GUJARAT TECHNOLOGICAL UNIVERSITY

Unit – 1

Introduction to Civil Engineering and Civil Engineering Materials

Question bank

1. Describe the Scope of Civil Engineer?

Answer:

The main scope of civil engineering or the task of civil engineering is planning, designing, estimating, supervising construction, managing construction, execution, and maintenance of structures like building, roads, bridges, dams, etc. ' One who designs and maintains works of public utility is known as civil engineer. Civil engineer should have qualities like scientific attitude, imaginative and intuitive approach, He should have good analysis and decision power. He should be able to solve engineering problems, by using mathematical modelling, scientific principles and laboratory techniques using computer and information technology. He should be able to use operation research techniques for solution of management problems.

2.     Explain the Branches in civil engineering?

Answer:

Civil engineering is the design, implementation, and maintenance of public works. This involves facilities and structures such as arenas, large scale monuments, government buildings, transportation routes as well as other structures. Engineers will either work for the city or for a private firm that has been hired by the city. Some civil engineers work in the private sector on projects for independent companies. There are several types of civil engineering. A civil engineer can specialize in a number of different civil engineering branches. Those branches are described briefly below:

• Structural Engineering
• Geotechnical Engineering
• Environmental Engineering
• Transportation Engineering
• Water Resource Engineering
• Earthquake Engineering
• Material Engineering
• Construction Engineering
• Surveying
• Municipal Engineering
• Coastal Engineering
• Tunnel Engineering

Scope of Civil Engineering Civil engineering is the oldest branch of engineering which is growing right from the stone age of civilization. American society of civil engineering defines civil engineering as the profession in which a knowledge of the mathematical and physical sciences gained by study, experience and practice is applied with judgment to develop ways to utilize economically the materials and forces of the nature for the progressive well being of man.

3.     What are the Role of Civil Engineers in various construction activities?

Answer:

A civil engineer has to conceive, plan, estimate, get approval, create and maintain all civil engineering activities.

Civil engineer has very important role in the development of the following infrastructure:

• Measure and map the earth’s surface.
• Plan new townships and extension of existing towns
• Build the suitable structures for the rural and urban areas for various utilities
• Build tanks and dams to exploit water resources.
• Build river navigation and flood control projects.
• Provide and maintain communication systems like roads, railways, harbours and airports
• Purify and supply water to the needy areas like houses, schools, offices etc.
• Build canals and distributaries to take water to agricultural fields
• Devise systems for control and efficient flow of traffic
• Provide and maintain solid and waste water disposal system
• Monitor land, water and air pollution and take measures to control them

Fast growing industrialization has put heavy responsibilities on civil engineers to preserve and protect environment.

4.     What is CEMENT? What are the uses of cement? And explain the engineering properties of cement?

Answer:

Cement is a binder, a substance that sets and hardens and can bind other materials together. Cements used in construction can be characterized as being either hydraulic or non-hydraulic, depending upon the ability of the cement to be used in the presence of water. Non-hydraulic cement will not set in wet conditions or underwater, rather it sets as it dries and reacts with carbon dioxide in the air. It can be attacked by some aggressive chemicals after setting. Hydraulic cement is made by replacing some of the cement in a mix with activated aluminium silicates, pozzolanas, such as fly ash. The chemical reaction results in hydrates that are not very water-soluble and so are quite durable in water and safe from chemical attack. This allows setting in wet condition or underwater and further protects the hardened material from chemical attack (e.g., Portland cement).

USE OF CEMENT

• Cement mortar for Masonry work, plaster and pointing etc.
• Concrete for laying floors, roofs and constructing lintels, beams, weather shed, stairs, pillars etc.
• Construction for important engineering structures such as bridge, culverts, dams, tunnels, light house, clocks, etc.
• Construction of water ,wells, tennis courts, septic tanks, lamp posts, telephone cabins etc.
• Making joint for joints, pipes , etc.
• Manufacturing of precast pipes, garden seats, artistically designed wens, flower posts, etc.
• Preparation of foundation, water tight floors, footpaths, etc.

ENGINEERING PROPERTIES OF CEMENT

Fineness

• This test is carried out to check proper grinding of cement.  The fineness of cement particles may be determined either by sieve test or permeability apparatus test.
• In sieve test ,the cement weighing 100 gm is taken and it is continuously passed for 15 minutes through standard BIS sieve no. 9.The residue is then weighed and this weight should not be more than 10% of original weight.
• In permeability apparatus test, specific area of cement particles is calculated. This test is better than sieve test. The specific surface acts as a measure of the frequency of particles of average size.

Compressive strength

• This test is carried out to determine the compressive strength of cement.
• The mortar of cement and sand is prepared in ratio 1:3.
• Water is added to mortar in water cement ratio 0.4.
• The mortar is placed in moulds. The test specimens are in the form of cubes and the moulds are of metals. For 70.6 mm and 76 mm cubes ,the cement required is 185gm and 235 gm respectively.
• Then the mortar is compacted in vibrating machine for 2 minutes and the moulds are placed in a damp cabin for 24 hours.
• The specimens are removed from the moulds and they are submerged in clean water for curing.
• The cubes are then tested in compression testing machine at the end of 3days and 7 days. Thus compressive strength was found out.

Consistency

• The purpose of this test is to determine the percentage of water required for preparing cement pastes for other tests.
• Take 300 gm of cement and add 30 percent by weight or 90 gm of water to it.
• Mix water and cement thoroughly.
• Fill the mould of Vicat apparatus and the gauging time should be 3.75 to 4.25 minutes.
• Vicat apparatus consists of a needle is attached a movable rod with an indicator attached to it.
• There are three attachments: square needle, plunger and needle with annular collar.
• The plunger is attached to the movable rod. The plunger is gently lowered on the paste in the mould.
• The settlement of plunger is noted. If the penetration is between 5 mm to 7 mm from the bottom of mould, the water added is correct. If not process is repeated with different percentages of water till the desired penetration is obtained.

Setting time

• This test is used to detect the deterioration of cement due to storage. The test is performed to find out initial setting time and final setting time.
• Cement mixed with water and cement paste is filled in the Vicat mould.
• Square needle is attached to moving rod of vicat apparatus.
• The needle is quickly released and it is allowed to penetrate the cement paste. In the beginning the needle penetrates completely. The procedure is repeated at regular intervals till the needle does not penetrate completely. (up to 5mm from bottom)
• Initial setting time equal to or less than 30min for ordinary Portland cement and 60 min for low heat cement.
• The cement paste is prepared as above and it is filled in the Vicat mould.
• The needle with annular collar is attached to the moving rod of the Vicat apparatus.
• The needle is gently released. The time at which the needle makes an impression on test block and the collar fails to do so is noted.
• Final setting time is the difference between the time at which water was added to cement and time as recorded in previous step ,and it is equal to or less than 10hours.

Soundness

• The purpose of this test is to detect the presence of un combined lime in the cement.
• The cement paste is prepared.
• The mould is placed and it is filled by cement paste.
• It is covered at top by another glass plate. A small weight is placed at top and the whole assembly is submerged in water for 24 hours.
• The distance between the points of indicator is noted. The mould is again placed in water and heat is applied in such a way that boiling point of water is reached in about 30 minutes. The boiling of water is continued for one hour.
• The mould is removed from water and it is allowed to cool down.
• The distance between the points of indicator is again measured. The difference between the two readings indicates the expansion of cement and it should not exceed 10 mm.

Tensile strength

• This test was formerly used to have an indirect indication of compressive strength of cement.
• The mortar of sand and cement is prepared.
• The water is added to the mortar.
• The mortar is placed in briquette moulds. The mould is filled with mortar and then a small heap of mortar is formed at its top . It is beaten down by a standard spatula till water appears on the surface. Same procedure is repeated for the other face of briquette.
• The briquettes are kept in a damp for 24 hours and carefully removed from the moulds.
• The briquettes are tested in a testing machine at the end of 3 and 7 days and average is found out

5.     What are bricks? What are the uses of bricks? And explain the engineering properties of bricks?

Answer:

BRICKS

Constituents of good brick earth: Bricks are the most commonly used construction material. Bricks are prepared by moulding clay in rectangular blocks of uniform size and then drying and burning these blocks. In order to get a good quality brick, the brick earth should contain the following constituents.

• Silica
• Alumina
• Lime
• Iron oxide
• Magnesia

Brick plays very important role in the field of civil engineering construction. Bricks are used as an alternative of stones in construction purpose.

• USES OF Bricks

1. Construction of walls of any size
2. Construction of floors
3. Construction of arches and cornices
4. Construction of brick retaining wall
5. Making Khoa (Broken bricks of required size) to use as an aggregate in concrete
6. Manufacture of surki (powdered bricks) to be used in lime plaster and lime concrete

• ENGINEERING PROPERTIES OF Bricks

To know the quality of bricks following 7 tests can be performed. In these tests some are performed in laboratory and the rest are on field.

• Compressive strength test
• Water Absorption test
• Efflorescence test
• Hardness test
• Size, Shape and Colour test
• Soundness test

Structure test Compressive strength test

This test is done to know the compressive strength of brick. It is also called crushing strength of brick. Generally 5 specimens of bricks are taken to laboratory for testing and tested one by one. In this test a brick specimen is put on crushing machine and applied pressure till it breaks. The ultimate pressure at which brick is crushed is taken into account. All five brick specimens are tested one by one and average result is taken as brick’s compressive/crushing strength.

Water Absorption test In this test bricks are weighed in dry condition and let them immersed in fresh water for 24 hours. After 24 hours of immersion those are taken out from water and wipe out with cloth. Then brick is weighed in wet condition. The difference between weights is the water absorbed by brick. The percentage of water absorption is then calculated. The less water absorbed by brick the greater its quality. Good quality brick doesn’t absorb more than 20% water of its own weight.

Efflorescence test The presence of alkalies in bricks is harmful and they form a grey or white layer on brick surface by absorbing moisture. To find out the presence of alkalis in bricks this test is performed. In this test a brick is immersed in fresh water for 24 hours and then it’s taken out from water and allowed to dry in shade. If the whitish layer is not visible on surface it proofs that absence of alkalis in brick. If the whitish layer visible about 10% of brick surface then the presence of alkalis is inacceptable range. If that is about 50% of surface then it is moderate. If the alkalies’ presence is over 50% then the brick is severely affected by alkalies.

Hardness test

In this test a scratch is made on brick surface with a hard thing. If that doesn’t left any impression on brick then that is good quality brick.

Size, shape and colour test

In this test randomly collected 20 bricks are staked along lengthwise, width wise and height wise and then those are measured to know the variation of sizes as per standard. Bricks are closely viewed to check if its edges are sharp and straight and uniform in shape. A good quality brick should have bright and uniform colour throughout.

Soundness test

In this test two bricks are held by both hands and struck with one another. If the bricks give clear metallic ringing sound and don’t break then those are good quality bricks.

Structure test In this test a brick is broken or a broken brick is collected and closely observed. If there are any flows, cracks or holes present on that broken face then that isn’t good quality brick.

6.     What are the uses of stones? And explain the engineering properties of stones?

Answer:

STONES

• USES OF STONES

1. Stone masonry is used for the construction of foundations, walls, columns and arches.
2. Stones are used for flooring.
3. Stone slabs are used as damp proof courses, lintels and even as roofing materials.
4. Stones with good appearance are used for the face works of buildings. Polished marbles and granite are commonly used for face works.
5. Stones are used for paving of roads, footpaths and open spaces round the buildings.
6. Stones are also used in the constructions of piers and abutments of bridges, dams and retaining walls.
7. Crushed stones with graved are used to provide base course for roads. When mixed with tar they form finishing coat.

Crushed stones are used in the following works also:

1. As a basic inert material in concrete.
2. For making artificial stones and building blocks.
3. As railway ballast.

• ENGINEERING PROPERTIES OF STONES

1. STRUCTURE

The structure of the stone may be stratified (layered) or unstratified. Structured stones should be easily dressed and suitable for super structure. Unstratified stones are hard and difficult to dress. They are preferred for the foundation works.

2. TEXTURE

Fine grained stones with homogeneous distribution look attractive and hence they are used for carving. Such stones are usually strong and durable.

3. DENSITY

Denser stones are stronger. Light weight stones are weak. Hence stones with specific gravity less than 2.4 are considered unsuitable for buildings.

4. APPEARANCE

A stone with uniform and attractive colour is durable, if grains are compact. Marble and granite get very good appearance, when polished. Hence they are used for face works in buildings.

5. STRENGTH

Strength is an important property to be looked into before selecting stone as building block. Indian standard code recommends, a minimum crushing strength of 3.5 N/mm2 for any building block

6. HARDNESS

It is an important property to be considered when stone is used for flooring and pavement. Coefficient of hardness is to be found by conducting test on standard specimen in Dory’s testing machine. For road works coefficient of hardness should be at least 17. For building works stones with coefficient of hardness less than 14 should not be used.

7. PERCENTAGE WEAR

It is measured by attrition test. It is an important property to be considered in selecting aggregate for road works and railway ballast. A good stone should not show wear of more than 2%.

8. POROSITY AND ABSORPTION

All stones have pores and hence absorb water. The reaction of water with stone causes disintegration. Absorption test is specified as percentage of water absorbed by the stone when it is immersed under water for 24 hours. For a good stone it should be as small as possible and in no case more than 5.

9. WEATHERING

Rain and wind cause loss of good appearance of stones. Hence stones with good weather resistance should be used for face works.

10. TOUGHNESS

The resistance to impact is called toughness. It is determined by impact test. Stones with toughness index more than 19 are preferred for road works. Toughness index 13 to 19 is considered as medium tough and stones with toughness index less than 13 are poor stones.

11. RESISTANCE TO FIRE

Sand stones resist fire better. Argillaceous materials, though poor in strength, are good in resisting fire.

12. EASE IN DRESSING

Cost of dressing contributes to cost of stone masonry to a great extent. Dressing is easy in stones with lesser strength. Hence an engineer should look into sufficient strength rather than high strength while selecting stones for building works.

13. SEASONING

The stones obtained from quarry contain moisture in the pores. The strength of the stone improves if this moisture is removed before using the stone. The process of removing moisture from pores is called seasoning. The best way of seasoning is to allow it to the action of nature for 6 to 12 months. This is very much required in the case of laterite stones.

7.     What is timber? What are the uses of timber? And explain the engineering properties of timber?

Answer:

TIMBER

TIMBER is the oldest material used by humans for construction after stone. Despite its complex chemical nature, wood has excellent properties which lend themselves to human use. It is readily and economically available; easily machinable; amenable to fabrication into an infinite variety of sizes and shapes using simple on-site building techniques;

• Exceptionally strong relative to its weight
• A good heat and electrical insulator
• It is a renewable and biodegradable resource

A tree basically consists of three parts namely, trunk, crown and roots. The function of the trunk is to support the crown and to supply water and nutrients from the roots to the leaves through branches and from the leaves back to the roots .The roots are meant to implant the trees in the soil ,to absorb moisture and the mineral substances it contains and to supply them to the trunk.

The quality of timber must be ensured before using it for a purpose. The quality can be ensured by investigating the properties of timber. Here we have discussed both physical and mechanical properties of timber which affects timber quality.

Followings are the physical and mechanical properties of Timber

• Colour
• Appearance
• Hardness
• Specific Gravity
• Moisture Content
• Grain
• Shrinkage and Swelling
• Strength
• Density
• Toughness
• Elasticity
• Warping
• Durability
• Defectless
• Workability
• Soundness
• Free of abrasion

Colour

Color is a uniform property by which most trees are characterized as they show variation from tree to tree. Light color indicates weak timber. For example, freshly cut teak, Deodar, and Walnut have a golden yellow, whitish and dark brown shades respectively.

Appearance

Smell is a good property as timbers for few plants as they can be identified by their characteristic aroma. Fresh cut timbers have a good smell. For example resinous smell from pine.

Hardness

For the resistance of any kind of damage, hardness is an obvious property.

Specific Gravity

Variation of timber in specific gravity (0.3-0.9) is found. It depends on pores present inside timber. The specific gravity of this light material is less than that of water (<1). But in case of compact wood where pores are almost absent and become heavier, their specific gravity increases up to 1.5.

Moisture Content

Timbers are hygroscopic and gain water from nature (atmosphere). The absorption of water or dehydration depends on atmospheric humidity. If timbers moisture content is high that means the timber quality is low. Water content is the risk of fungal attack.

Grain

Several types of grain arrangement found. On the grain structure quality of timber varies. Grains remain closely related.

1. Straight grain: Arrangement of vascular tissue (xylem and phloem) is important which grow parallel to the length of the timber that is termed as straight grain.
2. Coarse grain: vascular tissue and fibre arranged broadly and widely.
3. Interlocked grain: Instead of parallel arrangement twisted, a spiral arrangement may be found.

Shrinkage and Swelling

The percentage of shrinkage and swelling varies from plant to plant. Some give higher percentage after drying. Shrinkage starts when cell walls of timber start to release water. In moisture atmosphere timber swells when cell walls absorb water. Good quality timbers swell less. Timbers having thicker wall swell more than a thinner one.

Strength

Best quality timbers have the highest strength. Strength means capable to bear loads. Anisotropic material like timber has different structure at the different portion. So, the strength of timber is different at different points. Grain structure determines the strength of the timber. Some types of strength are

1. Compressive strength: 500 kg/cm2 to 700 kg/cm2 load is enough to test timbers strength.
2. Tensile strength: When timber is enough strong to the tensile force. If perpendicular force is made then timber is weaker. 500-2000 kg/cm2 is the range of tensile strength load.
3. Transverse strength: Enough bending strength indicates good quality timber.

Density

Timber having higher density have a thicker wall. An important property that quality of timber. Moisture content: Presence of defects: There may be some of the natural and artificial defects in timber such as cross-grain, knots, and shakes, etc. All of them cause a decrease in the strength of the timber.

Toughness

Timber has to have the capability to bear shocks, jerk. Anti-bending and ant splitting characteristic is needed. Old timbers have annual rings which indicate their age is a good indicator.

Elasticity

Another property elasticity means timber should attain its own shape after use. Because of this quality, it is used in sports bat.

Warping

Environmental change with season can’t effect good quality timber.

Durability

A good quality timber has the property to resist the attack the infection of fungus or other insects. This resistance quality makes timber better.

Defectless

This property is gained if the timber is from a sound tree. A defectless tree is free from sap, shakes, and dead knots.

Workability

A good timber is always easy to work on it. Easy to drag using saw on good timber. The finishing can be done well.

Soundness

A good quality timber gives good sound.

Texture

The texture of good timber is fine and even.

Free of Abrasion

Timber should not be damaged by the external environment. It has to gain the ability to protect its skin.

Wood is a plant part having multipurpose uses those are impossible to deny and difficult to note all in our daily life. From the ancient time wood is used by human and this continuation still remains in the modern civilization. A few of many uses of wood are mentioned below:

1. Construction and Fencing

• Home Construction:

During the early periods, use of wood in domestic construction was a common scene and this is still followed in this twenty-first century. In different parts of the world in the making of houses, wood is used commonly like the flooring, frames of doors and windows for its strength and internment quality. e.g. Deodar, walnut wood is used in Pakistan widely, teak in South Asia and all over the world, Chir pine etc. In Bangladesh during construction of buildings woods from mango,bur flower tree are used for casting and piling.  

• Fencing and Decorating Gardens:

In modern decoration system woods are also used for building the fencing and simple decoration for artificial gardening inside a home or on roofs.
E.g. Cedar, redwood, Shorea sp, Acacia sp.

2. Household Uses

• Utensils:

Utensils made up of wood instead of plastic and steel are a symbol of elegance which increases the charm and loveliness of the home corners.
e.g. Black walnut wood is used in the west for home utensils.  

• Hand Tools:

The handles of most common hand tools made of wood help as heat resistant when they are kitchenware used in an oven and closes the chance to shock while used on electricity.

3. Art Industry

• Artworks:

For artworks such as statues, sculptures, carvings and making decorative objects woods are widely used. The frames of art board, color plate are also made from wood in many cases. e.g. Pine, maple, cherry wood for framing work.  

• Musical instrument:

The musical instruments such as Piano, violin, cello, drums, flute, guitar, double bass and a number of other music instruments material requires wood for making a perfect tune. e.g. Mahogany , maple, ash wood for guitars.

4. Sports Equipment

• Wooden Toys:

These are preferred to plastic towards the health conscious people which were supposed as a fashion before. Plastic is nothing but the combination of chemicals which is hazardous to children's health. Cricket, hockey, billiard, table tennis etc. Toys and sports equipment have long made use of wood for handles and main parts. e.g. Willow wood for cricket, tennis bat; Mulberry  wood for hockey sticks.

5. Commercial Uses

• Furniture:

At present, the market for wooden furniture is very profitable. No one can deny the demand for wooden furniture as it is a sign of aristocracy since ancient time.
e.g. Teak  wood is the best for making furniture. Some other woods from Mahogany , Shimul , Sundari, Jackfruit, Mango trees are used in south Asia for making different types of furniture.

• Ship building

Ships and rural fishing boats were made from wood. For constructing boats and ships wood is one of the most important construction material. Hardwood and softwood were used in the past for ship industry.
e.g. Teak, shal , mango, Arjun were frequently used in the past. Now Cypress ,redwood ,white, oak are water resistant and used for shipbuilding and boat building. Woods like kauri  is used for making the frames of ships.  

• Fuel

Wood is an age-old source of energy all over the world. Before the exploration of gas, fuel was the main source we can also define as only one source of energy that people used by burning as woods were available in the forest easily. Generally, sticks, pellets, sawdust, and charcoal are used as an energy source from wood. Usually, woods from cheap plants are used in this sector.  

• Stationary

Some stationaries like paper pencil are made of wood. Wood pulp is used for making paper. Wood is used for making pencils too.
e.g. In the past Cyper papyrus trees were used to make paper.

8.     What is fly ash? What are the uses of fly ash? And explain the engineering properties of fly ash?

Answer:

FLYASH

It is one of the residues generated in combustion of coal. Comprises of fine particles which rise with the flue gases.

One of the major pollutants which originate from combustion.

Due to recent mandate of using pollution control equipments, these are now collected using electrostatic precipitators and other particle filters.

It is a heterogeneous material containing SiO2, Al2O3 and Fe2O3 as major constituents with CaO occasionally being the minor constituent.

USES

• Waste Treatment
• As a catalyst
• Geo polymers
• Embankments
• Asphalt Concrete
• Fly ash Bricks
• Soil Stabilization
• Admixture for Portland Cement

PROPERTIES

Physical Characteristic of Fly Ash

Fly ash is a fine grained material consisting mostly of spherical, glassy particles. Some ashes also containing irregular or angular particles. Fly ash is the pulverized fuel ash extracted from the fuel gases by any suitable process like cyclone separation or electrostatic precipitation.

Size and Shape of Fly Ash

The size of particles varies depending on the sources. Some ashes may be finer or coarser than Portland cement particles. Fly ash consists of silt sized particles which are generally spherical, typically ranging in size between 10 to 100 micron , Shows the scanning electron microscope (SEM) micrographs of polished sections of sub-bituminous and shows a secondary electron SEM image of bituminous of fly ash particles . Some of these particles appear to be solid, whereas other larger particles appear to be portions of thin, hollow spheres containing many smaller particles.

Colour of Fly Ash

Fly ash can be tan to dark gray, depending on its chemical and mineral constituents. Tan and light colours are typically associated with high lime content. A brownish colour is typically associated with the iron content. A dark gray to black colour is typically attributed to an elevated unburned content. Fly ash colour is usually very consistent for each power plant and coal source.

Fineness of Fly Ash

Dry and wet sieving are commonly used to measure the fineness of fly ashes. ASTM designation C311-77 recommends determining the amount of the sample retained after it is wet sieve done on a 45-m sieve, in accordance with ASTM method C 430, except that a representative sample of the fly ash or natural pozzolana is substituted for hydraulic cement in the determination. Dry sieving on a 45-m sieve can be performed according to a method established at Canada Center for Mineral and Energy Technology(CANMET). High-calcium fly ashes were finer than low-calcium fly ashes.

Specific Gravity of Fly Ash

The specific gravity of different fly ashes varies over a wide range. The specific gravity ranged from a low value of 1.90 for a sub-bituminous ash to a high value of 2.96 for an iron-rich bituminous ash. Some sub-bituminous ash had a comparatively low specific gravity of ≈ 2.0, and this shows that hollow particles, such as ceno spheres or plero spheres, were present in significant proportions in the ashes.

In general, the physical characteristics of fly ashes vary over a significant range, corresponding to their source. Fineness is probably influenced more by factors such as coal combustion and ash collection and classification than by the nature of the coal itself. Similarly, the type of fly ash showed no apparent influence on the specific surface as measured by the Blaine technique. Moreover, except in some cases, there was very little relationship between the specific surface as measured by the Blaine and the fineness as determined by percentage retained on a 45цm sieve.

9.     What is steel slag? What are the uses of steel slag? And explain the engineering properties of steel slag?

Answer:

STEEL SLAG

Steel slag, a by-product of steel making, is produced during the separation of the molten steel from impurities in steel-making furnaces. The slag occurs as a molten liquid melt and is a complex solution of silicates and oxides that solidifies upon cooling.

Virtually all steel is now made in integrated steel plants using a version of the basic oxygen process or in specialty steel plants (mini-mills) using an electric arc furnace process. The open hearth furnace process is no longer used.

In the basic oxygen process, hot liquid blast furnace metal, scrap, and fluxes, which consist of lime (CaO) and dolomitic lime (CaO.MgO or "do lime"), are charged to a converter (furnace). A lance is lowered into the converter and high-pressure oxygen is injected. The oxygen combines with and removes the impurities in the charge. These impurities consist of carbon as gaseous carbon monoxide, and silicon, manganese, phosphorus and some iron as liquid oxides, which combine with lime and do lime to form the steel slag. At the end of the refining operation, the liquid steel is tapped (poured) into a ladle while the steel slag is retained in the vessel and subsequently tapped into a separate slag pot.

There are many grades of steel that can be produced, and the properties of the steel slag can change significantly with each grade. Grades of steel can be classified as high, medium, and low, depending on the carbon content of the steel. High-grade steels have high carbon content. To reduce the amount of carbon in the steel, greater oxygen levels are required in the steel-making process. This also requires the addition of increased levels of lime and dolime (flux) for the removal of impurities from the steel and increased slag formation.

Physical Properties

Steel slag aggregates are highly angular in shape and have rough surface texture. They have high bulk specific gravity and moderate water absorption (less than 3 percent). Table 18-1 lists some typical physical properties of steel slag.

Chemical Properties

The chemical composition of slag is usually expressed in terms of simple oxides calculated from elemental analysis determined by x-ray fluorescence. Table 18-2 lists the range of compounds present in steel slag from a typical base oxygen furnace. Virtually all steel slags fall within these chemical ranges but not all steel slags are suitable as aggregates. Of more importance is the mineralogical form of the slag, which is highly dependent on the rate of slag cooling in the steel-making process.

USES

The use of steel slag as an aggregate is considered a standard practice in many jurisdictions, with applications that include its use in granular base, embankments, engineered fill, highway shoulders, and hot mix asphalt pavement.

10. What is copper slag? What are the uses of copper slag? And explain the engineering properties of copper slag?

Answer:

Copper slag is a by-product created during the copper smelting and refining process. As refineries draw metal out of copper ore, they produce a large volume of non-metallic dust, soot, and rock. Collectively, these materials make up slag, which can be used for a surprising number of applications in the building and industrial fields.

USES

• Copper slag is mainly used for surface blast-cleaning.
• Copper slag is just one of many different materials that may be used as abrasive grit.
• Copper slag can be used in concrete production as a partial replacement for sand.
• Copper slag is used as a building material, formed into blocks.
• In Sweden, fumed and settled granulated copper slag from the Boliden copper smelter is used as road- construction material.

Physical Properties

The specific gravity and density of copper slag and river sand were determined in accordance with IS 2386 part III. Copper slag has a specific gravity of 4.12 and bulk density of 2.31 g/cc which is higher than that for normal river sand (2.6, 1.53 g/cc) which may result in production of concrete with higher density. Also, the measured water absorption for copper slag was 0.40 % compared with 0.83 % for sand. This suggests that copper slag has less surface porosity and would demand less water than that required by sand in the concrete mix. Therefore due to the free water content in concrete matrix and also due to the higher coarseness of copper slag will increase the workability of the concrete as the copper slag content increases.