Introduction to the moisture content determination

This method covers laboratory moisture content determination in a sample. The sample may be of soil, aggregate or mix of soil aggregate.

DEFINITION: The ratio of the weight of water to the weight of dry soil in a given sample is called Moisture content. It is expressed in a percentage %.

Apparatus used in the moisture content determination of soil by oven drying method (ASTM D4643)

• Drying Oven: Thermostatically-controlled oven, capable of maintaining a uniform temperature of 110 ± 5°C throughout the drying chamber.
• Balances: Balance of 0.01 g readability is required for a sample having a mass of up to 200 grams. (excluding the mass of specimen container). and a balance of 0.1 g readability is required for specimens having a mass over 200 g sample.
• Containers: Suitable containers made of material resistant to corrosion and change in mass upon repeated heating, cooling and cleaning. Unless a desiccator is used, containers with close-fitting lids shall be used for testing specimens having a mass of less than about 200 g; while for specimens having a mass greater than about 200 g, containers without lids may be used. One container is needed for each water content determination.
• Container Handling Apparatus: Gloves, tongs, or suitable holders for moving and handling hot containers after drying.
• Miscellaneous apparatus: knives, spatulas, scoops, quartering cloth, sample splitters, etc, as required.

Thermostatically controlled oven

The procedure for the moisture content determination

1. Take a sufficient number of empty clean containers and mark them with an identifying number of codes.
2. Determine and record the weight/mass of the clean and dry container (and its lid, if used).
3. Select representative test specimens in accordance with the following Section.

Note: To be representative not less than 20 g shall be used.

4. Place the moist test specimen in the container and, if used, set the lid securely in position.

5. Determine the mass of the container and moist material using a balance selected on the basis of the specimen mass. Record this value in the calculation table

6. Remove the lid (if used) and place the container with moist material in the drying oven. Dry the material to a constant mass. Maintain the drying oven at 110 ± 5°C unless otherwise specified. The time required to obtain constant mass will vary depending on the type of material, size of the specimen, oven type and capacity, and other factors. The influence of these factors generally can be established by good judgment, and experience with the materials being tested and the apparatus being used.

NOTE —In most cases, drying a test specimen overnight (about 12 to 16 h) is sufficient. In cases where there is doubt concerning the adequacy of drying, drying should be continued until the change in mass after two successive periods (greater than 1 h) of drying is an insignificant amount (less than about 0.1 %). Specimens of sand may often be dried to constant mass in a period of about 4 hours when a forced-draft oven is used.

NOTE: Since some dry materials may absorb moisture from moist specimens, dried specimens should be removed before placing moist specimens in the same oven. However, this would not be applicable if the previously dried specimens will remain in the drying oven for an additional time period of about 16 h.

7. After the material has dried to constant mass remove the container from the oven (and replace the lid if used). Allow the material and container to cool to room temperature or until the container can be handled comfortably with bare hands and the operation of the balance will not be affected by convection currents and/or it is being heated.

8. Determine the mass of the container and oven-dried material using the same type/capacity balance used in before. Record this value in the calculation table.

NOTE: Cooling in a desiccator is acceptable in place of tight-fitting lids since it greatly reduces the absorption of moisture from the atmosphere during cooling especially for containers without tight-fitting lids.

Mathematical formulas

water content (%) = weight of water/weight of dry soil sample x 100

weight of water = (weight of container+wet sample) – weight of container+dry sample

weight of dry soil sample = (weight of container+dry sample) – (weight of the empty container)

Calculation of moisture content determination

Reporting the Results of water/Moisture content: Report the moisture content of the soil to two decimal figures.