pressure by keeping the cap of the instrument pointed away from the operator. 10. The pressure vessel is emptied and check for lumps if any. If the sample is not completely pulverized, the test is repeated for a new sample. 11. The dial reading obtained is the percentage of moisture by wet weight. It must be converted into dry weight percent.   Calculation and Result in Calcium Carbide Test The reading obtained is in wet moisture basis (m). This must be converted into water content on dry mass basis, which is calculated as: w = [m/(100-m)] x 100