1.1 This test method covers the determination of the California
Bearing Ratio (CBR) of laboratory compacted specimens.
The test method is primarily intended for, but not limited
to, evaluating the strength of materials having maximum
particle size less than 3⁄4 in. (19 mm).
1.2 When materials having a maximum particle size greater
than 3⁄4 in. (19 mm) are to be tested, this test method provides
for modifying the gradation of the material so that the material
used for testing all passes the 3⁄4-in. (19-mm) sieve while the
total gravel fraction (material passing the 3-in. (75-mm) sieve
and retained on the No. 4 (4.75-mm) sieve) remains the same.
While traditionally this method of specimen preparation has
been used to avoid the error inherent in testing materials
containing large particles in the CBR test apparatus, the
modified material may have significantly different strength
properties than the original material. However, a large experience
database has been developed using this test method for
materials for which the gradation has been modified, and
satisfactory design methods are in use based on the results of
tests using this procedure.
1.3 Past practice has shown that CBR results for those
materials having substantial percentages of particles retained
on the No. 4 (4.75 mm) sieve are more variable than for finer
materials. Consequently, more trials may be required for these
materials to establish a reliable CBR.
1.4 This test method provides for the determination of the
CBR of a material at optimum water content or a range of
water contents from a specified compaction test and a specified
dry unit weight. The dry unit weight is usually given as a
percentage of maximum dry unit weight determined by Test
Methods PS 4040 or PS 4041.

1.4.1 The client requesting the CBR test may specify the
water content or range of water contents and/or the dry unit
weight for which the CBR is desired.
1.5 Unless specified otherwise by the requesting client, or
unless it has been shown to have no effect on test results for the
material being tested, all specimens shall be soaked prior to
penetration.
1.6 Units—The values stated in inch-pound units are to be
regarded as standard. The SI units given in parentheses are
mathematical conversions, which are provided for information
purposes only and are not considered standard. Reporting of
test results in units other than inch-pound units shall not be
regarded as nonconformance with this test method.
1.6.1 The gravitational system of inch-pound units is used
when dealing with inch-pound units. In this system, the pound
(lbf) represents a unit of force (weight), while the unit for mass
is slugs. The slug unit is not given, unless dynamic (F = ma)
calculations are involved.
1.6.2 The slug unit of mass is almost never used in
commercial practice; that is, density, balances, etc. Therefore,
the standard unit for mass in this standard is either kilogram
(kg) or gram (g), or both. Also, the equivalent inch-pound unit
(slug) is not given/presented in parentheses.

1.6.3 It is common practice in the engineering/construction
profession, in the United States, to concurrently use pounds to
represent both a unit of mass (lbm) and of force (lbf). This
implicitly combines two separate systems of units; that is, the
absolute system and the gravitational system. It is scientifically
undesirable to combine the use of two separate sets of
inch-pound units within a single standard. As stated, this
standard includes the gravitational system of inch-pound units
and does not use/present the slug unit for mass. However, the
use of balances or scales recording pounds of mass (lbm) or
recording density in lbm/ft3 shall not be regarded as nonconformance
with this standard.
1.6.4 The terms density and unit weight are often used
interchangeably. Density is mass per unit volume whereas unit
weight is force per unit volume. In this standard, density is
given only in SI units. After the density has been determined,
the unit weight is calculated in SI or inch-pound units, or both.

1.7 All observed and calculated values shall conform to the
guidelines for significant digits and rounding established in
Practice D6026.
1.7.1 The procedures used to specify how data are collected/
recorded or calculated in this standard are regarded as the
industry standard. In addition, they are representative of the
significant digits that generally should be retained. The procedures
used do not consider material variation, purpose for
obtaining the data, special purpose studies, or any considerations
for the user’s objectives, and it is common practice to
increase or reduce significant digits of reported data to be
commensurate with these considerations. It is beyond the scope
of this standard to consider significant digits used in analytical
methods for engineering design.
1.8 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.
1.9 This 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.