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Flexural Test on Concrete, Its Significance, Procedures and Applications

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Flexural test on concrete based on the ASTM standards are explained. Differences if present in specification or any other aspects of flexural test on concrete between ASTM standard, Indian standard, and British standard are specified.

Fig.1: Flexural Test on Concrete (Three Point Loading Test)

Following topics regarding flexural tests on concrete is discussed:

What is Flexural Test on Concrete?

Flexural test evaluates the tensile strength of concrete indirectly. It tests the ability of unreinforced concrete beam or slab to withstand failure in bending. The results of flexural test on concrete expressed as a modulus of rupture which denotes as (MR) in MPa or psi. The flexural test on concrete can be conducted using either three point load test (ASTM C78) or center point load test (ASTM C293). The configuration of each test is shown in Figure-2 and Figure-3, respectively. Test method described in this article is according to ASTM C78.

Fig.2: Three-Point Load Test (ASTM C78)

Fig.3: Center Point Load Test (ASTM C293)

It should be noticed that, the modulus of rupture value obtained by center point load test arrangement is smaller than three-point load test configuration by around 15 percent. Moreover, it is observed that low modulus of rupture is achieved when larger size concrete specimen is considered. Furthermore, modulus of rupture is about 10 to 15 percent of compressive strength of concrete. It is influenced by mixture proportions, size and coarse aggregate volume used for specimen construction. Finally, the following equation can be used to compute modulus of rupture, but it must be determined through laboratory test if it is significant for the design: Where: fr: Modulus of rupture fc': concrete compressive strength

Fig.4: Flexural Test Machine and Concrete Specimen (ASTM C78)

What are the Applications of Flexural Test on Concrete?

Following are the applications of flexural test:

What Factors Cause Variability in Flexural Test Results?

Size of Concrete Specimen for Flexural Test

According to ASTM the size of the specimen is 150mm width, 150mm depth and the length should not be at least three times the depth of the specimen. Indian standard determined the size of the concrete specimen as 150mm width, 150mm depth, and span of 700mm. It also states that a size of 100mm width, 100mm depth, and span of 500mm can be used if the maximum aggregate size used is not greater than 19mm. British standard specifies square specimen cross section with 100mm or 150mm dimension and the span ranges from four to five times specimen depth. However, it preferred 150mm width, 150mm depth, and span of 750mm for the specimen.

Apparatus for Flexural Test on Concrete

Sample Preparation of Concrete

Procedure of Flexural Test on Concrete

Where: r: loading rate S: rate of increase of extreme fiber b: average specimen width d: average specimen depth L: span length

Computation of Modulus of Rupture

The following expression is used for estimation of modulus of rupture: Where: MR: modulus of rupture P: ultimate applied load indicated by testing machine L: span length b: average width of the specimen at the fracture d: average depth of the specimen at the fracture Read More: Compressive Strength of Concrete -Cube Test, Procedure, Results Why do We Test Concrete Compressive Strength after 28 Days? Tests for Workability of Concrete at Construction Site and Recommended Values Tests on Cement at Construction Site to Check Quality of Cement Testing of Sand Quality at Construction Site for Concrete Concrete Slump Test for Workability -Procedure and Results


British Standard: Testing Concrete: Part 118. Method for determination of flexural strength. [S.l.], p. 1-3. 1983. (BS 1881 : Part 118 : 1983). C09, A. C. Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory. ASTM Committee C09. [S.l.]. 2000. (C 192/C 192M – 00). C09, A. C. Standard Test Method for Flexural Strength of Concrete (Using Simple Beam With Center-Point Loading). ASTM Committee C09. [S.l.]. 2000. (C 293 – 00). C09, A. C. Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading). ASTM Committee C09. [S.l.], p. 1-3. 2002. (C 78 – 02). CEMENT AND CONCRETE SECTIONAL COMMITTEE, B. 2. Methods of tests for strength of concrete. Bureau of Indian Standards. New Delhi , p. 15-17. 1959 reaffirmed 1999. (IS : 516). Concrete in practice. National ready mix concrete association. [S.l.], p. 1-2. 2016. KETT, I. Engineering concrete: mix design and test methods. New York : CRC press LLC, 2000.
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