---
title: "Compressive strength test of brick wall"
subject: "Concrete Technology and Masonry Structure"
chapter: 10
key: "semester_5/concrete_technology_and_masonry_structure:compressive-test-masonry-wall"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/compressive-test-masonry-wall
site: BCT Engineering
---

# Compressive strength test of brick wall

Concrete Technology and Masonry Structure · Chapter 10: Testing of masonry elements

- Asked in: 2081 Bhadra, 4 marks; 2078 Bhadra, 4 marks; 2069 Chaitra, 6 marks; 2068 Chaitra, 6 marks (asked 4 times)
- Video: [Compressive Strength Testing](https://www.youtube.com/watch?v=NEgzKkpPm0c) — Acme Tech Training
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/compressive-test-masonry-wall
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-10

## Question

Explain (discuss) the compressive strength test of brick masonry wall (and of bricks) in the laboratory.

## Short answer

A masonry prism at least 400 mm high with height‑to‑thickness ratio between 2 and 5 is tested in compression after 28 days curing, using capping and a spherical platen. Compressive strength fₘ = (P/A) × kₕ, where kₕ corrects for slenderness. The basic compressive stress f_b = 0.25 fₘ. For bricks alone, test flat with frog up; the average of five gives the unit strength.

## Answer

#### Compressive strength test of brick masonry (wall/prism) in the laboratory

**Purpose:** to find the compressive strength $f_m$ of masonry (made of the same brick, mortar and workmanship), from which the basic compressive stress is derived (IS 1905 Appendix B).

**Specimen:** a wall panel or prism built in stretcher or English bond, at least 400 mm high, and height-to-thickness ratio ($h/t$) between 2 and 5. Tested after curing for 28 days.

**Procedure**

1. Construct the specimen with the actual mortar thickness, bond and moisture content of units to be used in the structure.
2. Cap the top and bottom with mortar or plywood sheets, 4 mm thick (to give uniform bearing).
3. Place in the compression testing machine with a spherically seated upper platen, centre carefully.
4. Apply load gradually at about 350 to 700 kN/m of the bed area per minute until failure; record the failure load $P$ and the failure pattern (vertical splitting cracks).
5. Optionally fix gauges to measure strain and find the stress-strain curve and modulus of elasticity.

```text
   | load P
   v
 +-------+  <- steel platen (spherical seat)
 |  cap  |
 |=======|
 | brick |  h = 400 mm min
 |=======|  mortar joints
 | brick |
 +-------+
 | cap   |
 =========  <- machine bed
```

**Calculation**

$$
f_m = \frac{P}{A}\times k_h
$$

where $A$ is the loaded bed area and $k_h$ is the correction factor for the slenderness of the prism (IS 1905 Table 12, brickwork): $h/t = 2.0, 2.5, 3.0, 3.5, 4.0, 5.0$ gives $0.73, 0.80, 0.86, 0.91, 0.95, 1.00$. Basic compressive stress of masonry $f_b = 0.25\,f_m$ (IS 1905 B-2.1).

**Bricks (separately):** compressive strength of bricks is found by testing a brick (flat, frog up, with mortar bedding) in the compression machine; the strength is the average of five bricks, e.g. 3.5 to 10 N/mm$^2$ for common burnt clay brick classes (IS 3495).

## Check yourself

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

1. What specimen proportions are required?
   A. Height at least 400 mm, h/t between 2 and 5
   B. Height 1.2 m square panel
   C. Single brick only
   D. h/t above 10
   Answer: A. The prism or panel is at least 400 mm high with h/t from 2 to 5, tested after 28 days. (Key point: Specimen size)

2. Why are the ends capped with mortar or 4 mm plywood?
   A. To raise strength
   B. To give uniform bearing
   C. To prevent shrinkage
   D. To measure strain
   Answer: B. Capping gives uniform contact with the platens, avoiding stress concentrations. (Key point: Capping)

3. How is the masonry strength f_m calculated?
   A. f_m = P/A x k_h, k_h from Table 12 for h/t
   B. f_m = 0.707 P/A
   C. f_m = P/A only, no correction
   D. f_m = 0.25 P/A
   Answer: A. The raw stress P/A is corrected for prism slenderness with k_h (e.g. 0.73 at h/t = 2, 1.00 at 5). (Key point: Strength formula)

4. How is basic compressive stress related to f_m?
   A. f_b = f_m
   B. f_b = 0.25 f_m
   C. f_b = 0.5 f_m
   D. f_b = 2 f_m
   Answer: B. IS 1905 B-2.1 takes the basic compressive stress as 0.25 f_m. (Key point: Basic stress)

## Related in Concrete Technology and Masonry Structure

- [Compressive strength test of masonry prism](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acompressive-test-masonry-prism) — Concrete Technology and Masonry Structure, chapter 10, asked 2×
- [Flat-jack test for brick masonry wall](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aflat-jack-test) — Concrete Technology and Masonry Structure, chapter 10, asked 2×
- [Single-room wall: brick strength and mortar](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Awall-single-room-8000kg) — Concrete Technology and Masonry Structure, chapter 8
- [Compressive strength test; acceptance criteria](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acompressive-test-procedure-acceptance) — Concrete Technology and Masonry Structure, chapter 5
- [Importance and method of compressive strength test](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acompressive-strength-importance-method) — Concrete Technology and Masonry Structure, chapter 5
- [Diagonal shear test of masonry wall](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adiagonal-shear-test) — Concrete Technology and Masonry Structure, chapter 10, asked 6×

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