Standard Test Method for
Dispersive Characteristics of Clay Soil by Double
Hydrometer1

This standard is issued under the fixed designation D 4221; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of the last revision. A number in parentheses indicates the year of the last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.

1. Scope

1.1 This test method, when used in conjunction with a test
performed by Test Method D 422 on a duplicate soil sample,
provides an indication of the natural dispersive characteristics
of clay soils (1).2

1.2 This test method is applicable only to soils with a
plasticity index greater than 4 as determined in accordance
with Test Method D 4318 and more than 12 % of the soil
fraction finer than 5-µm as determined in accordance with Test
Method D 422 (2).

1.3 This test method is similar to Test Method D 422, except
that this method covers the determination of percent of soil
particles smaller than 5-µm in diameter in a soil-water suspension without mechanical agitation and to which no dispersing
agent has been added.

1.4 The amount of particles smaller than 5-µm determined
by this method compared with the total amount of particles
smaller than 5-µm determined by Test Method D 422 is a
measure of the dispersive characteristics of the soil.

1.5 This test method may not identify all dispersive clay
soils. Pinholes (Test Method D 4647 and crumb tests, or both,
(3-5)or the analysis of pore water extract (4-7) may be
performed to help verify dispersion.

1.6 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.

2. Referenced Documents

2.1 ASTM Standards:
D 422 Test Method for Particle-Size Analysis of Soils3
D 653 Terminology Relating to Soil, Rock, and Contained
Fluids3
D 1193 Specification for Reagent Water4

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