Chapter 1.pptx

BULE HORA UNIVERSITY
COLLEGE OF ENGINEERING
Department of Architecture
Course Title: Building Materials and Construction II
Arch 2151
Target group: 2nd year Architecture Students
2nd semester
Lecturer: Anteneh D.
Academic Year: 2021 G.C

Chapter One
1. Construction techniques and structural concepts for masonry
constructions by using
1.1 Stone
General
• Natural Stone is one of the oldest construction material known. Various types
and forms of natural stone can also be processed to produced other
construction materials.
• As a part of the study of stones as a construction material, some understanding
of the origin and occurrence of rocks is essential.

Classification of Rocks
Rocks can be divided into three major categories depending on their geological
origin:
Igneous: formed by the cooling and crystallization of molten material
within or at the surface of the earth;
Sedimentary: formed from sediments derived from preexisting rocks,
by precipitation from solution, or by the accumulation of organic materials;
Metamorphic: resulting from the change of preexisting rocks into
new rocks

The Process of Rock Formation
 The earth's crust is dynamic and is subject to a variety of processes that act
upon all types of rocks. Given time and the effect of these processes, anyone of
these rocks can be changed into another type.
The temperature of the earth increases with depth at a rate of
about 30° C per kilometer of depth

Cont…
The rocks formed by solidification of magma within the mantle or crust are called
intrusive igneous rocks,(e.g. granite and gabbro) and those that form at the
surface from lavas are called extrusive igneous rocks(e.g. basalt and rhyolite).

Textures of Igneous Rocks
a) Phaneritic or Coarse-Grained: the constituent minerals are macroscopic in size.
b) Aphanitic or Fine-Grained: composed of mineral crystals or grains that are
microscopic in size
c) Porphyritic: the macroscopic mineral crystals or grains are embedded in a
matrix of microscopic crystals
e) Vesicular: This texture is characterized by the presence of vesicles- tubular,
ovoid, or spherical cavities in the rock.
f) Glassy: This texture resembles that of glass

Sedimentary Rocks
• Sedimentary rocks are derived from preexisting materials
through the work of mechanical or chemical agencies under
conditions normal at the surface of the earth, or they may be
composed of accumulations of organic debris.
• Rock weathering on land produces rock and mineral fragments
that are transported by gravity (falling) or by wind, water, or
ice and deposited elsewhere on the earth's surface as
sediments.
• The process or processes by which soft sediment is
transformed into rock is called lithification.
• Sedimentary rocks display various degrees of lithification.

Metamorphic Rocks
• Once formed, all rocks are subject to processes of change that occur
at the surface of the earth or within the crust of the earth.
• Metamorphic rocks are formed at varying depths within the crust
when preexisting rocks are changed physically or chemically under
conditions of high temperature, high pressure, or both. The process
of metamorphism, literally a "change in form," takes place deep
beneath the earth's surface and acts on all rocks-igneous,
sedimentary, and metamorphic.

Requirements of Building Stone
• Despite the abundance of rock, relatively few stones satisfy the
requirements as building stones.
• The important requirements are:
(1) strength,
(2) hardness,
(3) workability,
(4) durability,
(5) color and grain,
(6) porosity and texture,
(7) ease of quarrying, and
(8) accessibility.

Requirements of Building Stone
• Hardness is vitally important only where the stone is to be used in floors, steps,
walks, etc.
• Hardness does have a bearing on workability. It varies all the way from soft
sandstone, which can be easily scratched, to some stones harder than steel.
• Workability is important since the ease of producing the required sizes and
shapes has a direct bearing on the cost.
• Durability is the ability of the stone to withstand the effects of rain, spray, wind,
dust, frost action, heat, and fire
• Color is very important from the standpoint of aesthetics and location but is
also partially a matter of taste and fashion. The grain or surface appearance of
stone affects its desirability for decorative purposes.

Cont…
• Porosity has a direct bearing on the ability of the stone to withstand frost
action.
• Texture the fineness of grain, affects workability and therefore cost. Fine-
textured rock splits and dresses more readily than coarse rock. For many
ornamental purposes, also, the texture is important.
• The ease of quarrying is a prime consideration in judging the suitability of
stone for building. The bedding and joint planes must be such that the stone
can be produced in sizable, sound blocks.
• Accessibility also affects cost. Transportation over long distances is expensive
but in some cases becomes a necessity.

Quarrying and Finishing Of Stone
• Quarrying is the process of removing stone from its natural bed. The method
of quarrying will depend to some extent on the nature of the stone.
Dimension Stone Production
Processing stages applied in production:
Drilling of closely spaced boreholes
in rock for subsequent separation of
large lumps of stone from the massif.
Breaking of these lumps into
standard products or similar-size
stones.
Treatment of stone surface ,dressing
,grinding and polishing.
Loading and hauling of stone.

Quarry Stone Production
• Process stage applied in production:
• Stripping and clearing of overburden
• Drilling of boreholes in rock charging with explosives
• Blasting operations
• Drilling of boreholes in oversize stone, cleaning of boreholes, blasting
operations
• Loading of stone onto transport vehicles and hauling to a construction.

Crushed Stone Production
• Process stage applied in production:
• Stripping and clearing of overburden
• Drilling of boreholes in rock and charging with explosives
• Blasting operations
• Drilling of boreholes in oversize stone, blasting operations
• Loading of stone onto transport vehicles and hauling to a crusher plant
• Screening of crushed stone in size fractions
• Storage of crushed stone size fractions (Loading and hauling of crushed stone
and artificial sand to a construction site in size fraction)

• Stone which does, in general, satisfy the foregoing requirements
and which is commonly used for construction in Ethiopia
include: basalt, trachyte, granite, limestone, marble, sandstone,
ignimbrite, pumice, and scoria.
• Basalt and trachyte are very common in Ethiopia and are mostly
used for stone masonry work and as boulders or crushed stone
for road construction and crushed aggregate for concrete
making.
• Granite is generally hard, strong, durable, and capable of taking
a high polish. Granite has a wide variety of use in building,
including flooring, interior and exterior facing, stair trades and
skirting.
General Types of Stone Used in Ethiopia

General Types of Stone Used in Ethiopia
• Owing to its beautiful colors and durability marble is used as wall cladding
material, floor finishing and window sill.
• Sandstone and ignimbrite are widely used for decorative purpose. Ambo sand
stone is a typical example in this aspect.
• Pumice and scoria are found in large quantities in the rift valley .they are widely
used in the manufacture of light weight concrete block. Owing to its light weight
concrete made of pumice is used for forming slopes on flat concrete roofs.
Pumice is also used for production of Portland pozzolana cement.

1.2 Bricks (Fired Clay Products)
• A clay brick is a small solid block ,usually rectangular, made of
burned clay.
• A structural clay tile is a hollow clay unit ,larger than a brick,
developed for use where lightweight masonry is required.
• The word “brick” comes from the French word brique.
• The art of brick making have spread from Egypt to Greece and then
to Rome.

Fired clay products:
Can have high compressive strengths
Provide excellent fire-resistance
Weather resistant and can remain without any surface protection
Have no wastage
Disadvantages Fired Clay Products
 Relatively high fuel consumption of the firing process
 A possible defect of burnt bricks…"efflorescence“
 Good quality fired clay products tend to be expensive
 Capital investments for fuel efficient kilns are often too high
Advantages of Fired Clay Products

Suitability of bricks
At present, bricks are the most favored construction material
worldwide due to the following reasons:
• Availability-clays are available almost universally
• Construction methods-very experienced skill bricklayers
are available in all villages,& towns
• Size, shape and handling-Bricks are made in ready-to-use
sizes and shapes

Raw Materials
Bricks Are Manufactured From Clays.
 By Moistening And Mixing With Water, Clays Become Plastic,
Easy To Mold And Are Capable To Retain Their Shape On
Drying.
Clay Soils Are Of Two Types:
• Residual Clay (Formed From Decay Of Underlying Rocks)
• Transported Clay/Sedimentary(formed From Materials
Removed From Parent Rock ,Transported And Deposited
Somewhere Else By Wind Or Air.

Functions of The Constituent Of Clay
Clays generally consist of the following chemical
elements:
• Alumina- (Al2O3)
• Silica – (SiO2)
• Lime - (CaO)
• Iron oxide - (Fe2O3)
• Magnesia – (MgO)

Alumina- (Al2O3)
 Makes the major part of clay
 Responsible for plasticity of the mud
 When burnt, alumina becomes stronger and harder.
• Excess alumina content→ brick will shrink on drying→ cracking and
warping.
• Small alumina content→ the brick will not be molded easily.
Silica – (SiO2)
 Reduce shrinkage and warping in burning
Responsible for strength, hardness and durability or long life
A large percentage of uncombined silica is undesirable because it leads to
brittleness of the product

Lime - (CaO)
 Acts as a binder to the clay and silica particles leading to greater strength
 Acts as flux and lower the fusion point of silica.
• Excess lime case the brick to melt and lose the shape.
Iron oxide - (Fe2O3)
 Imparts the colors of the clay and the burnt product
 Acts as a flux i.e. it lowers down the softening temperature of silica
• Excess iron oxide → the brick becomes too soft during burning → dark in
appearance.
• If it is small in quantity than required it affects the color of the brick,
instead of being brick red, they may be yellow.

Magnesia – (MgO)
 Gives the brick darker or even black color
 Minimizes warping of bricks in burning
• Magnesia is present in small quantity (1%)

Manufacture of Bricks
The process of manufacture of bricks is carried out in a number
of stages.
1. Selection of suitable type of brick earth
2. Preparations and tempering of mud
3. Shaping and molding of brick units
4. Drying of molded bricks
5. Firing or burning of units
6. Cooling of the units

1. Selection of suitable type of brick earth
A clay soil for brick making should be such that when prepared
with water, it can be molded, dried and burnt without cracking or
changing its shape or warping. The ideal composition of a good
brick earth is:
• Clay (Alumina) – 20-30%
• Silica (free and combined) – 50%-60%
• CaO, MgO – 4.5%
• Iron oxide – 4%-6%
The earth should be free from alkalis, organic matter and free
lime.

2. Preparation and tempering of mud
A two stage process:
• Clay Wining: The operations of selecting the earth, clearing and
digging it, spreading it for weathering.
• Tempering: the process of converting the prepared brick earth into a
homogeneous mix of desired plasticity by mixing it thoroughly with
proper quantities of water.
3. Shaping and Molding of bricks
• Molding is the process of making properly shaped brick units from
thoroughly tampered clay.
• The brick at this stage is known as “green brick”.

4. Drying of bricks
After molding, the green bricks have to be dried.
Reasons for drying:
• To make them sufficiently rigid, strong for handling and stacking
• To minimize the risk of rapture
• To save fuel during burning stage
Drying of bricks is achieved either by natural methods or by artificial methods.
Drying of
bricks by
natural
methods

5. Firing
Firing of the dried bricks is essential to develop the desired building properties such as:
• Sufficient strength
• Hardness
• Durability and
• Resistance to decay and disintegration
The Firing Process
i. Temperature (20-150oc)…loss of moisture.
ii. Temperature (150-600oc)…loss of moisture, hardening starts.
iii. Temperature (600-950oc)…chemical changes start to occur which gives the brick
color ,hardness &durability.
iv. Temperature (950-1200oc)…verification occurs (glass like material forms which
glue all of the elements together.)

Methods of burning
There are two types of firing kilns for bricks:
• intermittent and
• continuous kilns
At present, there are two main methods of burning of bricks in developing
countries:
Kiln burning
Clamp burning

Effects of improper burning
1. Over or under sized bricks (due to difference in temp types of clay )
2. Glazed bricks (over burning)
3. Low strength bricks (poor quality clay, improper burning)
4. Cracked or broken bricks (opening the kiln before cooling,
burning before drying)
Types And Classification Of Bricks
Bricks can be classified according to their usage as:
1. Common bricks and
2. Facing Bricks

1. Common Bricks
• Common bricks are those that are used where they will not normally be
exposed to view and where there is no claim as to their appearance.
• They are suitable for general use in construction, given that they possess
adequate strength and durability for the location.
2. Facing Bricks
Facing bricks have a suitable
appearance for use where they
will be exposed to view so that
they give an attractive and
pleasant effect.

Solid and hollow clay bricks
Bricks can be classified according to their shape and nature as:
• Solid clay bricks and
• Hollow clay bricks
Solid Clay Bricks
According to the Ethiopian Standard, solid bricks are of the
following three types.
1. Brick without holes or depression
2. Brick with holes up to 20 mm in diameter each and having a total cross
sectional area not exceeding 25% of the base area of the brick.
3. Brick with depression not exceeding 25 percent of the base area having a
maximum depth of the depression not more than 10mm.

Hollow Clay Bricks
According to the Ethiopian Standard, hollow and beam tiles bricks
are of the following three types.
1. With two faces keyed for plastering or rendering
2. With two faces smooth and suitable for use with out
plastering or rendering on either side. and
3. With one face smooth and another face keyed for plastering.

Firebricks or Refractory bricks
These bricks are capable of withstanding very high temperatures without
melting or becoming soft.
• Firebricks are manufactured in exactly the same manner as the ordinary
bricks burnt in kilns at temperatures ranging from 13500c to 19000c.
• Firebricks are the white or yellowish white color and are used for lining
the interiors of fireplaces, ovens, kilns, chimneys and furnaces.
Properties of Bricks
The essential properties of bricks are:
• Physical properties,
• Chemical characteristics,
• Thermal characteristics and
• Durability.

Physical properties
a. Shape- rectangular
b. Size – 60 mmx120mmx250mm
c. Color – red
d. Density- density varies from 1600 kg/cubic meter to 1900 kg/cubic
meter. A single bricks (60x120x250) will weigh between 3.2kg to 3.5kg
depending upon its density.
Mechanical properties
Compressive strength is the most important property of bricks especially
because they are to be used in load bearing walls. The compressive
strength of a brick depends on the composition of the clay and degree of
burning.

Thermal properties
• The heat and sound conductivity of bricks varies greatly with their density
and porosity. Very dense and heavy bricks conduct heat and sound at a
great rate. They have therefore poor thermal and acoustic (sound)
insulation qualities. For this reason, bricks should be so designed that they
are light and strong and give adequate insulation.
Durability
By durability of bricks is understood the length of time for which they remain
unaltered and strong when used in construction.
The durability of bricks depends on a number of factors such as: absorption
value, frost resistance and efflorescence.

Tests for Clay Bricks
Two types of tests are used to determine the quality of building bricks.
A. Field test
B. Laboratory test
A. Field tests:
such as appearance, hammer and hardness
Appearance test is that: shape, plainness, color etc.
When stroked with hammer, a properly burnt dry brick free from cracks emits
a highly metallic ring.
The hardness of a brick sample can be checked by scratching its surface or
broken section with a knife or fingernail. A well-burnt brick will be scratched
with difficulty.
A rough test for the strength of the brick is to let it fall freely from a height of
about one meter on to a hard floor. It should not break.

B. Laboratory tests
1. Compressive strength test
2. Water absorption test
3. Efflorescence test and
4. Saturation coefficient test =
(absorption after 24 hrs in cold water)
absorption after boiling for 5hrs
Minimum Compressive Strength

Qualities of good brick
1. It should have a regular shape, surface and red colored appearance.
2. It should confirm in size to the specific dimensions
(60mmx120mmx250mm)
3. It should be properly burnt.
4. Absorption should not exceed 25% in any case.
5. A good building brick should posses requisite compressive strength,
which in no case should be less than 35kg/cm2.
6. Bricks should be hard enough so that it is not scratched by fingernail.
7. A good brick has a uniform color and structure through its body.

1.3 Concrete Block
• Concrete block construction is gaining importance in developing countries,
even in low-cost housing, and has become a valid alternative to fired clay
bricks and other common construction materials.
• The essential ingredients of concrete are cement, aggregates (sand, gravel)
and water,

Lightweight concrete
• Lightweight concrete is generally used for concrete blocks
• Lightweight concrete comprise lightweight aggregates (pumice,
scoria..)and/or a high particles of coarse proportion of single-sized
aggregate in a lean mix, which is not fully compacted.
Characteristics of concrete
Main characteristics of concrete are:
High compressive strength, resistance to weathering, impact and abrasion
Low tensile strength (but can be overcome with steel reinforcement)
Capability of being molded into components of any shape and size
Good fire resistance up to about 400°C.

Types of Concrete Blocks
• Concrete blocks are produced in a large variety of shapes and sizes either
solid, cellular or hollow, dense or lightweight, air-cured or steam-cured, load
bearing or non-load bearing, and can be produced manually or with the help
of machines.
Stretcher blocks
The most commonly used concrete blocks are the stretcher blocks
with a nominal dimensions of:
40 cm x 20 cm x 10cm

Solid blocks
• Solid blocks have no cavities, or have voids amounting to not
more than 25 % of the gross cross-sectional area.
Cellular blocks
Cellular blocks have one or more voids with one bed blind on the other face,
and are laid with this 'blind end' upwards, preventing wastage of bedding
mortar, which would otherwise drop into the cavities.
Hollow blocks
Hollow blocks are the most common types of concrete blocks, having one or
more holes that are open at both sides. The total void area can amount to 50
% of the gross cross-sectional area.

Advantages of hollow concrete blocks
The use of hollow concrete blocks has several advantages:
• if lightweight aggregate is used, can be very light
• they require far less mortar than solid blocks (because of the cavities and
less proportion of joints, due to large size), and construction of walls is
easier and quicker;
• the voids can be filled with steel bars and concrete, achieving high seismic
resistance;
• the air-space provides good thermal insulation, which is of advantage in
most climatic regions, except warm-humid zones; if desirable, the cavities
can also be filled with thermal insulation material;
• the cavities can be used as ducts for electrical installation and plumbing.

Materials For Concrete Blocks
• Cement
• Aggregate
• Water
Cement
• OPC, Portland blast furnace slag, sulfate resisting,
Aggregates
The maximum particle size of coarse aggregate is 13mm(10 mm ).
Rounded stones produce a concrete that flows more easily than angular
particles but the latter give high strength.

Production Process
1. Batching and Mixing
2. Molding
3. Curing
1. Batching and Mixing
Aggregates can be batched by volume or by weight, but the latter is more accurate.
For this reason,
Cement should only be batched by weight, or preferably by using only whole bags
of 50 kg.
2. Molding
Concrete blocks can be molded by several methods, ranging from manually tamping
the concrete in wooden or steel mold boxes to large-scale production with 'egg-
laying' mobile machines and fully automatic stationary machines.

Block making Machines
'egg-laying‘ machine Automatic stationary machines

Curing
• The blocks are either left to set and harden where they were molded, or
carried away on pallets to the curing place. In all cases it is important to
keep the concrete moist, for example, by regularly spraying with water,
until the concrete has obtained sufficient strength.
Air curing is the standard procedure for the strength development of
concrete, by which the concrete is kept wet for 7 days or more.
Steam curing, by which the concrete is exposed to low or high pressure
steam (in autoclaves), high early strengths can be achieved (with autoclaving
the 28 day strength of air-cured concrete can be obtained in 24 hours).
However, in developing countries, steam curing is unlikely to be
implemented, because of its high cost and sophistication.

Chapter 1.pptx

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