---
title: "Tensile strength tests of concrete"
subject: "Concrete Technology and Masonry Structure"
chapter: 5
key: "semester_5/concrete_technology_and_masonry_structure:tensile-strength-tests"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/tensile-strength-tests
site: BCT Engineering
---

# Tensile strength tests of concrete

Concrete Technology and Masonry Structure · Chapter 5: Testing of concrete and quality control

- Asked in: 2070 Chaitra, 3 marks; 2068 Baisakh (old course), 5 marks (asked 2 times)
- Video: [Lec-22_Split Cylinder Test of Concrete | Concrete Technology | Civil Engineering](https://www.youtube.com/watch?v=2-P8jiuw7gE) — Civil Engineering Department_LJIET
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/tensile-strength-tests
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-5

## Question

Describe in detail the tensile strength tests of concrete (also describe the importance of tensile strength).

## Short answer

Tensile strength is 7–12% of compressive strength and controls cracking, shear, and bond. The splitting tension test on a cylinder gives fsp = 2P/(pi L d) and is about 0.5–0.6 sqrt(fck). The flexure test on a beam (modulus of rupture) gives fcr = Pl/(b d^2) for third-point loading; IS 456 gives fcr = 0.7 sqrt(fck) MPa. Direct tension is lower and rarely used.

## Answer

#### Importance of tensile strength
Tensile strength of concrete is only about 7 to 12% of its compressive strength, but it controls cracking, shear, bond and the design of pavements, water tanks and prestressed members. Concrete is not designed to carry tension, but the tensile strength decides when the first crack appears. It is needed for crack control, shear and bond design, pavement thickness, water-retaining structures (IS 3370) and prestress release.

#### Direct tension test
A dog-bone or cylindrical specimen with embedded end grips is pulled axially. It is rarely used, because it is hard to avoid eccentricity and secondary stresses from the grips, and the result scatters. Direct tensile strength is about $0.35\sqrt{f_{ck}}$ to $0.45\sqrt{f_{ck}}$ (MPa).

#### Splitting tension test (Brazilian test, IS 5816)
A standard cylinder (150 mm dia × 300 mm long) is laid horizontally between the platens of the testing machine, with thin plywood or fibre strips (about 3 mm thick and 15 to 25 mm wide) along the contact lines. The compressive line load is increased at a rate of 1.2 to 2.4 N/mm$^2$/min (splitting tensile stress) until the cylinder splits along the vertical diameter. The load applied gives a nearly uniform tensile stress across the loaded plane:

$$
f_{sp} = \frac{2P}{\pi L d}
$$

where $P$ = failure load, $L$ = length and $d$ = diameter of cylinder. Splitting strength is usually a little higher than the direct tensile strength and is about $0.5\sqrt{f_{ck}}$ to $0.6\sqrt{f_{ck}}$ (MPa).

**Advantages:** simple, uses the same cylinders and compression machine as the compression test, gives a more uniform and reproducible result than direct tension, with no grip problem.

#### Flexure test (modulus of rupture, IS 516)
A plain concrete beam 150 × 150 × 700 mm is supported on a 600 mm span and loaded at the third points (two-point loading) at 0.7 N/mm$^2$/min extreme-fibre stress rate. If the crack occurs in the middle third:

$$
f_{cr} = \frac{P\,l}{b\,d^{2}}
$$

If the crack is outside the middle third but within 5% of the span from the load point, $f_{cr} = 3Pa/(bd^2)$ ($a$ = distance of crack from the nearer support); otherwise the result is rejected. For single (centre) point loading, $f_{cr} = 3Pl/(2bd^2)$. IS 456 (Cl. 6.2.2) gives the flexural strength $f_{cr} = 0.7\sqrt{f_{ck}}$ N/mm$^2$. The modulus of rupture is greater than direct tension (by about 1.5 to 2 times) since the stress distribution is assumed linear while the actual stress block is plastic.

The three results are related: direct tension < splitting < flexural.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Tensile strength is important mainly because it:
   A. Controls cracking, shear and bond
   B. Is high, so replaces steel
   C. Equals compressive strength
   D. Is unimportant
   Answer: A. It is only 7 to 12% of f_c but decides first crack. (Key point: Importance)

2. Why is direct tension test rarely used?
   A. Too high load needed
   B. Needs cubes
   C. Eccentricity and grip stresses, scattered results
   D. Gives flexural stress
   Answer: C. Hard to avoid secondary stresses from grips. (Key point: Direct test problem)

3. In the splitting test the cylinder is:
   A. Placed vertically
   B. Laid horizontally with plywood or fibre strips
   C. Bent as beam
   D. Pulled by grips
   Answer: B. Strips along contact lines; it splits along the vertical diameter. (Key point: Splitting)

4. The order of the three results is:
   A. Direct < splitting < flexural
   B. Flexural < splitting < direct
   C. Splitting < direct < flexural
   D. All equal
   Answer: A. Flexural is the highest, direct lowest. (Key point: Ranking)

## Related in Concrete Technology and Masonry Structure

- [Tests for compressive and tensile strength](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Astrength-tests-compression-tension) — Concrete Technology and Masonry Structure, chapter 5, asked 4×
- [Tensile tests; split test advantage; h/d ratio](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Atensile-tests-split-advantage-hd) — Concrete Technology and Masonry Structure, chapter 5
- [Splitting tensile strength of cylinder (400 kN)](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Asplitting-tensile-cylinder-400kn) — Concrete Technology and Masonry Structure, chapter 5, asked 2×
- [Splitting tensile strength of cylinder and cube (500 kN)](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Asplitting-tensile-cylinder-cube-500kn) — Concrete Technology and Masonry Structure, chapter 5, asked 2×
- [Destructive tests of concrete](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adestructive-tests-concrete) — Concrete Technology and Masonry Structure, chapter 5
- [Acceptance criteria of concrete strength](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aacceptance-criteria-concrete) — Concrete Technology and Masonry Structure, chapter 5, asked 5×

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