A structure has been designed based on the compression strength of concrete. So mostly the tensile strength of concrete test not required to perform at the site. The framed structure built up by the combination of brittle and ductile material.
Brittle Material – Concrete
Ductile Material – Reinforcement
The concrete is good in compression force and weak in tension force. So the reinforcement has been provided in concrete to prevent the crack formation.
An earlier post, we had discussed the Compressive strength of concrete test and now we are going to discuss the Tensile strength of concrete along with its test procedure.
What is a Tensile strength of Concrete?
The ability of the concrete withstand in pulling force (Tensile Stress) without broke is called Tensile Strength of concrete. The tensile strength of concrete is measured by the units of Force per Cross Sectional area (N/Sqmm or Mpa).
Why concrete weak in Tension?
As above said, the concrete is strong in the compressive force and weak in tension force because of its brittle nature.
The concrete is formed by the mixture of different material Cement, fine & coarse aggregates. Each material contains different properties.
During the period of concrete casting, the water-cement ratio gradient makes around the aggregate particles and the cement paste forms a different microstructure around the concrete. This zone is called the Interface Transits Zone.
Interface Transits Zone
The ITZ is the weakest zone of concrete because the bond between the cement paste and aggregates may poor due to the bleeding of concrete. In compressive stress, the load transfer from one aggregate to another aggregate and that was not required unprecedented strength.
At the same time, in tension force, the aggregate pull away from each other and it can be easily broke from its shape.
Tensile Strength of Concrete Test
The tensile strength of concrete an important property when it is to be used in making road and runways, this test shall follow as per the IS Code 5816.
The tensile strength of concrete is generally in the range of 10 % to 12% of its compressive strength.
The concrete cube was used to find out the compressive strength of concrete but to find the tensile strength of concrete a cylindrical specimen has to be used.
Specification of Test
The concrete specimen should be a cylindrical shape having diameter 150 mm and length 300mm.
Range of Load
The testing machine can able to apply the loads constantly in the range of 1.2 MPa/min to 2.4 Mpa/min.
Age of Test
The test shall be made at the age of 7 days and 28 days. Tests at any other age at which the tensile strength is desired may be made if so required.
Number of Specimen
At least 3 specimens should be tested for each age of test.
- Testing Machine (1.2 Mpa/min to 2.4 Mpa)
- Tamping Rod (Dia – 16mm and Length – 600mm)
- Concrete Mould (Made by Steel)
Procedure – Splitting Tensile Strength Test
- Estimate the adequate ingredients to prepare the concrete with a proper water-cement ratio.
- Ensure that the cube mould should be free from dust and rust.
- Now, pour the concrete into the mould by proper compaction with the help of tamping rod.
- Finish the top surface as smooth by the trowel.
- The mould should be covered with gunny bag and place undisturbed for 24 hours at a temperature of 27 ° Celsius ± 2.
- After 24 hours the cube specimen shall remove from the mould and it should be immersed into the water for 7 or 28 days based on the test.
- The concrete specimen shall be taken from the water 24 hours prior to the test and it should be in dry condition.
- The bearing surfaces of the machine and the loading strip free from dust.
- The specimen should be weighed in Newtons prior to the test.
- Now, place the specimen centrally between the loading strips and ensure the upper platen is parallel to the bottom platen.
- Then apply the load gradually until the specimen break and note down the Value.
- The same method has been executed for the other specimen.
Tensile Strength of Concrete Formula
The tensile strength of concrete is calculated by the below formula
Fct – Tensile Strength of Concrete
P – Maximum load in N/Sqmm
L – Length of the Specimen
D – Diameter of the specimen
The testing report should have the following
- Age of the Test
- Date of specimen cast
- The weight of the specimen
- The grade of the concrete
- Tensile Strength