CBR Testing Equipment

CBR Test Equipment | CBR Test Machine for Soil Strength Testing

Introduction to CBR Test Equipment

The California Bearing Ratio (CBR) test is a key method for measuring the strength of subgrade soils and base materials used in roads and pavements. By recording how well soil resists penetration, the test supports sound pavement design and long-lasting construction projects. A CBR test machine must follow internationally recognized standards, each of which sets out specific procedures for consistent, reliable results:

• ASTM D1883: Covers laboratory testing of soil samples to determine the CBR value. It is widely followed across North America for pavement and subgrade evaluation.
• AASHTO T193: A core standard for U.S. highway construction, describing how to determine CBR values for soil and aggregate mixtures.
• EN 13286-47: Used mainly in Europe, this standard defines the method for testing compacted unbound materials in civil engineering projects.
• BS 1377 and BS 1924: British standards offering detailed guidance on soil testing, including laboratory and field CBR tests, essential for geotechnical and structural work.

Qualitest’s QualiCBR™ Series CBR test equipment is built to meet and exceed these standards, delivering precision and repeatability in every test. The series includes two cost-effective models:

• Manual CBR Test Machine: A practical choice for smaller-scale testing, easy to operate and dependable in its results.
• Automatic CBR Test Apparatus: Packed with advanced features for streamlined operation, it delivers faster, more efficient testing with minimal manual intervention.

Whether you need a CBR testing machine for research, construction, or quality control, Qualitest offers reliable solutions that satisfy the strictest industry requirements. Improve your soil strength analysis with our state-of-the-art CBR test equipment.

ASTM Standard CBR Test Accessories

• CBR mould with collar and perforated base plate: plated steel, 6 in. (152.4 mm) diameter x 7 in. (177.8 mm) body height
• Spacer disc with “T” handle: 5 15/16 in. (150.8 mm) diameter x 2.416 in. (61.4 mm) height
• Annular surcharge weight: 2.27 kg
• Slotted surcharge weight: 2.27 kg
• Cutting edge
• Solid CBR base
• Straight edge: 3 x 30 x 300 mm

British Standard CBR Test Accessories

• CBR mould body with base plate: plated steel, threaded at both ends, 152 mm internal diameter x 127 mm height, with a 50 mm high collar
• CBR mould with three-plug collar
• “C” spanner for fitting and removing the collar from the mould body (1 kg)
• Split surcharge weight: selectable 2 kg or 2.27 kg

CBR Expansion (Swell) Test Apparatus

• Dial gauge tripod
• Aluminium swell plate
• Brass swell plate

CBR Test Principle and Theory

How much traffic load can a pavement subgrade carry before it cracks? The California Bearing Ratio (CBR) test answers this. It is the globally recognised laboratory method for measuring soil strength, and it works by pushing a standard piston into a compacted soil sample at a constant, mechanically controlled rate.

Accurate, repeatable results depend on a loading frame that does not flex under load. Qualitest CBR test equipment is built with thick structural steel instead of thin sheet metal, so your soil penetration curves stay precise from one test to the next.

How the CBR Test Works

The CBR test measures the load-bearing capacity of a soil by pressing a steel plunger into a tightly compacted sample at a steady rate. The force needed to reach a set penetration depth is then compared with the force needed to reach the same depth in a standard crushed limestone. This reference material is the global benchmark for CBR testing.

The ratio between the two forces shows whether your subgrade or base layer is structurally weak or stable.

CBR Test Apparatus and Components

A complete CBR test setup must meet ASTM D1883, AASHTO T193, EN 13286-47 and BS 1377/1924. The Qualitest QualiCBR™ Series is designed to those standards. A full set of CBR test equipment includes these main components:

• Motorised loading frame: Drives a 50 mm diameter piston into the soil at a constant 1.25 mm per minute. A steady penetration rate is essential for compliant results.
  • QualiCBR™ A (Automatic CBR Test Apparatus): Runs hands-free with minimal manual intervention, suited to high-volume laboratories.
  • QualiCBR™ M (Manual CBR Test Machine): A dependable, cost-effective option for smaller testing facilities.
• Plated steel CBR moulds and base plates: Heavy-wall cylindrical moulds with collars and perforated base plates, used to compact the soil sample at the correct moisture content.
• Standard surcharge weights: Annular and slotted weights, typically 2.27 kg each, placed on the sample to simulate the pressure of the pavement above it.
• Expansion (swell) test apparatus: Dial gauge tripods and brass or aluminium swell plates, used to measure how much the soil expands when soaked in water.
• High-precision force measurement: Digital load cells or mechanical dial gauges that display the applied force accurately and remove manual calculation errors.

Standard CBR Laboratory Procedure

The standard CBR test procedure has three main stages:

1. Sample preparation and soaking: Compact the soil into the plated steel mould. To simulate worst-case conditions such as heavy rainfall or flooding, soak the mould assembly in water for four days. Use the expansion test apparatus during this time to record how much the soil swells.
2. Penetration test: Place the soaked mould under the piston of the QualiCBR™ machine. The machine drives the piston down at 1.25 mm per minute while the penetration resistance is recorded.
3. CBR calculation: Read the force at 2.54 mm and 5.08 mm penetration. Divide each reading by the corresponding standard reference load, then multiply by 100 to get the CBR value used for pavement design.

CBR Values and What They Mean for Pavement Design

The results from your CBR test equipment guide pavement layer design directly:

• Above 20%: High-strength subgrade or base material.
• 10% to 20%: Satisfactory performance, suitable for the middle layers of a road.
• Below 5%: Insufficient strength. Building directly on this layer risks early cracking and structural failure.