Technical Services
Soil Characterization
  • California Bearing Ratio
  • Sand Equivalent
California Bearing Ratio

The California Bearing Ratio (CBR) test is a simple strength test that compares the bearing capacity of a material with that of a well-graded crushed stone (thus, a high quality crushed stone material should have a CBR @ 100%). It is primarily intended for, but not limited to, evaluating the strength of cohesive materials having maximum particle sizes less than 19 mm (0.75 in.). The basic CBR test involves applying load to a small penetration piston at a rate of 1.3 mm (0.05″) per minute and recording the total load at penetrations ranging from 0.64 mm (0.025 in.) up to 7.62 mm (0.300 in.)

Standard Test Methods are:
AASHTO T 193: The California Bearing Ratio
ASTM D 1883: Bearing Ratio of Laboratory Compacted Soils

Sand Equivalent

The sand equivalent test is a rapid field test to show the relative proportions of fine dust or clay-like materials in fine aggregate (or granular soils). The term “sand equivalent” expresses the concept that most fine aggregates are mixtures of desirable coarse particles (e.g., sand) and generally undesirable clay or plastic fines and dust (ASTM, 2003).These materials can coat aggregate particles and prevent proper asphalt binder-aggregate bonding.  In the sand equivalent test, a sample of aggregate passing the No. 4 (4.75 mm) sieve and a small amount of flocculating solution are poured into a graduated cylinder and are agitated to loosen the clay-like coatings from the sand particles. The sample is then irrigated with additional flocculation solution forcing the clay-like material into suspension above the sand. After a prescribed sedimentation period, the height of flocculated clay and height of sand are determined and the sand equivalent is expressed as a ratio of the height of sand over the height of clay. Higher sand equivalent values indicate “cleaner” (less fine dust or clay-like materials) aggregate.

The standard sand equivalent test is:
AASHTO T 176: Plastic Fines in Graded Aggregates and Soils by Use of the Sand Equivalent Test
ASTM D 2419: Sand Equivalent Value of Soils and Fine Aggregate