UNESCO-NIGERIA TECHNICAL & VOCATIONAL EDUCATION

REVITALISATION PROJECT-PHASE II

YEAR I- SE MESTER ITHEORY AND PRACTICE

Version 1: December 2008

NATIONAL DIPLOMA IN BUILDING TECHNOLOGY

WORKSHOP PRACTICE I

COURSE CODE: BLD 105

TABLE OF CONTENTS

WEEK 1: BLOCK LAYING AND CONCRETING EQUIPMENT

(1.1) Introduction(1.2) Bricklaying and concreting equipment

- Trowel - Pointing Trowel- Spirit Level- Builders Square- Lines and Pins- Straight Edge (Range)- Plumb Bob- Wooden Float

ActivitiesAssessment

WEEK2: CONCRETING EQUIPMENT(1.1) Concreting Equipment

- Concrete Mixer- Concrete Vibrator- Concrete Forms- Block Moulding MachineActivitiesAssessment

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) Introduction(2.1) Ventilation in the Workshop(2.2) Storage for Tools(2.2) First Aid Materials

ActivitiesAssessment

WEEK5: SAFETY

(2.3) Introduction(2.3) Introduction to the Factory Act(2.3) Safety Tools(2.3) Safety Rules(2.3) Safety Habits

(2.3) Causes of AccidentsActivitiesAssessment

WEEK6: LAYOUT OF A BLOCK LAYING AND CONCRETING WORKSHOP

(2.4) Introduction

WEEK7: AGGREGATES(3.1) Introduction(3.1) Classification of Aggregates(3.1) Characteristics of Aggregates(3.1) Grading of Aggregates(3.1) Maximum Size of Aggregates

ActivitiesTests on Aggregates

- Test for Cleanness of Sand - Silt Test

Assessment

WEEK 8: CONCRETE AND ADDITIVES

(3.1) Concrete(3.2) Additives

ActivitiesAssessment

WEEK 9: PRODUCTION OF CONCRETE

(3.1) Batching(3.1) Mixing(3.1) Handling(3.1) Specifying Concrete

ActivitiesAssessment

WEEK10: CONCRETE PRODUCTS

(3.2) Introduction Blocks

(3.4) Tests on Blocks- Compressive Test- Absorption Test

Other Tests on BlocksActivitiesAssessment

WEEK11: SETTING OUT A BUILDING

(4.1) Introduction(4.1) Setting Out Methods

The 3, 4, 5 MethodThe Builders Square MethodLeveling Instrument MethodActivities and Assessment

WEEK12: LAYING OF BLOCKS

(4.1) IntroductionTools Used for Block Laying

(4.1) Block Laying ProcedureActivitiesAssessment

WEEK13: LAYING OF CONCRETE

(4.2) Introduction(4.3) Concrete Laying Procedure

- Placing of Concrete- Compaction of Concrete- Finishing of Concrete- Curing of Concrete

ActivitiesAssessment

WEEK14: BONDING AND BLOCK WALL CONSTRUCTION

(5.1) Introduction(5.1) Principles of Bonding(5.1) Types of Bond

ActivitiesAssessment

WEEK15: BONDING AND BLOCK WALL CONSTRUCTION CONTINUES

Types of Bonds Continue(5.2) Setting Out Bonds

ActivitiesAssessment

WEEK 1 BLOCKLAYING AND CONRETING EQUIPMENT

(1.1) INTRODUCTION

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 days 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

times.

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 level.

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

1.2 m.

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

Builders Square: The builders 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 builders 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

ACTIVITIES

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.

ASSESSMENT

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

concreting operations.

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

0.75 m3 capacity and this is increased by 0.25 minute for every additional m3 or fraction

thereof.

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 of mixed

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

satisfactory results.

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

minute.

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.

ACTIVITIES

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.

ASSESSMENT

1. Depth and relevance of the report.

WEEK 3 CUTTING AND PLASTERING TOOLS

CUTTING 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

shape.

ACTIVITIES

1. Students should identify the various tools used for cutting of various items in the

workshop.

2. Demonstrate the use of these tools in the workshop.

3. Clean and properly maintain these tools.

ASSESSMENT

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

(2.1) INTRODUCTION

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

work places.

(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

the process.

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 Triangular bandage Various sizes of gauze Safety pin Moist antiseptic cleansing wiper Cotton wool 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.

ACTIVITIES

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.

ASSESSMENT

1. Proper identification of storage procedures for various tools used in the workshop.

WEEK 5 SAFETY

(2.3) INTRODUCTION

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

workers.

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:

Safety helmet Hand gloves Safety boots Protective clothing (apron, overall etc.) Face protector Ear protector Respirator

(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

and off-cuts

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:

Inspectors Safety officers Safety representatives 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

health

ACTIVITIES

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.

ASSESSMENT

1. Proper identification of various safety tools and proper usage by the student.

WEEK 6 LAYOUT OF A BLOCK AND CONCRETING WORKSHOP

(2.4) INTRODUCTION

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 Supervisors 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

the workshop.

Store Keepers Office

This should be located close to the supervisors 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 keepers

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.

ACTIVITIES

1. List some of the activities that may be allocated space in brick/block laying and

concreting workshop.

2. Sketch the layout of the brick/block laying and concreting workshop being used by

the students.

3. State reasons for the location of each activity at their respective point in the

workshop.

ASSESSMENT

1. Correctness of sketch with respect to the workshop being used by the student.

WEEK 7 AGGREGATES

(3.1) INTRODUCTIONAggregates 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

strength concrete.

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

exceed 15%.

Surface Texture

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.

ACTIVITIES

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.

Silt Test

Apparatus: Measuring cylinder (250 ml and 100 ml), beaker (250 ml) and stirrer, measuring

rule.

Materials: Common salt.

Specimen: Natural sand.

Method:

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%.

ASSESSMENT

1. Proper reporting of the tests together with the results.

WEEK 8 CONCRETE AND ADDITIVES

(3.1) CONCRETE

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.

(3.1) ADDITIVES

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

agents

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

hardening.

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

aluminium powder.

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

cement.

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%.

ACTIVITIES

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.

ASSESSMENT

1. Correct report on the effect of the soap solution on the fresh concrete.

WEEK 9 PRODUCTION OF CONCRETE

(3.1) BATCHING

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

called bulking.

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

Gauge box, Head pan/wheel barrow and Shovel/mixer.

(3.1) MIXING

Mixing of concrete is done by two means. These are hand mixing and machine mixing.

Hand 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.

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.

(3.1) HANDLING

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:

1:3:6/40mm aggregate.

1:2:4/20mm aggregate.

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.

ACTIVITIES

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.

ASSESSMENT

1. Consistence of mix produced using each method of mixing.

WEEK 10 CONCRETE PRODUCTS

(3.2) INTRODUCTION

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

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 102.521560 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

Fig. 10.1. Some Typical Block Shapes

Fig. 10.2. Typical sizes of blocks

(3.4) TESTS ON BLOCKS

Compressive Test

Apparatus: Compressive testing machine, weighing machine, ruler.

Procedure:

1. Remove the surface grit and projecting lips and record the dimensions and weight of

the specimen

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 per minute

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.

Absorption Test

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.

Procedure:

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 5 minutes, the unit needs not be

wetted, but if the blocks absorb the water in less than 5 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.

ACTIVITIES

1. Identify the common sizes of blocks.

2. Carry out tests on blocks and report on them.

ASSESSMENT

1. Proper reporting of the tests on the blocks.

WEEK 11 SETTING OUT OF A BUILDING

(4.1) INTRODUCTION

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 builders square method Surveying instruments.

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 ranging line.

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 first tape.

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

Advantages

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

and quick.

Disadvantages

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

buildings.

The Builders Square Method

Set out the front or building line in the usual manner with pegs or marks at the required distances.

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 building.

Transferring the builders 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

Advantages

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.

Disadvantages

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

screw.

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

Advantages

1. Can be used for large buildings with some accuracy.

2. Transfer of lines to profile boards done easily.

Disadvantages

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

tape measure.

ACTIVITIES

1. Set out a simple two bedroom flat using the three basic methods of setting out.

ASSESSMENT

1. Check the square of the angles set out using the respective method

WEEK 12 LAYING OF BLOCKS

(4.1) INTRODUCTION

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

of blocks.

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 external part.

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 spaces.

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

level

represents the ground floor level.

Fig. 11.1. Setting out of block wall

ACTIVITIES

1. Set out the block wall on a given foundation or floor slab.

2. Erect the wall up to at least three courses.

ASSESSMENT

1. Correct setting out of block work.

2. Proper alignment in horizontal and vertical direction.

WEEK 13 LAYING OF CONCRETE

(4.2) INTRODUCTION

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

concreting

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 avoid segregation

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.

Compaction

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

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 Compaction

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 ConcreteThe 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

short period.

ACTIVITIES

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.

ASSESSMENT

1. Depth and relevance of report to the concreting process.

2. Correct application of the concrete casting process.

WEEK 14 BONDING AND BLOCKWALL CONSTRUCTION

(5.1) INTRODUCTION

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

construction work.

(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 together.

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:

Stretcher bond Header bond English bond Flemish bond.

Stretcher Bond

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 English 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

importance.

Fig. 14.2. English Bond

ACTIVITIES

1. Lay blocks in stretcher bond

2. Lay bricks English bond up to three courses.

ASSESSMENT

1. Proper laying of the blocks and bricks in the appropriate bonds.

WEEK 15 BONDING AND BLOCKWALL CONSTRUCTION

CONTINUES

Flemish Bond

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 BondHeader 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 bondGarden 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 1 and 2 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 1 brick junction wall

adjoining a 2-brick such as 1 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

ACTIVITIES

1. Set out a brick wall and erect it in header bond up to three courses.

ASSESSMENT

1. Correct setting out of the brick wall and erection to the desired height.

CoverTable of ContentsWEEK 1 BLOCKLAYING AND CONRETING EQUIPMENTWEEK 2 BLOCKLAYING AND CONRETING EQUIPMENT CONTINUEDWEEK 3 CUTTING AND PLASTERING TOOLSWEEK 4 VENTILATION AND SAFETY IN THE WORKSOPWEEK 5 SAFETYWEEK 6 LAYOUT OF A BLOCK AND CONCRETING WORKSHOPWEEK 7 AGGREGATESWEEK 8 CONCRETE AND ADDITIVESWEEK 9 PRODUCTION OF CONCRETEWEEK 10 CONCRETE PRODUCTSWEEK 11 SETTING OUT OF A BUILDINGWEEK 12 LAYING OF BLOCKSWEEK 13 LAYING OF CONCRETEWEEK 14 BONDING AND BLOCKWALL CONSTRUCTIONWEEK 15 BONDING AND BLOCKWALL CONSTRUCTIONCONTINUESReturn to Table