ASTM D4944-18

5.1 The water content of soil is used throughout geotechnical engineering practice, both in the laboratory and in the field. Results are sometimes needed within a short time period and in locations where it is not practical to install an oven or to transport samples to an oven. This test method is used for these occasions.

5.2 The results of this test have been used for field control of compacted embankments or other earth structures such as in the determination of water content for control of soil moisture and dry density within a specified range.

5.3 This test method requires specimens consisting of soil having all particles smaller than the 4.75 mm (No. 4) sieve size.

5.4 This test method may not be as accurate as other accepted methods such as Test Method D2216. Inaccuracies may result because specimens are too small to properly represent the total soil, from clumps of soil not breaking up to expose all the available water to the reagent and from other inherent procedural, equipment or process inaccuracies. Therefore, other methods may be more appropriate when highly accurate results are required, or when the use of test results is sensitive to minor variations in the values obtained.

1.1 This test method outlines procedures for determining the water (moisture) content of soil by chemical reaction using calcium carbide as a reagent to react with the available water in the soil producing a gas. A measurement is made of the gas pressure produced when a specified mass of wet or moist soil is placed in a testing device with an appropriate volume of reagent and mixed.

1.2 This test method is not intended as a replacement for Test Method D2216; but as a supplement when rapid results are required, when testing is done in field locations, or where an oven is not practical for use. Test Method D2216 is to be used as the test method to compare for accuracy checks and correction.

1.3 This test method is applicable for most soils. Calcium carbide, used as a reagent, reacts with water as it is mixed with the soil by shaking and agitating with the aid of steel balls in the apparatus. To produce accurate results, the reagent must react with all the water which is not chemically hydrated with soil minerals or compounds in the soil. Some highly plastic clay soils or other soils not friable enough to break up may not produce representative results because some of the water may be trapped inside soil clods or clumps which cannot come in contact with the reagent. There may be some soils containing certain compounds or chemicals that will react unpredictably with the reagent and give erroneous results. Any such problem will become evident as calibration or check tests with Test Method D2216 are made. Some soils containing compounds or minerals that dehydrate with heat (such as gypsum) which are to have special temperature control with Test Method D2216 may not be affected (dehydrated) in this test method.

1.4 This test method is limited to using calcium carbide moisture test equipment made for 20 g, or larger, soil specimens and to testing soil which contains particles no larger than the 4.75 mm (No. 4) Standard sieve size.

1.5 The values stated in SI units are to be regarded as standard. The inch-pound units given in parentheses are mathematical conversions, which are provided for information purposes only and are not considered standard.

1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026 unless superseded by this standard.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.