---
title: "Cube versus cylinder compression test"
subject: "Concrete Technology and Masonry Structure"
chapter: 5
key: "semester_5/concrete_technology_and_masonry_structure:cube-vs-cylinder-test"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/cube-vs-cylinder-test
site: BCT Engineering
---

# Cube versus cylinder compression test

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

- Asked in: 2066 Chaitra (old course), 2+3 marks
- Video: [Compressive Strength Test of Concrete Samples.Cubes & Cylenders. #compressivestrengthloadcalculation](https://www.youtube.com/watch?v=zYjizre6j5Q) — Structure Design Experts
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/cube-vs-cylinder-test
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-5

## Question

State the merits and demerits of cube and cylinder as specimen for compression test. Write the steps for compression testing of concrete from sampling.

## Short answer

Cubes (150 mm) are easy to mould and store, but platen restraint gives 20-25% higher strength. Cylinders (150×300 mm) with h/d=2 give truer uniaxial strength but need capping and are heavier. Steps: sample at placement, cast cubes in 3 layers, tamp, cure 28 days at 27°C, test loaded on side faces at 14 N/mm^2/min, fc = P/A, average three cubes.

## Answer

#### Merits and demerits

| | Cube (150 mm) | Cylinder (150 × 300 mm) |
|---|---|---|
| Moulding | Easy to cast, handle and store; used in India, Nepal, UK | Heavier; casting and capping are more difficult |
| Platen restraint | High (h/d = 1), so strength appears 20 to 25% higher | Lower (h/d = 2), so nearer to the true uniaxial strength |
| Stress state | Not uniform; complex stress | More uniform and close to uniaxial |
| Surface | Cast faces are smooth and parallel, no capping needed | Needs capping of ends |
| Use | Quality control and acceptance (IS 456) | Used in USA, Europe, research; also for modulus and splitting tests |
| Conversion | $f_{cyl} \approx 0.8 f_{cube}$ | |

#### Steps for compression testing from sampling
1. Take the sample at the point of placing, as per the frequency of IS 456, Cl. 15.2 (1 sample for 1 to 5 m$^3$, etc.).
2. Fill 150 mm cube moulds in 3 layers, compact each layer by tamping (35 blows with a 16 mm rod) or by vibration, level the top, and mark the cube.
3. Keep at 27 ± 2 °C, covered, for 24 hours; demould and cure in water until 28 days.
4. Remove the cube from the water and wipe it. Place it between the platens so that the load acts on two opposite faces as cast (not on the top and bottom as cast), and apply the load at 14 N/mm$^2$/min until failure.
5. Calculate $f_c = P/A$, take the average of three cubes, and apply the acceptance criteria of IS 456, Table 11.

## Check yourself

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

1. Why does a cube show higher strength than a cylinder?
   A. h/d = 1 puts the whole cube in the platen restraint zone, raising strength by 20 to 25%
   B. Cubes are made of richer concrete
   C. Cubes are cured longer
   D. Cylinders always contain more voids
   Answer: A. Platen friction confines the entire cube, whereas a cylinder with h/d = 2 has a free central zone. (Key point: Cube strength vs cylinder)

2. What is a demerit of the cylinder specimen?
   A. Has non-uniform stress
   B. Needs capping of ends and is heavier to handle
   C. Cannot be used for splitting tests
   D. Gives strength 25% higher than the true value
   Answer: B. Cylinders need capping or grinding and are heavier; cubes have smooth parallel cast faces. (Key point: Cylinder demerits)

3. What is the approximate relation between cylinder and cube strength?
   A. fcyl = 1.25 fcyl
   B. fcyl = 2 fcube
   C. fcyl = 0.8 fcube
   D. fcyl = 0.5 fcube
   Answer: C. Cylinder strength is about 0.8 times the cube strength. (Key point: Conversion)

4. Where is the sample taken and which clause fixes frequency?
   A. At the cement store, as per IS 456 Cl. 6
   B. From hardened members by coring only
   C. At the batching plant, once per day regardless of volume
   D. At the point of placing, as per IS 456 Cl. 15.2
   Answer: D. Samples are taken from the concrete at the point of placing at the frequency of IS 456 Cl. 15.2. (Key point: Sampling frequency)

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