by Concrete has high compressive strength but comparatively low tensile strength. The split tensile strength test is an indirect method used to determine the tensile strength of concrete.
In this test, a cylindrical concrete specimen is placed horizontally in a compression testing machine and loaded along its diameter. The applied compressive load produces tensile stress across the vertical diameter of the cylinder, eventually causing the specimen to split.
The test is commonly known as the split cylinder test or Brazilian splitting test.
For Indian practice, the test method is covered by IS 5816:1999 – Splitting Tensile Strength of Concrete – Method of Test.
Concrete has high compressive strength but comparatively low tensile strength. For understanding how compressive strength is assessed using concrete cubes, see our Concrete Cube Casting Procedure guide.
Page Contents
What Is the Split Tensile Strength Test of Concrete?
The split tensile strength test is an indirect tensile test in which a concrete cylinder is subjected to compression along two opposite lines.
Although the load applied by the testing machine is compressive, the resulting stress distribution produces tensile stress across the vertical diameter of the cylinder. When the tensile stress reaches the capacity of the concrete, the cylinder generally splits along its diameter.
The maximum load at failure is recorded and used to calculate the splitting tensile strength.
Why is this test performed?
The test helps engineers and quality-control personnel assess the tensile-strength-related behaviour of concrete and compare the performance of different concrete mixes.
It is particularly useful because applying a direct tensile load to concrete specimens is comparatively difficult, whereas the splitting arrangement can be performed using a compression testing machine.
IS Code for Split Tensile Strength Test
The Indian Standard applicable to this test is:
IS 5816:1999 – Splitting Tensile Strength of Concrete – Method of Test
The standard covers the test method for determining the splitting tensile strength of concrete specimens.
Important: The applicable edition/reaffirmation and project specification should always be checked before conducting an actual laboratory or site test.
Standard Test Specimen
A commonly used standard cylindrical specimen for the test has the following dimensions:
| Parameter | Standard Cylinder |
|---|---|
| Shape | Cylindrical |
| Diameter | 150 mm |
| Length | 300 mm |
| Length-to-diameter ratio | 2.0 |
| Loading arrangement | Diametral compression |
| Testing machine | Compression Testing Machine |
The 150 mm diameter × 300 mm long cylinder is widely reported for splitting tensile testing according to IS 5816.
Apparatus Required
The following equipment is generally required:
- Compression Testing Machine (CTM)
- Cylindrical concrete mould
- Suitable loading/bearing strips
- Measuring scale
- Weighing equipment
- Concrete mixing equipment
- Curing tank
- Specimen identification/marking equipment
The loading arrangement should provide proper and controlled contact along the diametrically opposite lines of the cylinder.
Preparation of Concrete Cylinder Specimens
The concrete specimens should be prepared using the approved concrete mix and the applicable specimen-preparation requirements.
General preparation sequence
- Prepare the concrete using the approved mix proportions.
- Fill the cylindrical mould.
- Compact the concrete properly.
- Finish the top surface.
- Mark the specimen identification.
- Demould the specimen at the appropriate time.
- Cure the specimen under the specified curing conditions.
- Remove the specimen from curing before testing.
- Inspect and measure the specimen before placing it in the testing machine.
For an actual project, specimen preparation and curing should follow the applicable standard and project requirements rather than relying only on a general site procedure.
Split Tensile Strength Test Procedure
Step 1 – Remove the specimen from curing
Remove the concrete cylinder at the specified testing age and prepare it for testing.
Step 2 – Inspect the specimen
Check the cylinder for visible defects, damaged ends, abnormal cracks or other conditions that could affect the test.
Step 3 – Mark the loading lines
Mark the diametrically opposite generating lines along the length of the cylinder.
These lines indicate where the loading strips and testing-machine load should be applied.
Step 4 – Place the loading strips
Place the specified bearing/loading strips along the marked lines.
The strips help provide the required loading arrangement and reduce concentrated contact between the steel platen and concrete specimen.
Step 5 – Position the cylinder
Place the cylinder horizontally between the platens of the compression testing machine.
The marked diametrical lines should be properly aligned with the loading arrangement.
Step 6 – Apply the load
Apply the load continuously and without shock.
For the IS 5816 test, the rate of increase of splitting tensile stress is specified within approximately:
1.2 to 2.4 N/mm²/min
This value is a stress-rate requirement, not simply a universal machine load rate in kN/s.
Step 7 – Observe the failure
Continue loading until the cylinder develops a splitting failure, generally along the loaded diameter.
Step 8 – Record the maximum load
Record the maximum load P reached at failure.
The recorded maximum load is then used for calculating the splitting tensile strength.
Split Tensile Strength Formula
For a cylindrical concrete specimen, the splitting tensile strength is calculated using: fct=πLD2P
Where:
- fct = splitting tensile strength, N/mm²
- P = maximum applied load at failure, N
- L = length of cylinder, mm
- D = diameter of cylinder, mm
Since: 1 N/mm² = 1 MPa
the result may also be reported in MPa.
Worked Example of Split Tensile Strength Calculation
Consider a cylindrical concrete specimen having:
- Diameter, D=150 mm
- Length, L=300 mm
- Maximum failure load, P=157 kN
Step 1 – Convert load into Newtons
Step 2 – Apply the formula
Therefore:
Splitting tensile strength ≈ 2.22 N/mm² or 2.22 MPa
Important
This is an illustrative calculation example. It is not an actual site/laboratory test result.
Split Tensile Strength Calculation for Multiple Specimens
When several specimens are tested, calculate the individual splitting tensile strength of each specimen from its recorded maximum failure load.
For example:
| Specimen | Maximum Failure Load | Split Tensile Strength |
|---|---|---|
| Cylinder 1 | 157 kN | 2.22 MPa |
| Cylinder 2 | 160 kN | 2.26 MPa |
| Cylinder 3 | 155 kN | 2.20 MPa |
Note: The above values are only an illustrative example. For actual reporting, the applicable standard and project specification should be followed for the number of specimens, treatment of individual results and reporting of the test result.
Why Is the Cylinder Placed Horizontally?
The cylinder is placed horizontally so that the compression machine applies load along the two opposite sides of its diameter.
Although the machine applies a compressive force, the resulting internal stress distribution produces tensile stress perpendicular to the applied load.
When this induced tensile stress exceeds the tensile capacity of the concrete, the cylinder splits.
This makes it possible to estimate the splitting tensile strength using a compression testing machine.
Loading Rate for the Split Tensile Test
The loading rate is an important part of the test.
As per the commonly reported IS 5816 procedure, the rate of increase of splitting tensile stress should be within: 1.2 to 2.4N/mm2/min
The load should be applied continuously and without shock.
Do not confuse the stress-rate requirement with a fixed kN/s setting for every specimen. The actual machine loading rate depends on the specimen dimensions and the way the testing machine is controlled.
This distinction is important for site engineers and laboratory technicians.
7-Day and 28-Day Split Tensile Strength
Split tensile strength can be determined at different testing ages depending on the purpose of the test and project requirements.
For example, testing may be carried out at 7 days or 28 days when strength development is being studied.
However, the percentage increase from 7-day to 28-day splitting tensile strength is not a universal fixed value. It depends on:
- Cement type
- Water-cement ratio
- Mix proportions
- Supplementary cementitious materials
- Curing conditions
- Temperature
- Aggregate characteristics
- Age of concrete
- Other mix-specific factors
Therefore:
A 7-day splitting tensile strength result should not be judged using a universal percentage of the 28-day result unless the applicable project requirement or verified test data supports that comparison.
Split Tensile Strength vs Compressive Strength
| Parameter | Compressive Strength | Split Tensile Strength |
|---|---|---|
| Main property | Resistance to compression | Indirect tensile resistance |
| Typical specimen | Cube/cylinder | Cylinder |
| Loading | Compression | Diametral compression |
| Main failure mode | Crushing | Splitting |
| Main purpose | Assess compressive strength | Assess splitting tensile strength |
| Test machine | Compression Testing Machine | Compression Testing Machine |
Related Guide: See our Concrete Cube Casting Procedure guide for the preparation, curing and compressive-strength testing of concrete cubes.
Common Site and Laboratory Mistakes
The following mistakes can affect the test result:
1. Incorrect specimen dimensions
The specimen dimensions should be measured and recorded properly.
2. Incorrect positioning
The cylinder must be properly aligned with the loading arrangement.
3. Incorrect loading rate
Applying the load too quickly or too slowly can affect the test result.
4. Shock loading
The load should be applied continuously and without shock.
5. Improper loading strips
Incorrect strip placement or unsuitable contact conditions can affect the stress distribution.
6. Poor curing
Incorrect curing can significantly influence concrete strength.
7. Damaged specimens
Specimens with abnormal damage should be examined carefully before testing.
8. Unit conversion error
If the load is recorded in kN, it must be converted to N when using the formula with dimensions in mm.
For example: 1kN=1000N
9. Reporting an example as an actual result
Worked examples should always be clearly identified as examples and should never be presented as actual laboratory results.
Important Engineering Note
The split tensile test is an indirect tensile-strength test. The calculated splitting tensile strength should not be treated as a direct measurement of pure uniaxial tensile strength. Test results can be influenced by specimen preparation, curing, concrete composition, specimen dimensions, loading arrangement and testing conditions. Therefore, the applicable Indian Standard and project specification should be followed when conducting and interpreting an actual test.
Difference Between Split Tensile Test and Direct Tensile Test
The split tensile test does not pull the concrete specimen directly in tension.
Instead:
Compression load → internal tensile stress → splitting failure
This is why it is called an indirect tensile test.
A direct tensile test applies tensile force directly to the specimen, whereas the split tensile test produces tensile stress indirectly through diametral compression.
Frequently Asked Questions
1. What is the split tensile strength test of concrete?
It is an indirect tensile test in which a cylindrical concrete specimen is loaded in compression along its diameter until splitting failure occurs.
2. Which IS code is used for the split tensile test?
The test method is covered by IS 5816:1999 – Splitting Tensile Strength of Concrete – Method of Test.
3. What is the standard cylinder size?
A commonly used standard cylinder is 150 mm diameter × 300 mm length.
4. What is the formula for split tensile strength?
For a cylindrical specimen:
where P is the maximum failure load, L is the cylinder length, and D is the cylinder diameter.
5. Why is the cylinder placed horizontally?
It is positioned horizontally so that diametral compression produces tensile stress across the vertical diameter, eventually causing the cylinder to split.
6. What is the loading rate for the split tensile test?
The rate of increase of splitting tensile stress is approximately 1.2 to 2.4 N/mm²/min according to the commonly reported IS 5816 procedure.
7. Can split tensile strength be tested at 7 days?
Yes, a test may be performed at different ages when required for strength-development studies or project requirements. The testing age should be specified by the applicable requirement.
8. Is split tensile strength the same as direct tensile strength?
No. The split tensile test is an indirect tensile test and should not be treated as a direct measurement of uniaxial tensile strength.
Key Takeaways
- The split tensile test is an indirect tensile-strength test.
- A cylindrical specimen is loaded horizontally in diametral compression.
- The commonly used standard cylinder is 150 mm × 300 mm.
- The test method is covered by IS 5816:1999.
- The splitting tensile strength formula is:
- The commonly reported loading-stress rate is 1.2–2.4 N/mm²/min.
- Always distinguish code requirements, practical site procedures, and illustrative calculations.
- Actual test results should be interpreted according to the applicable standard and project requirements.
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