---
title: "h/d ratio effect; splitting tension test"
subject: "Concrete Technology and Masonry Structure"
chapter: 5
key: "semester_5/concrete_technology_and_masonry_structure:hd-ratio-splitting-tension"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/hd-ratio-splitting-tension
site: BCT Engineering
---

# h/d ratio effect; splitting tension test

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

- Asked in: 2075 Ashwin, 2+4 marks
- Video: [3.9 Effect of h/d ratio & Unit weight on Concrete Strength](https://www.youtube.com/watch?v=64rUMpvnCPU) — Interesting Engineering
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/hd-ratio-splitting-tension
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-5

## Question

Explain how the height/diameter ratio of a cylindrical test specimen affects the relative compressive strength of concrete. How can you determine the tensile strength of concrete using the splitting tension test method? Explain briefly.

## Short answer

As height/diameter ratio increases, measured compressive strength decreases because less of the specimen is confined by platen restraint; correction factors convert to the standard cylinder (h/d=2). The splitting test: a cylinder is loaded horizontally through packing strips until it splits, and tensile strength is f_sp = 2P/(pi L d).

## Answer

#### Effect of height/diameter ratio
In a compression test the platens restrain the lateral expansion of the specimen ends (platen restraint). A short specimen (low h/d) is mostly under this confinement and gives a higher strength; a taller specimen has a free central zone. Hence the measured strength **falls as h/d increases** from 1 to 2 and is nearly constant beyond 2.

| h/d | 1.0 | 1.25 | 1.5 | 1.75 | 2.0 |
|---|---|---|---|---|---|
| Correction factor (ASTM C42) | 0.87 | 0.93 | 0.96 | 0.98 | 1.00 |

The measured strength is multiplied by this factor to get the strength of the standard cylinder (h/d = 2). For example, a specimen with h/d = 1 shows about 15 to 25% more strength than the standard. For very large h/d (above 3), buckling and eccentricity reduce the strength.

#### 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 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 higher than direct tension by 5 to 12%, and about 0.5 to 0.6$\sqrt{f_{ck}}$ in MPa.

## Check yourself

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

1. How does measured strength change as h/d increases from 1 to 2?
   A. It falls, because the free central zone grows
   B. It rises, because the specimen is longer
   C. It stays constant
   D. It falls to zero at h/d = 2
   Answer: A. Lower h/d means more platen confinement and higher strength; strength falls to h/d = 2 and then is nearly constant. (Key point: Effect of h/d)

2. What h/d does the standard cylinder have?
   A. 1
   B. 2
   C. 1.5
   D. 3
   Answer: B. The standard 150 x 300 mm cylinder has h/d = 2. (Key point: Standard h/d)

3. What is the splitting tensile strength formula?
   A. fsp = P/(pi L d)
   B. fsp = 2P/(pi d^2 L)
   C. fsp = 2P/(pi L d)
   D. fsp = Pl/(bd^2)
   Answer: C. fsp = 2P/(pi L d) with L the cylinder length and d its diameter. (Key point: Splitting formula)

4. How is the cylinder placed in the splitting test?
   A. Vertically, as in the compression test
   B. Horizontally, with no strips
   C. Clamped by embedded grips and pulled
   D. Horizontally with plywood/fibre strips along the contact lines
   Answer: D. The cylinder lies on its side with thin strips along the load lines until it splits along the vertical diameter. (Key point: Splitting test set-up)

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