UNESCO-NIGERIA TECHNICAL &
REVITALISATION PROJECT-PHASE II
YEAR I- SE MESTER I
THEORY AND PRACTICE
Version 1: December 2008
NATIONAL DIPLOMA IN
WORKSHOP PRACTICE I
COURSE CODE: BLD 105
TABLE OF CONTENTS
WEEK 1: BLOCK LAYING AND CONCRETING EQUIPMENT
(1.2) Bricklaying and concreting equipment
- Pointing Trowel
- Spirit Level
- Builder’s Square
- Lines and Pins
- Straight Edge (Range)
- Plumb Bob
- Wooden Float
WEEK2: CONCRETING EQUIPMENT
(1.1) Concreting Equipment
- Concrete Mixer
- Concrete Vibrator
- Concrete Forms
- Block Moulding Machine
WEEK3: CUTTING AND PLASTERING
(1.2) Cutting Tools
- Club Hammer
- Bolster Chisel
- Cold Chisel
- Brick Saw
- Hack Saw
WEEKK4: VENTILATION AND SAFETY IN THE WORKSHOP
(2.1) Ventilation in the Workshop
(2.2) Storage for Tools
(2.2) First Aid Materials
(2.3) Introduction to the Factory Act
(2.3) Safety Tools
(2.3) Safety Rules
(2.3) Safety Habits
(2.3) Causes of Accidents
WEEK6: LAYOUT OF A BLOCK LAYING AND CONCRETING WORKSHOP
(3.1) Classification of Aggregates
(3.1) Characteristics of Aggregates
(3.1) Grading of Aggregates
(3.1) Maximum Size of Aggregates
Tests on Aggregates
- Test for Cleanness of Sand
- Silt Test
WEEK 8: CONCRETE AND ADDITIVES
WEEK 9: PRODUCTION OF CONCRETE
(3.1) Specifying Concrete
WEEK10: CONCRETE PRODUCTS
(3.4) Tests on Blocks
- Compressive Test
- Absorption Test
Other Tests on Blocks
WEEK11: SETTING OUT A BUILDING
(4.1) Setting Out Methods
The 3, 4, 5 Method
The Builder’s Square Method
Leveling Instrument Method
Activities and Assessment
WEEK12: LAYING OF BLOCKS
Tools Used for Block Laying
(4.1) Block Laying Procedure
WEEK13: LAYING OF CONCRETE
(4.3) Concrete Laying Procedure
- Placing of Concrete
- Compaction of Concrete
- Finishing of Concrete
- Curing of Concrete
WEEK14: BONDING AND BLOCK WALL CONSTRUCTION
(5.1) Principles of Bonding
(5.1) Types of Bond
WEEK15: BONDING AND BLOCK WALL CONSTRUCTION CONTINUES
Types of Bonds Continue
(5.2) Setting Out Bonds
WEEK 1 BLOCKLAYING AND CONRETING EQUIPMENT
Bricklaying and concreting processes consist of many operations and require the use of many
tools and equipment. They both require batching and mixing of concrete and mortar,
transportation of the mix to the required point of use placing the mix at the desired position,
positioning the bricks/block in the correct positions and aligning them correctly. The type and
choice of the tools and equipment depends on the operation to be carried out.
(1.1) BRICK/BLOCK LAYING TOOLS AND EQUIPMENT
The basic brick/block laying tools and equipment include the following:
Brick Trowel: this is used picking and spreading mortar during the laying of bricks/blocks or
stone, trimming or rough cutting them, rendering and for consolidating joint and cutting off
excess mortar. It consists of a wide steel blade and a wooden handle. The blade has a length
of between 225 mm to 350 mm. a typical trowel is as shown in figure 1.1
Fig. 1.1. A trowel
Pointing Trowel: This is similar to but smaller than the brick trowel. The blade is between
100 mm to 150 mm. It is used for filling the joints with mortar and carefully finishing them,
an operation referred to as pointing.
To maintain the trowel it should be washed clean of any mortar that might be sticking to it at
the end of each day’s work. Also it should not be used for excessive cutting. Rather an
appropriate cutting tool should be used. The handle should be rigidly fixed to the blade at all
Spirit Level: Two types of spirit levels are in use and for different purposes. These are the
plumb rule and plumb level, though both may be combined in one to serve as plumb rule and
Plumb Rule is used for checking the vertical faces of work and proving that they are
absolutely perpendicular (or plumb).
Plumb Level is used for the same purpose as the plumb rule but contains spirit bubble in both
directions. It can also be used for leveling horizontal surfaces.
Spirit level is used for leveling horizontal surfaces and checking the vertical faces of works to
ensure that it is absolutely perpendicular (or plumb). It ranges in length between 225mm to
It should be protected from having the edge dented by any slight knock as this interferes with
the setting of the tube of the level, thus affecting its accuracy. Any mortar sticking to its
surface should also be removed as this will affect the straightness and also affect the proper
observation of the spirit bubble. An example of a spirit level is shown in figure 1.2.
Fig. 1.2 A Spirit Level
Builder’s Square: The builder’s square is used to obtain a right angle during the setting out
process of a new building and also to obtain a right angle when forming a new wall. It is
made using either steel or timber. The steel square is made into an L-shape. The timber
square is made in the form of a right angle triangle. The hypotenuse of the triangle is
provided to enhance the rigidity of the square.
Fig. 1.3. A wooden builder’s square
Lines and Pins: This consists of two pins made of good quality steel and stout blades with
lines wound round them, the lines which should be of hemp and not too thick. Lines and pins
are used for transferring levels and alignment of straight walls above 1.20 m long. The
arrangement of the string and pins is as shown in figure 1.3.
Before preparing the lines and pins for use, insulating tapes should wound round the shanks
of the pins to prevent it from being affected by rusting. It should also be cleaned of any
mortar dropping after use as this may weaken the lines and cause it to break.
Fig. 1.3 Lines and pins
Straight Edge (Range): This is usually made of a piece of timber planed smooth on all sides
or two sides, of convenient length of about 2.0 m, could be beveled or straight at both ends.
It is used to check the level or flatness of a newly laid piece of wall to ensure that all
blocks/bricks are laid to same level. It also finds application in plastering work to obtain an
even surface for the plaster work before the finishing with a trowel. An example of a range is
as shown in fig. 1.4.
Fig. 1.4 Straight Edge
Plate 1.1 An artisan demonstrating the use of a spirit level and a range on site
Plumb Bob: This consists of thread and the bob (usually of lead) weighing about 2 kg. it is
used for checking vertical alignment of tall buildings and pillars.
Wooden Float: It is used to spread the mortar evenly over the surface at the joints during
block laying. This roughens the surfaces of the block work to act as key to receive the plaster
that might be applied to it later. As the name implies it is made from timber.
Fig. 1.5. Wooden float
1. Identify some brick/block laying tools in the workshop.
2. State the use of each one of the tools identified.
3. Demonstrate the use of these tools.
4. Student should demonstrate the maintenance of each of the tools.
1. Correct identification of the tools with their respective uses.
2. Correct maintenance procedure by the students.
WEEK 2 BLOCKLAYING AND CONRETING EQUIPMENT CONTINUED
(1.1) CONCRETING EQUIPMENT
Concreting tools and equipment are used in the production and placing of concrete. Some of
the tools are used for block laying purposes too but the following are used mainly for
Concrete mixers: They are used to mix the concrete ingredients to make the mix of specified
consistency. They are used mainly in projects where a large volume of concrete is required,
as well as where a high quality concrete is required for important works.
For best results correct setting of the machine, proper cleaning of the blades and the inner
surface of the drum, the sequence of materials charged into the drum, timely supply of water,
time of mixing, speed of mixing drum etc. Mixing time is usually 1 minute for mixers up to
capacity and this is increased by 0.25 minute for every additional m3
Mixers are specified by the volume of mixed concrete discharged after mixing of each batch
expressed in m3
. Sometimes the total volume of the unmixed ingredients in m3
is given as a
prefix. For example, 10/7 mixer takes 10m3
of unmixed material and gives 7 m3
concrete in each batch. The mixers drum speed is usually 18 to 20 revolutions per minute
(rpm). Concrete mixer may be tilting and non-tilting types. Mixers are made in stationary or
portable models. Portable units are mounted on wheeled trolleys and are equipped with draw
bar for towing or are, sometimes, mounted on trucks. Driving unit may be diesel engine or
electric power. A portable concrete mixer is shown in fig. 2.1.
Fig. 2.1 Concrete mixer
Concrete Vibrator: Vibrators are used for compaction of concrete after placement. They
have almost universally replaced hand tamping. There are two types of vibrators which are,
internal and external.
Internal vibrator is also called poker, needle or immersion vibrator. The internal vibrator is
immersed in the freshly placed concrete, while the external type is placed on the concrete
formwork or on the surface of the concrete through which vibrations are conveyed to the
interior. For mass concreting works poker vibrator is most effective. Immersion of poker for
5 to 15 seconds to full lengths of fresh concrete at points 45 cm to 75 cm apart gives
External vibrators are useful in the compaction of pavements, precast work, or canal concrete
lining. For effective compaction a vibrator must provide a minimum of 3600 vibrations per
Concrete Forms: Concrete in its fresh state needs to be retained in position so as to give the
desired shape and be in the desired position. This is achieved by the use of concrete forms or
formwork. Formwork could be made of many materials but the common materials are timber,
plywood, steel or any combination of these. The formwork is constructed in such a way that
the internal profile corresponds to the dimension and shape of the element to be constructed
using concrete. After the concrete has attained enough strength to retain its shape and hold its
own weight the formwork is then struck (removed).
Block Moulding Machine: Block is the predominant walling unit used in the Nigerian
construction industry. It is moulded using machines that are specifically designed for it. The
block moulding machine has a demountable mould which determines the size of the blocks to
be moulded. It is either powered by a diesel engine or electricity. The engine enables the
machine to induce the desired vibration to the mix placed in the mould in order to enhance
the strength of the blocks. A typical moulding machine is as shown in fig. 2.2.
Fig. 2.2. A typical moulding machine
Some of these blocks are sometimes hand-moulded.
1. Identify the various concreting equipment in the workshop.
2. Demonstrate the use and maintenance of each of these equipment.
3. Mould some blocks using the available machine in the workshop.
4. Students to submit reports which completely describe the specific types of these
equipment in their workshop with respect to type, capacity, area of application etc.
1. Depth and relevance of the report.
WEEK 3 CUTTING AND PLASTERING TOOLS
Most of the construction products supplied for use are manufactured in standard sizes and
shapes. They may therefore need to be trimmed or cut to shapes and sizes so that they might
fit into the element being constructed. It is for this reason that cutting tools becomes
necessary in construction.
Cutting tools include but not limited to the following:
Club Hammer: It is used in conjunction with bolster or chisel for accurate cutting of blocks
and concrete products. It has a steel head with bevel edges and weighs between 1.0 kg to 1.3
kg. The head has a wooden handle attached to it as indicated in fig. 3.1. They are generally
heavy enough for the cutting brick or cutting away holes and chases in brickwork.
Fig. 3.1. Club Hammer
Bolster Chisel: It used for accurate cutting of bricks or blocks in conjunction with club
hammer. The width of the blade varies between 50 mm – 100 mm; the 100 mm blade being
the most suitable for the bricklayer. It should not be used to cut holes in brick wall as it is not
intended for this type of job. A bolster chisel is as shown in fig. 3.2.
Fig. 3.2. A bolster chisel
Cold Chisel: This is used in conjunction with club hammer for cutting of holes and chases.
It is available in various sizes and length. The sizes are (i.e. length to width of cut):
(i) 100 mm x 6 mm
(ii) 600 mm x 25 mm or 32 mm
(iii)300 mm x 18 mm
(iv)350 mm x 18 mm
(v) 225 mm x12 mm.
Maintenance: the head of the cold chisel should never become mushroom shaped as the piece
of steel on the mushroom may break off when cutting and pierce the eye.
Fig. 3.3. Cold chisel
Brick saw: Brick saw is used specifically to cut bricks to specified dimensions and shape.
The blade is made of steel and it is fitted to the handle which is also made of steel.
Sometimes it is machined powered but in most cases it is operated manually.
Hack Saw: Hacksaw is similar to the brick saw except that the brick saw is larger in size than
the hacksaw. The hacksaw is used to cut reinforcement or other metals to the desired size and
1. Students should identify the various tools used for cutting of various items in the
2. Demonstrate the use of these tools in the workshop.
3. Clean and properly maintain these tools.
1. Correct choice of tools for any of the tasks they can be used for.
2. Precision and neatness of jobs produced by students using these tools.
WEEK 4 VENTILATION AND SAFETY IN THE WORKSOP
The work environment should be clean and safe as this enhances the quality of life.
Employees’ satisfaction is increased; illness is reduced, thereby contributing to higher
productivity as a result of the better working conditions. One means of providing an
improved working condition is the provision of adequate ventilation in the workshop.
During some of the operations in the workshop some gases, fumes and dust is released into
the air which might endanger human health. The type of substances generated and released
into the air depends on the kind of operation that is being carried out at the material time.
Effective protective measures have to be put in place to provide clean air for breathing at
(2.1) VENTILATION FOR THE WORKSHOP
The whole of the workshop should be properly ventilated. This is done by providing
extraction fans at strategic points in the workshop either in the walls or in the roof. If it is
being provided in the wall it should be located towards the top of the wall. This is to ensure
that the foul air being extracted is discharged above the normal height at which human beings
operate. The extraction fans could either be powered by electricity or it could be the
mechanical type which is operated by air current.
However, ventilating a complete workshop does not prevent hazardous result from reaching
the workers in the workshop. Sufficient protection can only be guaranteed by the use of local
exhaust and ventilation equipment at the workstations. Local extraction ensures that the
hazardous fumes are captured before they reach the breathing area of the worker.
(2.2) STORAGE FOR TOOLS
Proper storage of tools is one of the basic requirements for safety in the workshop. The tools
must therefore be properly kept to avoid injuries as well as damage to these tools. It is very
important to ensure that these tools are kept clean, in their correct positions, and under the
right conditions as specified by the standard requirement for each tool.
Tools like hammers and other heavy tools should not be stored at a position very high from
the ground. This is to reduce the possibility of falling from such heights either accidentally
slipping out of the hand of the person trying to pick it from the elevated position.
Trowels and similar tools should be stored in shelves provided specially for them. They
should be placed safely so as to prevent them from falling to the floor and getting damage in
Before being stored in their respective positions the tools should be properly cleaned oiled if
required and packaged if there is any provided for them.
(2.2) FIRST AID MATERIALS
In spite of safety or precautionary measures taken in the workshop, accidents do occur due to
one reason or the other. It is therefore necessary to provide first aid materials in the
workshop. The first aid materials should normally be kept in the First Aid Box.
The First Aid Box should be highly visible, usually coloured green and clearly marked with a
white cross, or coloured white and marked with a red cross. They should be fixed in an easily
accessible place. They usually fitted close to the wash hand basin in the workshop. On
construction sites they can be kept in the site offices or workers’ canteen or shelter.
The contents of a First Aid Box will vary according to where it is fitted, the number of
workers, and the type of work being carried out in the place. Typically a First Aid Box should
contain the following:
Various sizes of bandage
Various sizes of sterile dressing
Sterile eye pads with bandage
Various sizes of gauze
Moist antiseptic cleansing wiper
Dispensable plastic gloves
First Aid Boxes should not contain any medicines or pills. They should be kept in a clean and
tidy condition and anything used should be replaced immediately. An up to date list of
contents should also be kept inside.
1. Indentify proper storage for the various tools used in the workshop.
2. Identify the contents of a typical First Aid Box
3. Stock a given First Aid Box.
1. Proper identification of storage procedures for various tools used in the workshop.
WEEK 5 SAFETY
Safety can be defined as a condition under which we gain total or almost total degree of
freedom from danger, injury or damage. It should be considered as first thing to be observed
in our daily activity.
The wise mason/bricklayer should work with care for his own safety and for the safety of
others working with him. Careless and unsafe act may lead to injury and sometimes death on
the work in the workshop or site. Regulations concerning safety, health and welfare are
available to safeguard the safety of workers engaged in the workshop and on site too.
(2.3) INTRODUCTION TO THE FACTORY ACT
The Factory Act was enacted in 1961 in Britain and subsequently adopted in Nigeria. The Act
sets out to make provisions that will safeguard the safety and health of the workers in any
organization that employs people under the Nigerian labour law. With this development, the
Nigeria Industrial Standard came into being. It is intended to provide guidelines with respect
to the following:
General safety and health of workers.
Welfare of workers which entails anything to be done to improve the comfort of
Tools and materials: those things that are not hazardous to the workers shall be so
employed as the tools and materials for work.
(2.3) SAFETY TOOLS
Safety tools include the following:
Protective clothing (apron, overall etc.)
(2.3) SAFETY RULES
In using the workshop everyone should be ready to obey all acts and regulations relating to
safety of persons and equipment. Such safety rules include the following:
Ensure that the workshop is kept tidy at all times
Keep the working places clear of unnecessary tools and materials, and free of scraps
Remove all combustible materials such as timber, paper and cardboard packaging as
they may constitute fire hazards if left around in the workshop
Always use the right tool for the job intended
Never use files or similar tools without handles
There should be no running, jumping or any horseplay in the workshop
All appliances should be switched off in the event of power failure
Switch off all electrical appliances, switches and sockets when not in use and ensure
that this is done at the close of each day
Close and lock all doors when no one will be around in the workshop
Instruct others on safety and prevent others from engaging in unsafe acts
If in doubt ask for instruction
Implementation of Safety Rules
The implementation of safety rules involves the following group of people:
Users of the facility
(2.3) SAFETY HABITS
Always wear protective clothing regardless of the actual job done
Protect the eyes by wearing safety goggles
Welding goggles should be put on when engaged in electrical arc welding or gas
welding which produce intensely bright light
Safety helmet is required especially in very large workshops or large sites
Wearing of appropriate type of hand gloves is required to offer adequate protection to
the hand when necessary
Wearing of safety boots to prevent injury to the feet
Use face protector where necessary
Use ear protector where necessary
Keep the workshop tidy at all times
Keep working tools clean and clear of any material that may cause it to malfunction
Generally, it is essential that care should be taken when placing materials or tools
anywhere, whether overhead or on ground level
The whole of the workshop should be kept tidy at all times
Keep working areas free of wastes resulting from off-cuts excess material droppings.
(2.3) CAUSES OF ACCIDENT
Handling and using bad hand tools
Careless handling of portable power tools and machines
Stepping on or striking obstructions on the workshop floor
Lifting and moving materials and equipment
Wrong stacking or storage of materials and equipment
Using wrong tools for a job
Using flammable and corrosive liquid
Careless acts that endangers the health, safety and welfare of one and others
Lack of safe means of access and safe entrances and exits
Lack of planned and regular maintenance as well as system of work without risk to
1. Identify various safety tools and their uses.
2. Demonstrate the use of various safety tools.
3. Carry out the cleaning of the workshop to remove all materials that can cause accident
in the workshop.
1. Proper identification of various safety tools and proper usage by the student.
WEEK 6 LAYOUT OF A BLOCK AND CONCRETING WORKSHOP
Work being carried out in the workshop needs to be carried out smoothly, conveniently and
safely. This can be done if the facilities in the workshop are arranged properly so as to allow
quick access to materials, tools and equipment as well as workshop personnel. The common
features in a typical block laying and concreting and their layout are as discussed below.
Workshop Supervisor’s Office
The office of the overall person in charge of the workshop should be located close to the
main entrance into the workshop. This is to enable people that will be visiting the workshop
for administrative purposes to go straight to the office without interfering with the workshop
activities. This will also enables the person to clearly monitor the movement into and from
Store Keeper’s Office
This should be located close to the supervisor’s office. This will enable him to even act on
behalf of the supervisor in the event that the supervisor is not in the office.
Tools and Material Storage
This is where tools and some of the materials used in the workshop are stored. Cement,
additives and similar materials are stored in this place. It is located close to the store keeper’s
office for easy access and close monitoring.
Loose Material Storage
This is the place where such materials like planks and components for such things as scaffold
are stored. This should be located close to one of the access to the workshop.
Blocks and Brick Stack (Store)
This provides the space where blocks and bricks are kept in the workshop. It should be
located at a point in the workshop where it will not where free movement of people and
materials within the workshop will not be obstructed.
Block Moulding Bay
Blocks are sometimes moulded in the workshop. A place should be provided for it. It should
be enough for all the activities that block moulding will entail.
Concrete Mixing Bay
This space is provided for the concrete mixer for the purpose of mixing the concrete and
mortar that may be used in the workshop.
Beside the concrete mixer there should be a water tank in which water for mixing of the
concrete will be stored.
Open Loose Material Storage for Aggregates
This is where both coarse and fine aggregates are stored. There should naturally be located by
the position of the concrete mixer. This is to reduce the distance covered between the mixing
point and where the aggregates are obtained from.
Safety Office and Equipment Store
This is where the safety equipment will be kept. This should be clearly indicated and located
close to the main entrance to the workshop. This in addition to all things will heighten the
safety consciousness of people as they are entering the workshop.
Generally, the space provided for each of these activities will depend on the nature and scope
of the particular activity to be carried out in the workshop environment.
A typical layout of a brick/block laying workshop is as shown in fig. 6.1
Fig. 6.1. Typical Layout of Brick/Block Laying and Concreting Workshop.
1. List some of the activities that may be allocated space in brick/block laying and
2. Sketch the layout of the brick/block laying and concreting workshop being used by
3. State reasons for the location of each activity at their respective point in the
1. Correctness of sketch with respect to the workshop being used by the student.
WEEK 7 AGGREGATES
Aggregates are mineral filler materials used in concrete. Materials like sand, gravel, crushed
rock and other mineral fillers are used as aggregates. Aggregates occupy about 75% of the
volume in concrete. Almost any material provided it has required strength, durability and
soundness can be used as an aggregate for making concrete.
(3.1) CLASSIFICATION OF AGGREGATES
On the basis of their size, aggregates may be classified into two categories:
Coarse Aggregate: It is the aggregates whose particles pass through 75 mm mesh sieve and
are completely retained on 4.75 mm mesh sieve. Aggregate having its particles greater than
75 mm is known as cyclopean aggregate.
Coarse aggregate is further divided into natural and artificial aggregates. The natural
aggregate include natural gravel, crushed gravel or stone, and natural stone. On the other
hand, artificial coarse aggregate include clinker, foam slag, breeze and broken bricks.
Fine Aggregate: It is the aggregate whose particles pass through 4.75 mm mesh sieve but are
completely retained on 0.07 mm mesh. Particles smaller than 0.06 mm come under silt, and
clays and are considered as harmful ingredients.
(3.1) CHARACTERISTICS OF AGGREGATES
A good aggregate should not contain any deleterious material which may cause physical and
chemical changes in the concrete. An aggregate should have clean, uncoated, properly shaped
particles of strong, dense, durable mineral rock and materials.
Shape and Size
Aggregates may be classified as rounded, regular, angular or flaky. Rounded aggregates have
about 35% of voids. It gives minimum ratio of surface area to a given volume of concrete and
therefore requires minimum water for lubrication. It gives good workability for a given
amount of water and also requires less cement for a particular water/cement ratio. This type
of aggregate does not have good interlocking effect and hence, does not produce high
Irregular aggregate gives higher percentage of voids of up to 37%. This type exhibits less
workability and requires more cement. It has better interlocking effect than rounded
aggregate, but not enough for high strength concrete.
Angular aggregates have void percentage of up to 41%. It requires more water for lubrication
and exhibits least workability for a specified water/cement ratio. It has very good interlocking
effect and hence most suitable for high strength concrete.
Flat, elongated, or flaky particles in aggregate are objectionable. Beside decrease in
workability, flaky particles have the tendency to be oriented in one plane which is harmful
form durability point of view. Percentage of this type of particles in the aggregate should not
Bond between aggregate particles and cement paste is greatly dependent on the surface
texture of the particles. Surface roughness and surface porosity of aggregate are the main
elements on which the bond greatly depends. The rougher the surface of the aggregate, the
better the bond that can be developed between the aggregate and the cement mass. Surface of
aggregate may be glassy, smooth, granular, crystalline or honeycombed. Glassy surfaced
aggregate should not be used for concrete.
Porosity and Absorption
Small holes are usually found inside rocks during the formation to form what are referred to
as pores. All aggregates have certain amount of pores, through which water can penetrate.
Aggregate without any moisture in its pores or on its surface is referred to as bone dry
aggregate. A saturated surface dry aggregate has its pores filled with moisture but the surface
is dry. When all the pores are filled with moisture and the surface is also wet, the aggregate is
said to be moist.
In the field, all aggregates have moisture. Fine aggregates increase in volume due to the
presence of moisture, therefore suitable allowance has to be made while taking account of it.
(3.1) GRADING OF AGGREGATES
Grading of aggregate implies the particle size distribution of aggregate. If all particles of an
aggregate are of one size, more voids will be left in the aggregate mass. On the other hand,
and aggregate having particles of varying sizes will exhibit smaller voids. The principle of
grading is that the smaller sized particles fill up the voids left in large size particles.
Grading determines the workability of the mix which controls segregation, bleeding, water
and cement requirements, handling, placing and other characteristics of the mix. These
factors also affect the economy, strength and other properties. This is however more
pronounced than in coarse aggregates.
(3.1) MAXIMUM SIZE OF AGGREGATE
For the same workability and strength, concrete having larger aggregate requires less amount
of cement than concrete having smaller aggregate. In large bulk works large-sized aggregate
is preferred because it involves lesser consumption of cement. Less cement reduces heat of
hydration and, and consequently thermal stresses and shrinkage cracks are also reduced. But
there are other considerations also which control the size of aggregate. Large-sized aggregate
presents smaller surface area to be wetted per unit weight than that of small-sized aggregate
and hence for the same water/cement ratio workability of concrete having comparatively,
large-sized aggregate is more. Small-sized aggregate has poor bond with cement paste and
hence, its strength is lower than that having large-sized aggregate. The maximum size of the
aggregate is governed by the following factors as well:
It should be three quarters of the clear spacing between reinforcing bars or between
reinforcing bars and forms.
It should be one third of the concrete slab.
40 mm, 20 mm and 10 mm sized aggregates are most commonly adopted in concrete
works. For structures like abutments, piers, retaining walls, 40 mm size aggregate
should be used. For reinforced concrete 20 mm sized aggregate is used.
1. Classify aggregates into the two basic categories.
2. Identify various types of aggregate.
3. Identify the various sizes of aggregate.
4. Students should carry out tests on aggregates and report on them.
TESTS ON AGGREGATES
Test for Cleanness of Sand
Procedure: Pick up a handful of sand from a damp pile of sand. Rub the sand between the
palms of the hand.
Result: If the palms show signs of staining then the sand is not clean. If the hand is free of
any staining then the sand is clean.
Apparatus: Measuring cylinder (250 ml and 100 ml), beaker (250 ml) and stirrer, measuring
Materials: Common salt.
Specimen: Natural sand.
1. Prepare 1% solution of salt in water
2. Pour about 50 ml of the solution into the 250 ml measuring cylinder
3. Add sand up to the 100 ml mark
4. Add more salt solution until this reaches the 150 ml mark
5. Shake the mixture vigorously and leave it to settle in the cylinder for three hours
6. Measure the thickness of the visible silt layer formed at the surface
7. Measure the depth of the sand including the silt layer.
Result: Express the thickness of the silt layer as a percentage of the depth of the sand and
silt. The value obtained should not exceed 6%.
1. Proper reporting of the tests together with the results.
WEEK 8 CONCRETE AND ADDITIVES
Concrete is an artificial material, obtained by mixing cement, coarse aggregate, fine
aggregate and water, in suitable proportions. These ingredients, when freshly mixed, produce
a plastic mass which can be poured into suitable forms or moulds, to give the desired shape to
the resulting solid mass. The plastic mass gets converted into a solid stone-like hard mass
with the passage of time, as a result of the chemical reaction taking place between cement
and water. The aggregates do not undergo any chemical change. They simply act to give
mass volume to the concrete and reduce shrinkage effects. Hardened concrete resemble stone
in weight, strength, and hardness.
Concrete is an important and versatile material, and extensively used building material that
can be easily manufactured on site.
Concrete while in plastic state can be moulded into almost any shape; and when set (dry) it
possesses great strength and durability. Concrete as produced, achieves a great strength
depending on the quality and quantity of cement in it. The richer the concrete is in cement,
the greater the strength of the concrete. So also a dense and stronger concrete is obtained
depending on how dense and tough the coarse aggregate is.
Concrete is divided into two types. These are plain and reinforced concrete. When concrete is
embedded with reinforcement to increase its tensile strength, it is called reinforced concrete.
Without the reinforcement it is called plain concrete.
Production of good concrete is based on the following use of the materials that make it up.
The particles of aggregates should be clean and free from coatings of dust and clay if
the full bond is to be developed.
All aggregates should be inert in water and should not contain constituents that are
likely to decompose or change in volume through exposure to the atmosphere.
They should be free from organic impurities which may affect the setting and
hardening of cement.
They should have a low absorption value, if used for concrete exposed to the weather
or in contact with liquid.
Additives are those constituents of plastic concrete other than aggregates, cement and water.
They may be introduced into the concrete either as an integral part of the cement e.g. Soap
Naptha during grinding of the Ordinary Portland Cement to produce hydrophobic Cement, or
as an admixture during the mixing of concrete.
Additives are classified into accelerators, retarders, plasticisers, and permeability reducing
Accelerators are materials which are introduced into concrete to accelerate the rate of early
hardening of concrete in normal temperature. In cold weather they minimize the delay in
Chemical compounds used as accelerators include calcium chloride and some organic
compounds such as soluble carbonate, silicate, and flue-silicate. Calcium chloride is however
the most widely used and is usually introduced into the mixing water in quantities not
exceeding 2% by weight of cement. It is however not suitable for use in reinforced concrete if
it is to be subjected to steam curing and/or high temperature during its life. It should also not
be used for reinforced concrete made with sulphate resisting Portland cement as in both cases
there will be the risk of the chloride causing the corrosion of the reinforcement.
Retarders may be used to offset the acceleration effect of temperature from hot weather
concrete. Among the wide varieties of retarders there is much uncertainty and duration and
variability of action and so retarders should only be used on sound technical advice.
The most commonly known retarding admixtures such as carbohydrate derivatives (including
sugar) and calcium lingo-sulfonate are employed only in small fraction of a percentage by
weight of cement.
Plasticisers increase the workability of the concrete by offsetting the deficiencies in grading
that tend to produce harshness or segregation in the concrete.
The action of a gas forming agents to react with the hydrating hydroxides in concrete to
permeate the mass with minute hydrogen bubbles and the leading gas forming agent is
Air entraining agents are usually foam forming agents. Their action is physical rather than
chemical and the air entrainment is largely through interaction with sand rather than with
Unsol resins, natural resins, tallow oils and soap have been used to impact air entrainment
properties if used in small quantities.
Permeability Reducing Agents: in concrete exposed to moisture on one face and to air on
the other, there will be a slow moisture movement across the concrete. Properly proportioned,
concrete well placed and cured should normally be highly impervious under pressure.
Anything that decreases the size, number and continuity of the capillaries shall be beneficial
and this includes decreasing the water/cement ratio, air entrainment and favourable curing.
Among the more effective water-proofers used are soap 0.2% by weight of cement or less,
about 1% of butyl stearate, some heavy mineral oils and cut-back asphaltic oils up to 5%.
1. Make 0.2% solution of soap and add to concrete made with cement quantity of which
the quantity of soap also makes 0.2%. State the observed effect on the concrete
produced in its plastic state.
1. Correct report on the effect of the soap solution on the fresh concrete.
WEEK 9 PRODUCTION OF CONCRETE
Batching is the process of measuring the desired quantity of the various constituents of
concrete to obtain the desired mix for the concrete. Batching can be by weight or by volume.
Batching by Volume.
In this method an open top box called a gauge box is used to measure the quantity of the
various materials. Cement is most times supplied for use in a unit 50 kg bag and has a volume
of about 0.035 m3
. For a 1:2:4 mix ratio, the gauge box is filled once with cement, two times
with fine aggregate and four times with coarse aggregate. At all times the top of the gauge
box is struck off level each time.
If the fine aggregate is damp or wet its volume will increase by up to 25% and therefore the
amount of fine aggregate should be increased by this amount. This increase in volume is
Batching by volume is not a very accurate method. This is because the weight of cement per
unit volume varies depending on the degree of compaction during loading into the gauge box.
This method is therefore not suitable for high quality work. It is however adequate for most
small size jobs.
Batching by Weight.
This method entails measuring out the exact quantities of the various materials using any
suitable weighing method depending on the quantity of the materials to be batched. This is
the better method since it has a greater accuracy and the weighing balance can be attached to
the mixing machine.
It water is usually measured by volume and specified as to the number of litres per bag of
cement to be mixed.
Tools Used for Batching
Tools required for batching are as follows
Head pan/wheel barrow and
Mixing of concrete is done by two means. These are hand mixing and machine mixing.
Hand mixing should be carried out on a clean hard surface. The materials should be
thoroughly mixed in the dry state twice before the water is added. The water should be added
slowly and mixed at least three times.
Machine mixing is done in stationery or transit mixers. The mix should be turned over in the
mixer for at least two minutes after adding the water in the stationery mixer. The first batch
from the mixer tends to be harsh since some of the mix will adhere to the sides of the drum.
This batch should be used for some less important work such as filling in weak pockets in the
bottom of the excavation. In the transit mixer, the batched materials are charged into the
mixer and the mixing takes place as the concrete is taken to the point where it is to be used.
Ready mixed. This is used for large batches with lorry transporters up to 6m3
capacity. It has
the advantage of eliminating site storage of materials mixing plant, with the guarantee of
concrete manufactured to quality – controlled standards. Placement is usually direct from the
lorry; therefore site- handling facilities must be co-ordinated with deliveries.
If concrete is to be transported for some distance over rough ground, the runs should be kept
as short as possible since vibration of this nature can cause segregation of the materials in the
mix. For the same reason concrete should not be dropped from a height of more than 1m. If
this is unavoidable a chute should be used.
(3.1) SPECIFYING CONCRETE
Concrete can be specified by any of the four following methods.
Designed Mix. The mix is specified by a grade corresponding to required characteristic
compressive strength at 28days.There are 12 grades from C7.5 to C60, the C indicates the
compressive strength in N/mm2
or MPa. Flexural (F) strength grades may also be specified as
F3, F4 or F5 i.e. 3, 4 or 5 N/mm2
. Also the requirement must specify the cement and
aggregate content and maximum free water/ cement ratio.
Prescribed Mix. This is a recipe of constituents with their properties and quantities used to
manufacture the concrete. The specification must be made for
The type of cement
Type of aggregates and their maximum size
Mix proportions by weight
Degree of workability
Prescribed mixes are based on established data indicating conformity to strength, durability
and other characteristics. Examples of prescribed mix include the following:
Suitable mixes for different jobs are:-
1: 3:6 - Mass concrete
1:2:4 - Reinforced concrete
Standard Mix. Mixes are produced from one of five grades, ranging from ST1 to ST5, with
corresponding 28 days strength characteristics of 7.5 to a limit of only 25N/mm2. Mix
compositions are specified as in prescribed mix.
These mixes are most suited to site production, where the scale of operations is relatively
small. Alternatively, they may be used where mix design procedures would be too time
consuming, inappropriate uneconomical.
Design mix. This mixes are selected relative to particular applications and site conditions, in
place of generalizations or use of alternative design criteria that may not be entirely
appropriate. Grading and strength characteristics are extensive and vary with application.
General (GEN), grade 0-4. They range from 7.5 to 25N/mm2
in characteristic strength. These
are used for foundations, floors and external works.
Foundations (FND), graded 2, 3, 4A and 4B. they have characteristic strength of 35N/mm2.
These are particularly appropriate for resisting the effects of sulphates in the ground.
Paving (PAV), graded 1 or 2 in 35 or 45N/mm2
strengths, respectively. A strong concrete for
use in driveways and heavy duty paving.
Reinforced (RC) and prestressed concrete grade 30, 35, 40 and 50 corresponding with
characteristic strength and exposures ranging from mild to most severe.
Quality control is of paramount importance in this mix. Therefore, producers are required to
have quality assurance product conforming to BS EN ISO 9001.
1. Prepare mixing bay by mixing and spreading weak concrete to form mixing slab on
which the materials are to be mixed.
2. Batch a concrete mix of 1: 2 : 4
3. Mix the concrete by manual method
4. Batch a similar mix and then mix the concrete in a concrete mixer.
1. Consistence of mix produced using each method of mixing.
WEEK 10 CONCRETE PRODUCTS
Concrete products are made from concrete and vary in shapes, types and uses. They include
tiles, kerbs, precast paving slabs and blocks. The mix ratio and the constituents depend on the
type and place of use. The most commonly used concrete product is the blocks.
Blocks are building units which forms the walls of a building. It can be produced of different
materials such as sand or crushed stones mixed with cement to form sandcrete blocks. Other
types of blocks known as concrete blocks is made of cement, sand and coarse aggregates is
also used extensively and it can be the dense or lightweight type.
Blocks are usually hollow or solid core and vary in sizes. The standard sizes are
450 mm x 225 mm x 225 mm used for external walls
450 mm x 225 mm x 150 mm used for internal walls
450 mm x 225 mm x 112.5 mm used for partition only
102.5×215×60 brick for erecting external and partition walls
Other decorative blocks are required for fancy work only.
Block provides an improved thermal insulation and since it is so much lighter, units
convenient for buildings can be made several times larger than ordinary bricks thereby
making the building operation faster. They can be readily cut and chased and permit the easy
driving in of nails or screws.
A variety of concrete blocks are shown in fig. 10.1
(3.4) TESTS ON BLOCKS
Apparatus: Compressive testing machine, weighing machine, ruler.
1. Remove the surface grit and projecting lips and record the dimensions and weight of
2. Place the specimen on the plate of the machine in such a way that the load is applied
to the top and bottom of the specimen
3. Apply the load (without shock) at the rate of approximately 15 N/mm2
until the specimen fails.
Result and Calculation:
Record the maximum applied load to the specimen.
Calculate the compressive strength.
Compressive Strength = Max applied load/Net area of block.
A good field test which can be used to measure absorption rate of block is as follows:
Apparatus: Wax pencil or crayon, medicine dropper or pipette, timer.
1. Draw a circle about 25 mm in diameter with the crayon or wax pencil on the surface
of the block which will be in contact with the mortar
2. With the pipette or medicine dropper, place 20 drops of water inside the circle
3. Note the time it will take for the water to be absorbed.
Result: If the time taken to absorb the water exceeds 5½ minutes, the unit needs not be
wetted, but if the blocks absorb the water in less than 5½ minutes, wetting is needed.
Other Tests on Blocks
Other tests that may be carried out on the blocks include the following:
Soundness Test: This entails striking a nail into the block with the hammer. The block
should give a metallic ring to it.
Non-Disintegration Test: This entails having to leave the block in the water for seven days.
The block should not disintegrate inside the water at the end of this period.
1. Identify the common sizes of blocks.
2. Carry out tests on blocks and report on them.
1. Proper reporting of the tests on the blocks.
WEEK 11 SETTING OUT OF A BUILDING
Before a building is erected by laying the blocks, it has to be set out. Setting out also known
as ground tracing is the process by which excavation lines, centre lines etc. of all the walls in
the plan of a proposed building are put on the ground on the actual site of the building.
(4.1) SETTING OUT METHODS
Setting out is carried out using three basic methods. These are
The 3, 4, 5 method
The builder’s square method
The 3, 4, 5 Method Procedure
Mark out the building line from the road by measuring the required distance from the
centre of the road, or by stretching a line along an existing building to the proposed
site. The building line is then represented by a line known as the ranging line, which
also marks the front wall of the buildings as shown.
Mark out the overall length of the building by driving in pegs at A and B, along the
Procure two steel tape measures and mark out four equal distances on the ranging line
starting from the corner peg at B. These distances may be in any unit of measurement,
i.e millimeters, meters, etc.
Pull a tape measure from point B to C and an assistant to hold it, ready with a hammer
and a peg.
Pull the second tape from the fourth mark at D on the ranging line to point E on the
The distance 5 m, if using meters, on tape DE should coincide with the point 3 m on
tape BEC, to prove that the angle B is 90° (from Pythagoras' theorem). If this does not
happen, the tape B C is either shifted outwards or inwards until 5 m on the second
tape coincides with the 3 m mark on the first tape.
Repeat the same procedures to obtain the right angle for BAF, and mark out the
overall widths of the building.
Establish corner pegs and erect profiles.
Mark the positions of partition walls on the profiles with either nails or saw cuts.
Ranging lines are stretched through these nails and the corner pegs to mark the ground
to indicate the line of excavation for the foundation trenches.
Fig. 11.1. Setting out using the 3, 4, 5 method
1. Simple to use, does not require any calculations. .
2. Can be applied to large buildings.
3. Accuracy of setting out is self-evident and adjustment in the event of error is simple
1. Two tape measures are required, which may be difficult to obtain in rural areas.
2. Effect of wind on tapes and line may lead to inaccurate work especially on long
The Builder’s Square Method
Set out the front or building line in the usual manner with pegs or marks at the
Place the builder's square so that the front line touches one side of the square right
through its length as shown.
Stretch a line from the corner peg so that it is parallel to the second side of the square
and establish the third peg. A corner with an angle of 90° is thereby obtained.
With the aid of a tape measure, mark I out the length and breadth of the proposed
Transferring the builder’s square to the remaining corners and repeating the above
operations, a simple rectangular building can be set out.
After establishing the four corner pegs, profiles, (separate or continuous) may be
erected in the same way as described earlier.
Note that the builder's square can only be used with accuracy for small buildings such
as farmhouses and typical single room and parlour compound buildings.
Fig. 11.2. The builder's square
1. Simple to use.
2. Does not require any calculation.
3. Can be very accurate when used for small rectangular buildings.
4. Quick in application.
1. Unseasoned timber can twist and warp leading to errors when used.
2. Unsuitable for large buildings.
Leveling Instrument: The Site Square
When a right angle is to be set out, the corner of the angle is always known and also one side
of the corner. One has only to find the position of the second side. The site square solves this
problem in a very simple, quick and reliable way.
The front or building line is set out in the usual manner, with pegs or marks at the
required distances as shown
Set up the tripod at No.2 peg so that the datum rod is directly over the peg or mark
which represents the corner point. Make sure that the legs are firm on the ground.
Release the spike screw and extend the spike so that it sits firmly on the nail or mark.
Tighten the screw, as shown
Before mounting the instrument on to the tripod head, ensure that the locking screw is
tightened screw on the site square. Release the locking screw. By rotating the site
square, point the lower telescope along the front or building line. Tighten locking
Check the circular bubble over the top of the instrument. This will probably be found
to be 'off-centre'. To correct this, release tripod leg screws and adjust the instrument
until the bubble comes into the centre of the black circle. When this is achieved,
tighten the tripod leg screws. The instrument is now ready for use.
Sight on to peg No.1 through the lower telescope to obtain the 'dead on' position by
means of the fine setting screw which moves the telescope to the right or to the left
and by tilting the telescope up or down as shown.
When this position is obtained, measure the distance required to peg No.3. Now by
sighting through the top telescope, taking care not to rotate the instrument to the right
or left, signal an assistant to move the peg sideways until it is 'dead on'. Peg No.3 is
now positioned at an angle of 90°.
By moving the site square to peg No.3 and 'lining up' on peg No.2 the remaining
corner peg, No.4, can be set out using the procedures already given.
Profiles can be marked easily by tilting the telescope upwards, having sighted on to
the peg, and placing a nail in the 'dead on' position on the profile board.
Fig. 11.3. The site square
1. Can be used for large buildings with some accuracy.
2. Transfer of lines to profile boards done easily.
1. The range of accuracy is limited to only 33 m.
2. Distances cannot be read off the instrument directly but need to be measured with a
1. Set out a simple two bedroom flat using the three basic methods of setting out.
1. Check the square of the angles set out using the respective method
WEEK 12 LAYING OF BLOCKS
After the foundation of a building has been constructed the next stage in the construction of a
building is the construction of the wall. Construction of walls in most buildings entails laying
Tools Used For Block Laying
The common tools required for wall construction include:
- Trowel - Tape
- Spirit level - Straight edge
- Line - Head pan
- Batten - Shovels
- Steel square
- Cutting axe
(4.1) BLOCK LAYING PROCEDURE
The basic steps in block laying are:
Lining to ensure straightness of wall
Level to obtain true horizontal top surface
Plumbing to give true vertical surface
Before the blocks are laid, the corner walls are first of set out by following process:
Set up lines, along the wall lines from the profile boards either from the internal or
Spread mortar at the corner points.
Use straight edge and spirit level to plumb down the line and mark on the mortar.
Place the block and check against the line using same tools.
After ensuring proper setting of the blocks at the corners, level them and erect two or
three layers at each corner and partitions. Fill the joints properly.
Stretch line in-between the corner blocks and set the straight line blocks to fill the
Ensure the blocks are truly straight and level.
Lines can be used both at the top and sides of the wall during the block-laying to ensure true
level and plumb of the block wall, The spirit level bubble must always be in the centre of the
glass and likewise bubble must also be at the centre for true plumb line. i.e true vertical
alignment of the blocks
The walls should be properly set up and erected in the trench; this is erected up until the
building is out of the trench.
The blocks should be taken out of the ground at least 150mm above the ground level. This
represents the ground floor level.
Fig. 11.1. Setting out of block wall
1. Set out the block wall on a given foundation or floor slab.
2. Erect the wall up to at least three courses.
1. Correct setting out of block work.
2. Proper alignment in horizontal and vertical direction.
WEEK 13 LAYING OF CONCRETE
Concrete after it has been mixed and transported to the point where it is required place is then
placed at the desired position. Concrete should be placed and compacted before it begins to
set. The method of placing concrete should be such as to prevent to segregation. It should not
be dropped from a height exceeding 1 m. In case the placing of concrete will take sometime
after mixing, it should be kept in an agitated condition.
Before concrete is placed in position, the formwork should be thoroughly checked to ensure
that it is rigid and has the desired shape and size. The formwork should be prepared and
soaked very well with water. The surface should be cleaned to remove any loose materials
spread over it. Having carried out all the necessary checks and preparations the concrete
placing process is started.
(4.3) CONCRETE LAYING PROCEDURE
Placing of Concrete
The following precautions are taken during concrete placing.
Concrete should be laid continuously to avoid irregular and uneven lines
To avoid sticking of concrete, the formwork should be oiled before
The position of the formwork and the reinforcement should not be disturbed
while placing the concrete
Concrete should not be dropped from a height exceeding one metre, to
Concrete should not be placed during rain
Concrete layer should be laid in layers between 30 – 45 cm in case of mass
concrete and 15 – 30 cm for reinforced concrete
Walking on freshly laid concrete should be avoided
Concrete should be placed near its final position as close as possible.
When concrete is laid it needs to be consolidated in its position. This referred to as
compaction. Compaction aims at reducing the voids in the compacted concrete. Compaction
can be done either manually or mechanically. When done manually it is called hand
compaction or tamping. When done mechanically it is called machine compaction.
Hand compaction is done with the help of steel tamping rods or timber screeds. Narrow and
deep members are compacted with tamping rods. Thin slabs and floors are tamped with help
of the screeds. Compaction should be carried out for such a time as that the layer of mortar
begins to appear on the compacted surface.
Machine or mechanical compaction of concrete is done with the help of vibrators. These
produce vibrations which when transmitted to plastic concrete make it to flow and produce
compaction. The air bubbles are forced out of concrete due to vibration.
Finishing of Concrete
Finishing is giving the desired smoothness to the surface of the compacted concrete.
For finishing slab and floor surfaces the following are the alternatives that can be adopted.
Screeding: This process involves striking off the excess concrete to proper grade. After
screeding, voids left on the surface are filled with concrete and the process is repeated until a
uniform surface is obtained. Screeding should not be excessive as this will affect the strength
of the concrete negatively.
Floating: The floating operation helps to remove irregularities left on the surface of concrete.
For the purpose of screeding a 20 cm wide and 1.5 m long float, made of wood is used. Any
low spots noticed are filled with extra concrete and worked with the float.
Trowelling: This is the final operation of the finishing. This operation is done after all the
excess water from the surface has evaporated. For large works, power trowels are used.
Concrete which dries out too quickly will not develop its full strength; therefore new concrete
should be protected from the drying winds and sun by being covered with canvas, straw,
polythene sheeting or damp sawdust. This protection should be continued for at least three
days since concrete takes about twenty-eight days to obtain its working strength.
Curing of Concrete
The process whereby moisture is made available to finished concrete to promote continued
hydration of cement in concrete is known as curing. Proper curing of concrete will enable it
to acquire its desired strength. It will also reduce the incidence of shrinkage crack in the
concrete. Curing also brings about the improvement in the durability, impermeability, wear
and weather resistance qualities of concrete as well as reduces shrinkage.
Methods of Curing
There are several methods of curing. The method chosen at particular time depends on the
nature of work and the climatic condition. The methods are as follows:
Shading: The object of shading is to prevent evaporation of water from the surface of the
concrete. It helps to protect concrete surfaces from heat, direct sun rays, and wind. In cold
weather it helps to preserve the heat of hydration of cement to prevent the freezing of
concrete. It however, has limited application.
Covering the concrete surface with polythene jute bags or hessian: The surface of
concrete to be cured is covered with any of these materials which are wetted periodically.
This is the proper method to cure vertical and sloping surface.
Sprinkling water: In this method, water is sprinkled on the concrete at suitable intervals.
This method uses a large amount of water for curing.
Ponding Method: This is the best method for curing horizontal surfaces such as floors, roof
slabs, roads etc. After placing and finishing the concrete, the exposed surface is first of all
covered with moist hessian or canvas. After 24 hours the covers are removed and the area is
divided into rectangular areas with help of sand or clay bounds. Lastly, these rectangular
areas are filled with water and kept filled for the duration of the curing. The water
requirement for this method is very large. Also, after curing it might become difficult to clean
the cured surface of clay.
Membrane curing: The earlier methods described are known as moist curing. In the
membrane method concrete covered is kept covered by a waterproof membrane which is kept
in contact with the concrete for one week. The membrane prevents evaporation of water from
the concrete. Membrane compounds are also known as sealing compounds. They include wax
emulsion, bitumen emulsion, bituminized waterproof paper, and plastic films are the common
membrane materials. Strength of concrete cured using this method is not as much as that
cured using the moist method.
Concrete should be cured for a period of at least seven days.
Steam Curing: This method of curing is adopted for precast concrete. At elevated
temperature the rate of gain of strength of concrete of concrete increases. This enables
concrete to acquire full strength within short period and hence, curing is also finished within
1. Students should cast simple concrete slabs
2. Prepare a suitable surface to receive concrete
3. Remove loose materials from the surface
4. Wet the surface with water
5. Lay the concrete
6. Compact the concrete
7. Finish the concrete.
8. Apply anyone of the moist curing methods to the slabs.
9. Write a report on the concrete placing process as carried out in the workshop.
1. Depth and relevance of report to the concreting process.
2. Correct application of the concrete casting process.
WEEK 14 BONDING AND BLOCKWALL CONSTRUCTION
The construction of a wall of brick or blocks usually follows the pattern of laying the bricks
or blocks in some regular arrangement. The brick /blocks courses or rows in a wall are
arranged to ensure that each brick/block overlaps or bear upon two or more bricks /
immediately below it. The process of laying the bricks across each other and binding them
together is called bonding. Bonding is intended to prevent the existence of continuous vertical
joints both in the face and the inside of the wall. Walls that have continuous vertical joints do
not act homogeneously and do not distribute the superimposed load effectively and as such
the strength of the block work is reduced greatly. The amount of overlap and the part of the
brick used determine the pattern or bond of brick work.
The main purpose of bonding is to provide maximum strength, lateral stability and resistance
to side thrust, and it distributes vertical and horizontal load over a large area of the wall. A
secondary purpose of bonding is to provide appearance (decoration).
The choice of any brick bond depends on the following factors
Prevailing environmental or site conditions.
Thickness of the wall.
The purpose for the wall construction i.e. either strength or decoration
The choice of mortar used for wall construction depends on the purpose of the wall. The
following could act as a guide
Cement and sand mortar mix of 1:4 is used for load bearing wall and water works
Lime, cement and sand mortar mix of 1:1:4, 1:1:6 is used for general wall
(5.1) PRINCIPLES OF BONDING OF BRICKWORK
The correct lap should be set out and maintained by introduction of:
(a) A closer next to the quoin header.
(b) A three-quarter bat starting the stretcher course.
There should be no straight joints in a wall.
Perpends or cross-joints in alternate courses should be kept vertical.
Closer should never be built in the face of the wall except next to the quoin header.
The tie bricks at junctions or quoins should be well-bonded to secure the walls
The bricks which are laid in the interior of thick walls should be laid header wise as
far as possible.
Sectional bond should be maintained across the wall, that is, the bond on the back
should be in line with the bond on the face side of the wall.
To achieve the maximum strength in a wall, all the joints in the interior of the wall
should be kept filled or flushed in with mortar in every course. This can be done by
mixing a quantity of mortar to a grout or slurry and running it into the joints between
the bricks which have been laid in the wall.
(5.1) TYPES OF BOND
There are very many types of bond but the most common ones are as follows:
This consists of all bricks laid as stretchers on every course with the courses laid half-bond to
each other as fig. 14.1. This is affected in a plain wall with stopped ends by introducing a
half-bat as the starting brick to alternate courses. It is used usually only in walls of a half-
brick in thickness.
Fig. 14.1.Strecher bond
This consists of alternate courses of headers and stretchers with a closer placed next to the
quoin header to form the lap. There is, however, a variation where a closer is not used in the
header course, and the lap is formed by starting each stretcher course with a three-quarter bat.
Such variation is not very common. It is considered one of the strongest bonds. It is suitable
for the construction of load-bearing walls and for places where strength is of utmost
Fig. 14.2. English Bond
1. Lay blocks in stretcher bond
2. Lay bricks English bond up to three courses.
1. Proper laying of the blocks and bricks in the appropriate bonds.
WEEK 15 BONDING AND BLOCKWALL CONSTRUCTION
This consists of alternate headers and stretchers, with the headers in one course being placed
centrally over the stretcher in the course below. A closer is placed next to the quoin header to
form the lap. Flemish bond is said to give a more attractive face appearance than English
bond as it appears less monotonous. It affords a saving in facing bricks because of the header.
English bond requires approximately eighty-nine facing bricks per square metre, while
Flemish bond requires only seventy –eight facings. The header face of many bricks is dark,
and they are separated in this bond as against the English where they are continuous.
Fig. 14.3. Flemish Bond
In this bond the arrangement shows the header face of every brick, with 215 mm thickness.
The bond is formed by three-quarter bats at the quoin. It is rarely in use, because it has now
attractive finish (too many joints). It is used in footing courses or walling curved on plan.
Fig. 14.4. Header bond
Garden Wall Bond
This is designed to reduce the number of header faces to facilitate a fair finish both sides in
walls where appearance is important. There is one course of header bricks to every three
courses of stretchers in English garden wall bond, and one header to every three stretchers in
each course of Flemish garden wall bond.
Fig. 14.5. Brick bonds
(5.2) SETTING OUT BONDS
In some cases it may be difficult to apply the standard patterns to the quoin, junction walls
and stopped ends. The reason is that consistency of bonding is impossible to maintain. For
example when setting out English bond for walls of 1 and 2 bricks in thickness, the pattern is
the same on both faces, whereas on one 1½ and 2½ brick walls the pattern is different. That is
headers on one face and stretchers on the other.
Any rules concerning bonding can be applied as far as practicable. A general rule for quoins,
stopped ends and junction walls in English bond is that where a wall changes direction, the
bond will also change, that is if there are stretchers on one face then the adjoining face will be
headers. This however, cannot be applied in every case, as in a 1½ brick junction wall
adjoining a 2-brick such as 1½ and 2 bricks in thickness. There must be two adjoining faces
having similar bonds.
One rule, however, should always be applied. When setting out quoins or junction walls, care
should be taking to ensure correct lining in the walls at the internal angles to achieve the
maximum resistance against cracking due to shrinkage or uneven settlement. The bonding
arrangements to quoin vary according to the bonds which are used and the sizes of the walls
comprising the corners.
Plate 15.2. A brick wall
1. Set out a brick wall and erect it in header bond up to three courses.
1. Correct setting out of the brick wall and erection to the desired height.