What is flexural strength of concrete?

The indirect tension or stress that concrete must withstand is typically represented by flexural strength. Having a perfect understanding of what the flexural strength of concrete is, makes it possible to create structural elements like seamless shafts, beams, and cantilevers. It is also helpful to predict the durability of the raw material and structure. 

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What is flexural strength of concrete?

The tensile strength of unreinforced concrete is determined by the flexural strength of the concrete. A concrete beam's ability to bend is typically tested. Notably, it's essential to check for comparable compressive strength before using a concrete beam or structure in construction. The flexural strength of a given concrete typically falls between 10 and 20 percent of the compressive strength. Concrete's flexural strength is expressed in terms of the Modulus of Rupture (MR) unit.

How to find flexural strength of concrete?

To determine the flexural strength of concrete, tests like the three-point load test (ASTM C78) and the centre point load test (ASTM C293) are usually conducted. It is used in concrete design mixes and evaluates the durability of pavement and slabs of concrete.

The following formula can be used to calculate the flexural strength of any concrete:

• fb = pl/bd2 (when a > 20.0cm for 15.0cm specimen or > 13.0cm for 10cm specimen)

or

• fb = 3pa/bd2 (when a < 20.0cm but > 17.0 for 15.0cm specimen or < 13.3 cm but > 11.0cm for 10.0cm specimen.)

Where,

• a = The distance between the line of fracture and the nearer support which is measured on the centre line of the specimen

• b = Width of the specimen (cm)

• d = Failure point depth (cm)

• l = Supported length (cm)

• p = Max load (kg)

By understanding how much the flexural strength of concrete is, engineers can ensure that their structures are strong enough to withstand the loads that they will be subjected to.

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The indirect measure of the tensile strength of concrete is called flexural strength. It is also known as the Modulus of rupture. When there is extreme fibre stress on the slab it can easily bend. As a measure to prevent this action flexural strength of concrete is required. Besides the external loading, the tensile stress can lead to warping, corrosion of steel, drying shrinkage and temperature gradient. Therefore, in every concrete there is a flexural strength which accounts for only 10% to 20% of the compressive strength. Now, that we what is flexural strength of concrete is, let us understand why we should test the flexural strength of concrete.

Why test flexural tensile strength of concrete?

Designers use theories based on flexural strength. The laboratory mix is dependent on a flexural strength test. At times, cementitious material content may be chosen from the past to get the needed design MR. MR is also required during the field control and acceptance of pavements. If the agency is not testing the flexural they use compressive strength more reliable to judge the quality of the concrete.

The use of flexure is more convenient for designing purposes. But for concrete the use of compressive strength is more convenient. Both flexural and compressive tests should be conducted during the trial batches to the effective results.

I would like to end here on this note.

I hope I was able to clear the doubt regarding flexural strength of concrete now.

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