Range of building materials

1
Session 1 Range of building
materials Properties of Concrete Clay and none
clay building products
2
Introduction
Introduction In this module you will learn about
the characteristics and quality standards of
building materials commonly used in residential
scale buildings There is a wide range of
possible building materials available for our use
and the performance of these materials has an
impact on the cost, aesthetics and function of
the building. A well designed, economical
building takes the following factors into account
the properties and behaviour of building
materials the initial and long-term costs the
effects on the environment how the materials
interact with each other.
3
Introduction
Introduction
Well designed buildings take into
account Properties and behavior of materials
Initial and long term costs Effects of the
environment How building materials interact
with each other
4
Introduction
Introduction
Learning outcomes On completion of this unit,
you should be able to Nominate the various
factors that limit the life and durability of
building materials. Understand the various
physical, chemical and biological factors that
affect the performance of building materials in
use Understand the basic characteristics of
different building materials.
5
Introduction
The Range of building materials

• Factors affecting the selection of building
  materials
• The selection of materials is affected by a range
  of factors including
• Economic
• physical.
• Lets examine these factors in detail.

6
Factors affecting the selection of building
materials

• Economic factors
• Energy content
• Building materials are sometimes described as
  having a certain energy content. This refers to
  the cost of their production. timber or sand are
  materials having a low energy content, they do
  not require a primary manufacturing process.
• By-products of other industrial processes (eg
  wood particles, blast furnace slag and pulverised
  ash) also have a low energy content.

7
Introduction
Factors effecting the selection of building
material
Energy content Other materials require energy in
their production, and therefore have a high
energy content. These include, glass, bricks,
plastics, metals and cement. This adds to their
cost, and if local supplies of the raw materials
are exhausted or unavailable, then purchase and
transport costs are also added to the overall
cost.
8
Factors effecting the selection of building
material
Labour and Materials costs The cost ratio for
housing is approximately 55 per cent
materials 45 per cent labour
9
Factors effecting the selection of building
material
Labour and Materials The choice of materials
should not depend only on the purchase and
installation cost, but also on the cost of
repair, maintenance and replacement of short
life-span products. Less durable materials may
be cheap to buy but repair or replacement costs
are usually high. Cheap materials usually lower
the value of a building, whereas more durable
materials, such as stone and brick, mellow with
age and give the structure a more aesthetic
appearance.
10
Factors effecting the selection of
building material
Conservation of resources Most world resources
of metals, rainforest timber, fossil fuel and
limestone are non-renewable and limited. It is
important for us as consumers not only to be
aware of those resources which are threatened or
have bad effects on the environment, but also to
use those which are, with management, safe both
to our health and to the environment as a whole.
Where possible we should use renewable resources,
such as timber from re-planting programs. It is
also important that world fuel energy is not
wasted by unnecessary processing and
transportation. As well as being environmentally
desirable, these savings mean cheaper materials.
11
Factors effecting the selection of building
material
Physical properties Materials have different
characteristics, or properties. These properties
are affected by physical, chemical and biological
factors. Here we will be looking at the
following properties Density and specific
gravity Strength Electrical conductivity Therma
l conductivity and capacity Moisture
absorption Acoustics.
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Factors effecting the selection of building
material
Density and specific gravity Different
substances have different densities. Iron is much
denser than aluminium which is why a piece of
aluminium is much lighter than a piece of iron of
the same size. Ice floats in water because the
ice is less dense than the water. Density is
measured by specific gravity. Specific gravity
is the ratio of the mass of a given volume of a
liquid or solid to that of the same volume of
water. The density of pure water is taken as 1 at
4C.
13
Factors effecting the selection of building
material
Strength A structure (eg a beam or a bridge)
must be able to safely support its own weight
plus the load it carries without distortion.
Distortion will reduce the efficiency of the
structure or make it unstable or look
unattractive. A structure can be made much
stronger without increasing its weight, by being
made in a different shape. Structures have
different strength when used in different ways.
See, for example, in Figure 1.1, where the steel
beam A is much stronger than the steel beams B or
C, even though they all contain the same amount
of steel.
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Factors effecting the selection of building
material
Figure 1.1 Different types of steel beams
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Factors effecting the selection of building
material
Some materials strongly resist being squashed.
They are said to have compressive strength.
Concrete, stone and brick are such materials.
Other materials, such as steel, are strong under
tension and will resist being stretched. The
behaviour of concrete under pressure is
illustrated in Figure 1.2. Concrete cracks easily
when stretched. It has low tensile strength.
16
Factors effecting the selection of building
material
By using steel reinforcing in concrete, we
combine the tensile strength of steel with the
compressive strength of concrete, resulting in a
product that is strong in tension as well as
being strong in compression (see Figure
1.3) Figure 1.3 The tensile (under tension)
strength of steel is combined with the
compressive strength of concrete when reinforcing
mesh or bars are used in concrete
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Factors effecting the selection of building
material
A piece of 25 mm wide galvanised steel strap,
which is often used in bracing timber frames, is
very difficult to stretch, but crumples easily
when compressed lengthways. It has high tensile
strength and low compressive strength. Materials
that are undergoing force are said to be
stressed, and their change in shape is called
strain. An elastic material is one which will
recover its original shape when the stress is
removed. A steel spring is elastic. A piece of
chewing gum is not very elastic. The response of
materials to stress will depend on how stress is
applied to them whether the stress is continuous
(eg a load-bearing arch) whether the material is
compressed, stretched or twisted whether it is
affected by moisture or temperature.
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Factors effecting the selection of building
material
Complete the check progress 1 questions in
your Guide Electrical conductivity Materials
that easily carry electricity through them are
said to be conductors. Materials that do not are
non-conductors. For example, most metals are good
conductors and most plastics are not. This is why
electrical wiring is copper and the protective
sheathing is plastic.
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Factors effecting the selection of building
material
Thermal conductivity and capacity The
thermal properties of a material are concerned
with how a material reacts to changes in
temperature. The thermal properties include heat
expansion or contraction, insulation, heat
storing ability, cooling, and reaction to frost,
snow and ice. Thermal conductivity is a measure
of how fast heat travels through materials. This
rate may be affected by density, temperature,
porosity and moisture content.
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Factors effecting the selection of building
material
Moisture absorption Some very porous materials
will absorb moisture more readily than others.
However, most materials may take up moisture from
the air, from the ground (eg through poor
dampcourses), from damaged roofs or gutters, or
by condensation. Condensation from moisture in
the air will form on surfaces colder than the
air. Condensation often becomes trapped on the
inner surface of water-tight materials (eg
flat-roof coverings, metal and glass
wall-cladding, foil insulation). This can be
prevented by the correct use of vapour barriers
(materials which are designed to prevent surface
condensation by being placed on the warm side of
walls or ceilings in such a way that there is no
gap in them).
21
Factors effecting the selection of building
material
Acoustics Insulation from noise can be achieved
by the use of dense materials, by avoiding
openings directly onto noise areas and by
avoiding direct paths (eg a hall with a bend
leading from a noisy machine shop to the workers
tea room or a hall with lobbies or double doors
would both reduce noise). Some porous materials
are used for modifying the acoustics in a room
but sound can only be prevented from travelling
from one space to another by the use of dense
materials . On the inside of a building,
double-glazed windows, heavy curtains,
wall-hangings and carpet all help absorb noise.
On the outside, walls, fences, hedges, trees and
bushes may be used to reduce traffic or
industrial noise.
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Factors effecting the performance of building
material Complete the check progress 2 questions
in your Guide
Building materials undergo changes over time and
the following factors affect their
performance Movement caused by applied
loads Movement caused by temperature Movement
caused by moisture Durability of the
materials Fire resistance Compatibility of
different materials. Movements may be
substantial and result in considerable stresses.
If these stresses are greater than the strength
of the material then, obviously, cracks or
buckling will result.
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Factors effecting the performance of building
material
Movement caused by applied loads These loads may
occur by design or by accident. They may be
caused by error in structural design or from
overloading. Movement caused by
temperature Most substances are affected by
temperature changes, expanding when heated and
contracting when cool, but some are affected more
than others. This is called thermal movement.
Figure 1.4 shows a comparison of the relative
changes due to temperature in a number of
materials.
24
Factors effecting the performance of building
material
Dark coloured materials set into light coloured
ones Dark coloured materials, when exposed to
the sun, can heat up and expand greatly, causing
cracks in the material in which they are set. Or
else the dark materials may themselves crack or
buckle. For this reason, roof surfaces (such as
sheet metal) are best finished with a solar
heat-reflecting surface or paint. Coloured glass
in a sunny wall must be able to move freely, as
it will expand and contract with temperature
changes. If the glass is set between metal screws
or beading that prevents this movement, it will
crack. Putty or silicone caulk allows such
movement.
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Factors effecting the performance of building
material

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Factors effecting the performance of building
material
Movement caused by moisture A change in the
moisture content of most materials will result in
deformation they will swell when wet and shrink
when dry. These changes, called moisture
movements, can result in warped, twisted, shrunk
or cracked items.
27
Factors effecting the performance of building
material
Durability Since all materials deteriorate over
time to some extent, we should be able to
anticipate these changes and take them into
account when designing a structure, whether it is
a house, a shed or a cupboard. We should foresee
normal wear and tear, as well as the occasional
very heavy stress caused by storms, fire, flood
or burglary for example. Durability will be
different for different exposures. A coat of
paint will last for many years inside a cupboard
or less than a year in a sunny exposed position
in a heavily polluted industrial area. We are all
aware of the effect of salt spray on a car.
Buildings are similarly affected, though it is
not always so obvious.
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Factors effecting the performance of building
material
Corrosion of metals The effects of metal
deterioration on surrounding materials can be
significant, and will be looked at in the context
of these materials when they are dealt with in
later units. Sunlight Sunlight causes drying
and cracking of timbers. It also fades colours
and pigments and its heating of dark coloured
materials can greatly speed up their
breakdown. Ultraviolet radiation causes breakdown
of clear finishes, stains, paints, rubber, some
plastics and polythenes, tars and bitumen,
fabrics and canvas. Metals, bricks and stones
are largely unaffected by sunlight.
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Factors effecting the performance of building
material
Biological agencies Certain bacteria in the soil
break down sulphur chemicals which cause
corrosion of metals such as iron, steel and
lead. Burrowing animals or birds making nests can
tunnel foundations, undermining footings they
can also excavate loose unsound material allowing
rain in or weakening supports. Tree roots and
vines growing in cracks exert a very strong and
destructive force, expanding and extending cracks
in masonry, pipes, concrete or timber. They also
hold moisture, encouraging the growth of moulds
and fungi, and the uneven drying of brickwork
(which causes uneven movements within the wall).
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Factors effecting the performance of building
material
Water and frost Care should be taken in the
selection of materials for use in damp areas
since some building materials react less well in
such situations than others. For instance,
limestone and marble slowly dissolve in water.
Timber, chipboards, hardboards and other similar
wood products lose some of their strength, and
many flooring materials are less hard-wearing
when wet. Water can encourage fungal attack and
certain destructive chemical reactions. Repeated
wetting and drying causes surface crazing and
cracking of timbers. Water also often carries
destructive acids, salts and other soluble
chemicals.
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Factors effecting the performance of building
material
Salt crystallisation Salts that are dissolved in
water can come from the sea, the ground and from
some building materials. As moisture evaporates
from a surface, the salts are left behind in the
form of powder or crystals, called efflorescence.
Sometimes this is just an unattractive coating,
usually white, but sometimes yellow, green or
brown. However, it can be destructive if allowed
to persist for a long time. Salts crystallising
on the surface of a porous material can cause
gradual erosion or flaking. This surface
deterioration, called fretting or spalling, often
occurs in soft sandstones, bricks (such as
sandstocks) or in mortar layers in masonry. When
moisture rises in the walls of a building these
salts cause paint to bubble and peel. Fixing this
problem can involve costly installation of
dampcourses and removal of all affected plaster
or render from the walls.
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Factors effecting the performance of building
material
Chemical action Cause swelling, shrinking,
weakness or damaged appearance. Due to chemical
changes within the material itself, or changes
brought on by attack from outside chemicals. Heat
and moisture aid most reactions. The presence of
aggressive gases, in the air or in factories or
dissolved in rainwater, can mean that some
materials may need special protection, or that
other more suitable materials should be used
instead.
33
Factors effecting the performance of building
material
Groundwater, industrial wastes, soil, ash and wet
clays are some of the substances that can produce
soluble sulphates which attack cement products
and metals. Loss of volatiles Volatiles are
liquids and gases. Plastics, paints, varnishes,
finishes, mastic, rubber, tar and bitumen shrink
and become brittle when their volatiles are lost.
34
Factors effecting the performance of building
material
Abrasion and impact In situations of abnormal
impact or abrasion, suitable materials and
finishes need to be chosen. For example, a
concrete path or floor that will take heavy
traffic requires correct concreting techniques to
be followed so as to produce a hard, durable
surface. Vibration Vibration caused by proximity
to machinery or heavy vehicular traffic can cause
problems in light constructions and with brittle
materials. Complete the check progress 3
questions in your guide
35
Factors effecting the performance of building
material
Fire resistance Fire is usually the fastest,
most destructive and dangerous way in which a
building can be damaged or destroyed. It is a
very important consideration for both city and
country dwellers. Government bodies test
materials and publish regulations and codes which
are implemented by local councils concerned about
fire hazards in public or private
buildings. Fire hazard indices (published by the
Experimental Building Station as Notes on the
Science of Building, Nos 66, 98, 136, 137, 142)
are lists based on extensive experiments on
structures and materials.
36
Factors effecting the performance of building
material
Combustibility Materials that ignite, that give
off flammable gases or that show considerable
self-heating when exposed to a set heat in a
furnace, are called combustible. Non-combustible
materials, on the other hand, do not feed the
fire, and flame does not spread over them.
Non-combustibility does not mean fire resistance.
Table 1.1 lists some combustible and
non-combustible materials. Non-combustible
materials (such as steel) may expand and disturb
attached structures, or lose strength and
collapse. Other non-combustible materials may
spall (flake) and shrink or crack. On the other
hand, some combustible materials (such as timber)
can often provide a useful degree of fire
resistance.
37
Factors effecting the performance of building
material
Fire resistance Fire is usually the fastest,
most destructive and dangerous way in which a
building can be damaged or destroyed. It is a
very important consideration for both city and
country dwellers. Government bodies test
materials and publish regulations and codes which
are implemented by local councils concerned about
fire hazards in public or private
buildings. Fire hazard indices (published by the
Experimental Building Station as Notes on the
Science of Building, Nos 66, 98, 136, 137, 142)
are lists based on extensive experiments on
structures and materials.
38
Factors effecting the performance of building
material
Fire Resistance Fire resistance is expressed as
the amount of time in hours and minutes a
component survives a fire test of set temperature
before it can no longer perform its function. It
is considered to fail the test when any of the
following occur It collapses. It forms holes or
cracks through which flame can pass. It gets hot
enough to ignite other combustible materials it
is in contact with and which the fire hasnt yet
reached.
39
Factors effecting the performance of building
material
How certain materials behave in
fire Timber Timber easily ignites at about
221298C. However, some timber (particularly
large pieces, at least 100 by 75 mm in section or
larger) are resistant to the fire once the
surface has been charred. Many Australian
hardwoods have this characteristic and, in fact,
have proved to be more fire resistant in
buildings than steel. However, all timbers do
burn readily if temperatures stay high enough.
Therefore, timber buildings are not classified as
fire resistant.
40
Factors effecting the performance of building
material
How certain materials behave in
fire Timber Timber has good thermal
insulation, preventing materials not in contact
with the fire from heating up to extreme
temperatures. When hot, timber does not expand in
length (unlike steel) and neither does it
markedly lose strength. Laminated timber
structures glued with synthetic resins have
similar fire resistance to solid timber, although
resistance will vary according to the type of
timbers and glues.
41
Factors effecting the performance of building
material
Stone Stone blocks and slabs are usually
satisfactory in fires, but overhanging features
and lintels are liable to fail. Free quartz (eg
in granites) explodes suddenly at 575C and
should not be present in any stone that is
required to be fire resistant. Sandstones behave
better than granite, but in drying they may
shrink and crack, with 3050 loss of
strength. Plastics Although many plastics are
made in fire-retardant grades, all are
combustible and some give off large quantities of
toxic smoke. PVC (polyvinyl chloride) melts at
fairly low temperatures, and most thermoplastics
(plastics that can be heated and shaped) char
above 400C and burn at 700900C.
42
Factors effecting the performance of building
material
Clay products Most clay products perform well in
fires, having been made at kiln temperatures
higher than most fires reach. Brickwork failure
is often caused by expansion of enclosed or
adjoining steel work. Concrete Ordinary
Portland cement concrete disintegrates at
400500C. However, how the concrete performs
depends very much on the presence of
reinforcement and the type of aggregate it
contains.
43
Factors effecting the performance of building
material
Metals Metals used in building are
non-combustible, but they lose strength when
heated. Aluminium, lead and zinc melt in building
fire temperatures. As previously mentioned, the
expansion of the hot metal can cause problems.
Also, the high thermal conductivity of metals
means that the temperature of surfaces remote
from a source of heat will approach the
temperatures near the fire, causing fires to
spread. Steel Mild steel behaves in an
interesting way when heated. Up to 250C, it
gains strength, then gradually returns to normal
strength by 400C. After that, it rapidly weakens
so that, at 550C (referred to as the critical
temperature), it begins to fail. Generally,
structural steelwork must be protected with
fire-resistant encasements, such as concrete or
brickwork.
44
Factors effecting the performance of building
material
Glass Although glass is non-combustible, it
readily transmits heat and often shatters
unpredictably at an early stage in a fire.
Toughened glass is not fire-resistant. Glass
fibre and rockwool Resin-bonded glass fibres are
combustible. Glass fibres themselves melt at
about 600C. Fibrous cement This material
tends to shatter when heated, sometimes
explosively. It does not contribute to making a
fire-resistant structure.
45
Factors effecting the performance of building
material
Paints Generally, paint films are combustible
and may help spread flame over surfaces. However,
as they are thin, they only contribute a small
amount to the fire load. When applied to
combustible materials, certain paints can reduce
the spread of flames. They delay but never
prevent the spread of flame. Complete the check
progress 4 questions in your guide
46
Factors effecting the performance of building
material
Compatibility of materials The large range of
new materials on the market today, many of which
are chemically based, plus widespread pollution,
has led to new chemical and physical problems
with materials. A material may break down many
times faster than normal in the presence of
another particular substance. Problems do not
always show up until a product has been on the
market for a number of years. Incompatibility of
building Materials can be grouped roughly under
the following headings Corrosion of
metals Stains and discolouring effects Problems
with surface finishes Chemical reaction between
materials.
47
Factors effecting the performance of building
material
Corrosion of metals Galvanic reactions These
occur between metals that have different levels
of electronegativity. This is often seen as
corrosion of one metal or a deposition of metal
scale on the other metal. Offcuts or filings of
metals left around in moisture can cause rapid
destruction of nearby metal building components.
Some common galvanic reactions are listed
below. Lead used with zinc or aluminium promotes
corrosion. Therefore, metal roof-flashings need
to be carefully chosen. Steel screws or nails
should not be used with aluminium or zinc
roofing, unless they are zinc or cadmium
coated. Copper should not touch or drain onto
zinc, aluminium, zincalume or galvanised
materials.
48
Factors effecting the performance of building
material
Corrosion of metals As heat speeds up
corrosion, different metals should not be mixed
in hot water systems. Copper and brass are
permanently resistant to water. Aluminium This
becomes encrusted in coastal atmospheres. Mortar,
cement or concrete pit the surface of aluminium
if splashed on it. Industrial atmospheres These
are usually acidic and corrode all
metals. Stains and discolouring
effects Copper Water dripping off copper causes
green stains. Rust Water running off exposed
iron or steel will stain surrounding
surfaces. Eucalypt timbers When wet, many
eucalypt timbers produce brown stains on masonry.
49
Factors effecting the performance of building
material
Problems with surface finishes When finishes
wont stick to the surface they are applied to,
it is usually due to the two being unsuitable for
each other. The surface may either be too smooth
or it may be powdery or flaky or there might be
a chemical incompatibility between the surface
and the finish. Many silicone sealants will not
accept paint. Acid-resisting grouts (for
floor-tiles) cannot be satisfactorily cleaned
from the tile surface. Primers, undercoats,
finish paints, lacquers, varnishes and stains
should all be used according to manufacturers
instructions as many are incompatible with
certain materials.
50
Factors effecting the performance of building
material
Testing of materials The testing of materials is
carried out by the manufacturer or supplier
before delivery (eg stress testing of timber).
Upon delivery, an inspection should be carried
out with respect to the quality and suitability
for the construction situation it is
intended. Concrete is one material which is
tested on site (the slump test), and later
laboratory tested for compressive strength at 28
days. Materials such as paints, adhesives, glass
and the like have been developed and trialled
under strict laboratory controls and conform to
Australian Standards. Building The builder or
supervisor of a project, needs to be informed of
all the information relating to products being
used. Details such as handling, storage,
application, installation and warranties should
be kept in a product file and updated to provide
ready access to this information to avoid
warranty problems associated with incorrect
handling and installation.
51
Factors effecting the performance of building
material
Handling and storage Planning for storage and
handling of materials on site is an important job
for building staff. Many materials are easily
damaged if due care is not taken in handling, and
some can deteriorate if exposed to moisture and
direct sunlight. Materials should be stored in
accordance with manufacturers instructions for
example, stacked flat, off the ground, in a dry
area or in a secure area for flammable or toxic
materials. Transportation to the site and
unloading arrangements need to be given careful
consideration and appropriate equipment must be
organised. When handling materials on site, safe
working practices must be followed and all OHS
regulations implemented.
52
Factors effecting the performance of building
material
Tolerances All building work in Australia is
covered by the Building Code of Australia and
many Australian Standards. These standards have
been developed for most building materials and
detail tolerances, application, testing (if
applicable) and method of installation. These
tolerances should be followed and best industry
practice adhered to. Complete the progress check
5 in your learner guide
53
Properties of Concrete
54
Properties of Concrete

• Learning outcomes
• On completion of this unit you should be able to
• Identify the properties of concrete
• Understand the nature and purpose of the
  materials which make up concrete
• Identify the procedures used in the transport and
  placement of concrete
• Understand the reason for and the methods of
  curing concrete
• list the uses of concrete in residential
  construction.

55
Properties of Concrete
Cement In Australia, all Portland cements are
made to meet the requirements of AS39721991
Portland and Blended Cements. General purpose
cements Type GPgeneral purpose Portland
cement Type GB general purpose blended
cement. Special purpose cements Type HE high
early strength cement Type LH low heat
cement Type SR sulphate resisting cement.
56
Properties of Concrete
Special purpose cements Type HE cement is used
where high strength is required at an early
stage for example, where it is required to move
forms as soon as possible or to put concrete into
service as quickly as possible. It is also used
in cold weather construction to reduce the
required period of protection against low
temperatures. Type LH cement is intended for use
in massive concrete structures such as dams. In
such structures the temperature rise resulting
from the heat generated during hardening of the
concrete is likely to be a critical factor Type
SRsulphate resisting cement has better
resistance to attack by sulphates in ground water
than other types because of its special chemical
composition.
57
Properties of Concrete
White and off-white cements Off-white cement is
in general use in cottage construction but white
cement usually proves cost prohibitive. High
alumina cement High alumina cement is not a
Portland cement. If mixed with Portland cement it
can give a rapid or flash set. It is
characterised by a very high rate of strength
development accompanied by a high heat of
hydration and by a greater resistance to sulphate
and weak acid attack than Portland cements.
Curing conditions require very close control for
24 hours after placement. Answer the questions
on the your guide
58
Properties of Concrete
Storage of cement Cement will retain its quality
indefinitely if it does not come in contact with
moisture. If it is allowed to absorb appreciable
moisture it will set more slowly and its strength
will be reduced. Therefore, storage of bagged
cement requires storage facilities to be as
airtight as possible, and the floor should be
above ground level to protect against dampness.
The bags should be tightly packed to reduce air
circulation, but they should not be stacked
against outside walls. If they are to be held for
a considerable period the stacks should be
covered with tarpaulins or water-proof building
paper. Doors and windows should be kept closed.
A first-in-first-out rotation of bags should be
maintained at all times.
59
Properties of Concrete
Setting and hardening Setting is the initial
stiffening of the cement paste during the period
in which the concrete loses its plasticity and
before it gains much strength. This period is
affected by the water content of the paste and
the temperature. The more water in the paste the
slower the set, the higher the temperature the
faster the set. Hardening is the gain in
strength which takes place after the paste has
set. It is affected by the type of cement used
and the temperature. High temperatures cause more
rapid hardening.
60
Properties of Concrete
Water Water suitable for drinking will generally
be suitable for concrete making. Aggregates Aggr
egates used in concrete should consist of clean,
hard, durable particles strong enough to
withstand the loads to be imposed upon the
concrete. In general they should consist of
either natural sands or gravels or crushed rocks,
although some manufactured aggregates such as
blast furnace slag and expanded shale and clays
can be equally satisfactory. Commonly used
crushed rocks include basalt, granite, diorite,
quartzite and the harder types
61
Properties of Concrete
Grading Both coarse and fine aggregates should
contain a range of particle sizes. Graded
aggregates produce more workable oncretes which
are less prone to segregation and
bleeding. Particle shape and surface texture The
particle shape and surface texture of aggregates
affect the workability. For workability,
particles should be smooth and rounded. On the
other hand, angular materials result in greater
strength, so that, in the final analysis, there
is little or no difference in effectiveness. The
ultimate decision is one of economics and
availability. Maximum size of aggregates The
greatest economy is achieved when the largest
maximum size aggregate is used. The factors
limiting size are the availability, transporting
and placing equipment to handle the larger sizes,
and the clear spacing between reinforcing bars
and the clear spacing between the reinforcement
and the formwork.
62
Properties of Concrete
Manufactured aggregates Blast furnace slag If
sound and free from excessive quantities of
ferrous iron, blast furnace slags are
satisfactory concrete aggregates. Generally they
are angular in shape and require a higher
percentage of fines to produce workable
concrete. Lightweight aggregates Expanded shale
aggregates produce concrete having approximately
two-thirds the density of those made with dense
aggregates, but with comparable strengths.
Lightweight aggregates may be smooth and rounded
or harsh and angular, depending on the method of
manufacture.
63
Properties of Concrete
Testing of aggregates Since aggregates comprise
up to 75 per cent of the volume of concrete,
their properties are obviously important. These
properties include size and grading as well as
cleanliness. The testing of concrete aggregates
is generally carried out to determine Presence
of organic or other deleterious material which
may severely limit the strength of the
concrete Resistance to abrasion, which may limit
the durability of the concrete the presence of
any alkalis which may react with the cement and
cause expansion of the aggregate.
64
Properties of Concrete
Conclusion Good concrete can be made from a
wide variety of aggregates provided these are
clean and free from harmful impurities. As the
quality of concrete becomes higher, the quality
of the aggregate becomes more important and
factors such as grading more critical. Good
aggregates, although sometimes higher in initial
cost, are generally more economical because of
the higher quality and lower overall cost of the
concrete they produce.
65
Properties of Concrete

• There are several properties of concrete which
  affect its quality.
• These are
• Compressive strength
• Tensile strength
• Durability
• Workability
• Cohesiveness.
• Lets examine these properties in detail.

66
Properties of Concrete
Compressive strength Compressive strength
remains the common criterion of concrete quality
and will frequently form the basis of mix design.
For fully compacted concrete made from sound
clean aggregates the strength and other desirable
properties under given job conditions are
governed by the net quantity of mixing water used
per bag of cement. This relationship is known
as the water/cement ratio, that is, the quantity
of water in the mix to the amount of cement
present. Example A concrete mix having a
water/cement ratio of 0.51 would require 20
litres (20 kg) of water for each 40 kg bag of
cement. The ultimate strength of concrete depends
almost entirely on the water/cement ratio, for as
the ratio increases the strength of the concrete
decreases.
67
Properties of Concrete
Tensile or flexural strength This is the measure
of the concretes ability to resist flexural or
bending stresses. The tensile or flexural
strength of concrete is dependent on the nature,
shape and surface texture of the aggregate
particles to a much greater degree than does the
compressive strength. Durability Concrete may
be subject to attack by weathering or chemical
action. In either case the damage is caused
largely by the penetration of water or chemical
solutions into the concrete and is not confined
to action on the surface. The resistance to
attack may therefore be increased by improving
the watertightness of the concrete. This is
achieved by lowering the water/cement ratio,
assuming the concrete is fully compacted.
68
Properties of Concrete
Workability The workability of concrete, or the
effort required to handle and compact it, depends
on several factors, as follows Water/cement
ratio The higher the water/cement ratio, the
more workable concrete becomes. However, the
water/cement ratio should be fixed by
considerations other than workability (eg
strength and durability), and should not be
increased beyond the maximum dictated by these
considerations. Cement content The cement paste
in concrete acts as a lubricant, and at a fixed
water/cement ratio, the higher the cement
content, the more workable the concrete becomes.
It follows then that any adjustments to increase
workability should be made by increasing the
cement and the water content at a constant
water/cement ratio. Grading of aggregates
Grading tends to produce more workable concrete.
69
Properties of Concrete
Particle shape Particle shape and size of
aggregates Smooth, rounded aggregates will
produce more workable concrete than rough,
angular aggregates. Also, for a given
water/cement ratio and cement content,
workability increases as the maximum size of the
aggregate increases.
70
Properties of Concrete
Cohesiveness The cohesiveness of concrete means
the ability of plastic concrete to remain
uniform, resisting segregation (separation into
coarse and fine particles) and bleeding during
placing and compaction. Concrete in the plastic
state should be cohesive to prevent harshness
of the mix during compaction, and to avoid
segregation of the coarse and fine components
during handling. Segregation may occur during
transporting over long distances, discharging
down inclined chutes into a heap, dropping over
the reinforcement or falling freely through a
considerable height and placing in formwork which
permits leakage of mortar. Maximum cohesiveness
usually occurs in a fairly dry mix, so as a rule
the wetter the mix the more likely it is to
segregate. Segregation can, however, occur in
very dry mixes.
71
Properties of Concrete
Testing of concrete Concrete is tested on the
site or in the laboratory to determine its
strength and durability or to control its quality
during construction. These tests must be
carried out carefully and in the correct manner
or the results may be misleading and cause
unnecessary delays while they are being checked.
Worse still, faulty tests may result in either
substandard concrete being accepted or even good
concrete being rejected. There are several ways
in which testing can be carried out by
sampling by slump testing by compression
testing.
72
Properties of Concrete
Sampling To make a composite sample from the
discharge of a mixer or truck, three or more
approximately equal portions should be taken from
the discharge and then remixed on a non-absorbent
board. The sample portions should be taken at
equal intervals during the discharge and none
should be taken at the beginning or the end. The
concrete at these points may not be truly
representative of the whole mix. When sampling
freshly deposited concrete, a number or samples
should be taken from different points and
recombined to make a composite sample. Care
should be exercised to make certain the sample is
representative by avoiding places where obvious
segregation has occurred or where excessive
bleeding is occurring.
73
Properties of Concrete
Slump testing The slump test is a measure of the
consistency or mobility of concrete and is the
simplest way of ensuring that the concrete on the
site is not varying. It should be done often as
an overall control on the various factors that
can affect the result. Most important among these
factors is the water content of the mix,
variation of which can result in varying
strengths of concrete. A consistent slump means
that the concrete is under control. If the
results vary it means that something else has
varied, usually the water, which can then be
corrected. Details are contained in your guide
74
Properties of Concrete
Compression testing The strength of concrete
is determined by making specimens, curing them,
and then crushing them to ascertain their
strength. The preparation of specimens is most
important as a badly prepared specimen will
nearly always give a low result. Compressive
test specimens are normally cylinders 150 mm in
diameter and 300 mm high. Details are contained
in your guide Complete the questions in your
guide
75
Properties of Concrete
Proportioning and mixing Design strength The
designer of a concrete structure determines
during the design stage, the concrete properties
that are necessary to ensure that the structure
performs in the desired manner. Since compressive
strength is usually the most important property
required and since most other desirable
properties are directly related to it, it is
usual for the designer to specify the minimum
compressive strength required, usually at 28
days. The design strength is the minimum
strength required by the designer.
76
Properties of Concrete
Target strength The mix designer must design a
mix which will produce concrete with a strength
in excess of the design strength It is known
that when a series of compressive tests are made
from samples of concrete taken from time to time
through the course of a job, the results will be
scattered to either side of an average value.
This means that the concrete produced is never
completely uniform in quality some weaker than
the average strength and some stronger. Since
the designer has specified the minimum strength
required, the mix designer must aim at an average
strength, between the target strength and the
design strength. Generally, a target strength 33
per cent higher than the design strength meets
the requirements of the building codes.
77
Properties of Concrete
Specification of concrete In writing the
specification to ensure that the concrete has the
properties required, the designer has two
alternatives specify the concrete by strength
(the usual method) specify concrete by
proportions. Concrete specified by
strength The designer specifies the minimum
compressive strength required in the concrete and
the age at which the concrete should have this
strength, usually 28 days.
78
Properties of Concrete
Batching All materials, including water, should
be accurately measured to ensure that concrete of
uniform quality is produced. Batch proportions
are often specified in relation to the bag of
cement for example, one 40 kg bag of cement to
so many kilograms of coarse aggregate and so many
kilograms of fine aggregate with perhaps 20 L or
20 kg of water. One Litre of water has a mass of
one kg and is not subject to variation. With
mass batching, there is no need to make allowance
for the bulking of damp sand but allowance must
be made for the non-absorbed water held by the
aggregates as this moisture forms part of the
mixing water.
79
Properties of Concrete
Notes on mixing contained in your
guide Premixed concrete Premixed concrete is
used almost universally on residential building
sites. The use of premixed concrete has
advantages which include Better quality control
is possible at a large plant than under most site
conditions. Premixed concrete is controlled by
AS13791991 Specification and Manufacture of
Concrete, which should be referred to for
information on methods of ordering, mixing and
delivery.
80
Properties of Concrete
Transporting concrete Irrespective of the
methods used to transport, place and compact the
freshly mixed concrete, the following
requirements are basic to good practice The
concrete must be transported, placed and
compacted with as little delay as possible. The
concrete must not be allowed to dry out before
compaction. There must be no segregation of the
materials. The concrete in the forms should be
fully compacted.
81
Properties of Concrete
Pumps and pipelines Pumps and pipelines enable
concrete to be transported across congested sites
and where space is limited. Concrete for
pumping must be of medium workability with a
slump of 70 mm to 120 mm and must be free from
any tendency to segregate. The introduction of
fly ash to the concrete improves pumpability and
workability of the mix, and therefore adds
appreciably to the distance concrete can be
pumped. More detailed information is contained
in your guide
82
Properties of Concrete
Placing concrete Certain precautions must be
taken when placing concrete, to ensure
that Formwork and reinforcement is not damaged
or dislodged The concrete is free from
segregation Other qualities of the concrete are
not impaired. Study the notes in your guide
83
Properties of Concrete
Compacting It is essential that concrete be
properly compacted to ensure maximum density. Air
holes must be eradicated, voids between aggregate
particles must be filled and all aggregate
particles must be coated with cement
paste. Thorough compaction results
in Maximum strength Watertight
concrete Sharp corners Good bond to
reinforcement Protective cover to
reinforcement Good surface appearance.
84
Properties of Concrete
Vibration Concrete is usually vibrated to
achieve good compaction. There are three types of
vibrators Immersion vibrators Form
vibrators Surface or screed vibrators The
immersion vibrator is driven either electrically,
mechanically or pneumatically and is probably the
most efficient type of vibrator as it vibrates
the concrete directly by immersion in the
concrete. They are particularly suited to the
compaction of large volumes of concrete.
85
Properties of Concrete
Curing Concrete increases in strength and
other desirable properties with age, this is so
only so long as drying is prevented. The
hydration of cement is a chemical reaction and
this reaction will cease if the concrete is
permitted to dry. Evaporation of water from
newly placed concrete not only stops the process
of hydration, but also causes the concrete to
shrink, thus creating tensile stresses at the
drying surface and if the concrete has not
developed sufficient strength to resist these
stresses, surface cracking may result.
86
Properties of Concrete
Curing As in many other chemical reactions,
temperature affects the rate at which the
reaction between the cement and water progresses
the rate is faster at high temperatures than at
lower temperatures. It follows then that
concrete should be protected so that moisture is
not lost during the early hardening period and
should also be kept at a temperature that is
favourable to hydration.
87
Properties of Concrete
Curing methods Curing methods can be
classified as follows The supply of additional
moisture to the concrete during the early
hardening period. Sealing the surface to prevent
loss of moisture from the concrete. Ponding Spr
inkling Wet coverings Waterproof paper,
plastics Curing compounds
88
Properties of Concrete
Length of curing period For most structural
purposes, the curing time for concrete varies
from a few days to two weeks according to
conditions for example, lean mixes require
longer curing time than rich mixes and
temperature affects the curing time as does the
type of cement used. Since all the desirable
properties of concrete are improved by curing,
the curing period should be as long and as
practicable in all cases. Answer the questions
in your guide
89
Properties of Concrete
Reinforced concrete Basic principles Concrete
, Is strong in compressive strength, and
comparatively weak in tensile strength. To
overcome this weakness in tension, concrete which
is to be subjected to tensile stresses is
reinforced with steel bars or mesh which is so
placed that it will resist such stresses. The
designing and detailing of reinforcement is the
job of the designing engineer and will not be
dealt with in any great detail here, but it is
important that those who supervise the fixing of
reinforcement on the job have an appreciation of
the basic principles of reinforced concrete.
90
Properties of Concrete
Figure 3.5 Types of stress found in a structure
91
Properties of Concrete
Reinforced concrete design combines the steel
reinforcement with the concrete in such a manner
that enough steel is included to resist the
tensile stresses and excess shear stresses while
the concrete is used to resist the compression
stresses. The bond between concrete and steel
directly counteracts any tendency for the
concrete to stretch and crack in a region
subjected to tension Concrete and steel expand
and contract the same amount. If this were not
so, the different expansion rates would break the
bond between the two materials and so prevent the
transfer of tensile stresses to the
steel Concrete has a high fire-resistance and
protects the steel from the effects of fire.
92
Properties of Concrete
Design of reinforced concrete In order to be
effective, the tensile reinforcement must be
prevented from sliding in the concrete. The
adhesion or bond between the concrete and the
steel is related to the surface area of the steel
embedded in the concrete. Adequate anchorage
is effected by extending the rods past the
critical points (where no longer required to
resist tensile and shear stresses) and by the use
of Standard hooks Plain rods extended into the
supports (rarely used) Deformed bars (rolled
with lugs or projections). Study Figure 3.6 in
your guide
93
Properties of Concrete
Good formwork The guiding principles for the
production of good formwork are Quality Safety Ec
onomy.
94
Properties of Concrete
Quality First quality formwork should
be Accurate True to the shapes, lines and
dimensions required by the contract
drawings. Rigid Forms must be sufficiently
substantial so as to prevent any movement,
bulging or sagging during the placing of the
concrete. Tight-jointed If joints are not
tight, they will leak mortar. This will leave
blemishes in the shape of fins on the surface of
the concrete and may result in honeycombing of
the concrete close to the leaking
joint. Well-finished The quality of the finish
of the concrete is dependent on the finish of the
forms. Nails, wires, screws and so on should not
be allowed to mar the surface of the finished
concrete.
95
Properties of Concrete
Safety Strength For the safety of the workers
and of the structure, the formwork must be strong
enough to withstand not only the mass of the wet
concrete but also the live loads of workers,
materials and equipment. It is impossible to over
emphasise how important this aspect of safety
really is. Soundness Materials must be of good
quality and durable enough for the job. The time
will come, no doubt, when it will be essential to
use for structural load-bearing members, only
timber that has been tested with the mechanical
stress grading process.
96
Properties of Concrete
Economy For economy, formwork should
be Simple Formwork should be designed for
simplicity of erection and removal. Easily
handled Shutters and units should be light
enough to permit easy handling. Standardised
Where standardisation of formwork is possible,
the ease of assembly and the possibility of reuse
serve to lower the formwork cost. Reusable
Formwork should be designed for easy removal and
in sections that are reusable. This will minimise
the amount of waste material and thus decrease
the cost of the formwork.
97
Properties of Concrete
Supervision NoteStudy the notes in the guide
carefully regarding supervision Surface
Treatments There are many proprietary surface
treatments available, some prevent adhesion to
the formwork, others provide architectural
finishes.
98
Properties of Concrete
Stripping times The time of the removal of
forms is generally specified by the architect or
engineer Forms can usually be safely stripped
when the concrete has developed about two-thirds
of its 28-day strength. However, the earliest
possible removal of forms is desirable for the
following reasons To allow the reuse of forms
as planned. In hot weather, to permit curing to
begin. To permit any surface repair work to be
done while the concrete is still green and
favourable to good bonding. Vertical forms can
generally be removed before the forms to the
soffits of beams and slabs.
99
Properties of Concrete
Table 3.1 Times for stripping formwork and
supports Study the chart in your guide
100
Properties of Concrete
Concrete finishes Many types of off form
finishes Smooth Wood grain Architectural
patterns Textured and patterned surfaces
101
Properties of Concrete
Joints in concrete construction If the
concrete is allowed to stiffen to the extent that
it cannot be worked, then a joint must be made.
Other cases will occur when it is necessary, for
structural reasons, to break the continuity of
placing and to form a joint. Joints can be of
two general types Construction joints Bond
the new concrete to the hardened concrete in such
a manner that the concrete appears to be
monolithic and homogenous across the joint and
allows for no relative movement of the concrete
on either side of the joint. Control joints
These allow for relative movement on either side
of the joint, thus they can be either
construction joints or expansion joints.
102
Properties of Concrete
Construction joints In practice, it is very
difficult to obtain a perfect bond at a joint and