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

# Compressive strength test of masonry prism

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

- Asked in: 2082 Bhadra, 4 marks; 2079 Bhadra, 6 marks (asked 2 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-prism
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-10

## Question

Explain the compressive strength test of brick masonry prism (procedure to test a brick masonry prism in the laboratory).

## Short answer

Construct a masonry prism at least 400 mm high (h/t=2–5), cure 28 days under damp cloth. Cap bed faces with plywood, center in compression machine, load at 350–700 kN/m/min to failure. Calculate fm = (P/A)*k (correction factor from IS 1905 Table 12, e.g. 0.73 for h/t=2, 1.00 for h/t=5); basic compressive stress = 0.25 fm.

## Answer

#### Compressive strength test of a brick masonry prism (IS 1905 Appendix B)

**Aim:** to determine the compressive strength of masonry $f_m$ built with the actual brick, mortar and workmanship, so that the basic compressive stress can be fixed.

**Specimen:** a prism of bricks laid in a stack bond or the actual bond, at least 400 mm high, with height-to-thickness ratio ($h/t$) of 2 to 5 (preferably 4 to 5), joints and mortar as in the work. Moisture content of the bricks and mortar consistency are the same as will be used on site. Test after 28 days.

**Procedure**

1. Build prisms on a flat base; cure under damp cloth and polythene for 28 days.
2. Cap the bed faces with sheets of plywood (4 mm) slightly larger than the prism.
3. Centre the prism in the compression testing machine with a spherically seated platen so that load is applied evenly over the whole top and bottom surfaces.
4. Apply load at a rate of 350 to 700 kN/m per minute (uniform) to failure; record failure load $P$ and the mode of failure (vertical splitting).
5. Test at least 5 prisms and average.

```text
    P
    v
  +-----+ <- ply/cap
  |=====|
  |brick|   h
  |=====|   (h/t = 2 to 5)
  |brick|
  +-----+
  ply cap
```

**Calculation**

$$
f_m = \frac{P}{A}\times k,\qquad f_b = 0.25\,f_m
$$

where $A$ = bed area, $k$ = correction factor for $h/t$ (Table 12): 0.73 for $h/t=2.0$, 0.80 for 2.5, 0.86 for 3.0, 0.91 for 3.5, 0.95 for 4.0 and 1.00 for 5.0. The basic compressive stress is 0.25 times the prism strength.

## Check yourself

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

1. What are the prism requirements?
   A. At least 400 mm high, h/t of 2 to 5
   B. 1.2 m square
   C. Height 100 mm
   D. h/t = 10
   Answer: A. IS 1905 Appendix B requires at least 400 mm height and h/t of 2 to 5, preferably 4 to 5. (Key point: Prism size)

2. How many prisms are tested?
   A. One
   B. At least 5, averaged
   C. At least 20
   D. Two, the higher taken
   Answer: B. At least 5 prisms are tested and the average used. (Key point: Number of tests)

3. What is k for h/t = 3.0 and what does it do?
   A. 0.86, corrects strength for prism slenderness
   B. 1.00, no change
   C. 0.73, converts to shear
   D. 0.95, converts to bricks
   Answer: A. Table 12 gives 0.86 at h/t = 3.0; shorter prisms read higher, so k reduces the strength. (Key point: Correction factor)

4. Given f_m = 12 N/mm^2, what is f_b?
   A. 3.0 N/mm^2
   B. 6.0 N/mm^2
   C. 1.2 N/mm^2
   D. 12 N/mm^2
   Answer: A. f_b = 0.25 f_m = 3.0 N/mm^2. (Key point: Basic stress)

## Related in Concrete Technology and Masonry Structure

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## Related in other subjects

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