Determining the Moisture Content of Soil (Microwave Oven Method) - Soil Properties: Testing, Measurement, and Evaluation - page 52

In using microwave ovens for drying, care must be exercised to en-
sure that soil is not overheated, thereby causing a spuriously high read-
ing of moisture content. To avoid this, the method presented uses an
incremental drying procedure. Using microwave ovens having settings
at less than full power can also be helpful in reducing overheating.
It should also be noted that when soil is subjected to microwave
energy, its behavior depends on its mineralogical composition. There-
fore, no one procedure is applicable to all types of soil. The procedure dis-
cussed in this chapter serves only as a guide when using microwave
ovens to determine moisture content of soils.

Microwave oven (preferably with a vented chamber and variable
power controls; input power ratings of 700 W are adequate)
Balance (with accuracy of 0.01 g)
Containers (must be suitable for microwave ovens—i.e., nonmetal-
lic and resistant to sudden and extreme temperature change; porce-
lain, glass, and even paper containers are generally satisfactory)
Glove or potholder
Desiccator (a cabinet or jar of suitable size containing silica gel,
anhydrous calcium phosphate, or equivalent)
Heat sink (a material or liquid placed in the microwave to absorb en-
ergy after the moisture has been driven from the test specimen; the
heat sink reduces the possibility of overheating the specimen and
damage to the oven; glass beakers filled with water and materials
that have a boiling point above water, such as nonflammable oils,
have been used successfully; moistened bricks have also been used)
Stirring tools (spatulas, putty knives, and glass rods for cutting and
stirring the test specimen before and during the test; short lengths
of glass rods have been found useful for stirring and may be left in
the specimen container during testing, reducing the possibility of
specimen loss due to adhesion to the stirring tool)

APPARATUS
AND SUPPLIES [1]

(1) Handle hot containers with a container holder. Some soil types
can retain considerable heat, and serious burns could result from
improper handling.

HAZARDS [1]

(2) Suitable eye protection is recommended due to the possibil-
ity of particle shattering during the heating, mixing, or mass
determinations.

(3) Safety precautions supplied by the manufacturer of the mi-
crowave should be observed. Particular attention should be paid to
keeping the door sealing gasket clean and in good working condition.

Note 1 —The use of a microwave oven for the drying of soils
may be considered abusive by the manufacturers and consti-
tute voiding of warranties. Microwave drying of soils contain-
ing metallic materials may cause arcing in the oven. Highly