Introduction to speedy moisture tester

speedy moisture tester is used to determine the moisture content or water content of soil on site or field, by means of calcium carbide gas pressure. The speedy moisture tester provides a quick result of moisture content of soil or aggregate on-field or site.

It is mainly useful for site or field determinations of moisture contents on the spot within 3 minutes. The speedy moisture tester is also known as calcium carbide gas pressure moisture tester.

Speedy moisture tester is a portable system for measuring the moisture content of a material that is passed on sieve no 4 (sieve #4) including soils, aggregates. The system of speedy moister tester consists of a low-pressure vessel fitted with a pressure gauge and an electronic scale and other accessories.

Types of speedy moisture tester

There are three types of speedy moisture tester

• large speedy moisture tester:

sample required for testing is 20-22 grams according to ASTM – D – 4944
sample required for testing is 20-22 grams according to AASHTO – T – 217
4 scoop of calcium carbide is required
the material used for this test is Sieve no 200 passed material

• small speedy moisture tester:

sample required for testing is 6 grams
2 scoop of calcium carbide is required
the material used for this test is Sieve no 200 passed material

• D-200 speedy moisture tester:

For aggregate, we use D-200 speedy moisture tester, the material used for this test is Sieve no 200 retained material.

Definition of Moisture Content:

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 percentages (%)

Mathematical Formula

moisture content= Dial reading/100-Dial reading x 100%

Apparatus

1. speedy moisture tester: speedy moister tester is capable to test a sample having a mass of at least 20 grams or 10 grams for half measure.
2. sieve no 4 (sieve #4, size 4.75 mm) passing materials
3. speedy moisture tester reagent is (calcium carbide cac₂)
4. steel balls: two steel balls
5. beam balance:
6. scoop: small scoop for measuring reagent
7. brush and cloth: for cleaning and other incidental items
8. Two pressure vessel: tightening of the head with a large chamber for not allowing the escape of gas.

components of speedy moisture tester

1. head/cap/small chamber
2. large chamber
3. Gauge for Dial Reading
4. screw
5. clamp
6. two rubber vessel
7. two steel balls

The chemical equation used in speedy moisture tester: CaC₂+H₂O → CaO + C₂H₂

calcium carbide CaC₂ reacts with water H₂O to form calcium oxide (CaO) and ethylene gas (C₂H₂).

The procedure of speedy moisture tester:

1. firstly pass the sample from sieve no 4
2. Before beginning the test, verify the inside of the body (large chamber) and cap (small chamber) are free from the residue of any previous test.
3. place the two steel balls into the body (large chamber) of the speedy moisture tester.
4. place two scoops of calcium carbide (CaC₂) in the body of speedy moisture tester.
5. weigh the sample of the exact weight specified by the manufacturer of the instrument in the balance provided i.e 6 grams of capability.
6. Place the sample in the cap (small chamber) of the tester.
7. with the pressure vessel in an approximately Horizontal position, Insert the cap in the pressure vessel and seal it by tightening the clamp.
   Note: taking care that no calcium carbide comes in contact with the soil until a complete seal is achieved
8. Hold the speedy moisture tester vertically so that the material in the cap falls into the speedy moisture tester body (large chamber).
9. Return the speedy to a horizontal position, shake it to break all the lumps, and mix the soil and reagent to start a reaction.
10. Shake with a rotating motion i.e (clockwise or anti-clockwise) to put the steel balls into orbit around the inside circumference. Rotate for 10 seconds, rest for 20 seconds. The rest time allows for the dissipation of the heat generated by the chemical reaction. Continue this cycle for a minimum of 3 minutes.
11. shake the instrument with a rotatory motion so that the steel balls will not damage the speedy moisture tester body or damage the dial gauge of the speedy.
12. when the needle stops moving or moves in reverse order, hold the instrument at Horizontal position at eye level with the dial reading facing you. read and record the dial reading to the nearest 0.1.
13. Hold tester away from the body. Point the directional release away from yourself and anyone else, then slowly release the pressure. Empty the contents and examine for lumps. If the material contains lumps, repeat the test.
14. Thoroughly clean the tester with the brush provided.
15. if the moisture content of the sample exceeds the limit of the pressure dial gauge (maximum reading 20), then one half (1/2) the size sample is used and the dial reading must be doubled.

Precautions:

• Do not mix the chemical (CaC₂₎ in an open atmosphere or before tightening the clamp.
• keep the speedy moisture tester in a horizontal position while clamping it.
• The tester should be shaken in a rotatory motion to save the speedy moisture tester from any damage.
• At the time of releasing the cap of the speedy keep it away from your body or anything else.
• Horizontal and vertical shaking is prohibited because it hits the sensor with the steel ball and damages the dial gauge of the speedy moisture tester. the shaking must be clockwise or anticlockwise.
• Note down the dial reading horizontally in front of your eye level.

Mathematical Formulas:

Moisture content= dial reading/100-dial reading x 100

Calculation: