ME31B: CHAPTER TWO

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ME31B: CHAPTER TWO

BUILDING MATERIALS

2.1 INTRODUCTION



A

wide

range

of

building

materials

is

available

for

rural

building

construction
.



The

proper

selection

of

materials

to

be

used

in

a

particular

building

can

influence

the

original

cost,

maintenance
;

ease

of

cleaning,

durability

and

of

course,

appearance
.



Proper

selection

of

material

is

very

important

and

the

following

factors

are

to

be

considered
.


Properties of Building Materials


a)

Strength

and

Durability
:

This

includes

tensile

and

compressive

strength,

hardness,

toughness,

shear

strength

etc
.



The

materials

should

also

be

durable

ie
.

able

to

retain

strength

and

other

properties

over

a

considerable

period

of

time
.


b)

Workability
:

Ease

of

working

with

the

material

eg
.

Cutting

and

shaping
.



This

should

be

considered

hand

in

hand

with

skilled

labour

or

otherwise

available
.

Properties of Building Materials Contd.


c)

Cost
:


Cheaper

materials

should

be

preferred

without

sacrificing

other

characteristics
.



d)

Availability
:

Local

materials

should

be

preferred,

all

other

things

being

equal

over

imported

or

transported

materials
.



Other Properties of Building Materials


Other

properties

to

consider

include



Esthetics,



Resistance

to

corrosion

and

to

fire,



Easy

transportability

and

ease

of

cleaning,



Resistance

to

environmental

changes,

and

to

insect

attack

as

well

as

imperviousness
.


2.2 Soil(Earth)


This

is

one

of

the

oldest

materials

for

building

especially

in

rural

areas
.

Advantages

of

earth

as

a

building

material

are
:


i)

It

is

resistant

to

fire



(ii)

It

is

cheap

and

readily

available



(iii)It

has

a

high

thermal

capacity

which

enables

it

keep

the

inside

of

the

building

cool

when

the

outside

is

hot

and

vice

versa
.



(iv)

It

is

a

good

noise

absorbent


Soil (Earth) Contd.


(v)

It

is

easy

to

work

using

simple

tools

and

skills
.


The

following

properties

of

earth

need

improvement

for

it

to

be

a

good

building

material
:



Look,



Crackness,



Weakness,



Lack

of

water

proofness
.


2.2.1 Methods of Improving Soil Properties



Soil

can

be

improved

by

compaction
.

Adobe

bricks(made

from

soil)

can

be

used

to

build
.

This

improves

the

looks

and

reduces

cracking
.


a) Cracks:

Soil particles range from
clay to sand.


Clay is strong but cracks, while sand
does not crack but is weak.


A mixture of clay and sand can be used
to avoid cracking.

Improving the Soil Contd.


This

is

the

principle

of

brick

making
.

Cracks

can

also

be

controlled

by

using

fibres

of

certain

plants

e
.
g
.

straw
.

The

fibre

reinforces

the

soil

particles

by

bridging

the

gap

between

them
.


b)

Weakness
:

Soil

strength

can

be

improved

by

adding

clay

or

chemicals

eg
.

cement
.

Other

stabilizers

include

lime,

bitumen,

rice

husk

ash,

natural

fibres

e
.
g
.

grass,

straw,

sisal,

saw

dust,

resins,

cow

dung

and

gypsum
.

Improving Earth Contd.


c)

Water

Proof
-
ness
:

The

soil's

waterproof

qualities

can

be

improved

by

adding

some

chemicals

e
.
g
.

benzene
.



Emulsified

asphalt

can

also

be

added

but

it

is

very

expensive
.



The

earth

wall

should

be

protected

from

rain

by

extending

the

roof
.


2.3 MASONRY


Masonry

is

an

art

of

building

with

stones,

bricks

or

concrete

blocks
.


2
.
3
.
1

Stones
:


Soft

stones

are

preferred

for

building

to

ease

reshaping
.




Stones

generally

show

good

strength,

high

durability,

low

cost(especially

if

available

in

site),

resistance

to

fire,

insects

and

environmental

changes
.



Stones

have

high

compressive

strength

and

hence

good

for

walls,

columns,

foundations

etc
.



2.3.2 Clay Bricks


Bricks

are

made

from

clay
;

the

clay

paste

is

placed

in

proper

moulds,

hardened

and

burnt

in

kilns

(oven)

in

high

heat
.




Bricks

are

generally

strong,

durable,

resistant

to

environmental

changes,

fire

and

insects
.


2.3.3 Mortar


Used

to

put

stone

materials

together
.

It

is

a

mixture

of

sand,

water

and

a

binding

material

like

clay,

cement

or

lime
.



Cement

is

more

expensive

that

lime

which

is

more

costly

than

clay
.



Lime

is

produced

by

burning

calcareous

stone

(Caco
3
)

in

water
.



CaCo
3

+

H

2
O

=

Ca(OH)
2

+

CO
2



Cement

is

a

mixture

of

lime

and

clay
.


2.3.4
Cement or Concrete Blocks


Made

using

mortar

of

cement

and

sand

with

necessary

quantity

of

water
.



The

blocks

can

also

contain

low

sized

gravel

also
.



The

blocks

are

generally

made

hollow

with

the

core

making

about

25
%

of

the

gross

area
.

These

blocks

are

quite

strong,

durable

and

have

most

other

characteristics

of

a

good

building

material
.



The

core

of

the

block

increases

the

acoustical

and

thermal

properties

and

reduces

the

self
-
weight
.



2.4 CONCRETE


Concrete

is

probably

the

most

important

structural

material

today
.



It

has

the

following

ingredients
:


i)

Cement

:

Portland

cement


ii)

Fine

aggregate
:

Sand,

granite

granules

etc
.


iii)

Coarse

aggregate
:

Gravel,

crushed

stone,

broken

bricks

etc
.


iv)

Water
.


2.4.1 Ratio of Concrete


Normal

ratio

of

concrete

is

1
:

2
:

4

(by

volume)
.



This

means

1

part

cement,

2

parts

fine

aggregates

and

4

parts

coarse

aggregates
.



Fine

aggregates

fill

the

pores

of

coarse

aggregates,

cement

fills

the

pores

of

fine

aggregates
.



Cement

with

water

forms

a

very

good

binding

material

which

binds

the

concrete

into

a

homogeneous

mass
.


2.4.2 Water
-
Cement Ratio (w/c
ratio)


The

best

w/c

ratio

is

0
.
45

to

0
.
65

by

weight
.



Too

high

w/c

ratio

increases

workability

of

concrete

but

reduces

strength

of

the

paste

while



Very

low

values

reduce

workability

and

binding

ability

leading

to

cracking

of

concrete
.


2.4.3 Processes in Concreting


a)

Batching
:

This

involves

bringing

all

the

ingredients

together

in

a

proper

ratio
.

It

is

normally

done

by

volume

but

better

results

are

obtained

if

the

ration

is

taken

by

weight
.


For 1 m of concrete, take approximately 1
m
3

of coarse aggregate.



With 1: 2: 4 ratio, 0.5 m
3

of sand and
0.25 m
3

of cement are used.


Water is normally added by experience.

Processes in Concreting: Batching
Contd.


With these mixtures, a little more than 1
m
3

of concrete is obtained.



For more accurate results, for 1 m
3

of
concrete, take 0.96 m
3

of coarse
aggregate and others accordingly using
the mixing ratio
.

Processes in Concreting: Mixing


Mixing

can

be

done

manually

or

mechanically
.



In

manual

mixing,

cement

and

sand

are

mixed

thoroughly

and

then

mixed

with

the

coarse

aggregate,

and

then

water

is

added

and

mixed

thoroughly
.



In

mechanical

mixers,

all

aggregates

and

water

are

added

in

the

rotating

mixer

and

rotated

to

mix

them

thoroughly
.

Other Processes in Concreting


c)

Conveyance

or

Transport
:

Done

using

barrows

or

mechanical

dumpers
.

Should

be

done

quickly
.


d)

Placing
:

Before

placing

concrete

in

sites,

the

formwork

is

to

be

checked,

cleaned

and

oiled
.


e) Compaction:

Concrete must be
compacted adequately to secure maximum
density.


This is done either manually or using rods or
mechanical vibrators.



Processes in Concreting: Curing


f)

Curing
:

The

setting

of

cement

and

hardening

of

concrete

depends

on

the

water

content
.



The

placed

concrete

has

to

be

protected

against

evaporation
.



Curing

is

done

by

keeping

the

exposed

surface

of

concrete

wet

continuosly
.



It

is

done

by

flooding

in

case

of

slabs

or

by

continuous

spraying

in

other

cases
.




Curing

is

done

for

7

to

10

days,

but

21

days

of

curing

gives

maximum

strength
.


2.4.4 Reinforcement of Concrete


Concrete

is

strong

in

compression

but

weak

in

tension
.



Reinforcement

involves

inserting

steel

bars

into

concrete

to

make

it

resist

tension
.



Beams,

slabs

etc
.

need

reinforcement

in

order

to

make

them

resist

bending

which

produces

tension
.


Example


Find

the

required

quantities

of

cement,

sand

and

coarse

aggregate

required

to

concrete

a

slab

10

m

long,

5

m

wide

and

12

cm

thick
.

Calculate

the

quantity

of

water

required

also
.

Specific

gravity

of

cement

is

1
.
5
;

ratio

of

ingredients

is

1

:

2

:

4

and

water

cement

ratio

is

0
.
5
.


Solution


Total

volume

of

concrete

needed

=

10

m

x

5

m

x

12
/
100

m

=

6

m
3


Assume

0
.
96

m

of

coarse

aggregates

per

m
3

of

concrete


Coarse

aggregate

required

is

6

x

0
.
96

=

5
.
76

m
3


Fine

aggregate

required

is

5
.
76

x

2
/
4

=

2
.
88

m
3


Cement

required

=

5
.
76

x

1
/
4

=

1
.
44

m
3

Solution Concluded


Note
:

Bulk

density

of

water

is

1000
kg/m
3

;

with

specific

gravity

of

1
.
5
;

bulk

density

of

cement

is

1
.
5

x

1000

=

1500

kg/m
3


Wt
.

of

cement

=

1
.
44

m
3

x

1500

kg/m

3

=

2160

kg
.



Assuming

1

bag

of

cement

weighs

40

kg,



Cement

required

=

2160
/
40

=

54

bags
.


w/c

ratio

is

0
.
5
,

water

required

=

0
.
5

x

wt
.

of

cement

=

0
.
5

x

2160

=

1080

kg

=

1080

litres


Note
:

1

litre

of

water

weighs

1

kg
.



2.5 WOOD


Wood

is

a

traditional

building

material
.

The

quality

of

wood

varies

widely
.



Wood

is

generally

durable,

strong,

dependable,

workable

and

possesses

many

other

characteristics
.



It

is,

however,

highly

inflammable

and

liable

to

insect

attacks

if

not

properly

protected
.

Wood

is

mainly

used

for

roof

skeleton,

doors

and

windows,

walls

and

partitions

in

small

buildings
.



Properties of Wood Contd.


Wood

may

be

hard

or

soft
.



Hard

ones

include

ebony,

mahogany,

etc
.

while

soft

ones

include

Douglas

fur,

palm

tree

etc
.



Strength

of

wood

increases

with

decreasing

moisture

content
.



By

seasoning

(drying),

the

strength

can

be

improved
.

Wood

is

highly

workable
.


Plywood


Produced by gluing many layers of split
wood together.



The grains are arranged alternatively
to eliminate distortion.


The plywood is a very good modern
construction material whose quality
depends on type of wood used, glue
used and pressure of steam used in
gluing.


Wood can be cut into many shapes.

a) Plank:
The thickness is small when compared to its width.



t







t < < B

B


Plank



b) Beams:
Width and thickness dimensions are almost same.








Beams


Shapes of Wood Contd: Block


c)

Blocks
:

Very

thick

eg
.

25

x

25

mm(width
-
depth)

or

20

x

25

mm

or

30

x

30

mm




BLOCK








Many

grades

of

wood

exist

depending

on

the

strength
.


BLOCK

2.6 METALS


These

are

man
-
made

materials

whose

properties

are

known
.

The

most

widely

used

metal

is

steel
.


2
.
6
.
1

Steel
:


Steel

is

very

strong,

highly

durable,

resistant

against

weather,

fire

and

insects

and

possesses

almost

all

good

characteristics
.



Steel

is

used

in

reinforcement

in

concrete,

gates,

windows,

roof

trusses,

steel

sheets

for

partitions

and

tanks

etc
.


2.7 Other Building Materials
(Synthetic Materials)



a)

Asbestos

Cement
:

Used

for

making

roof

sheets,

drain

pipes

and

accessories
.

It

is

also

used

for

partitions

and

ceilings
.


b)

Plastics
:

used

in

water

supply

and

sanitary

systems
.

Also

electric

fittings
.


c)

Ceramics,

fibre

glass

etc
.

are

new

materials

used

in

some

restricted

areas
.


2.8 PROTECTION OF
BUILDING MATERIALS


Plastering

with

cement

mortar,

lime

mortar

etc
.

is

common

to

protect

the

super

structure
.



Painting

is

used

to

protect

steel

from

rusting,

timber

from

insect

attack

and

shrinkage

etc
.



Painting

of

walls,

ceilings

etc
.

are

done

for

light

control

and

beauty
.



Galvanizing

and

other

protective

coverings

of

certain

materials

especially

metals

are

common
.