ASTM D4959-16

5.1 The water content of a soil is used throughout geotechnical engineering practice both in the laboratory and in the field. The use of Test Methods D2216 for water content determination can be time consuming and there are occasions when a more expedient method is desirable. Drying by direct heating is one such method. Results of this test method have been demonstrated to be of satisfactory accuracy for use in field control work, such as in the determination of water content, and in the determination of in-place dry unit weight of soils.

5.2 The principal objection to the use of the direct heating for water content determination is the possibility of overheating the soil, thereby yielding a water content higher than would be determined by Test Methods D2216. While not eliminating this possibility, the incremental drying procedure in this test method will minimize its effects. Some heat sources have settings or controls that can also be used to reduce overheating. Loose fitting covers or enclosures can also be used to reduce overheating while assisting in uniform heat distribution.

5.3 The behavior of a soil when subjected to direct heating is dependent on its mineralogical composition, and as a result, no one procedure is applicable for all types of soils or heat sources. The general procedure of this test method applies to all soils, but test details may need to be tailored to the soil being tested.

5.4 When this test method is to be used repeatedly on the same or similar soil from a given site, a correction factor can usually be determined by making several comparisons between the results of this test method and Test Methods D2216. A correction factor is valid when the difference is consistent for several comparisons, and is reconfirmed on a regular specified basis.

5.5 This test method may not be appropriate when precise results are required, or when minor variations in water content will affect the results of other test methods, such as borderline situations where small variations in the measured water content could affect acceptance or rejection.

5.6 This test method is not appropriate for specimens known to contain flammable organics or contaminants, and other test methods should be utilized in these situations.

1.1 This test method covers procedures for determining the water content of soils by drying with direct heat, such as using a hotplate, stove, blowtorch, and the like.

1.2 This test method can be used as a substitute for Test Methods D2216 when more rapid results are desired to expedite other phases of testing and slightly less accurate results are acceptable.

1.3 When questions of accuracy between this test method and Test Methods D2216 arise, Test Methods D2216 shall be the referee method.

1.4 This test method is applicable for most soil types. For some soils, such as those containing significant amounts of halloysite, mica, montmorillonite, gypsum, or other hydrated materials, highly organic soils or soils that contain dissolved solids, (such as salt in the case of marine deposits), this test method may not yield reliable water content values due to the potential for heating above 110°C or lack of means to account for the presence of precipitated solids that were previously dissolved.

1.5 The values stated in SI units are to be regarded as standard. Performance of the test method utilizing another system of units shall not be considered non-conformance. The sieve designations are identified using the “standard” system in accordance with Specification E11, such as 2.0-mm and 19-mm, followed by the “alternative” system of No. 10 and ³/₄-in., respectively, in parentheses.

1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in D6026, unless otherwise 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 and health practices and determine the applicability of regulatory limitations prior to use.