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CONSTRUCTION
TECHNOLOGY &
maintenance
CEM 417
SOURCES FROM slide:
MOHD AMIZAN MOHAMD
MOHD FADZIL ARSHAD
SITI RASHIDAH MOHD NASIR
FKA, UiTM Shah Alam.
PILES
WEEK 10
At the end of week 10 lectures, student will be able to :
Explain various types, functions and factors of
selections for piling. (CO1; CO3)
LEARNING OUTCOME
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INTRODUCTION
Function:-
To transmit foundation loads through soil strata
of low bearing capacity to deeper soil or rock
strata having a high bearing capacity, or used in
normal ground condition to resist heavy uplift
forces or in poor soil conditions to resist
horizontal loads.
PILES CAN GENERALLY BE CLASSIFY WITH RESPECT
TO THEIR FUNCTION :- FRICTION PILES OR END
BEARING PILES.
FRICTION PILES
In cohesionless soils – the applied load is
transferred to the surrounding soil mainly
through skin friction along the surface of the
piles. A large part of load is also carried by the
pile toe. The skin friction resistance varies
mainly with relative density of the soil and with
the shape of the pile.
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FRICTION PILES IN COHESIVE SOIL – ALMOST
THE WHOLE LOAD ON THE PILE IS
TRANSFERRED TO THE SURROUNDING SOIL
ALONG THE PILE SURFACE THROUGH SKIN
FRICTION AND ONLY A VERY SMALL PART
THROUGH THE PILE TOE.
END BEARING PILES – pilesdriven down to a layer with high
bearing capacity, the applied load is transferred from the pile to
the surrounding soil mainly through the pile toe
CLASSIFICATION OF PILES
Displacement Piles
Piles are driven or
pushed, vibrated or
screwed into the
ground, displacing the
soil outwards and
downwards but no
materials are
removed.
Replacement Piles
A hole is form in the
ground by removal of
material from the
ground and thus
material is displaced
by a concrete material
formed in the ground.
DISPLACEMENT PILES DRIVEN PILES – Preformed unit driven into the soil
by blows of hammer.
Materials of performed pile are :-
Timber ;
Concrete; or
Steel
Advantage of performed unit – can be inspected and
checked as a sound structural member before it is driven into
the ground
•
•Length of pile to be driven depends on the local variation of
soil strata. Disadvantages when cutting off unwanted pile or
the addition of extra lengths can become an expensive
additional cost.
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DRIVEN -TIMBER PILES
Usually square sawn timber of sizes 225 x 225 to 600 x 600mm.
Easy to handle and driven by percussion or drop hammer.
Most timber piles are fitted with an iron or steel driving shoe to prevent splitting due to driving, and have iron ring around the head to restrict ‘brooming’ of the pile head due to overdriving.
Timber pile is not suitable of driving through dense strata or strata with obstruction.
CONT..
DRIVEN -TIMBER PILES
Characteristic of Timber Piles :-
1. Must be free from short or reverse bends, large or
loose knots, slake, splits and decay.
2. Must be free from short or reverse bends and from
crooks > 11/2 diameter of the pile at the middle of
the bend.
3. Straightness of grain line between centres of butt
and tip must be within the body of the pile.
4. Uniform taper from the butt to tip.
DRIVEN – PRECAST CONCRETE PILES
Used where soft soils overlaying a firm strata are encountered. Lengths up to 18m with section sizes ranging from 250 x 250mm to 450 x 450mm carrying loadings up to 1000kN.
The precast concrete driven pile has little frictional bearing strength since the driving operation moulds the cohesive soils around the shaft which reduces the positive frictional resistance.
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CONT..
DRIVEN – PRECAST CONCRETE PILES
Available Precast Concrete Piles are :-
Precast Reinforced Concrete Piles – made of concrete statically cast in uniform section before driving into ground and reinforced with steel bars.
Precast Pretensioned Concrete Piles - made of concrete statically cast in uniform section & suitably reinforced with pretensioned prestressingsteel.
Precast Pretensioned Spun Concrete Piles –hollow pile made of concrete cast by centrifugal spinning. Suitably reinforced with pretensionedprestressing steel.
CONT..
DRIVEN – PRECAST CONCRETE PILES
Problem encounter when using this pile in urban area :-
Transporting the complete length of pile through narrow or congested streets;
The driving process which is generally percussion can set up unacceptable noise or vibration;
Many urban sites are themselves restricted or congested thus making it difficult to manoeuvre the long piles length around the site.
DRIVEN – STEEL PILES
Two main types of steel pile in general use:-
H-section pile – usually in the form of wide
flange sections. It do not cause large displacement
of the soil, thus useful where upheaval of the
surrounding ground would damage adjoining
property or where deep penetration is required
through loose or medium dense sands.
Disadvantage is the tendency to bend on the
weak axis during driving. Results in considerable
curvature if driven in deep penetration. Also has
low resistance to penetration in loose sandy soil.
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CONT..
DRIVEN – STEEL PILES
Box Piles – steel box piles are fabricated by
welding together steel plates or trough section to form
hollow piles capable of carrying very high compressive
uplift or lateral loads.
DRIVEN AND CAST –IN- PLACE PILES
Displacement pile formed by driving a tube with a closed end either with a plug or loose shoe into the soil to the required depth or set. A reinforcement and concrete is filled in the tube. This tube may or may not be withdrawn.
Suitable where the length of pile required varies.
Economically formed in diameter of 300 to 600 mm and can carry loads of up to 1300kN.
Required heavy piling rig, open level site and site where noise is restricted.
CONT..
DRIVEN AND CAST –IN- PLACE PILES
Franki driven in-situ piles
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BORED AND CAST –IN- PLACE PILES Is a replacement pile . Pile formed by boring a hole
in the soil, thus removing a column of soil and replace it with in-situ concrete.
Suitable to use in sites where piling work to be carried out close proximity to existing building or where vibration or noise restricted.
It is carried out by dropping a heavy cutter to dig into the ground and then raising and remove the spoil material which it brings with it.
Formation of holes can be by :-
percussion bored, or
rotary bored.
ADVANTAGES
Length can be readily varied to suit varying ground condition.
Soil remover in boring can be inspection and if necessary sampled or in situ test made.
Can be installed in vary large diameter. End enlargement up to two or three diameters
are possible in clay. Material of piles is not dependent on handing
or driving conditions. Can be installed in vary long length. Can be installed without appreciable noise or
vibration. Can be installed in condition of very low head
room. No risk of ground heave.
DISADVANTAGES
Susceptible to waisting or necking in squeezing ground.
Concrete is not places under ideal condition and cannot be subsequently inspection.
water under artesian pressure may pipe up pile shaft washing out cement.
Enlarge and cannot be formed in cohesionless material.
cannot be readily extended above ground level especially in river and marine structures.
Boring method may loosen sandy and gravelly soils.
Sinking piles may cause loose of ground in cohesionless soil, leading to settlement of adjacent structures.
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CONT..
DRIVEN AND CAST –IN- PLACE PILESProblems normally encountered :-
1. Necking – due to ground water movements washing away some of the concrete thus reducing the effective diameter of the pile shaft and consequently the cover of concrete over the reinforcement.
2. Ground heave – caused by displacement of the soil by the drive tube. Can cause tension failure in the shafts of adjacent piles already driven and in worst case lifting of the completed piles. However, this can be minimized by the enlarged base of the piles in conjunction with reinforcement in the shaft thus anchoring the piles against uplift.
CONT..
PERCUSSION BORED PILES Suitable for clay and / or gravel subsoil.
Diameter from 300 to 950 mm and designed to carry load up
to 1500 kN.
CONT..
PERCUSSION BORED PILES
Steel tube of length 1 to 1.4m screwed together is sunk by extracting the soil from within the tube liner using percussion cutters.The tube liner normally sink under its own weight but can also be driven in with slight pressure using hydraulic jack.
When correct depth achieved, a cage of reinforcement is placed within the liner and then filled it with concrete. Tamping is carried out as the liner is extracted by using a winch or hydraulic jack operating against a clamping collar fixed to the top of the steel tube lining.
An internal drop hammer can also be used to tamp and consolidate concrete but usually compressed air is used.
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CONT..
ROTARY BORED PILES Suitable for most cohesive soil e.g. clay.
Formed using an auger which may be operated in conjunction with the steel tube liner.
This auger is normally mounted on a lorry or tractor, raised to the surface and spun off the helix to the side of the bore hole where the spoil is removed. If flight auger is used,the spiral motion will brings the spoil to the surface.
GRAB CONSTRUCTION - CASED
Using crawler crane and casing oscillator
Main soil – sand and gravels with high demands on casing technology
Used chisels to break up bedrock and boulders
Pile diameter ranging from 620-2000mm
Depths generally up to 50m
ROTARY DRILLING WITH KELLY -CASEDStandard cast-in-place pile :-
Use in all types of soil
Use where site conditions are restricted
Vibration free drilling. Casing installed by rotary drive
Casing oscillator can be used for larger pile diameters and greater depths.
Pile diameter generally 600 –1800 mm
Depth generally up to 40 m but greater depth possible.
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ROTARY DRILLING WITH KELLY – BOREHOLE
SUPPORTED BY HYDROSTATIC PRESSURE
1. Rotate or vibrate
starter casing to
required depth.
2. Remove driilling spoil
with bucket attached
to kelly bar with
borehole supported
by slurry.
3. Recycle slurry to
remove soil and
insert reinforcing
cage.
4. Place concrete
simultaneously
displacing slurry.
5. Complete pile
1 2 3 4 5
ROTARY DRILLING USING TWIN ROTARY
HEAD – FRONT OF WALLSuitable for all types of soil and on restricted sites.
Vibration free, and can be installed against existing wall. Continuous
flight auger and casing installed simultaneously by counter rotating twin
rotary drives. Pile diameter from 305 to 550mm and depth generally up to
15m
1 2 3 4
1. Install casing and
continuous flight auger
to require depth using
counter rotating drives.
2. Inject concrete through
hollow stem auger,
simultaneously
withdrawing auger and
casing.
3. Insert reinforcement
cage into concreted
borehole.
4. Completed pile
ROTARY DRILLING USING FLIGHT AUGER –
CONTINUOUS FLIGHT AUGER SYSTEMAll types of soil and at restricted sites.
Vibration free. Reinforcement can be pushed or vibrated into fresh the fresh
concrete. Diameter from 400 – 1000mm . Depth generally up to 18 m.
1 2 3 4
1. Rotate continuous
flight auger to required
depth.
2. Inject concrete
through hollow stem,
simultaneously
withdrawing auger
without rotation.
3. Vibrate or push
reinforcement cage
fitted with spacers into
fresh concrete.
4. Completed pile.
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COMPOSITE PILES
Combination or two or more types as mentioned or
combination of different materials in the same types of
pile.
Used in ground conditions where conventional piles are
unsuitable or uneconomical.
Examples of composite piles :-
‘Prestcore’ pile
Shell pile
Cased pile
COMPOSITE PILES :-Prestcore pile – formed inside a line bored hole. It is a
replacement pile and can be of precast or insitu concrete.
Advantage – Problem of necking is eliminated which made it suitable to use in waterlogged soils.
Construction stage :-
1. Lined bored hole formed by percussion bored method.
2. Precast units which form the core of the pile are assembled on a special mandrel and reinforcement is inserted before the core unit is lowered into position.
3. By means of pneumatic winch, the raising and lowering the pile core which is attached to the head of lining tube to consolidate the bearing stratum.
4. Withdraw the lining tube and grouting with the aid of compressed air to expel any ground water.
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COMPOSITE PILES :-
Shell – Is a driven or displacement pile consisting of a series of precast shells threaded on to a mandrel and top driven to the required set. After driving and removing the mandrel the hollow core can be inspected, cage of reinforced can be inserted and void filled with in-situ concrete.
Suitable in waterlogged and soft substrata with readily adaptable
length.
Advantages :-
1. The shaft can be inspected internally before in-situ concrete is introduced,
2. the flow of water or soil into the pile is eliminated,
3. The presence of corrosive conditions in thes soil can be overcome using special cements in the shell construction.
COMPOSITE PILES :-
Cased Pile
Using steel strip or plate which is formed into a continuous
helix with
adjoining edge butts welded
as driving tube and filled
with in-situ concrete.
Driven into position by
internal drop hammer
operating within the casing.
FACTOR GOVERNING THE SELECTION OF PILES :-1. Location and type of structure – driven or driven and cast in-
place pile where shell remains in position are most favour for works over water. Structures on land provide wide choice of types –usually chosen the cheapest for moderate loading and unhampered site condition. If proximity of existing structure should choose the types without giving ground heave, vibration or noise.
2. Ground condition – influence the pile types and techniques.E.g. driven piles not economical to use in ground condition containing boulders and where ground heave would be detrimental. Driven piles preferred for loose water bearing sands or gravels where compaction due to driving can develop the full potential bearing capacity of these soils. Steel H-pile gives low ground displacement suitable where deep penetration require in sand and gravel. Stiff clay favour for bored and under-reamed types.
3. Durability – in marine condition suitable to use precast concrete pile, while timber is rejected in such condition.
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TYPE OF PILE SHOE FOR VARIOUS GROUND CONDITION
PILE TESTING
Objective is to confirm that
the design and information of
the chosen pile type is
adequate.
Test piles are usually
overloaded by at least 50% of
the design working load to
near failure or to actual
failure.
Record of driving
resistance of test pile
LOAD TEST
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BRICKS
WEEK 10
At the end of week 10 lectures, student will be able to :
Explain the definition, classifications, types and process of bricks. (CO1; CO3)
Identify the various types of brickworks bonding, dampness protections and anchorage. (CO1; CO3)
LEARNING OUTCOME
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HISTORY
The art of brick making can be traced back to before 6000
B.C. Peoples of Mesopotamia built palaces and temples of
stones and sun-dried brick by 4000 B.C. Roman then used
bricks for arches and roof vaults in their basilicas, baths,
palaces and aqueducts.
In mid century, the development brought by the Islamic world
by building magnificent palaces, markets and mosques of
brick, while the Europeans built fortresses and cathedrals
In the 19th century, the effects of the industrial
revolution transformed brickmaking from a hand
craft to a mechanized factory. Machines were
invented and developed to mould, press and
exclude clay bricks and improved kiln were designed
to fire greater quantities of bricks, quicker and with
more consistency.
In 20th century, development in the masonry construction -
new techniques for steel reinforced masonry, high strength
mortars, high structural strength masonry units and
masonry units of many types that reduce the number of
labour required.
HISTORY Fortress
In Malaysia, brick is widely used for buildings, civil engineering
works and landscapes features. our rich heritage masonry
buildings built during the pre-war era. One of the best examples
is the Sultan Abdul Samad Building.
Areas where bricks are commonly applied are as partition walls,
cladding and facings, perimeter and garden wall, hard
landscaping and paving and flooring. Bricks can also serve as
external and internal load bearing wall or load bearing piers and
column.
APPLICATIONS
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Figure 3: Low Rise – Loadbearing and Cladding
Figure 4: High Rise – Loadbearing and Cladding
Figure 5: Reinforced Structures and Low-Energy Building
Figure 6: Exterior wall and interior wall and flooring
Figure 7: Bricks in Hard Landscaping
Retaining wall Freestanding wall Pathways
Patio Barbecue Steps and walkways
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Figure 8: Load bearing arch bridge
Figure 9: Column and Pier spine wall
Figure 10: Window sill and Arch
door
Bricks, stones, concrete blocks are collectively known as
masonry units.
Masonry is the building technique.
Mason is a person who stacks pieces of masonry unit a top one
another to make walls and also known as bricklayer.
Brickwork is the exterior of most houses and is not only a
structural component but also protects against weather and
decorates.
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coordinating
size
work size
65mm
215mm
102.5mm
Figure 11: Brick dimension
Brick as defined by MS 76: 1972: Part 2 and BS 3921: 1985:
Clay Bricks as a walling unit not exceeding 337.5 mm in length,
225 mm in width or 112.5 mm in height.
Bricks are known by their coordinating size; that is the actual size
plus a 10 mm joint allowance to three faces and tolerances. The
standard brick of nominal dimension of 225 x 112.5 x 75 mm has
actual work size of 215 x 102.5 x 65 mm. (see Figure 11)
Malaysian Standard, MS 76: 1972 classifies bricks under three
headings:-
1. VARIETIES
The standard divides varieties into three forms and they are
common, Facing and Engineering:-
Figure 12: Common, Facing
and Engineering bricks
COMMON : bricks made without any particular attention to give
an attractive appearance and for general construction work such as
for backing walls, internal walls, walls with applied finishes and
foundation work. Figure 13 shows example of common brick use
as backing wall.
Figure 13: Common brick use as perimeter wall
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Figure 14: Facing brick used as an external
wall
FACING :
bricks of consistent colour and texture,
reasonably free from surface defect or
blemishes, customize or selected to
have an attractive appearance intended
for the construction of fair-faced
walling without plastering or other
surface treatment. Figure 14 shows
facing brick used as an external wall.
ENGINEERING :
having a dense and strong semi-
vitreous body, conforming to define
limits for water absorption and
compressive strength,
i.e. strong dense bricks.(Figure 15)
Figure 15 : Engineering bricks
The standard recognizes three qualities of bricks, and they are:-
INTERNAL QUALITY : suitable for internal use only.
ORDINARY QUALITY : less durable than the special quality,
but normally durable in the external face of the building.
SPECIAL QUALITY : durable even when used in situations of
extreme exposure where the structure may become saturated, e.g.
retaining walls, sewerage plants or paving. Such bricks have
clearly defined limits for soluble salts content.
QUALITIES
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The standard distinguishes types of brick according to their physical
form, and they are:-
SOLID :
have cores or cells passing through or nearly through the brick and
constitutes no more than 25 percent of their gross cross-sectional area,
or frogs that is a depressions in the bed face of brick that do not exceed
20 percent of its gross cross-sectional area. A core or cell is defined as
a hole less than 20mm wide or less than 500mm2 in area with a
maximum three larger holes not exceeding 3250 mm2.
PERFORATED :
if the holes passing through the brick exceed 25 percent of its gross
cross-sectional area and with a maximum three larger holes not
exceeding 3250 mm2. Small holes lesser than 25 percent.
TYPESPerforated brickSolid Brick
HOLLOW : means holes passing through the brick exceed 25
percent of its gross cross-sectional area and the holes are larger
than those defined as small holes. Large holes greater than 25
percent.
CELLULAR : means a brick which holes are closed at one end
and exceed 20 percent of its gross cross-sectional area.
TYPES
Hollow brick Celular brick
Squint
Circular
Bullnose
Figure 20: Special shapes brick Figure 21: Arch over an opening.
SPECIAL SHAPES : bricks of special shape and size, other than the
normal rectangular prism. These are accessory bricks used to form
curves or non right-angled corners, curved walls, arches or to form
features or construction details that cannot be built using standard
units unless they are cut and pieced together.
E.g. squints, circular and bullnose bricks. (Figure 20)
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CLAY BRICKS
The materials used for making clay brick range from soft and
plastic surface deposits to hard mudstone and shale.
Clay bricks are produced by mixing the finely ground clay with
water, moulding, extrusion or pressure into the desired shape,
drying it, and burning it.
The shape obtained should retain its original shape without
undue shrinkage, warping or cracking when the bricks are dried
and fired.
Manufacture of Clay Bricks
The various methods of production of clay bricks are governed
by the nature of the clay or shale, and may be divided into:-
Semi-dry Process or
Semi-plastic Process
The clay or shale is comparatively dry. The raw
material is ground to a fine powder by heavy rollers,
passed through the screen, mixed to a uniform
consistency, pressed and re-pressed in moulds and
burnt.
Stiff-plastic Process Similar to the semi-dry or semi-plastic process, except
that the water content of the material is increased and
less powerful machinery is needed to mould the brick.
Plastic Process The clay or shale suitable for this process contains a
large proportion of moisture. This type of process is
used for making wire-cut and hand-made bricks. The
bricks must be carefully dried before being burnt in
the kiln.
The stages involved in manufacturing clay bricks :- preparation of
the raw materials, moulding, drying and burning.
PREPARATIONClay or shale dug either by hand or mechanical excavators from the
quarry or pit need to be cleaned to remove any undesirable material
such as stone or coarse vegetable matter, etc. For making common
bricks, the raw material obtained will be quarried direct to the
crushing machinery. However, for producing of more expensive
bricks, requires the selection of material from different strata and this
is normally made at the quarry-face.
These materials are blended together by mechanical mixer in
conjunction with the grinding or crushing machine. After being
ground the material is passed through a screening machine to ensure
that only fine, well graded material passed forward for moulding.
Those coarse material retained on the screen is returned for further
grinding.
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MOULDING – The prepared clay or shale is machine mould
by either the wire-cut process or pressed process, or it may be
hand moulding
Machine mould :- Wire Cut Process
Figure 22: Wire cut machine
The clay usually fairly soft and of fine
texture is extruded as a continuous plastic
band or column and propelled over oiled
rollers to the cutting table. This cutting
table consists of a frame containing
several wires at a distance apart equal to
the thickness of the bricks plus the
shrinkage allowance. Bricks made by wire cut process
contain about 15% to 25% moisture and therefore must be
partly pre-dried in chamber or tunnel dryers before placed
it in the kiln for firing. Wire cut bricks do not have frogs.
(Figure 22)
Pressure Process
The prepared clay is automatically fed into the moulds which are
the size of a brick plus shrinkage allowance.
Moulding bricks by pressure can be done either by hand or by
steam or electric power.
In the steam or electric power, the rotary press or belt driven press
machine with a number of moulds are brought in turn under the
plunger where the prepared clay will be discharged and
consolidated it under great pressure. After consolidation, the bricks
are removed either by an upward movement of the base or by the
dropping of the sides.
Hand Mould
Good quality clays are normally a prerequisite for hand
moulding.
They are made up of softer consistency having a rich texture,
beautiful colouring and durability. The prepared plastic clay is
left to stand or sometimes resorted as ageing for a period varying
from one day to several weeks in cool chamber to ensure a
uniform distribution of the water throughout the mass and the
decomposition of any organic matter.
This process is to increase the plasticity and workability of the
paste and preventing the development of cracks, blisters and
other defects.
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Figure 23: Artificial drying –
brick stackedDRYING
Normally bricks made of stiff-plastic
process or having water content exceeding
25% have to be dried before being placed
in the kiln.
Drying can be done either by artificial
drying or by natural drying. In artificial
drying, the heating mediums can be of
steam, direct heat from fires or waste heat
from kilns and boilers. The dryers include
the hot floor, shed, chamber and tunnel
types.
In natural drying, normally a well ventilated shed is used where the
bricks are stacked on racks and dried by the circulation of un-
heated air.
BURNING
In this process, bricks are fired in the kiln. Firing of bricks
produces a number of complicated chemical and physical
changes in clay, therefore the degree of control of the inside
temperature of the kiln is very important.
Typically the temperature of firing is about 900oC to 1200 oC.
The colours of the clay bricks are generated by the reaction of
the raw materials to the firing.
Differences in temperature and atmospheric conditions during
firing give rise to variations of colour. Kilns may be classified
into intermittent, continuous and tunnel.
Table 3: Types of kiln
Intermittent Kiln For firing special bricks or other requirements. It is a
permanent structure with either down drought, horizontal
draught or up-draught kiln according to the direction of the
fire. The most commonly used is of down drought. Consists of
rectangular chamber lined with fire brick having four walls and
an arched top which incorporates a heat-insulating ring
composed of porous bricks to reduce the amount of heat
transmitted through the structure and therefore effects a saving
in fuel. The heat from the fuel will passes upwards to the arch
and deflected it down through the openly stacked green brick.
The produced gases will escaped through perforations in the
floor to a horizontal flue connected to a tall chimney.
Continuous Kiln Suitable for large and regular outputs. It consists of a number of
chambers connected in such a way that the operations are
uninterrupted and the waste heat is utilized to dry and pre-heat
the green bricks. Each chambers in turn being loaded with
green brick, fired, burnt, cooled and emptied. The structure
consists of walls of ordinary brickwork, lined with firebricks
jointed with refractory cement. The top is generally arched and
the floor is usually constructed of hard bricks bedded on sand
or concrete. The kiln is divided into compartments or chambers
and the number of compartment varies.
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Tunnel Kiln In tunnel kiln, the stacked bricks will be ferried by cars or
trucks on a track by a powerful hydraulic ram, while the
fires stay still. The brick will be traversed on kiln car,
passes along a tunnel through preheating, firing and
cooling zone. The firing zone and part of the cooling zone
are lined with firebrick. The temperature and track speed
of the kiln car are controlled to provide the optimum
conditions in each zone, and may be varied to produce a
specific functional and / or appearance characteristics.
KILN
Figure 24: Intermittent kiln and Continuous kiln
Properties of Clay BricksThere are many kinds of clay bricks available and they vary
considerably in appearance and function properties depending on
the purposes for which they are intended. The British Standard, BS
3921: 1985 has specifies certain requirements for clay brick for
use in walling, and they are dimensions, compressive strength,
water absorption, soluble salt content, efflorescence and sampling.
Dimensional
Deviation
The individual size should not exceed the coordinating
size 225 x 112.5 x 75 mm, and the overall measurement
taken from 24 samples of bricks should not fall outside
the limit as given in the BS 3921: 1985, i.e. maximum of
5235 x 2505 x 1605mm and minimum of 5085 x 2415 x
1515mm.
Compressive
Strength
Compressive strengths ranging from about 7 to more than
100 N/mm2. The strength varies depending on the clay
composition and the firing. It is subjected to creep at normal
temperature and the Young’s modulus lies between 5 and 30
N/mm2. The strength of a brick is taken from mean of 10 nos.
of bricks of random sampling. (See Table 1)
Water Absorption The water absorption of the bricks used in a wall affects the
mode of rain penetration. It is the percentage increase in
weight when it is saturated. The rate of absorption plays an
important role in the bonding of the brick to the mortar in
the joint. If the brick absorbs water from the mortar too
quickly a poor bond will result, causing leaks and other
damage.
The amount of water absorption depends on the clay
composition, duration and temperature of firing. The
percentage of water absorption is taken from the mean of 10
nos. of bricks of random sampling. (See Table1)
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Soluble salt
content and
Efflorescence
Soluble salts particularly calcium sulfate in brick are liable
to become discoloured by the formation of a whitish deposit
known as efflorescence or salting. These salts were brought
to the surface and deposited there by water that had seeped
into the brickwork, dissolved the salts, then migrated to the
surface and evaporated.
Commonly found in new brickwork and on faces of old
external walls which are subjected to excessive dampness.
Therefore in order to minimize the risk of efflorescence and
soluble salt attack is to design the brickwork so that it
remains dry, i.e. not saturated. (See Figure 25)
Most types of newly form efflorescence can be easily
removed with water and brush.
Sampling The required number of brick for testing can either be
from random or representative sampling, which ever is
possible. Standard required 10 nos. of bricks for each
testing to be taken from each consignment.
Table 1: Classification of bricks by compressive strength and water
absorption
Class Compressive Strength
(N/mm2)
Water Absorption
(% by mass)
Engineering A
Engineering A
≥ 70
≥ 50
≤ 4.5
≤ 7.0
Damp-proof course 1
Damp-proof course 2
≥ 5
≥ 5
≤ 4.5
≤ 7.0
All others ≥ 5 No limits
Source: BS 3921 : 1985
Table 2: Categories for soluble salt content and efflorescence of clay brick
Soluble salt content:-
Percentage by mass
(%)
Designation Remarks
Calcium ≤ 0.300 Low (L) Normal (N) – No limit on
soluble salt contentMagnesium ≤ 0.030 Low (L)
Potassium ≤ 0.030 Low (L)
Sodium ≤ 0.030 Low (L)
Sulphate ≤ 0.500 Low (L)
Efflorescence:-
Nil No perceptible deposit of salts
Slight Up to 10% of the area of the face covered with a deposit of salts, but
unaccompanied by powdering or flaking of the surface.
Moderate More than 10% but not more than 50% of the area of the face covered
with a deposit of salts, but unaccompanied by powdering or flaking of the
surface.
Heavy More than 50% of the area of the face covered with a deposit of salts
and/or powdering or flaking of the surface.
Source : BS 3921 : 1985
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Figure 25: Efflorescence in brickwork
CALCIUM SILICATE BRICKS - in BS 187: 1978(Also known as sandlime, or sometime as flintlime bricks)
The raw materials are siliceous aggregates, high calcium lime
and water.
A very fine aggregate with the majority passing a 1.15mm BS
410 test sieve is generally used. The ratio of aggregate to lime
by weight is in the range 10 to 20. Their natural colour is off-
white and they are smooth and regular in shape. Coloured
pigments are sometimes added if various colours and textures
are required by mechanical texturing before autoclaving.
Calcium silicate bricks are made to the same standard size as
clay bricks and they are either solid or may have frogs, but not
perforated.
Manufacture of Calcium Silicate Bricks (CSB)
CSB also commonly known as autoclaved calcium silicate-
bonded bricks.
The moulded CSB are hardened in sealed and steam
pressurized autoclaves process. This highly mechanized or
automated process normally takes from seven to ten hours to
allow reaction between the sand and the lime, resulting in a
strong homogenous brick. The performance characteristic of
CSB can be adjusted to suit the requirements by varying the
autoclaving time and the steam pressure.
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Figure 26: Autoclaving kiln
Properties of Calcium Silicate Bricks
BS 187: 1978 specifies certain requirements and they are dimensions,
compressive strength, drying shrinkage and sampling.
The standard gives 6 classes and the higher the numbered class the
stronger is the brick, i.e. loadbearing bricks, facing bricks and
common bricks. The appearance of the loadbearing bricks and facing
bricks must be free from visible cracks and noticeable balls of clay,
loam and lime. For facing brick, it should be of the colour and texture
agreed upon and reasonably free from damage.
Typically the range of mean comp. strengths in general use is 14 to
27.5 N/mm2, depending on the quality of bricks being produced.
Drying shrinkage for common bricks of strength class 2 should not
be more than 0.040 percent. In term of water absorption for calcium
silicate bricks, it varies between about 6 and 16 percent by weight.
Table 3: Compressive strength classes, requirements and colours of calcium silicate
bricks
Designation Class Mean compressive
strength not less than
(N/mm2)
Predicted lower limit of
compressive strength
not less than (N/mm2)
Colour
Loadbearing brick
or
Facing brick
7
6
5
4
3
48.5
41.5
34.5
27.5
20.5
40.5
34.5
28.0
21.5
15.5
Green
Blue
Yellow
Red
Black
Facing brick or
common brick 2 14.0 10.0 -
Source : BS 187 : 1978
Calcium silicate bricks of the appropriate class can be used in all types of brickwork
including underbuilding (i.e. foundation walls and basement walls), external and
internal facework, loadbearing walls, piers and column, and non-loadbearing panel
walls and partitions.
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Table 4: Minimum quality of calcium silicate bricks
Element of construction Minimum quality of bricks
class
Inner-leaf of cavity walls and
internal walls
Unplastered 2
Plastered 2
Backing to external solid
walls
2
External walls including the
outer-leaf of cavity walls and
facing to solid construction
above damp proof course
near to ground level
2
below damp proof course but
more than 150mm above
finished ground level
2
Within 150mm of ground or
below ground
3
External free-standing wall 3
Parapets Unrendered 3
Rendered 3
Sills and copings of bricks 4
Earth retaining walls 4
Source : BS 187 : 1978
SAND CEMENT BRICKS (SCB) - BS 1180 : 1972Material for SCB is Portland cement and sand. Common ratio between
sand and cement is of 6 parts of sand to 1 part of cement by volume,
with max. size of sand passing through a 4.8mm mesh of BS 410 test
sieve. deals with the minimum requirement for these brick.
Manufacture of Sand Cement BricksMoulding of SCB can be done either by hand or by machine. The
machine is operated either electric power or mechanical motor and
incorporated with the pressing machine.
After removal from the machine, the surface of the bricks are normally
scratched and left to be matured on the pallets under shade (stacked in
a separate rows one brick high with a space between each brick).
Normally for the first 24 hours after removal from the machine, the
bricks will be kept wet by watering through a fine spray. Removed
from the pallets after 2 days removal from the machine & allow to
mature for a period of 26 days.
Properties of Sand Cement BricksBS 1180: 1978 has specifies certain requirements for sand cement
bricks for used in walling, and they are dimensions, compressive
strength and drying shrinkage and sampling.
Table 5: Physical requirements
Physical property Compressive strength category
7.0 10.0 15.0 20.0 30.0 40.0
Compressive strength (wet):
average of 10 bricks to be not
less than (N/mm2)
7.0 10.0 15.0 20.0 30.0 40.0
Coefficient of variation of
compressive strength not to
exceed (%)
30 30 30 20 20 16
Drying shrinkage not to exceed
(%)
0.06 0.04 0.04 0.04 0.04 0.04
Source:
BS 1180 : 1978
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CONCRETE BRICKS
Concrete bricks are made from a mixture of inert aggregate and
cement same as calcium silicate brick and are cured in either by
weathering or in an autoclave.
These concrete bricks are harder, more difficult to cut and less
pleasant to handle than clay or calcium silicate bricks and are
less commonly used.
The drying shrinkage varies from 0.019 to 0.080 % of the
length and is greater than that of calcium silicate bricks. BS
6073: Part 1: 1981 deals with the min. requirements for these
bricks and the classification of the types and their properties.
Mortar work is serves to cushion the brick units, giving full
bearing against one another despite their surface irregularities.
The purpose of mortar is:-
- 1. it bonds the bricks together;
- 2. to seal between the bricks against penetration by
air and moisture;
- 3. it adheres the brick units to one another to bond
them into monolithic structural unit;
- 4. accommodates small movements within the wall.
- 5. the appearance of the finished brick wall.
MORTAR MIXES BS 5628: Part 1: 1978.
Figure 26: Mortar
mixture
Mortar is composed of an inert aggregate
(sand) and a binding material of lime or
cement or both.
The proportion of cement and lime in the
binder affects the properties of mortar, and it
can be carried out by volume or by weight.
Most mortar mixes are based on a ratio of 1
binder to 3 aggregate (Figure 26). The
reason is because the air spaces between
particles of sand account for about one
quarter of the total volume.
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Lime Mortar- slake lime mix with sand and water.
Cement–lime is a mixture of cement, lime and sand.
Masonry cement- mixture of OPC and inert pulverized
limestone or hydrated lime.
Mortar is a mixture of sand, cementitious materials and
water used to bond bricks.
Slaking is the chemical reaction that produces hydrated
lime when limestone and water are mixed
CEMENT - Portland cement is the bonding agent in the mortar,
besides providing strength and durability. The type of cement
used will governs the setting characteristics, workability and
the strength development of mortar. More cement produces a
strong mortar and reduces the risk of sulphation as it absorbs
less water.
LIME – Imparts workability, water retention, elasticity and
bond strength. However, if the amount of lime is too much, it
delays the setting of the mortar and walls may be unstable and
liable to wind and other damages. The period of slaking,
composition and strength of mortar depend upon the class of
lime used.
SAND - Sand used must be cleaned and screened to eliminate
particles that are too coarse or too fine. Changes in sand type and
gradation affect the workability of the mortar. Sands deficient in
fines generally produce harsh mortars, while sands with excessive
fines result in weak mortars.
The purpose of sand in mortar is to :-
act as a filler which enhances the strength of mortar;
reduce shrinkage therefore prevent the development of
cracks;
assist in the hardening of pure limes by allowing the
penetration of air which provides CO2 for the development of
carbonization;
control dimensional stability by retaining its shape and
thickness;
reduce cost as sand is cheaper than lime or cement.
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WATER – Is a mixing agent which adds to workability and
without water cement hydration and subsequent setting and
hardening of the mortar would not be possible.
Mortar joint
Is a narrow line with a conventional nominal joint thickness of
10 mm.
It account for over 17% of the surface area of the brickwork.
e.g. in English bond, about 20% of the surface area is mortar,
while bond consisting of all headers the proportion is nearly
25%.
Brickwork is jointed by striking, raking or rubbing the mortar
while it is still ‘green’.
Mortar joints should be finished at the surface with a
consistently shape profile as this also affects the appearance of
the work, i.e. each profile casts a characteristic shadow in
sunlight as can be seen in Figure 27.
A recessed joint casts a dense, bold shadow and darkens the
tone of the brickwork by the darkness in the joint.
A flush joint has no shadow and does not modify the tone of the
wall by this effect.
The concave surface of the keyed joint creates a soft shadow to
the bed joints.
Pointing in brickwork is the finish given to the joints by raking
out to a depth of approximately 13mm to 20mm and then
refilling the joint and the face with a hard setting cement
mortar.
Figure 27: The profile of bed joints view at close distance
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Flush Joint Recessed Joint Weathered Joint Keyed Joint
Weathered Pointing
20mm
Raked Out Joint
20mm
Figure 28: Mortar
Joint Profile
Mortar and grout differ conceptually from concrete in this primary
respects: water content, stiffness of the mix, aggregate size and
permitted cementitious materials.
Grout is a mixture of cementitious material, aggregate and enough
water to cause the mixture to flow readily into cores or cavities in the
brickwork.
Concrete, mortar and grout are all permitted to have OPC and blended
cement as their cementitious materials.
However, mortar may also incorporate lime, which is not used in
concrete and may only be used sparingly in grout.
The brick in a length of wall must be properly bonded in order
to distribute vertical and horizontal loads over a larger area and
so minimize the possibility of differential movement between
bricks, i.e. structural integrity to the wall.
Bonding is part of the bricklayer’s skill in producing a pleasing
appearance, besides ensuring stability of the brickwork.
It is a disposition of brick in a wall designed to ensure that the
cross joint in each course are not less than one-quarter of the
length of the brick from those in adjacent courses.
A bond is usually identified by the appearance of the external
face of the wall.
Bricklaying is an art!
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Figure 29: Header Bond
METHOD OF BONDING
Various methods of bonding are used giving rise to different
bond patterns which have special name.
Header Bond - it has only headers in each course of a wall.
Normally used in the construction of footings and walls with
sharply curve. (See Figure 29)
Stretcher Bond
It has only stretchers in each course of the wall, except at
stopped end of a wall at each alternate course, a half bat brick is
placed. (See Figure 30)
Figure 30: Stretcher Bond
English BondIt has courses of headers alternate with courses of stretchers. In this
bonding, every alternate header in a course sits centrally over the
joint between two stretchers in the joint, except at certain stopped
end. In each heading course a queen closer is placed next to the quoin
header, and the rest will be headers as shown in Figure 31.
Comparatively lack of straight joints therefore it gave this bond as
the strongest of all bonds. Use particularly in civil engineering work.
Figure 31: English Bond
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Flemish Bond – it comprises of alternate headers and
stretchers in each course as shown in Figure 32. There are two
kinds of Flemish bond :-
Double Flemish bond - both external and internal faces of the
wall have the characteristic appearance of Flemish;
Single Flemish bond - it has a facing of Flemish bond with a
backing of English bond. It has a large number of short
continuous vertical joints which occur in the longitudinal
joints.
Figure 32: Flemish Bond
Garden wall bond – Suitable for garden and division, and be
of two forms, i.e. English garden wall bond and Flemish garden
wall bond.
English garden wall bond – it has three or five courses of
stretchers to one course of headers. A queen closer is introduced
next to quoin header in the heading course. A header is placed
at the quoin of each middle (or alternate) course of stretchers to
give a necessary lap and face appearance of the stretching bond
can can be seen in Figure 33.
Figure 33: English Garden Wall Bond
Flemish garden wall bond
It has one header to every three or five stretchers in each course. A
three-quarter bat is placed next to quoin in every alternate course,
and a header is laid over the middle of each central stretcher. (See
Figure 34)
Figure 34: Flemish Garden Wall Bond
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Dutch bond
Consists of alternate courses of headers and stretchers, but
each stretching course begins at the quoin with a three-quarter
bat and every alternate stretching course have a header placed
next to the quoin three-quarter bat. Figure 35 shows the Dutch
bond.
Figure 35: Dutch Bond
TERMS USED IN BRICKWORK
Arris an angle or edge of a brick.
Bed the lower 215mm by 102.5mm surface of a brick when placed in
position, or the underside of the brick.
Header the end or 102.5mm by 65mm surface of a brick and lay with its
length perpendicular to the face of the wall.
Stretcher the side or 215mm by 65mm surface of a brick and lay with its
greatest dimension horizontal and its face parallel to the wall
face.Face a surface of a brick such as a header face and stretcher face; is
also applied to an exposed surface of a wall.
Frog a shallow sinking or indent formed on rather one or both of the
215mm by 102.5mm faces of a brick.
Bed Joints is a horizontal mortar joint parallel to the beds of the brick.
Course a complete horizontal layer of bricks plus its mortar bedding
joint.
Continuous
Vertical Joints or
Straight Joints
it comes immediately over each other in two or more consecutive
courses.
Quoin is a connection form by two walls (a corner or external angle)
which meet at 90o.
Stopped or Closed
End
is a square termination to a wall.
Perpends Is an imaginary vertical lines which include vertical joints and
should be perpendicular or plumb.
Junction in brickwork means a connection between two walls, i.e. T-
junctions and cross- junctions or intersections.
Lap the horizontal distance which one brick projects beyond a vertical
joint in the course immediately above or below it.
Racking back The stepped arrangement formed during construction of a wall
when one portion is built to a greater height than that adjoining.
Toothing each alternate course at the end of a wall projects in order to
receive or to provide adequate bond if the wall is continued at a
later date.
Bat a portion of an ordinary brick with the cut made across the width
of the brick, usually greater than one quarter. There are three types
of bat, i.e. half bat, three-quarter bat and bevelled bats.
Closer a portion of an ordinary brick with the cut made longitudinally.
Common types of closer are queen closer, bevelled closer and
mitred closer.
Queen closer obtained by cutting an ordinary brick into two half bats and
usually placed next to the first brick in a header course.
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Quoin
Racking Back
Heading course
Stretching
course
Toothing
Quoin Headers
Queen Closers Bed Joints
Vertical Joints
Mortar Joints
ArrisesFrog
Header Face
Stretcher FaceBed Face
Figure 27: Terms in Brick and Brickwork
Pilaster also known as attached pier is a thickened wall
section or a vertical support built contiguous with and
forming a part of the brick wall. Used for stiffening brick
walls and to provide all or part of their lateral support. It
functions primarily as flexural member.(See figure 36)
Pilaster
Figure 36: Pilaster
Piers also known as pillars or column in brickwork used to support
concentrated loads or to strengthen walls.
There are many ways that dampness can penetrate into a
building through the brick wall, and they are :-
By the rain beating against the external walls and
absorbed the water to show dampness on the internal
walls.
Moisture rising up the walls at or near to the base by
capillary action and moves up the wall and enter the
building above the ground floor level.
Moisture penetrates down into the head of the wall and
moving down into the building below the roof level.
The above can be overcome by placing a suitable damp-proof
course in the thickness of the wall.
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DAMP PROOF COURSE (D.P.C)
It is An impervious material place horizontally or vertically to
provide a barrier to the passage of moisture from the external
source into the wall of the building or from part of the structure to
another. Damp-proof course (dpc) is normally placed at a
distance of 150mm to 300mm above the ground level
The materials to be used as d.p.c should satisfy the criteria as
stipulated in BS 743, and they are :-
1. should be completely impervious,
2. should be durable and long lasting,
3. should be of thin membrane or sheets so as to
prevent disfiguration of the wall,
4. should be strong to support load imposed on it
without exuding out from the wall,
5. should be of flexible material and able to deflect
accordingly with any settlement without fracturing.
Arrow indicate
weep holes
DPC
G.L
Figure 37: Damp-proof course in brick wall and sills
around timber window.
Table 7: Materials used for damp-proof course
Lead It is very costly but effective damp-proof course. It is very
durable and flexible material and available in rolls of thin sheets
with varying widths, therefore large irregular shapes with few
joints can be produced. However, lead liable to exude under
heavy loadings and should be scratched as it does not adhere
readily to mortar.
Copper It is also a very excellent damp-proof course and should have a
minimum thickness of 0.25mm. Available in rolls of thin sheets,
lapped and jointed as described for lead.
Mastic Asphalt An excellent damp-proof course and it is applied in situ in two
layers with a total thickness of 25mm and it is jointless. This
damp-proof course is impervious, indestructible and does not
fracture if on account of unequal settlement or cracks in the
brickwork.
Bitumen It comes in the form of felt or rolls usually to brick widths and
can be laid quickly with min. number of joints. There are many
varieties available such as hessian, fibre, asbestos & lead which
is impregnated with and covered by a layer of hot natural
bitumen, and sanded on the surface to prevent the layers from
adhering to each other. Should be lapped 75mm where joints
occur and lapped full width at all crossings and angles.
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Polythene It is of low density black polythene sheet of single
thickness not less than 0.5mm thick. It is easily laid,
however care should be taken when lay as it is easily torn
and punctured.
Slate It is very efficient damp-proof course. It is laid in two
courses set breaking the joint embedded in cement mortar
with a minimum length of 230mm long and thickness not
less than 4mm thick. It has limited flexibility and liable to
be broken if unequal settlement occurs, but are
impervious and very durable.
Bricks Effective damp-proof course and are built in two courses
in cement mortar. It should comply with the requirement
of BS 3921.
Metal anchors are positioned in the brick walls to provide
structural integrity of the walls.
It will attach a wall to its supports, either to another wall, floor,
beam, column or other structural support.
Ties are one of the examples of a metal anchor which used to
hold a brick walls together, whilst fasteners attach other
building elements to walls.
Ties must be strong for it purpose, be non-corrodible (copper
or galvanized wrought iron) and normally shape so that water
from the outer leaf of the wall will not pass along them to the
inner leaf.
Figure : Ties
Rectangular tie
with crimp or
drip for cavity
wall
Z-tie for use
with solid
bricks onlyRectangular
tiec. Fixed unit
ties
b. Adjustable brick
ties
a. Twisted cavity ties
Double Triangle Polypropylene
Tie
Twiste
d Butterfly
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Brickwork is reinforced by introducing steel or wrought iron in
the form of flat or rod bars, woven wire or expanded metal. This
reinforcement is placed in joints or in grooves or perforations in
bricks and capable of resisting compression, tensile and shear
stresses.
In order to improves the longitudinal bond of the wall, a
reinforcing metal meshed strips, best known as ‘Exmet’ is
placed at the bed of every third course of the wall height. It is
made from thin rolled steel plates which are cut and stretched by
a machined to a diamond meshwork form.
It is normally used in walls and partitions to resist both
horizontal and vertical pressure.
The strips should lap at intersection and at joint with a lapped of
75 mm.
Brickwork can be reinforced using rod wire reinforcement. It
is used vertically to strengthen walls of reduced thickness and
to resist lateral stresses.
‘Brickforce’ is a welded reinforcement used to improve
resistance of the horizontal pressures occurring from either
side.
‘Wallforce’ is use to strengthen cavity wall. (See Figure 39)
‘Bricktor’ which is a stainless steel or galvanized wire mesh is
used in brick walls to bond and strengthen corners and
intersections of the walls. (See Figure 39)
e. Rod reinforcement
Figure 39: Reinforced brick walls
b. ‘Brickforce’
a. ‘Wallforce’
c. ‘Bricktor’
d.‘Exmet’