Moisture Content Determination Using Rapid Moisture Meter
The purpose of this test is to determine the moisture content of soil quickly, without having to wait for the moisture to evaporate.
This test requires about 6 g of soil sample. Sand requires no special preparation. Coarse powders may be ground and pulverized. Cohesive and plastic soils and material are tested with addition of stee1 balls in the pressure vessels.
1. Rapid moisture meter
The apparatus required for the test includes one metallic pressure vessel with clamp for sealing cup and a gauge calibrated in percentage water. One counterpoint balance, a scoop for measuring calcium carbide and three steel balls of 12.5 mm diameter and one steel ball of 25 mm diameter.
Set up the balance and place the sample in the pan till the mark on the balance arm mass lines up with the index mark.
Unclamp the clamping screw to move the U-clamp off the cup. Lift off the cup. Clean the cup and the body.
Hold the body horizontally and gently deposit one level scoopful of calcium carbide halfway inside the chamber. Then lay the chamber down without disturbing the calcium carbide charge and transfer the soil weighed out as above from the pan to the cup.
Holding cup and chamber approximately horizontal bring them together, without disturbing sample or calcium carbide, bring the U clamp round and clamp the cup tightly into place.
With the gauge downwards, shake the moisture meter up and down vigorously for 5 seconds, then quickly turn it so that the gauge is upwards, give a tap to the body of the moisture meter to ensure that all the contents fall into the cup.
Hold the rapid moisture meter downward, again shake for 5 seconds, then turn it with gauge upwards and tap. Hold for one minute. Repeat this for a third time. Once more invert the rapid moisture meter and shake up and down to cool the gas. Turn the rapid moisture meter with the gauge upwards, and dial horizontal held at chest height when the needle comes to rest, take the reading. The readings on the meter are the percentages of water on the wet mass basis.
Alternatively, the three smaller steel balls can be placed in the cup along with the soil and the larger one in the body along with the absorbent and seal up the unit as usual. Hold the rapid moisture meter vertical so that the material in the cup falls into the body. Now holding the unit horizontally, rotate it for 10 seconds so that the balls are rolled round the inside circumference of the body. Rest for 20 seconds. Repeat the rotation – rest cycle until the gauge reading is constant (usually this takes 4 to 8 min). Note the reading as usual.
Finally release the pressure slowly (away from the operator) by opening the clamp screw and taking the cup out, empty the contents and clean the instrument with a brush.
Calculate the water content (W) on the dry mass from the water content (M) obtained on the wet mass basis as the reading on the rapid moisture meter, as follows: