CBR Machine Calibration
(Force & Displacement — IS 2720 Pt.16 / ISO 7500-1)
NABL-accredited calibration of CBR (California Bearing Ratio) machines — verifying load ring or load cell force accuracy, plunger displacement measurement and penetration rate for IS 2720 Part 16 compliant subgrade CBR testing.
What is the CBR Machine Calibration?
The CBR Machine applies a controlled force through a 50mm diameter plunger at 1.25mm/min into a compacted soil specimen. Force is measured by load ring (proving ring) and dial gauge, or by electronic load cell and LVDT. Both the force measurement system and displacement system require calibration — along with verification of the penetration rate — to ensure IS 2720 Part 16 compliant CBR results.
At Global Lab, CBR machine calibration covers: load ring (proving ring) calibration by NPL-traceable reference load cell per ISO 7500-1, LVDT/dial gauge displacement calibration per ISO 13225, and penetration rate motor speed verification. The proving ring calibration factor (N/div) is updated in the calibration certificate — critical because an out-of-date proving ring factor is the most common source of CBR error.
Non-Destructive
Fast Turnaround
NABL Certified
Pan-India Coverage
Digital Reporting
High Accuracy
CBR Machine Calibration — Site Images
How the CBR Machine Calibration is Conducted
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1
Surface Preparation
A shallow groove (approx. 25mm deep) is cut into the concrete surface using a diamond-tipped cutting tool. The surface is cleaned of dust and debris. -
2
Insert Disc Placement
A specially designed steel insert disc is placed into the groove. A thin rod connects the disc to the pullout apparatus above the surface. -
3
Hydraulic Pullout Force Application
A hydraulic jack applies a steady, controlled pullout force to the insert disc via the reaction ring resting on the concrete surface. -
4
Failure Load Recording
The maximum force at which the concrete cone is extracted is recorded. A digital load indicator provides real-time readings with data logging. -
5
Strength Calculation & Reporting
The pullout force is correlated to cube compressive strength using established calibration curves. NABL-accredited reports are issued via Autovity QLMS.
Applicable Test Standards
| Standard | Title | Scope | Type |
|---|---|---|---|
| ISO 7500-1 | Metallic Materials — Calibration of Static Uniaxial Testing Machines | Force Calibration | ISO |
| IS 2720 Part 16 | Methods of Test for Soils — Laboratory Determination of CBR | CBR Test Standard | Indian Standard |
| ISO 13225 | Dimensional Metrology — Local Calibration of Contact Measuring Instruments | Displacement | ISO |
| NABL-141 | NABL Policy on Metrological Traceability | Traceability | NABL |