LimsPulse
Construction materials testing

California Bearing Ratio (CBR) Test Apparatus

A load frame that pushes a 50 mm plunger into a compacted soil specimen at 1.25 mm/min and compares the load needed with that for a standard crushed stone. The ratio (CBR) is used to design road and pavement thickness.

  • Road and highway construction
  • Geotechnical testing
  • Airports and railways
  • Construction materials testing
  • Academic labs
Illustration of California Bearing Ratio (CBR) Test Apparatus
TROUBLESHOOTING

Common problems, causes and fixes

Load–penetration curve concave upward at the start
Likely causes
  • • Uneven specimen surface
  • • Plunger not properly seated
What to do
  • • Apply the standard zero correction
  • • Level the surface and seat the plunger before zeroing
CBR at 5.0 mm higher than at 2.5 mm
Likely causes
  • • Typical of some granular soils
  • • Surface softened by soaking
What to do
  • • Repeat the test; if confirmed, report the 5.0 mm value as the standard requires
Penetration rate uneven
Likely causes
  • • Worn gearbox or slipping drive
  • • Motor speed variation
What to do
  • • Service the drive
  • • Verify rate with a stopwatch and dial gauge
Load dial does not return to zero
Likely causes
  • • Ring overloaded and permanently deformed
  • • Dial gauge sticking
What to do
  • • Withdraw the ring and recalibrate or replace it
  • • Service or replace the dial gauge
In LimsPulse · Calibration Management

Keep every CBR apparatus in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.

See how