Standard Method of Test for
The California Bearing Ratio
AASHTO Designation: T 193-99 (2007)
1.1.This test method covers the determination of the California Bearing Ratio (CBR) of pavement subgrade, subbase, and base/course materials from laboratory compacted specimens.
The test method is primarily intended for but not limited to, evaluating the strength of cohesive materials having maximum particle sizes less than 19 mm (314 in.).
1.2.When materials having maximum particle sizes greater than 19 mm (3/4 in.) are to be tested, this test method provides for modifying the gradation of the material so that the material used for tests all passes the 19.0-mm (314-in.) sieve while the total gravel 4.75-mm (No. 4) to 75-mm (3-in.) fraction 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 base has 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.
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