1

UNESCO-NIGERIA TECHNICAL & VOCATIONAL EDUCATION

REVITALISATION PROJECT-PHASE II

YEAR I- SE MESTER II

THEORY

Version 1: December 2008

NATIONAL DIPLOMA IN

BUILDING TECHNOLOGY

BUILDING SCIENCE AND PROPERTIES OF MATERIALS II

COURSE CODE: BLD102

2

TABLE OF CONTENT

WEEK 1 1.0 Concert of heat

1.1 vibration of string (practical)

WEEK 2 2.0 Basic Principles of Sound Insulation and acoustic WEEK 3 3.0 Characteristic of light WEEK 4 4.0 Principles of Illumination WEEK 5 5.0 Properties of Different Species of Timber Week 6 6.0 preservation of timber 6.1site Visit (Preparation of Timber) WEEK 7 7.0 ferrous and non ferrous metals 7.1 Tensile And Hardness Test for Ferrous And Non

Ferrous metals WEEK 8 8.0 composition and properties of paint and varnishes 8.1 types of paint and manufacturing process WEEK 9 9.0 Glass and Glass products 9.1 Site Visit (Manufacturing Process of Glass Product).

3

WEEK 10 10. 0 Asphalt and bitumen (properties) 10.1 site view of asphalt plant WEEK 11 11.0 uses of asphalt and bitumen in building construction WEEK 12 12.0 Adhesive Glue (chemicals composition and uses) Week 13 13.0 Asbestos and Asbestos Products (manufacture and uses)

13.1 site visit to asbestos company WEEK 14 14.0 courses, effect and prevention of corrosion 14.1 practical (test on corrosion of iron) Week 15 15.0 Causes of Termites in Building 15.1damage and destruction by termites and prevention

4

BUILDING SCIENCE AND PROPERTIES OF MATERIALS II

Week 1 MICROSCOPIC PROPERTIES OF SOLID Introduction

Semiconductor: Material able to conduct electricity at room temperature more readily than an insulator, but less easily than a metal. Electrical conductivity, which is the ability to conduct electrical current under the application of a voltage, has one of the widest ranges of values of any physical property of matter. Such metals as copper, silver, and aluminum are excellent conductors, but such insulators as diamond and glass are very poor conductors (see Insulation). Semiconductors Substances which allow electricity to flow through them are called conductors. Example of conductors are metals (such as copper, silver, iron among other) salts and inorganic acids solutions. Substances which do not allow electricity to flow are called insulators. Examples are plastic materials, glass, wood, air, rubber, etc. Insulators therefore have high electric resistances while conductors have low electric resistances. In other words, electric conductivity is high in conductors and low in insulators. Certain materials have an electric resistance between the high value of the electric and the low value of conductors. In other words, the electric conductivity of such materials is intermediate in value between those of conductors and insulators. Such materials are therefore called semiconductors. Examples of such semiconductors are silicon and germanium.

Semiconductors: are materials which have an electric conductivity intermediate in value between that of pure metal (good conductor) and that of good insulators.

Semiconductors are widely used in the electric industries, e.g. in computers and communications. Semiconductors materials posses a crystalline structure, i.e. the atoms are arranged in an orderly manner. In both germanium and silicon each atom has four electrons orbiting in the outer most shell, and therefore are said to have four valence electrons. At low temperatures, pure semiconductors behave like insulators. Under higher temperatures, or with the addition of impurities, or in the presence of light, the conductivity of semiconductors can be increased dramatically. The physical properties of semiconductors are studied in materials science and condensed-matter physics.

5

FIGURE 1.1

CONDUCTION ELECTRONS AND HOLES

FIGURE 1.2 The common semiconductors include chemical elements and compounds such as silicon, germanium, selenium, gallium arsenide, zinc solenoid, and lead telluride. The increase in conductivity with temperature, light, or impurities arises from an increase in the number of conduction electrons, which are the carriers of the electrical current. In a pure, or intrinsic, semiconductor such as silicon, the valence electrons, or outer electrons, of an atom are paired and shared between atoms to make a covalent bond that holds the crystal together. (See Chemical Reaction). These valence electrons are not free to carry electrical current. To produce conduction electrons, temperature or light is used to excite the valence electrons out of their bonds, leaving them free to conduct current. Deficiencies, or holes, are left behind that also contribute to the flow of electricity. (These holes are said to be carriers of positive charge.) This is the physical origin of the increase in the electrical conductivity of semiconductors with temperature. The energy required to excite the electron and whole pair is called the energy gap. P-N Junction

6

When p-type and n-type semiconductor regions are adjacent to each other, they form a semiconductor diode, and the region of contact is called a p-n junction. (A diode is a two-terminal device that has a high resistance to electric current in one direction but a low resistance in the other direction.) The conductance properties of the p-n junction depend on the direction of the voltage, which can, in turn, be used to control the electrical nature of the device. Series of such junctions are used to make transistors and other semiconductor devices such as solar cells, p-n junction lasers, rectifiers, and many others. See Electronics; Rectification; Solar Energy. Semiconductor devices have many applications in electrical engineering. Microelectronic engineering developments have yielded small semiconductor chips containing hundreds of thousands of transistors. These chips have made possible a high degree of miniaturization and complexity of electronic devices. More efficient use of such chips has been developed through what is called complementary metal-oxide semiconductor circuitry, or CMOS, which consists of pairs of p- and n-channel transistors controlled by a single circuit. Advanced layered semiconductor materials can be made using techniques such as molecular-beam epitaxial.

7

WEEK 2 BUILDING STONE Types of Building Stones Gravel: for concrete mixture Sandstone concrete mixture or road work and walls Chips ashlartacin Marble Terrazzo Limestone cement Uses of Stones MARBLES Marble is a typical building stone. The physical properties are always regarded as very attractive and durable building stone. In recent years the use thin marble in the form of panel, slabs, through the wall units in curtain walling structures as become more prevalent. Commercially marble is any crystalline rock capable of taking a high polish and composed predominantly of one or more of the following materials: calcite, dolomite, serpentine. The physical properties of marble is the mean by laboratory, text are given in tables. Text also shows that flexural strength of marble is reduced after aging to compensate for the effect. the ultimate flexural strength of marble is considered to be half of each tested strength. To calculate the allowable stress in the design of transversely loaded wall, multiply one half the ultimate failure stresses by 40%. This produces a total safety of five which for marble safety is recommended for temporary cutting wall and veneer design. Where marble is used for stair treads, lintel or otherwise, as a load bearing materials, a safety factors of ten recommended. The actual strength of the marble being used should be determined and this value should be used for the final design. Classification of Marble Stones Marble has been classified by producers into four group A, B, C, D. Group A: These are sand marbles and stones with uniform and favorable working quality. Group B: There are marbles and stones similar to those of group A but with somewhat less favorable working qualities. They may have occasional natural faults. A limited amount of waxing and sticking may be necessary. Group C: are marble and stone with certain various qualities, geological flaws, voids, veins, lines of separation. Standard shop is to repair this variation of nature by sticking waxing or filing. Group D: are marbles and stones similar to group C subjects to the same method of finishing and manufacture but with a layer proportional of natural fault. These marble are used for monumental structural and veneer purposes. Marble which are exposed to the weather are generally selected from group A. marbles in group B, C & D are usually selected for their

8

color and decorative qualities. Occasionally carefully selected marble are use for surface exposed to weather. Lime Stone This is an important building stone and made of different type of stones which includes the following a. Oalitic limestone this is a calcite cement calcareous stone formed from shells, and

shell fragments particularly non-crystal in character. This limestone is free stone without cleavage plane processing uniformity of composition and tension. It processes high internal electricity adopting itself without damage to entrees temperature changes.

b. Polonites types: This is a limestone rich in Mg C03 (Magnesium carbonate) frequently

somewhat crystal in nature. it is found in ledge formation in a wide variation of color stones and texture. Generally speaking its crushing and tensile strength are greater than orlitic stone and its appearances shoes greater variety in texture.

c. Crystal type: it is predominantly compose of calcium carbonate crystalline. Thus not

of real crystalline nature, it has Characteristics of marbles It is high in crushing and tensile strength very low in absorption and usually shows a slight variation from a uniform light grey colour and smooth tension. Sandstone This is a sedimentary rock consisting usually of quartz cemented with silica iron oxide or calcium carbonate. Sand stone is durable has a very high crushing and tensile strength and a wide variation of crystal and tension. Sand stone are usually found in rich and mountain and usually used for veneer in Ashlatacin construction either in form of random rubber or of a regular facing.

Sandstone Quartzite Stone Quartzite stone compact granular rock compose of quartz crystal usually so homogenous and as hard as any granite rock. the stone is usually quarreled rock in stratified layers the surface of which are usually smooth. Its crisping and tensile strength are high the color range in wide. Stone Walling

9

Substitutes for natural stones are available in the form of cast-stone either as reconstructed or artificial stones or in form of worked stone such as Ashlars and Rubble walling in order to reduce the cost. Reconstructed Stone: Natural stone, sand and cement form the basic material sand reinforcement can be introduce during casting, special facing mixes permit a wide range of finishes. It eliminates the defect of natural stone but problem may arise through crazing (formation of fine hair cracks). Composite Walling: consist partly a facing material and partly of a structural Concrete. The facing is a mixture of fine aggregate of natural stone and pigmented cement to resemble the natural stone and have a minimum thickness of 20mm. Merit: they are cheaper than reconstructed stones but have the disadvantage that if damaged the concrete core may be a exposed. Ashlars Walling: this form of stone walling is composed of carefully worked stone s, regularly coursed ,bonded and set with tin joints and is used for the majority of High class facing work-in stone.

10

WEEK 3

CLASSIFICATION OF NATURAL STONES The rocks of earths crust may be classified in three main groups:

Primary(volcanic or igneous):Those which are been formed by the cooling and solidification of molten material in the earths crust. Example granite and basalt (finely crystalline in nature) Uses:- For casting in building work. Polish surfaces as a decorative finish in public and commercial buildings. Also in civil engineering work for the fencing of bridges, quays and other construction is requires Merits:- non porous hard and tough and of durable strength materials.

Secondary (Sedimentary): These small particles are swept down water courses and deposited in the beds in the localities where the flow of the streams slackens. Example quarrying and dressing stones or sand stone. Uses:- Decorative purpose e.g. bath stones, Shelly limestone and Portlandstones.etc.

Tertiary (Metamorphic) These are secondary rocks which have been change subsequent to their formation e.g. sandstone change to quartzites, limestone to marbles, clay to slates. Uses:- For decorative of building work. Properties; Impervious to water and capable of being split into sheet of uniform thickness.

QUARRYING AND DRESS STONES Almost all type of building has make use of stone and this stone include quartzite stone. This is a compact granular rock compose of quartz crystals usually cemented so as to make the mass modulus and as hard as any granite. The stone is generally quarried in stratified layers, the surfaces of which are usually smooth. Its crunching and stench (or trencher) is height and color range is wide.

Blue ridge Crab Orchard

Belmond Wall stone

11

Chestnut Fieldstone

Emerald Green Difference types of dress stones (Diagrams) Activities

Give an example of building faced with sandstone. State the name of the stone used, the location of the quarrying from which it was obtained, and whether the quarrying still produces stone for building purposes. Mention other building stones which come (or use to come) from the same area.

Indicate factors which are principally important in influencing the selection of natural stones for use in a building and describe briefly the use which is made of the various types of stones that are specially available for building purposes.

12

WEEK 4 MANUFACTURE OF CLAY PRODUCTS Introduction Clay is used in the manufacture of many building materials. Although this may have to be processed before the final product is got, nevertheless clay forms the bedrock of masonry construction. This building material include brick tiles, (both floor and roofing tiles) and wall tiles. However, the one common used is the burnt bricks used for block work. Manufacture of Clay Bricks Products

Ingredients:-These bricks are made from clay compose mainly of silica and alumina, with small of lime, iron manganese and other substances.

Kiln burnt:- fire is passed through a series of chambers. That is the bricks passes through a long chamber through a firing zone in the centre.

Hand made:- bricks are rather irregular in shapes and sizes with uneven arises; use for facing work and weather to attractive shapes.

Machine pressed:- the clay is fed into steel moulds and shapes under heavy pressure, with a continuous band and then cut into bricks by wire attached to a frame.

Clay Bricks In the manufacture of clay bricks, it is usual first to grind the clay with water to reduce the it to the required plasticity for moulding. Sometimes two or more types of clay are mixed in order to produce a more suitable material. The plastic clay is then moulded into bricks, which are dried and then burn at a temperature (about 850-11000C) in kilns. The burning process hardens the clay and gives the bricks the strength and durability required. Clays suitable for brick making are found associated with many geological formations. Nature of clay, methods of preparation, moulding and burning all influences the properties of clay bricks, but of these, methods of moulding probably exercises the greatest influence, and will be used as a basis of classification. Hand-Made Bricks. Bricks are moulded by hand from clay which contains sufficient water to render it thoroughly plastic, and the finished products usually have a high porosity (about 28-35%). Their durability is, however, quite satisfactory except where temperatures of burning are not high enough. Under- burned bricks may be recognized by their lightness in color and lack of ring when struck and should not be used for building work. Hand- made bricks are usually sand faced, since the moulds are dusted with sand to prevent the clay sticking. This gives to the bricks a surface texture which contribute greatly to their good appearance. Old bricks work in hand made bricks sometimes displays some variety of colour, due the fact that there was little effective control of fire condition in the old fire kilns. The modern demand for multicolor to imitate this effect is sometimes met by the addition of colouring pigments to the sand used on the mould faces, and much special colour effects are now obtained by this and similar devices. Good appearance is the principal advantage of hand made bricks, and it is this factor which enable them to maintain their position in the face of mechanization (see color in plate 1)

13

Diagrams of various types of clay products e.g. roofing tiles, floor tiles etc.

14

WEEK 5 BRICKS Brick, block of clay or other ceramic used for construction and decorative facing. Bricks may be dried in the sun but are more usually baked in a kiln. They cost relatively little, resist dampness and heat, and can last longer than stone. The color varies according to the clay used and in proportions according to architectural tradition. Some bricks are made of special fireclays for use in fireplaces or ovens. Others may be made of glass or they may be textured or glazed. Bricks may be arranged in various patterns, called bonds, according to the way the long sides (stretchers) or short sides (headers) are placed. The basic ingredient of brick is clay, finely grinded and mix with H20 molded and burnt in oven to form brick. One of the oldest materials known to man sizes and sharp of units have charge consider ably over the years and there is still some variation from one area to another, but as a result of consultation and co-operation along planners, designers, manufacturers and governmental authorities. a great deal have been accomplished in the way of standardization of bricks sized and in the application of principle of modular or co-ordination to the manufacture of bricks. Bricks Shape The best known shape in the bricks is known as common brick universally recognized as a brick shape in generally accepted set of dimension in addition. a no of shapes has been developed, some for special purpose and some for case of economic. Internationally, bricks type includes the following (1) D Roman (2) D Norman (3) Grant (4) Titan (T.T.W) through the wall (5) Norman (6) Sax Each shape has a range of width in which it is normally product in this country. Bricks types include the normal firm pat (N.F.S, (Solid), N.F.P (Perforated)). (1) BB3/4, BB3 BB2, however which ever the classification is base the essential ting is to

recognized them especially by there sizes. Exercises

Draw and named various types of bricks. State the different sizes used in the production of bricks.

15

WEEK 6

TYPE OF CEMENT

Ordinary Portland cement

Rapid Hardening Portland cement

Extra Rapid hardening Portland cement

Low heat Portland cement

Sulphate Resisting Portland cement

White Portland cement

Composition of Cement

Ordinary Portland Cement:- This consist of about 46% calcium tri silicates 24% dicalcium silicate, 11% tri calcium aluminates 7% tetra calcium aluminates ferrite 5%

gypsum (Calcium Sulphate it is grind so that it has about 300m2lkg on average (Bs 12

state that min as 225m2lkg).

Rapid Hardening Portland Cement:- The main difference is not that the final strength is hgher, but that of the strength is reached more quickly. In 3days a strength

equivalent To that of 3days ordinary Portland CaCO3 concrete strength may be obtain.

It consists of 74% calcium tri silicate 5% di calcium silicate. 5% tri calcium

aluminates, 4% tetra calcium aluminates, ferrite 5% gypsum. (Calcium Sulphate)

An increase in calcium tri silicate will increase the rate of strength but the CaCO3 is

usually grind more finely and 13s 12 states that it must have a minimum of surface

area of 325m2lkg. Because of its rapid hydration. It should not be used in mass

concrete where it might lead to a serious increase in temperature. It can be very useful

where rapid strength is needed to allow the removal and raise of form work. The price

is less, more than that of ordinary Portland CaCO3.

Extra Rapid Hardening Portland cement: - This is rapid hardening Portland CaCO3 with the addition of about 1-5% of calcium chloride (cac12) acceleration, ground in at

16

the manufacturing stage. Both setting and hardening are speeded off, with the result

that it must be placed immediately after mixing and more heat of hydration can be

executed in the earlier stages. This can be very useful for cold weather concreting. Its

two days strength often compare with the 3days strength of rapid hardening CaCO3 on

7days of ordinary Portland CaCO3. (O.P.C)

Unfortunately there is an increased shrinkage between the plastic stage and hardening

states.

Low Heat Portland CaCO3:- The heat of hydration even from (O.P.C) can lead to considerable rises in temperature in mass concrete particularly in hot weather. The

2compounds which hydrate most rapidly have been reduced. This does not affect the

ultimate strength is not slow. The specific surface should be greater than 320m2kg-1.

Sulphate Resisting Portland CaCO3:- All the compounds produce in Portland CaCO3 react to some extent with surface. By far the worst is the calcium sulphate aluminates

which has a volume about 2 times that tri calcium aluminates, and because of the

solid state of the concrete cause stresses and eventually disintegration.

The main culprits are the sulphate of Mg and Na particularly in condition of alternate

wetting and drying where their concentrate can become very high porous concrete

will far more than well compacted less porous concrete sulphate CaCO3 is produced

by the same method describe earlier but the amount of tri calcium aluminates by

Fe3O3 to the raw material at the kiln. The result is tetra calcium aluminates ferrite

formed instead of the tri calcium aluminates. Typical proportion are:- 45% tri calcium

silicate, 23% di calcium silicate, 2% tri calcium aluminates 18% tetra calcium

aluminates ferrite 45 gypsum. (Calcium Sulphate).

White Portland CaCO3 (Cement):- All the compounds are white except tetra calcium aluminates ferrite which is black. This explains the characteristics column of p.c. for

decorative purpose white and light colored finished may be required. White Portland

CaCO3 is China clay which is free from Fe2O3. Cost is rather higher due to need of

chines clay higher kiln temperature and the difficulties are grounding without

contamination with Fe. Colored CaCO3 may be produce either by grinding up to 10%

pigment at the work. Suitable color aggregate are needed and the cost can be high.

Lime and Mortar (manufacture)

17

Lime is manufactured by burning limestone or chalk and the result of this burning is a

dirty white lumpy material known as quicklime.

When quicklime is mixed with water a chemical change occurs during which heat is

generated in the lime and water, and the lime expands to about three times its former

bulk.

Quicklime must be slaked before it is used in mortar otherwise the mortar would increase

in bulk and squeeze out of the joints.

Lime for building is delivered to the site ready slaked and is termed hydrated lime.

Lime mixes; a lime mortar is usually mixed with 1 part of lime to 3parts of sand by

volume.

Mortar for general work is made from a mixture of cement, lime and sand in the

proportions set out in the table below

Mortar mixes

Mortar mix

Bricks concrete blocks

Internal walls & cavity

walls

5 5

Ext. walls (above d.p.c) 4 4

(below d.p.c) 3 3

Parapet walls, chimneys 2 3

Sills, retaining walls 1 2

Mortar mix 5-1:3:10:12

Cement 4-1:2:8-9

Lime 3-1:1:5-6

18

Uses of cement

Serves as a binding agent between bricks and blocks.

Use as a surface protection from weathering effect e.g.

plastering and rendering.

Basic requirements of mortar

It harden to such an extent that it can carry the weight normally carried by bricks without

crushing.

It should be sufficiently plastic when lay to take the variying sizes of bricks

It must have porousity similar that bricks and not deteriorate due to the weathering action.

Interacting Questions

State two materials used for binding in building construction.

Unwashed sand contains some quantities of clay, what then is the consequence of this mixture when this sand is delivered to site?

19

WEEK 7

MANUFACTURING PROCESS OF CEMENT

Neat cement paste shall be formed by gauging cement the quantity of water required

to give a paste of standard consistence.

The test block shall be made by filling the mould with paste

The mould shall be completely filled, and the surface of the paste shall be smoothed off

level with the top of the mould.

Clean appliances shall be used for gauging, and the temperature of the materials and that

of the test room, at the time when the operation are being performed, shall be 64-

740f(17.7-23.30C),in the atmosphere of at least 90% relative humidity and away from

draughts.

Site Testing (Hand) Of Cement

PROCEDURES:-

Examine to determine whether it is free from lumps and of a flour-like consistency ( free from dampness and reasonably fresh)

Place hand in cement and check if of blood heat then it is in satisfactory condition.

Settle with water at paste in a close jar to see whether it will expand or contract.

STORAGE OF CEMENT

Prior to the use of cement needs to be stored in damp proof and draught proof structure.

Staging of wood on floor before placement.

20

WEEK 8

CONCRETES PRODUCTION.

Workability as defined in the production of concretes is as follows:

- Compatibility: ease of compacting.

- Mobility: ease with which concrete can flow into moulds.

- Stability: ability to remain stable during handling and vibration without segregation of the

mix.

The water / cement ratio is the most important factor in concrete quality

It should be kept as low as possible consistent with sufficient workability to secure fully

compacted concrete with the equipment available on the site. The high the proportion of

water, the weaker will be the concrete. Water/cement ratio are usually in the range 0.40 to

0.60 (weight of water divided by the weight of cement). Allowance has to be made for

absorption by dry and porous aggregates and the surface moisture of weight aggregates.

Badly proportioned aggregates require an excessive amount of water to give adequate

workability, and these results in low strength and poor durability. A common test for

measuring workability on the side is the slump test, although for greater accuracy the

compacting factor test or consist meter test should be used.

Concrete mixes.

Concrete must be strong enough, when it has hardened, to resist the various stresses to which

it will be subjected and it often has to withstand weathering action. When freshly mixed it

must be of such a consistency that it can be readily handled without segregation and easily

compacted in the formwork. The fine aggregate (Sand) fills the interstices between the coarse

aggregate and both aggregates need to be carefully proportioned and graded.

The strength of concrete is influenced by a number of factors:

i. Proportional and type of cement.

ii. Type, proportion, grading and quality of aggregates

iii. Water cement.

21

iv. Method and adequacy of batching, mixing transporting, placing, compacting and curing

the concrete.

Concrete mixes can be specified by the volume or weight of the constituent materials or by

the minimum strength of the concrete.

22

WEEK 9

LIGHT WEIGHT CONCRETE AND NON-FINE CONCRETE.

This is concrete with density between 400 and 1760kgm-3 and it can be produced in three

ways;

i. By omitting the fine aggregates ( non fines)

ii. By using light weight aggregates.

iii. By aerating or foaming the concrete.

Advantages of Light Weight Concretes

i. It is used for thermal insulation.

ii. It is used as load bearing member, reduces design load greatly. This is because the

dead load of a result of this foundation is subjected to fewer loads than with dense

(normal) concrete use of light weight.

iii. Concrete produced with natural sand would be heavier but the weight and workability

will be greater as crushed light weight aggregate produces very hash mixes thus they

are more suitable for cast work concrete e.g. pre-cast blocks where compaction is

affected by pressure.

iv. Light weight aggregates concretes requires a high water (H2O) cement ratio and it is

essential to weight the aggregate properly before use to prevent absorbing H2O from

the mix.

v. Light weight aggregate concrete is used for internal partitioning either as load bearing

or non load bearing.

vi. Mix proportions are usually between 1:6 and 1:10 by volume.

Exercise

The students should generate the various demerits of Light weight concretes.

23

Differentiate between the light weight and non fine concretes.

24

WEEK 10 V-B CONSISTOMETER

Consistometer consisting of a vibrating table T, on which is fixed a cylindrical container C. A slump cone S(of size as for the slump which rest centrally in the container. A funnel F is held on a ;swivel arm, for filling with concrete. On the swivel arm on the opposite side is a rod R, holding the transparent disc D, with aa weight W(270g) including the rod and disc. Tamping rod, 16mmdiameter, 600mm long. Stop watch accuracy 0.5s. diagram

The cone is filled with concrete as for the slump test. The set screw G is loosened and the funnel is swung to one side. The surface of the concrete is struck off. The mould is removed carefully and the slump is measured if required. These can be done when the disc is swung round into position and lowered down the rod just to touch the slump concrete. The slump may read off the rod scale. With the arm fixed in these position, holding the disc resting on the concrete and with the stop watch ready, the watch is started the instant the vibration is begun ;and the watch is stopped at the moment the concrete has been fully compacted as observed through the disc, i.e. when the disc is fully covered underneath with cement grout. The result is the time in seconds recorded to nearest 0.5s being expressed as V-B degrees. An approximate guide to compacting factors, slump, and vebe degrees suitable for concrete for different purposes.

25

WEEK 11

SIEVE ANALYSIS

In selecting aggregates for concrete, it is principally important to avoid the following:

(a) The presence of impurities which will react with the cement and interfere with its

strength development (e.g. sulphate) or impurities which will cause staining (e.g. fine

coal particles) or crystallization (e.g. salt in sea shore sand).

(b) The presence of excessive amount of very fine material (passing no. 100 sieve) or of soft

particle which may break down during mixing. Very fine particle increases the water

requirement and reduces strength clay, silt; dust and organic matter are the principal

sources of fine material in aggregates.

(c) Badly graded aggregates containing an excessive proportion of particles of one size ( e.g.

sea shore sand stone )such aggregates cause trouble mainly when used alone (e.g. sand in

mortar or plaster, ballast in concrete). Where fine and coarse grain aggregates are

provided separately for concrete, there is less danger of bad grading of one them causing

trouble.

Impurities as mentioned in a above can usually be removed by efficient washing,

but the process requires a substantial plant and increase the cost of the aggregates.

The control of permissible quantity of fine material is not easy because a certain

quantity is desirable to improve plasticity of mixes, particularly for plastering and for

mortar for brick work, but increase of very fine material puts up the water requirements

very rapidly. There is, in consequence, a tendency for the men doing the work to prefer

too much for fine material and for those responsible for supervision to prefer too little. A

maximum of about 5% passing no 100 sieve in the case of sand is safe, though care must

be taken that the fine material does not include undesirable impurities.

Bad grading will usually be detected because it results in harsh mixes, difficult to

work. Where a well graded sand is difficult to find the locally, the difficulty may

sometimes be overcome without great expense by mixing two sands, a fine and coarse.

26

Week 12 Title: SOUNDNESS OF CEMENT TEST Objectives: To Determine the Soundness of cement test. Apparatus: le chatelier apparatus Diagram Procedure

mix10gofcementwiththequantityofwaterrequiredtogiveapasteofstandardconsistency,vigorouslyfor240sonanonporoussurfacebymeansoftwotrowels.

Placethemouldononeglassplateandfillitwiththepastetakingcaretokeepthesplitofthemouldgentlyclosedwhilethisoperationisbeingperformed.

Coverthemouldwithotherglass,uponwhichasmallweightisplaced. Immersethewholeimmediatelyinwateratatemperatureof20+10Candleavethesefor

twentyfourhours.

Removethemouldfromthewaterthenmeasurethedistanceseparatingtheindicatorpointstothenearest0.5mm.

Immersethewholeandbringthewatertoboilin2530minutesandkeepboilingfor1hour.

Removethemouldfromthewatertocool. Measurethedistanceseparatingtheindicatorpointtothenearest0.5mm.

Result

The difference between the two measurements represents the expansion of the cement to the nearest 1mm

27

Week 13 FIELD SETTING TEST TO DETERMINE SILT CONTENT Prepare an approximately 1m solution of common salt by dissolving 2.5g of sodium chloride in 250ml of tap water. Pour 50ml of this solution into a 250ml measuring cylinder and then add sand until the volume of sand is about 100ml; add more of the salt solution until the total volume in the measuring cylinder is 150ml. Placing the palm of the hand over the open end of the cylinder, shake vigorously, place on a level bench, tap until the sand surface is level. Allow to stand for three hours. Record the height of the sand, and of the silt above it.

Calculate the percentage of silt present. Report on the suitability of the sand as a fine aggregates in the preparation of

concrete.

Note: the presence of salt out and coagulates the colloidal particles which may be present and which otherwise would remain suspension in the water layer.

28

Week 14

TYPES OF IRON AND THEIR PROPERTIES

Pig Iron: This is the iron which is obtained directly from the blast furnace and it is quiet impure. It contains of up to 5% of carbon which is present both as graphite and

iron Carbide (Fe3C) together with impurities like phosphorous, Sulphur, silicon and

manganese in various proportions depending on the ore and operating temperature.

The presence of these impurities lowers the melting point of iron from 153oc to

1,200oc. Pig iron is hard and brittle and therefore has limited industrial uses.

Cast Iron: This is the iron that is obtained from pig iron which has been re-melted with some scrap iron and then cooled into moulds of required shapes.

Cast iron has a slightly lower percentage of impurities than pig iron and has almost

the same physical properties. It is brittle and cannot be welded or forged. Its use for

making object which do not require high tensile strength; for example cookers, stoves,

radiators, lamp post, railing, base of bunsin burner and certain types of machinery.

Cast iron is comparatively easy to melt and expand slightly when cooled. Thus, it fills

every part of the mould into which it is spoil.

Wrought Iron: This is the purest commercial form of iron, and it contains only about 0.1% carbon. Wrought Iron is obtained by heating cast iron in a furnace with haemitie

(Fe2O3). During this process, carbon and sulphur are oxidized and removed as carbon

dioxide and sulphur dioxide respectively.

2Fe2O3 + 3C 4Fe + 3CO2

2FeO3 + 3S 4Fe + 3SO2 Wrought iron is almost pure iron. Therefore it is soft but very tough and malleable. It

can be shaped by hammering at about 1000oC (about 500oC below its melting points).

It can be easily welded and forged.

It is used for making nails, chains, iron rods, iron sheets and agricultural implement

and core of electromagnet because it cannot be permanently magnetized.

Steel:- It is an alloy of iron containing a small but definite % of carbon and some other metals. The quantity of carbon in steel usually varies from 0.15% to 1.5%. Steel

is by far the most important form of commercial iron. The hardness and tensile

strength of steel depends largely on the % of carbon present and on how the carbon is

united with the iron. As a result several method are adopted for the production of

various types of steel; this includes (a) Bessemer process (b) Open Hearth process (c)

The electric furnace process.

29

The chemical reactions are involved in steel making. These can be described broadly

as follows:-

Pig iron is purifies until it consist largely on pure iron. Calculated amount are added generally in the form iron / carbon alloys. Other

substances like manganese are added to produce different types of steel.

Stainless steel which is very popular for its resistance to wear and especially

to rusting, contains a good % of chrome metal in some cases as high as 18%.

PROPERTIES OF METALS (FEROUS & NON-FERROUS)

Tensile Strength: The tensile strength of metal is a measure of its tenacity, and it isdeterminedbyclampingashortlengthofmetal(Steel)betweenthejawsofatensiletesting

machine.Thejawsaremadetopullinoppositedirectionsandthusimposepallingstresses

onthetestpiece,whichstretchesuntilitfinallybreaks.

Elasticity: This denotes the ability of amaterial to resume its normal shape after beingpushedorpulledoutofshape.

Rubber is a good example of an elastic material. Certain steeds, hard brass and hard

copper can be made into springs which possess elasticity, cast iron is not elastic to any

appreciable extents, and neither are lead or dead soft copper, or aluminum.

FusibilityorMeltingPoint:denotesthetemperatureatwhichametalchangefromitssolidstatetoamoltenliquid.Itshouldbenotedthatcastironmeltsatmuchlowerstemperature

thanmildsteel,whichisapurestformofiron.

Malleability:Thisdenotestheabilityofametaltobebossedorworkedtoshapewithoutbreaking.Heathasthispropertytoaremarkabledegree,whereasordinarycast iron isnot

appreciablymalleable.

The Metal Conductivity: Denotes a materials ability to transmit heat from particle toparticle throughout its mass or length. All metals possess through property, though to

differentdegrees.

ELECTRICALCONDUCTIVITY:Isapropertypossessedbyallmetals,thoughsomearebetterconductionsthanothers.CopperandAluminumaregoodconductorsofelectriccurrent.

30

CoefficientofThermalExpansion:Denotestheextenttowhichametalwillexpandwhenitstemperatureisraised10C.Theeffectoftheexpansionofmetalmustbecarefullyallowed

forinbuildingconstruction.

Ductility:Denotesthepropertyofstretchability,whichenablesametaltobeworked,andespeciallywiresor tubes tobedrawnwithoutbreaking.Annealedorsoftenedcopperand

aluminumareveryductile.

WorkHardening:Denotes that ametal, though ductile in the normal or soft statewillbecomegraduallyharderasitisworkeduponoftools;forexampleinbossingprocesses,Or

indrawingprocessesusedinwireortubemanufacture.

Annealing: is anotherway inwhich heat can affect the properties ofmetals, and it haspracticalapplication in theworkingof sheetofcopperandAluminumand thebendingof

tubes.

Creep:denotesthetendencyofmaterialstoflowundertheinfluenceofaload.Allmetalstendtocreep,andtheydosowhenthereisachangeinshapeofthemetalcrystals;when,

forexample,aheavyloadtendstosquashthemorastrongpulltostretchthemcreepistied

up with tenacity, hardness, and ductility and an increase in a metals temperature will

increaseitstendencytocreep.

Durability: Denotes the quality of lasting, and is therefore very important. Inorder formetalstobedurable,itisnecessarytoprovideartificialprotectioninsomeforme.g.paintor

galvanizing.

Colour:Isproducedasaresultofasurfacereflectingcertainlights.Asapropertyofmetals,itisimportantbecauseitisameansofidentification.

Tenacity:Denotesabilitytoresistpullingforces

31

Week 15

STEEL MAKING

Steel :- It is an alloy of iron containing a small but definite % of carbon and some other

metals. The quantity of carbon in steel usually varies from 0.15% to 1.5%. Steel is by far

the most important form of commercial iron. The hardness and tensile strength of steel

depends largely on the % of carbon present and on how the carbon is united with the iron.

As a result several method are adopted for the production of various types of steel; this

includes (a) Bessemer process (b) Open Hearth process (c) The electric furnace process.

The chemical reactions are involved in steel making. These can be described broadly

as follows:-

(A) Bessemer Process

The air used to supply the blast in a blast furnace is preheated to temperatures

between approximately 1350 and 1400 C (2450 and 2550 F). The heating is performed in

stoves, cylinders containing networks of firebrick. The bricks in the stoves are heated for

several hours by burning blast-furnace gas, the waste gases from the top of the furnace. Then

the flame is turned off and the air for the blast is blown through the stove. The weight of air

used in the operation of a blast furnace exceeds the total weight of the other raw materials

employed.

32

An important development in blast-furnace technology, the pressurizing of furnaces, was

introduced after World War II. By throttling the flow of gas from the furnace vents, the

pressure within the furnace may be built up to 1.7 atmosphere or more. The pressurizing

technique makes possible better combustion of the coke and higher output of pig iron. The

output of many blast furnaces can be increased by 25 per cent in this way. Experimental

installations have also shown that the output of blast furnaces can be increased by enriching

the air blast with oxygen, a level of 2.5 to 5 per cent being common.

The process of tapping consists of knocking out a clay plug from the iron hole near the

bottom of the bosh and allowing the molten metal to flow into a clay-lined runner and then

into a large, brick-lined metal container, which may be either a ladle or a rail car capable of

holding as much as 100 tonnes or more of metal. Any slag that may flow from the furnace

with the metal is skimmed off before it reaches the container. The molten pig iron is then

transported to the steel-making shop.

Modern blast furnaces are operated in conjunction with basic oxygen furnaces and

occasionally an electric arc furnace, or in a few countries the older open-hearth furnaces, as

part of a single steel-producing plant. In such plants the molten pig iron is used to charge the

steel furnaces. The molten metal from several blast furnaces may be mixed in a large mixer

vessel before it is converted to steel, to minimize any irregularities in the composition of the

individual melts.

Pig iron is purifies until it consist largely on pure iron. Calculated amount are added generally in the form iron / carbon alloys. Other

substances like manganese are added to produce different types of steel.

Stainless steel which is very popular for its resistance to wear and especially to rusting,

contains a good % of chrome metal in some cases as high as 18%.

Heat Treatment Of Iron

When steel is heated and cools at a certain temperature, certain quality are observed due to

heat treatment. When heat treatment produced equilibrium conditions a result of heating

followed by slow cooling this may give rise to (a) Annealing (b) Normalizing (c)

Hardening (d) Tempering.

33

Annealing

This process is applied to steel to remove stress, produce uniformity and induced softness so

that it can be cold work. Cold working implies bending, rolling etc. at room temperature for

example overhead cables. (Annealing involves the heat treatment of the steel) and then very

slowly cooled at room temperature. The cooling of the steel should be controlled by packing

them in refactory line and sealed boxes.

Normalizing

Steel is normalized to produce a fine grain, uniformity of structure improved mechanical

properties. Normalizing is usually performed after forging or casting to put steel in best

conditioned for machining or hardening.

The process of normalizing is similar to annealing but the heating and socking are carried out

at a temperature high enough to ensure a fully austenitic structure is produced before the free

cooling in steel air that follows:

The authentic temperature of steel is from 700oCtemperature upward. In other words, the

steel should be treated to about 700oCupwards before cooling it in still air.

Hardening

In this process, the steel is heated to a suitable temperature (depending on the carbon content)

to produce ore, or sufficient austenitic head at that temperature so that each temperature is

uniform across its section and then quenched. The rate of quenching is controlled by the

quenching medium, a solution of salt or caustic soda in H2O and oil produces intermediate

quenches and a common quenching media.

TEMPERING

After hardening, steel is usually related to a suitable of sub critical temperature to improve

their toughness and ductility at the expense of hardness and strength to make the more

suitable for service requirement. The tempering temperature depends upon the particular

combination of properties required, it is about 180oC. The direction of the heating depends

upon the thickness of the materials and the cooling is usually in air to avoid the destruction of

the part. As already stated the overall effect of hardening and tempering depends upon the

carbon content of the steel, the rate of quenching during the hardening process:

34

Rolling process of steel finishing

Steel is marketed in a wide variety of sizes and shapes, such as strip in coils, strip cut to

sheet, plate, bars or rods, pipes, railway rails, tees, channels, and I-beams. These shapes are

produced at mills by rolling. This working of steel also improves its quality by refining its

crystalline structure and making the metal tougher.

The basic process of working steel is known as hot rolling. In hot rolling, the cast steel is first

heated to bright-red heat in a furnace and is then passed between a series of pairs of metal

rollers that squeeze it to the desired size and shape. The separation between the rollers

diminishes for each successive mill stand (pair of rollers). As the steel is reduced in thickness

it becomes longer, but the width stays almost unchanged. In a modern continuous mill, a

dozen or more rolling stands are placed in a long line. As a length of steel passes through

these stands, it is simultaneously rolled in more than one stand. This requires careful

matching of the stand speeds, which most increase down the line to match the growing length

of the rolled steel.

When ingot or continuously cast bloom steel is rolled, the first mill stand is called the

blooming mill. From the blooming mill, the steel is passed on to roughing mills and finally to

finishing mills that reduce it to the correct cross-section. The rollers of mills that produce

railway rails and such structural shapes as I-beams, H-beams, and angles are grooved to give

the required shape.

35

Modern manufacturing requires a large amount of sheet steel. Continuous mills roll steel strip

in widths up to about 1.8 m (5.9 ft). The first stage of rolling is hot rolling. A slab of hot steel

at a temperature of about 1050 C (1920 F) and up to 250 mm (9 in) thick is fed through a

series of rollers that reduce it progressively in thickness to 2 to 3 mm and increase its length

from 4 m (13 ft) to 370 m (1,210 ft). Continuous mills are equipped with a number of

accessory devices, including edging rollers, descaling devices, and devices for automatically

coiling the strip after rolling when it reaches the end of the mill. The edging rollers, normally

located on the first five or six stands, consist of sets of vertical rolls set opposite each other at

either side of the strip to ensure that the width is maintained. Descaling apparatus removes

the oxide scale that forms on the surface of the sheet by knocking it off mechanically,

loosening it by means of high-pressure water sprays, or bending the sheet sharply at some

point in its travel. Following hot rolling, the oxidized surface is cleaned by passing the strip

through tanks of acid, followed by a rinse in water. The strip is then ready for cold rolling to

its final dimension, which is generally from 1 mm to as little as 0.05 mm thick. The cold mill

is also a continuous mill, consisting of four or five mill stands that are kept very clean, the

rolls being sprayed with a lubricant to help give the steel a bright polished surface. At the end

of the cold mill, the strip is wound into a coil and taken to annealing furnaces to soften it, as

cold rolling makes it too hard for shaping into, for example, parts of a car body. Annealing

can be carried out in batch furnaces with the strip still wound in a coil, or in continuous

annealing lines, where the strip is unwound and fed through a long furnace. In both cases, an

inert atmosphere is used to prevent oxidation of the steel. The continuous line is quicker,

requires less manpower, and imparts more uniform properties to the steel, but its capital cost

is much higher than batch annealing furnaces and it is less flexible, requiring large tonnages

36

of similar steels to be processed by joining the head of one coil to the tail of the coil in front

to form a continuous band travelling through the line, which may be up to 600 m (1,970 ft)

long. Following annealing, the steel is lightly reduced by 1 to 2 per cent on a single mill to

improve its surface properties.

Since its introduction in 1989, the thin slab linked mill has offered a more efficient way to

produce thin sheet steel in some electric steel-making mills. The starting slab is cast between

50 and 150 mm thick, instead of the conventional 250 mm, and the caster passes the slab

directly to the rolling mill, travelling through a temperature-equalizing furnace on the way.

This provides a significant time and energy saving. The mill is also smaller, since the hot

blooming stand (for ingot-rolling mills) and the roughing mills are not required, reducing the

number of mill stands to between 4 and 6, from the 12 to 14 in a typical conventional mill.

This provides a reduction in capital cost to build the mill and in maintenance costs to run it.

This type of mill is rapidly proliferating, with installed capacity or capacity on order reaching

35 million tonnes in 1995. At present, the surface quality of the steel is not as good as that

rolled on conventional mills, but it is suitable for many applications in the construction

industry, unseen parts of a car, such as suspension brackets, and for general-purpose welded

pipe production.

About half of all strip steel produced today is coated in the mill after rolling to improve its

corrosion resistance. Zinc is most commonly used, but zinc with a few per cent of aluminium

or nickel is also sometimes applied. Zinc coatings can be applied by passing the strip through

a bath of molten zinc, the thickness of the coating being accurately controlled by a continuous

blast of nitrogen played across the surface of the strip as it leaves the zinc pot. Alternatively,

the coating can be applied by electrodeposition, in which the steel strip is made the cathode

of a giant electrode, as it passes between anodes of the metal or alloy to be deposited on the

steel in a series of tanks containing an electrolyte. Zinc and zinc-nickel alloy coatings are

deposited in this way, as well as chromium coatings and tin coatings.

Paint coatings or varnishes may be applied on top of zinc-coated strip for such applications as

cladding for buildings, kitchen appliances (called white goods), or electrical equipment such

as computer cases and music systems.

Classifications of Steel

Steels are grouped into five main classifications.

37

A Carbon Steels

More than 90 per cent of all steels are carbon steels. They contain varying amounts of carbon.

Steels to make sheet for car bodies, domestic appliances, cans, and so on have very low

carbon contents, typically 0.04 per cent or less. Structural steels and steels for engineering

applications have carbon levels up to about 0.8 per cent, while very hard steels for

applications such as hand-working tools may have carbon contents up to 1.4 per cent. Other

elements present are: manganese at not more than 1.65 per cent, 0.60 per cent silicon, and

small amounts of sulphur and phosphorus. In steels made from 100 per cent scrap there are

also significant levels of copper and tin, which are detrimental to their properties. Machines,

car bodies, most structural steel for buildings, ship hulls, bedsprings, and hairgrips are among

the products made of carbon steels.

B Alloy Steels

These steels have a specified composition, and contain, in addition to carbon, specific

quantities of alloy additions such as vanadium, molybdenum, or other elements, as well as

larger amounts of manganese, silicon, and copper than do the regular carbon steels. Vehicle

gears and axles, roller skates, and carving knives are some of the many things that are made

of alloy steels.

C High-Strength Low-Alloy Steels

These, called HSLA steels, are the newest of the five chief families of steels. They cost less

than the regular alloy steels because they contain only small amounts of the expensive

alloying elements. They have been specially processed, however, to have much more strength

than carbon steels of the same weight. For example, railway freight wagons made of HSLA

steels can carry larger loads because their walls are thinner than would be necessary with

carbon steel of equal strength; also, because an HSLA wagon is lighter than an ordinary one,

it is less of a load for the engine to pull. Numerous buildings are now being constructed with

frameworks of HSLA steels. Girders can be made thinner without sacrificing their strength,

so that additional interior space is left in the building.

D Stainless Steels

Stainless steels contain chromium, or a combination of chromium and nickel, as well as

significant amounts of other alloy additions such as molybdenum. The chromium content is

generally greater than 12 per cent, and it is this alloy element that chiefly keeps the steel

bright and rust resistant in spite of moisture or the action of corrosive acids and gases. The

presence of nickel further improves corrosion resistance, as does molybdenum. When the

38

nickel content is above about 8 per cent, the crystal structure of the steel changes, imparting

properties that make it suitable for very-low-temperature (cryogenic) applications. Also,

nickel-containing steels are non-ferromagnetic, which is important for such applications as

components for geophysical surveying equipment and full-body X-ray scanners where

magnetic steels would distort the X-ray paths. Some stainless steels are very hard; some have

unusual strength and will retain that strength for long periods at extremely high or low

temperatures. Because of their lustrous surfaces, architects often use them for decorative

purposes. Stainless steels are used for the pipes and tanks of petroleum refineries and

chemical plants, for jet planes, and for space capsules. Surgical instruments and equipment

are made from these steels, and they are also used to patch or replace broken bones because

the steels can withstand the action of body fluids. In kitchens and in workplaces where food

is prepared, handling equipment is often made of stainless steel because it does not taint the

food and can easily be cleaned.

E Tool Steels

These steels are made into many types of tools for use in powered machinery such as drills,

lathes, milling machines, and metal-cutting saws, where friction during use causes the

temperature of the tool to rise as high as 500 C (930 F). They contain tungsten,

molybdenum, and other alloying elements that give them extra strength, hardness, and

resistance to wear at high temperatures.

CoverTable of ContentsWeek 1Week 2Week 3Week 4Week 5Week 6Week 7Week 8Week 9Week 10Week 11Week 12Week 13Week 14Week 15Return to Table