Types of Bricks in Construction

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Questions and Answers

What is the primary factor that affects the limit of water absorption in bricks?

Compressive strength

Type of brick class (correct)

Type of Government organization

Weathering conditions

What is the recommended use of First Class Bricks?

Building temporary structures

Foundation and floors in lime concrete and road metal

Pointing, exposed face work, flooring, and reinforced brick work (correct)

Hidden masonry works

What is the main difference between First Class Bricks and Second Class Bricks?

Color and texture

Weight and size

Crushing strength

Small cracks and distortions are permitted (correct)

What is the minimum crushing strength required for Second Class Bricks?

7.0 N/mm2 Signup and view all the answers

What is the characteristic of Third Class Bricks?

Under burnt, soft, and light-colored Signup and view all the answers

What is the primary use of Fourth Class Bricks?

Foundation and floors in lime concrete and road metal Signup and view all the answers

What is the purpose of the saturation coefficient in ASTM C62?

To classify bricks according to weathering conditions Signup and view all the answers

What is the recommended application of Grade SW bricks?

Areas subjected to frost action, especially at or below ground level Signup and view all the answers

What is the consequence of using highly absorptive bricks?

Efflorescence and other problems in the masonry Signup and view all the answers

What percentage of the volume of the brick is permitted for small holes?

25 per cent Signup and view all the answers

What is the purpose of silica in brick making?

To prevent shrinkage and warping Signup and view all the answers

What should be the colour of a good brick?

Uniform deep red or cherry colour Signup and view all the answers

What should be the texture of a good brick?

Precise and uniform to prevent slipping of mortar Signup and view all the answers

What should be the minimum crushing strength of a good brick?

10 N/mm2 Signup and view all the answers

What is the maximum percentage of water absorption of a good brick?

20 per cent of its dry weight Signup and view all the answers

What should be the shape of a good brick?

Uniform size and plane, rectangular surfaces with parallel sides Signup and view all the answers

What should be the characteristics of the surface of a good brick when scratched by a finger nail?

No impression is made Signup and view all the answers

What should be the sound produced when two bricks are struck together?

A metallic sound Signup and view all the answers

What is the purpose of the final drying stage in a tunnel kiln?

To evaporate free water from the bricks Signup and view all the answers

What is the temperature range for the dehydration stage in a tunnel kiln?

149 ºC to 982 ºC Signup and view all the answers

What is the purpose of the cooling stage in a tunnel kiln?

To change the color of the bricks Signup and view all the answers

What is the maximum time for the cooling process in tunnel kilns?

10 hours Signup and view all the answers

What is the purpose of de-hacking in brick manufacturing?

To unload the kiln cars after the bricks have cooled Signup and view all the answers

What is the effect of excess lime in the clay?

It changes the color of the brick from red to yellow Signup and view all the answers

What is the effect of organic matter in the clay?

It makes the bricks porous Signup and view all the answers

What is the role of alkalis in the clay?

They are of great value as fluxes Signup and view all the answers

What is the effect of pebbles and gravels in the clay?

They do not allow the clay to be mixed thoroughly Signup and view all the answers

What happens to the bricks when they come in contact with moisture?

The alkalis in the brick crystallize and a grey or white powder forms on the surface Signup and view all the answers

What is the recommended way to remove efflorescence from a brick surface?

Dry brush it away before rendering or plastering Signup and view all the answers

What is the effect of sulphur in clay on the brick structure?

It forms a spongy, swollen structure and decolours the brick Signup and view all the answers

What type of water can cause similar effects as sulphur in clay?

Water containing small quantities of magnesium or calcium carbonates Signup and view all the answers

What happens to the brick when it contains carbon and insufficient time is given for proper oxidation during burning?

The sulphur forms a spongy, swollen structure and decolours the brick Signup and view all the answers

What is the main reason for the formation of efflorescence on bricks?

The absorption of moisture by the brick and subsequent crystallization of alkalis Signup and view all the answers

What is the effect of free water on clay during drying?

It causes the clay to shrink considerably Signup and view all the answers

Why is it important to remove efflorescence before rendering or plastering a wall?

To prevent the salts from being carried back into the wall and reappearing later Signup and view all the answers

What is the effect of combined water on clay during burning?

It causes the clay to shrink considerably Signup and view all the answers

What is a necessary property of clay for brick manufacturing?

Plasticity Signup and view all the answers

What is the primary difference between surface clays and shales?

Physical structure Signup and view all the answers

What is the purpose of mixing clays from different sources and locations?

To minimize variations in chemical composition and physical properties Signup and view all the answers

What is a characteristic of fire clays?

Usually mined at deeper levels Signup and view all the answers

What do surface clays and fire clays have in common?

Chemical composition Signup and view all the answers

What is a result of varying manufacturing processes?

Compensation for differences in chemical composition Signup and view all the answers

What can be said about brick from different manufacturers with the same appearance?

They have different properties Signup and view all the answers

What is the common composition of all three types of clay?

Silica, alumina, and varying amounts of metallic oxides Signup and view all the answers

What is the result of mixing clays from different sources and locations in the pit?

Bricks with the same properties in each production run Signup and view all the answers

Study Notes

Classification of Bricks

First-class bricks: recommended for pointing, exposed face work, flooring, and reinforced brick work
Second-class bricks: permitted to have small cracks and distortions, higher water absorption (16-20%), and crushing strength not less than 7.0 N/mm2
Third-class bricks: under-burnt, soft, and light-colored, producing a dull sound when struck; water absorption is about 25% of dry weight
Fourth-class bricks: over-burnt, badly distorted, and brittle; used for ballast in foundation and floors in lime concrete and road metal

Strength and Durability

Clay building bricks are graded according to properties related to durability and resistance to weathering
ASTM C62 classifies three available grades: severe weathering (SW), moderate weathering (MW), and negligible weathering (NW)

Characteristics of Good Bricks

Size and shape: uniform size and plane, rectangular surfaces with parallel sides and sharp straight edges
Color: uniform deep red or cherry color
Texture and compactness: surfaces not too smooth, pre-compact and uniform texture
Hardness and soundness: hard enough to prevent scratching with a finger nail, producing a metallic sound when struck
Water absorption: not exceeding 20% of its dry weight when kept immersed in water for 24 hours
Crushing strength: not less than 10 N/mm2
Brick earth: free from stones, kankars, organic matter, saltpetre, etc.

Ingredients of Good Bricks

Clay used for brick making consists mainly of silica and alumina, mixed with small proportions of lime, iron, manganese, sulphur, etc.
Functions of various ingredients:
- Silica: enables the brick to retain its shape, imparts durability, and prevents shrinkage and warping
- Alumina: mixed with silica in a proportion that makes the clay plastic when water is added

Types of Clay

Three principal forms: surface clays, shales, and fire clays
Surface clays: found near the surface of the earth, may be the up thrusts of older deposits or of more recent sedimentary formations
Shales: clays subjected to high pressures until they have nearly hardened into slate
Fire clays: usually mined at deeper levels, have refractory qualities

Manufacturing Process

Tunnel kiln: brick are loaded onto kiln cars, which pass through various temperature zones
Firing stages: final drying, dehydration, oxidation, vitrification, and flashing or reduction firing
Cooling: important stage in brick manufacturing, affects color

Harmful Substances in Bricks

Lime: when in excess, changes the color of the brick from red to yellow and causes disintegration
Pebbles, gravels, and grits: do not allow the clay to be mixed thoroughly, spoil the appearance of the brick, and may cause cracking
Organic matter: increases water absorption, reduces strength, and makes bricks porous
Alkalis: when in excess, melt the clay on burning, make bricks unsymmetrical, and cause efflorescence
Sulphur: when present with carbon, causes the formation of a spongy, swollen structure in the brick and decolouration by white blotches
Water: excessive free water causes clay to shrink, while combined water causes shrinkage during burning

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Description

Learn about the differences between First Class and Second Class bricks, including their uses and characteristics in construction and masonry.