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California Bearing Ratio (CBR, IBI)

The California Bearing Ratio (CBR) or Immediate Bearing Index (IBI) is calculated by expressing the force on the ram for a given penetration of the standard mandrel as a percentage of the standard force.




a force required to push the mandrel to the specified depth in the testing mixture [kN]



a standard force required to push the mandrel to a specified depth in standard aggregate (crushed limestone) [kN]

The values of standard forces for standard aggregates are 13.2 kN for 2.5 mm penetration and 20 kN for 5 mm penetration.

Test types:

  • CBR (California Bearing Ratio) - the ratio used to determine the load-bearing characteristics of the mixture, determined immediately after compaction or after the aging period
  • IBI (Immediate bearing index) - immediate CBR value without using the load ring

CBR or IBI tests are suitable for mixtures with a maximum particle size of up to 22.4 mm.

Output protocol of CBR Test

The form of the entered data and the output protocol print is purely user-defined, following the specified template.


CSN EN 13286-47

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