Building Materials Chapter 3

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Questions and Answers

What is the primary reason why clay bricks are widely used in construction?

Because they are highly durable and expensive

Because they are only used for exterior walls

Because they are economical and easily available (correct)

Because they are difficult to handle and work with

What is the minimum crushing strength of a first-class brick?

10 N/mm2 (correct)

15 N/mm2

5 N/mm2

8 N/mm2

What is the acceptable water absorption percentage for a first-class brick?

15-18% of its dry weight

12-15% of its dry weight (correct)

10-12% of its dry weight

8-10% of its dry weight

What is the characteristic of the surface of a first-class brick?

Smooth and rectangular Signup and view all the answers

What is the significance of the sound produced when two bricks are struck against each other?

It indicates the absence of flaws and cracks Signup and view all the answers

What is the characteristic of the fractured surface of a first-class brick?

It does not show lumps of lime Signup and view all the answers

What is the primary purpose of classifying clay bricks?

To determine their physical and mechanical properties Signup and view all the answers

What is the typical colour of a first-class brick?

Deep red, cherry or copper Signup and view all the answers

What is the minimum time required for immersing a brick in cold water to test its water absorption?

24 hours Signup and view all the answers

What is the primary factor that affects the compressive strength of clay bricks?

All of the above Signup and view all the answers

What is the maximum allowable absorption by 5-hour boiling according to ASTM C67?

25 % Signup and view all the answers

What type of brick is used for all load bearing structures?

Engineering Bricks Signup and view all the answers

What is the primary characteristic of Facing Bricks?

Good appearance Signup and view all the answers

What is the texture of Sand-Faced Brick?

Textured Signup and view all the answers

What type of brick is obtained from the outer portion of the kiln?

Pale Bricks Signup and view all the answers

What is the purpose of Common Bricks?

Filling and backing in walls Signup and view all the answers

What is the characteristic of Rustic Brick?

Mechanically textured Signup and view all the answers

What is the standard that governs the physical requirements for clay building bricks?

ASTM C62 Signup and view all the answers

What is the primary reason for mixing clays from different sources and locations in the pit?

To create a uniform chemical composition Signup and view all the answers

What happens to clay particles when subjected to appropriate temperatures?

They fuse together Signup and view all the answers

What is the main difference between surface clays and fire clays?

Their physical structure Signup and view all the answers

Why do bricks from different manufacturers that have the same appearance differ in other properties?

Because of variations in manufacturing processes Signup and view all the answers

What is the primary characteristic of shales?

They have been subjected to high pressures until they have nearly hardened into slate Signup and view all the answers

What is the purpose of clay having wet and air-dried strength?

To maintain its shape after forming Signup and view all the answers

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

Silica, alumina, and metallic oxides Signup and view all the answers

What is the main difference between surface clays and shales?

Their physical structure and location Signup and view all the answers

Why do bricks from the same manufacturer have slightly different properties in subsequent production runs?

Due to variations in chemical composition within the pit Signup and view all the answers

What is the primary purpose of blending raw materials in the manufacturing process?

To produce more uniform raw materials and control color Signup and view all the answers

What is the primary function of inclined vibrating screens in the preparation phase?

To control particle size Signup and view all the answers

What is the range of water percentage mixed into the clay to produce plasticity in the stiff-mud process?

10 to 15 percent Signup and view all the answers

What is the first step in the forming process?

Tempering Signup and view all the answers

What is the purpose of storing sufficient quantities of raw materials?

To ensure continuous brick production regardless of weather conditions Signup and view all the answers

What is the name of the machine used to break up large clay lumps and stones?

Size reduction machine Signup and view all the answers

What is the primary function of a pug mill?

To produce a homogeneous, plastic clay mass Signup and view all the answers

How many principal processes are there for forming brick?

3 Signup and view all the answers

What is the final phase of the manufacturing process?

De-hacking and storing finished products Signup and view all the answers

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

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

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

From 149 ºC to 982 ºC Signup and view all the answers

What is the primary cause of disintegration in bricks due to excess lime?

Lime absorbs moisture, swells and causes disintegration Signup and view all the answers

Why are pebbles, gravels, and grits considered harmful substances in brick manufacturing?

They do not allow the clay to be mixed thoroughly and spoil the appearance of the brick Signup and view all the answers

What is the primary effect of organic matter on bricks during burning?

It leaves pores and makes the bricks porous Signup and view all the answers

What is the role of alkalis in brick manufacturing when present in small amounts?

They act as a flux and reduce the melting point of the clay Signup and view all the answers

What is the primary purpose of the cooling stage in brick manufacturing?

To control the rate of cooling and affect the color of the brick Signup and view all the answers

What is the typical cooling time for bricks in a tunnel kiln?

Less than 10 hours Signup and view all the answers

What is the process of unloading a kiln or kiln car after the brick have cooled?

De-hacking Signup and view all the answers

Study Notes

Bricks

Bricks are a popular and leading construction material due to their affordability, durability, and ease of handling.
Clay bricks are commonly used for building exterior and interior walls, partitions, piers, footings, and other load-bearing structures.
Bricks can be made of burnt clay, a mixture of sand and lime, or Portland cement concrete.

Classification of Bricks

Based on field practice: • First-class bricks: thoroughly burnt, deep red, cherry or copper color, smooth surface, free from flaws, and have a uniform texture. • Second-class to fourth-class bricks: classified based on physical and mechanical properties.

Physical Requirements for Clay Building Bricks (ASTM C62)

Compressive strength: not less than 10 N/mm2.
Water absorption: 12-15% of its dry weight when immersed in cold water for 24 hours.

Classification of Bricks Based on Use

Common bricks: general-purpose units, manufactured economically, used for filling, backing, and in walls where appearance is not important.
Facing bricks: made for good appearance, durable, and used in fronts of building walls for a pleasing appearance.
Engineering bricks: strong, impermeable, smooth, table-molded, hard, and conform to defined limits of absorption and strength.

Classification of Bricks Based on Finish

Sand-faced bricks: textured surface manufactured by sprinkling sand on the inner surfaces of the mold.
Rustic bricks: mechanically textured finish, varying in pattern.

Classification of Bricks Based on Burning

Pale bricks: under-burnt bricks obtained from the outer portion of the kiln.
Body bricks: well-burnt bricks occupying the central portion of the kiln.
Arch bricks: over-burnt bricks, also known as clinker bricks, obtained from the inner portion of the kiln.

Types of Clay

Surface clays: found near the surface of the earth, used for brick manufacturing.
Shales: clays subjected to high pressures, nearly hardened into slate.
Fire clays: usually mined at deeper levels, refractory qualities, and used for brick manufacturing.

Phases of Manufacturing

Mining and storage of raw materials.
Preparing raw materials.
Forming the brick.
Drying.
Firing and cooling.
De-hacking and storing finished products.

Manufacturing Process

Mining: surface clays, shales, and some fire clays are mined in open pits with power equipment.
Preparation: breaking up large clay lumps and stones, and mixing the raw material.
Forming: tempering, producing a homogeneous, plastic clay mass, and then forming the brick using stiff-mud, soft-mud, or dry-press processes.
Firing: tunnel kiln or periodic kiln, divided into five general stages: final drying, dehydration, oxidation, vitrification, and flashing or reduction firing.
Cooling: important stage, as the rate of cooling has a direct effect on color.
De-hacking: unloading the kiln or kiln car after the brick has cooled.

Harmful Substances in Bricks

Lime: excess lime can change the color of the brick from red to yellow and cause disintegration.
Pebbles, gravels, grits: can spoil the appearance of the brick and cause cracking.
Organic matter: can make the brick porous, increase water absorption, and reduce strength.
Alkalis (alkaline salts): can be beneficial as fluxes, but excess can make the clay unsuitable for bricks.

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Description

This quiz assesses understanding of building materials, covering topics related to civil engineering. It is part of the course materials for the University of Halabja's Civil Engineering Department.