WATER CONTENT DETERMINATION (BY DIERCT HEATING METHOD) OBJECTIVE:

OBJECTIVE:

To estimate the amount of water or moisture present in the given quantity of soil in terms of its dry weight by direct heating.

NEED AND SCOPE OF THE EXPERIMENT

Determination of natural moisture content of the soil is required in almost all soil tests. The familiarization of the natural moisture content is essential in all studies of soil mechanics. Natural moisture content is used for evaluation of several parameters of soil properties such as bearing capacity and settlement etc. The natural moisture content will give an idea of the state of soil in the field.

THEORY

Water content or moisture content determination is a routine field test, the results of which are used in evaluation of several important engineering properties of soil. The determination of moisture content by direct heating involves removing of soil moisture by direct heating of a soil sample until the weight remains constant. The moisture content is expressed in percentage and is calculated from the sample weight before and after heating. 

The moisture content of a soil is frequently used throughout geotechnical engineering practice both in the laboratory and in the field. Moisture content determination of soils using Oven Drying Method ASTM D2216 needs considerable time which may not be feasible on occasions where more rapid results are required. Drying by direct heating is one such method can compensate urgency of results in field. Results of direct heating test have been demonstrated as satisfactory accurate for use in filed control work, such as in the determination of in-situ dry density of soils.

Mathematically it can be written as;

ω = (W_w  / W_s ) x 100

W_w       = Weight of Soil Water

W_s        = Weight of Soil Solids

APPARATUS

1. Moisture tins/containers
2. Weighing balance (Least count of 0.01 grams)
3. Electric, gas, butane or oil stove (temperature control at 110 ^OC)
4. Container handling tools (gloves or any suitable apparatus
5. Miscellaneous (as required)

PROCEDURE:

1. Take empty, clean moisture tin and mark it with an identifying number or code.
2. Weigh the container and record the weight as W₁ to the nearest 0.01 grams.
3. ake representative wet soil sample (not less than 20 grams) and place it quickly in the moisture tin.
4. Weight the moisture tin containing wet soil sample to the nearest 0.01 gram and record this weight as W_2.
5.  Place the moisture tin containing wet soil sample in any direct heating stove drying oven at constant temperature of 110^OC.
6. Continue application of heating until the specimen appears to be relatively dry. A comparatively uniform color should be visible at this stage. Record this weight as W₃.

LIMITATIONS

1. This test method is not suitable for flammable organic specimens or contaminants and use of other test methods is recommended.
2. Specimens tested in this test should not be used for performance of other test as localized high temperatures in the soil during testing may lead to change in physical characteristics, degradation of individual soil particles along with vaporization, chemical transition or loss of organics.
3. This test method may not be suitable when precise results are required or when minor variations in moisture content will affect the results of other test methods. a correction factor is required by making several comparisons between the results of this test method and Test Methods ASTM D2216.

PRECAUTIONS:

1. Additional care must be taken while testing sand and gravel size particles to avoid possibility of particle shattering.
2. Container holders or gloves should be used for handling of hot containers. Due to improper heating, some soils may retain considerable heat resulting into serious burns.
3. Safety glasses or goggles are recommended for suitable eye protection during testing for account of particle shattering during heating, mixing, or weighing.
4. Care should be taken from steam emerging during heating of the specimens and proper ventilation should be used over the specimen.

OBSERVATIONS AND CALCULATIONS

ω = (W_w  / W_s ) x 100 = ( W₂ - W₃/ W₃ - W₁) x 100

Where;

W₁ = Weight of container                                  =                                  (grams)

W₂= Weight of moist soil + container                =                                  (grams)

W₃= Weight of dried soil + container                 =                                  (grams)

Can No.
Wt. of wet soil + can (grams)
Wt. of dry soil + can (grams)
Wt. of can (grams)
Wt. of dry soil (grams)
Wt. of moisture (grams)
Water content (%)

             Moisture Content, ω = 

REFERENCE

ASTM D4959-07

Standard Test Method for Determination of Water (Moisture) Content of Soil by Direct Heating

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