Object: To determine the water content of soil sample by

Object: To determine the water content of soil sample by

1. Oven Drying Method
2. Hot Plate Method
3. Sand Bath Method
4. Speedy Moisture Tester
5. Infrared Moisture Tester

Standard:

AASHTOT265-80

ASTMD2216-8

BS1377: part 4

Apparatus:

Theory:

Dry basis:

• Water or moisture content is the measure of the water in the soil.
• Water is present in most naturally occurring soils and has a profound effect on soil behavior. Knowledge of moisture content is used as a guide to classification and as a subsidiary to almost all other field and laboratory tests of soil.
• The oven-drying method is the definitive method of measuring soil moisture content. Where oven drying is not possible, mainly on-site, the sand bath and hot plate methods are used.

Wet basis:

Speedy Moisture Tester:

The speedy moisture test, or calcium carbide method, is a rapid and reasonably accurate method of determining the water content of soil using a portable moisture content kit.

1. The method is based on the principle that when the water in the soil reacts with calcium carbide, acetylene gas is produced, and the pressure exerted by the acetylene gas on a diaphragm gives a measure of the water content.
2. The water content obtained from the calcium carbide method is based on the initial weight of wet soil. It should be converted to water content based on the dry weight of the soil.

Infrared Moisture Tester:

• This method enables rapid determination of the water content of soils by employing a device providing an infrared lamp for drying and a torsion balance for getting a percentage of water on a wet basis from a scale. The infrared torsion balance method allows rapid and accurate determination of water content. The result can be obtained in 15–30 minutes. The results obtained are convertible to water content on a dry basis.
• For both methods, the results obtained, i.e., water content, are converted to moisture content by formula.

Procedure:

Oven Drying Method:

1. Clean and dry the container, then weigh it to the nearest 0.1 g (W₁).
2. A representative sample should be crumbled and loosely placed in the container.
3. The container with the sample shall immediately be weighed (W2) and placed in the oven to dry at 105°C for a minimum of 12 hours.
4. After drying, weigh the container with the sample (W₃).

Hot Plate Method:

1. Clean and dry the container, then weigh it to the nearest 0.1g (W₁).
   
2. Obtain a sample of wet material.
   
3. Weigh the material to the nearest 0.1 gram (W₂).
   
4. Place the steel plate on the burner of the stove or gas hot plate. Steel plates are not required on electric hot plates. Place the pan holding the material on the steel plate
   
5. Stir the material during drying to prevent the temperature of the sample from exceeding 230° ± 9°F.
   
6. After drying, weigh the container with the sample (W₃ )
   

Sand Bath Method:

1. Clean and dry the container, then weigh it to the nearest 0.1 g (W₁).
2. Obtain a sample of wet material.
3. Weigh the material to the nearest 0.1 gram (W₂).
4. A metal tray or dish is filled with clean, coarse sand.
5. The sand bath is placed on some form of heater, such as a kerosene stove, a gas ring, or an electric ring.
6. The sample to be dried is placed in a heat-proof dish that is embedded in the surface of the sand. A low heat should be applied so that the sand becomes heated without causing damage to the bath.
7. The sample should be stirred and turned frequently to ensure the material at the base does not become too hot.
8. After drying, the sample is removed from the sand bath, and the sample is allowed to cool. When cool, the container and the dry soil are weighed in grams (W₃).

Speedy Moisture Tester:

1. Place 3 scoops of calcium carbide and two 1 1/4” steel balls in the chamber of the moisture tester.
2. Place the soil sample in the cap of the tester. Then, with the pressure vessel in an approximately horizontal position, insert the cap in the pressure vessel and seal the unit by tightening the clamp, taking care that no calcium carbide comes in contact with the soil sample until a seal is achieved.
3. Raise the moisture tester to a vertical position so that the soil in the cap falls into the pressure vessel.
4. Then shake the tester vigorously so that all the lumps will be broken up, permitting the calcium carbide to react with all the available free moisture. When steel balls are used in the tester, the instrument should be shaken with a rotating motion. This will prevent damage to the instrument and eliminate the possibility of soil particles becoming embedded in the orifice, leading to the pressure diaphragm.
5. Continue shaking for approximately one minute for granular soils and up to three minutes for other soils to allow for the complete reaction between the calcium carbide reagent and free moisture. Time should be permitted to allow dissipation of the heat generated by the chemical reaction.
6. When the dial indicator stops moving, read the dial while holding the instrument in a horizontal position at eye level.
7. Record the sample weight and the dial reading.
8. With the cap of the instrument pointed away from the operator, slowly release the gas pressure. Empty the pressure vessel and examine the material for lumps. If the sample is not completely pulverized, the test should be repeated using a new sample.
9. 
   
   
   The dial reading is the percent of moisture by wet weight and must be converted to dry weight percent.

Infrared Moisture Tester:

1. The lamp housing is raised, and the soil is evenly distributed on the sample pan.
   
2. The lamp housing is then lowered, and the infrared lamp is switched on.
   
3. A thermometer is inserted in its socket. The control knob is set between 105°C and 110°C. The soil sample now begins to lose water.
   
4. When the thermometer indicates a temperature of 110°C, the knob is adjusted in such a manner that there is no further increase in temperature.
   
5. The drum scale is rotated by turning the drum drive knob until the pointer returns to the index. The percentage of water content is directly read from the scale. The final reading is taken when the pointer is steady on the drum scale, which indicates that the soil has dried to a constant mass.
   
6. The water content read from the scale is based on the initial wet weight of soil.
   

Observations and Calculations:

Results:

The water content of the soil sample by the oven drying method is %. The water content of the soil sample by the hot plate method is %.

The water content of the soil sample by the sand bath method is %.

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