AASHTO T 193-13 (2021) PDF Download

The AASHTO T 193-13 (2021) standard is a test method used to determine the California Bearing Ratio (CBR) of pavement subgrade, subbase, and base/course materials. It is designed for evaluating the strength of cohesive materials with maximum particle sizes less than 19 mm (¾ in.), but it can also be modified to test materials with larger particle sizes.

When testing materials with larger particle sizes, the standard allows for modifying the gradation of the material so that it passes through a 19.0-mm (¾-in.) sieve. However, it acknowledges that this modification may result in different strength properties compared to the original material. Despite this, the standard has been widely used, and design methods based on the results of tests using this procedure exist.

Materials with a substantial percentage of particles retained on the 4.75-mm (No. 4) sieve tend to have more variable CBR results, requiring more trials to establish reliable values. The standard specifies that the CBR can be determined at optimum water content or within a specified range of water content, based on a specified dry unit mass obtained from compaction tests.

Unless otherwise specified, or unless it has been demonstrated to have no effect on test results, all specimens are required to be soaked prior to penetration. This standard provides a standardized and consistent method for determining the CBR of materials used in road construction and helps ensure the quality and durability of pavements.