Moisture Content Experiment

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  • Topic: Water, Water content, Mass
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  • Published : March 23, 2013
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Date: 09-02-2013
Experiment 1(a)
Laboratory determination of water (moisture) content of a soil sample by oven drying method Reference:
ASTM D2216-98

Need and scope of the experiment:
In almost all soil tests natural moisture content of the soil is to be determined. The knowledge of the natural moisture content is essential in all studies of soil mechanics. To sight a few, natural moisture content is used in determining the bearing capacity and settlement. The natural moisture content will give an idea of the state of soil in the field.  Apparatus:

1. Containers (Tin or Aluminum) with lids.
2. Balance, sensitive to 0.01gm
3. Oven with accurate temperature control at 110 + 5oC (230 + 9oF) Discussion:
1. Moisture Content (w)
It is defined as “the ratio of the mass of the ‘pore’ or ‘free’ water in a given mass of material to the mass of the solid material”. w=MwMs×100
Mw = Mass of water in grams
Ms = Mass of solid particles in grams (i.e. oven dried weight of soil)

2. Representative quantity of Test Specimen
The minimum mass of moist material selected to be representative of the total sample shall be in accordance with the following: Maximum particle size (100% passing)| Standard Sieve Size| Recommended minimum mass of moist test specimen for water content reported to ±0.1%| Recommended minimum mass of moist test specimen for water content reported to ±1%| 2 mm or less| No. 10| 20 g| 20 g|

4.75 mm| No. 4| 100 g| 20 g|
9.5 mm| 3/8-in.| 500 g| 50 g|
19.0 mm| ¾-in.| 2.5 kg| 250 g|
37.5 mm| 1½-in. | 10 kg| 1 kg|
75.0 mm| 3-in.| 50 kg| 5 kg|
NOTE-1If it is suspected that gypsum is present in the soil, the soil sample should not be subjected to a temperature beyond 80oC. Otherwise gypsum would lose its water of crystallization, thereby affecting the results of moisture content. Oven drying at 80oC may, however, be continued for a longer time in order to ensure complete evaporation of free water present in the sample. NOTE-2To assist the oven drying of large test samples, it is advisable to use containers having large surface area and break up the material into smaller aggregations. NOTE-3Since some dry materials may absorb moisture from moist specimens; the dried specimens should be removed before placing new wet soil samples in the oven. Procedure:

1. Take sufficient number. of empty, clean containers and mark them (if they are not marked) with an identifying number or code. 2. Weigh the container and record the weight as M1 to the nearest 0.01gm. 3. Take representative sample from different depths (0.25, 0.5, 0.75m) from the field. 4. Quickly place the representative sample of the wet soil in the container. 5. Immediately weigh the container with the wet soil sample to the nearest 0.01 gm. Record the weight as M2. In case it is not feasible to determine the weight immediately, cover the container with a lid. 6. Place the container with the soil sample in the drying oven at constant temperature of 110+5oC for 24 hours (till constant weight is achieved). 7. After 24 hours remove the container from oven and weigh to the nearest 0.01 gm. Record the weight as M3. Calculations:

Mass of empty container = M1=4.71(g)
Mass of empty container + wet soil = M2= 43.88(g)
Mass of container + dry soil = M3=37.41(g)
Mass of water = Mw = M2 - M3 = 6.47(g)
Mass of soil solids = Ms = M3 - M1 = 33.24(g)
Moisture Content = w=MwMs×100=M2-M3M3-M1×100
Soil Moisture Content Determination:
1| Depth ( )| |
2| Soil Description| |
3| Container No.| 143|
4| Mass of empty container (M1), g| 4.71|
5| Mass of Container + Wet Soil (M2), g| 43.88|
6| Mass of Container + dry Soil (M3), g| 37.41|
7| Moisture Content w = (M2 - M3)/(M3 - M1) %| 19.46 %|

Comments:
1) Oven drying is a time taking process and not much accurate as speedy moisture meter. 2) It needs caring for...
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