What is a brick? Types of brick, testing performed on it, Properties and application of brick

Types of Bricks

(a) Specially Shaped Bricks:Manufacturers produce bricks of special shapes to meet different requirements. Figure 3 shows some of these bricks.

(b) Facing Bricks: Builders use these bricks on the outer face of masonry. Once they lay these bricks, they do not need to apply plaster. These bricks typically measure 190 × 90 × 90 mm or 190 × 90 × 40 mm.

(c) Perforated Building Bricks: Manufacturers produce these bricks with a perforation area ranging from 30 to 45 percent. Each perforation covers no more than 500 mm². They distribute the perforations uniformly across the surface. They manufacture these bricks in sizes of 190 × 190 × 90 mm and 290 × 90 × 90 mm.

(d) Burn’t Clay Hollow Bricks: Figure 4 shows a burnt clay hollow brick. Builders use these lightweight bricks for constructing partition walls. They offer good thermal insulation for buildings. Manufacturers produce them in sizes of 190 × 190 × 90 mm, 290 × 90 × 90 mm, and 290 × 140 × 90 mm. They ensure that the thickness of any shell is at least 11 mm and any web at least 8 mm.

(e) Sewer Bricks: Builders use these bricks for constructing sewage lines. Manufacturers produce them from surface clay, fire clay, shale, or a combination of these materials. They make them in sizes of 190 × 90 × 90 mm and 190 × 90 × 40 mm. These bricks must have an average strength of at least 17.5 N/mm². Their water absorption must not exceed 10 percent.

(f) Acid Resistant Bricks: Builders use these bricks for flooring areas exposed to acid attacks, for lining chambers in chemical plants, and for lining sewers that carry industrial waste. Manufacturers make these bricks from clay or shale with a suitable composition that contains low lime and iron content. They add flint or sand and vitrify the bricks at high temperatures in a ceramic kiln.

Properties of Bricks

1. Colour: Colour should be uniform and bright.
2. Shape: Bricks should have plane faces. They should have sharp and true right angled corners.
3. Size: Bricks should be of standard sizes as prescribed by codes.
4. Texture: They should possess fine, dense and uniform texture. They should not possess fissures, cavities, loose grit and unburnt lime.
5. Soundness: When struck with hammer or with another brick, it should produce metallic sound.
6. Strength: Crushing strength of brick should not be less than 3.5 N/`mm^2`. A field test for strength is that when dropped from a height of 0.9 m to 1.0 mm on a hard ground, the brick should not break into pieces.
7. Water Absorption: After immercing the brick in water for 24 hours, water absorption should not be more than 20 per cent by weight. For class-I works this limit is 15 %.
8. Efflorescence: Bricks should not show white patches when soaked in water for 24 hours and then allowed to dry in shade. White patches are due to the presence of sulphate of calcium, magnesium and potassium. They keep the masonry permanently in damp and wet conditions.
9. Thermal Conductivity: Bricks should have low thermal conductivity, so that buildings built with them are cool in summer and warm in winter.
10. Sound Insulation: Heavier bricks are poor insulators of sound while light weight and hollow bricks provide good sound insulation.
11. Fire Resistance: Bricks usually offer good fire resistance. Builders often encase steel columns with bricks to protect them from fire.

Tests on Bricks

1. Crushing strength
2. Absorption
3. Shape and size
4. Efflorescence

(i) Crushing Strength:Technicians soak brick specimens in water for 24 hours. Next, they fill the frog with 1:3 cement mortar and keep the specimens in damp jute bags for another 24 hours. Afterward, they cure the bricks in water for an additional 24 hours. Then, they place them in a compression testing machine with 6 mm plywood sheets on both faces. Subsequently, they apply a uniform axial load of 14 N/mm² and calculate the crushing strength by dividing the applied load by the loaded area. Finally, they take the average of five specimens to determine the final crushing strength.

(ii) Absorption Test: Technicians first weigh the brick specimens in a dry state. Then, they immerse the specimens in water for 24 hours. Afterward, they remove the bricks, wipe them with a cloth, and weigh them again in the wet condition. Next, they determine the water absorbed by calculating the difference between the wet and dry weights. To calculate the percentage absorption, they divide the water absorbed by the dry weight and multiply the result by 100. They repeat this process for five specimens and take the average. Ideally, this average value should not exceed 20 percent.

(iii) Shape and Size: Bricks must conform to standard size, and their edges must be truly rectangular and sharp. To verify this, inspectors randomly select 20 bricks and stack them along their length, width, and height. For example, for standard bricks measuring 190 mm × 90 mm × 90 mm, the IS code specifies the permissible limits for each dimension.:

The following field tests help in acertaining the good quality bricks:

1. Uniformity in Size:A good brick has a rectangular, plane surface and uniform size.In practice, inspectors check this in the field through direct observation.
2. Uniformity in Colour: A good brick shows uniform color throughout. Therefore, buyers can observe this in advance before making a purchase. In fact, such visual and auditory cues can serve as helpful indicators of quality. As a result, they are better equipped to make informed decisions.
3. Structure:Break a few bricks in the field and observe their cross-section. Additionally, ensure the section appears homogeneous, compact, and free from defects such as holes and lumps. Moreover, pay attention to any irregularities in texture or composition. If possible, compare multiple samples to ensure consistency across the batch. Ultimately, such careful inspection helps verify overall brick quality.
4. Sound Test: When two bricks are struck together, they should produce a clear ringing sound. The sound should not be dull.
5. Hardness Test: For this a simple field test is scratch the brick with nail. If no impression is marked on the surface, the brick is sufficiently hard.

(vi) Efflorescense: Alkalies in bricks are undesirable as they absorb moisture and form gray powdery patches. A specific test is conducted to detect their presence:

Place the brick specimen in a glass dish containing water to a depth of 25 mm in a well-ventilated room. Once all the water is absorbed or evaporated, add water again to maintain a depth of 25 mm. After the second evaporation, observe the bricks for white or grey patches. Finally, report the observation as ‘nil’, ‘slight’, ‘moderate’, ‘heavy’, or ‘serious’ depending on the extent of the patches. In other words, classify the severity based on how widespread or concentrated the patches appear. Therefore, accurate assessment is essential to ensure consistent reporting.

1. Nil: No patches
2. Slight: 10% of area covered with deposits
3. Moderate: In this case, between 10% and 50% of the surface area is covered with deposits; however, flaking of the surface does not occur.
4. Heavy: In this condition, more than 50% of the surface area is covered with deposits; nevertheless, the surface does not exhibit any flaking.
5. Serious: Heavy deposits of salt accompanied by flaking of the surface.

Classification of Bricks Based on their Quality

1. First Class Bricks: These bricks are of standard shape and size. They are burnt in kilns. They fulfill all desirable properties of bricks.
2. Second Class Bricks: These bricks are ground moulded and burnt in kilns. The edges may not be sharp and uniform. The surface may be some what rough. Such bricks are commonly used for the construction of walls which are going to be plastered.
3. Third Class Bricks: These bricks are ground moulded and burnt in clamps. However, their edges appear somewhat distorted. Consequently, they produce a dull sound when struck together. This, in turn, suggests possible structural inconsistencies. Moreover, the lack of a sharp ringing tone may indicate internal flaws.Typically, builders use them for temporary and unimportant structures.
4. Fourth Class Bricks: These are the over burnt bricks. They are dark in colour. The shape is irregular. They are used as aggregates for concrete in foundations, floors and roads.

Uses of Bricks

1. As building blocks.
2. For lining of ovens, furnaces and chimneys.
3. For protecting steel columns from fire.
4. As aggregates in providing water proofing to R.C.C. roofs.
5. For pavers for footpaths and cycle tracks.
6. For lining sewer lines.