Clay and clay products
CPCCBC4006B
Select, procure and store construction
materials for low rise projects
Clay Bricks
Properties of clay bricks
• Tests are carried out on bricks to ensure that the
limits set for dimensions, tolerances, efflorescence,
transverse strength and compressive strength are
adhered to.
• Tests are also conducted for characteristic
expansion, initial rate of absorption and water
absorption properties.
Clay Bricks
Properties of clay bricks cont.
• To test the bricks a sample is taken
from a consignment and this sample
is assumed to be typical of the rest of
those bricks.
Clay Bricks
Manufacture
• Bricks have great fire resistance
• Their size enables easy handling and placement in
walls can be easily adapted to small-scale and large-
scale structures
• Brick can give a pleasing appearance and texture
Clay Bricks
Constituents:
• Brick clays are produced by blending together various
clays (surface clays, shales, and fire clays) to produce
the desired chemical composition and physical
properties
Clay Bricks
Constituents cont:
• Clays can be divided into calcareous clays (containing
15% Calcium Carbonate), which gives a yellow colour
when burnt, or
• non calcareous clays (containing silicate of alumina,
feldspar, and iron oxide), Iron oxide gives a buff, red or
salmon colour, when burnt
Clay Bricks
Moulding of Brick:
• The raw material is dug from pits, crushed, ground, and
screened to reduce it to a fine consistency.
• Then it is tempered with water to produce a plastic
clay ready to form into shape.
Clay Bricks
Methods of forming :
Three different processes are used to form bricks:
• (i) Soft Mud Process: A relatively moist clay (containing
20% to 30% of water) is pressed into moulds, either by
hand or machine - The mould may be dipped in water
(water-struck bricks) or dusted with fine sand (sand-
struck bricks) before filling it with clay
Clay Bricks
Methods of forming :
• (ii) Dry press bricks are formed with clays that shrink
excessively during drying - Is mixed with minimum
amount of water(10%)
• (iii) Stiff mud Process: Most widely used process
nowadays - contains 12 % to 15% of water - passed
through vacuum to remove any pocket of air, and then
extruded through a rectangular die to form bricks
Clay Bricks
Methods of forming :
The rectangular column of moist clay extruded through
the die is cut by automatic wire cutters to form individual
bricks - After moulding and cutting, the bricks are dried in
low-temperature kilns, they are then ready for firing or
burning.
Watch Boral Youtube Video to see this process
http://www.youtube.com/watch?v=cFgKRpd4_o4
Clay Bricks
Moulding of Brick:
Q. Where did the term Frog come from?
A. The actual term "frog" comes from the Dutch word
"kikker" Traditional brick making consisted of a wooden
box which a "kicker" in the middle was used to force the
clay out wards to form the arises.
Clay Bricks
Dimensions:
The length of a clay brick is to be not less than
• 1.5 times the width, nor more than 390 mm.
• The height is to be not more than 70% of the length
with the gross volume of the unit not exceeding 0.004
cubic metres.
Clay Bricks
Dimensions:
Standard sizes are:
Common Bricks: 230x110x76
Modular Bricks: 290x90x90
Jumbo Bricks: 390x110x90
Clay Bricks
Durability:
Durability is the resistance of the brick to attack by
soluble salts.
It will vary depending on the environmental conditions the
bricks are exposed to (that is, moisture and the
availability of soluble salts) and the amount of glass
formed in
the body of brick during firing.
Clay Bricks
Durability:
There are different durability classes for every
requirement.
These include:
• Internal - bricks suitable for use in an internal wall
above a sheet or membrane damp-proof course
• Above damp-proof course – bricks suitable for use in
an external wall only
Clay Bricks
Durability:
• General purpose - bricks suitable for use in an external
wall under ordinary exposure conditions
• Exposure - bricks suitable for use in external walls
exposed to saline environments
Clay Bricks
Mortar
The function of mortar is:
• to provide a joint of sufficient thickness, usually about 10
mm, to accommodate bricks of slightly different sizes
• to provide a bond of sufficient strength to resist lateral
(bend) loads
• to provide an even bedding for the bricks with sufficient
strength to carry the compressive loads of the brickwork
Clay Bricks
The basic materials of mortar are:
• Cement
• Lime
• Sand.
Sand For Mortar:
The principal constituent of mortar is sand which should
be 'well graded'. This means that there should be an even
distribution of particle sizes from the finest to the most
coarse.
Clay Bricks
Sands for mortars are often referred to as 'builder’s sand',
'bricklayer’s sand' or 'mortar sand'. 'Soft sands' should not
be used for mortars as these contain fine silts and clay
particles which can lead to unacceptable shrinkage
movement in the set and hardened mortar. 'Sharp sands'
are also unsuitable because their lack of finer particles
causes poor water retention during application resulting in
a harsh unmanageable mortar.
Clay Bricks
Masonry Joints
Weathered
• Size
Concave
• Joint Tooling
Vee
• Joint Profiles
Flush
Racked
Concave
Struck
Clay Bricks
Control of external movement
The sources of movement in brickwork are:
• foundation and footing movements
• frame movements
• temperature movements - expansion in hot weather,
contraction in cold weather
• vertical shortening - shorten as loads increase during
construction and occupation of the building
Clay Bricks
Control of external movement cont.
• horizontal concrete shrinkage - shrinkage of concrete
during drying.
Design of external control joints will minimise movement
by providing:
• vertical gaps for horizontal movements
• horizontal gaps for vertical movements.
Clay Bricks
Control of external movement cont.
In clay brick walls the main movement is a slight
expansion which can cause
cracking in the brickwork.
The correct location of an expansion joint is very
important.
The first and last expansion joint in a wall should always
be placed near the corners of the building as well as near
openings.
Clay Bricks
Expansion Joints:
Extruded – Smooth
Extruded – Wire Cut
Wood Mould Extruded – Raked
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