Civil Engineering Module 1

Question 1

Give the American society of civil engineering definition of Civil Engineering.

Answer 1

American society of civil engineering defines civil engineering as
the profession in which 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 wellbeing of man.

Question 2

List any 5 roles of Civil Engineering

Answer 2

1. Plan new townships and extension of existing towns.
2. Providing shelter to people in the form of low cost houses to high rise apartments.
3. Laying ordinary village roads to express highways.
4. Constructing irrigation tanks, multipurpose dams & canals for supplying water to
   agricultural fields.
5. Supplying safe and potable water for public & industrial uses.
6. Protecting our environment by adopting sewage treatment & solid waste disposal
   techniques.
7. Constructing hydro-electric & thermal-power plants for generating electricity.
8. Providing other means of transportation such as railways, harbor& airports.
9. Constructing bridges across streams, rivers and also across seas.
10. Tunneling across mountains & also under water to connect places easily & reduce
    distance.

Question 3

State the roles of Management Techniques and Computer Applications in Civil Engineering.

Answer 3

1. Management Techniques: Civil engineers must manage men, materials and equipment
   sufficiently. Since huge funds are to be handled in civil engineering projects, a civil engineer
   must know the basics in financial management and legal obligations. Knowledge of
   management techniques is an asset to practicing civil engineer.
2. Computer Applications: Since the magnitude of designing the structures and storing
   information is increasing very fast nowadays civil engineers go for computer applications in
   planning and designing of structures. There is good number of civil engineering software
   commercially available.

Question 4

Name the different Fields of Civil Engineering.

Answer 4

Surveying, .Geo-Technical Engineering (Soil Mechanics), .Structural Engineering, Transportation Engineering, Irrigation& Water resources engineering (Hydraulics Engineering), Water Supply and Sanitary Engineering (Environmental Engineering),

Question 5

What is surveying? Describe its scope and types of surveying.

Answer 5

Surveying: It is a science and art of determining the relative position of points on the
earth’s surface by measuring distances, directions and vertical heights directly or indirectly.
Surveying helps in preparing maps and plans, which help in project implementation. (Setting
out the alignment for a road or railway track or canal, deciding the location for a dam or
airport or harbor) The cost of the project can also be estimated before implementing the
project. Now-a-days, using data from remote sensing satellites is helping to prepare maps &
plans & thus cut down the cost of surveying.

Types Of Surveying:

The survey in which the shape or curvature of earth is not taken into account is called plane
surveying.
The survey in which the shape or curvature of earth is taken into account is called Geodetic surveying.

SCOPE OF SUREYING

1. To prepare the plan or map
2. To determine the dimension and contour of any part of the earth’s surface
3. To establish boundaries of land
4. To measure the area and volume of land
5. To select suitable site for an engineering project

Question 6

Explain Geo-Technical Engineering (Soil Mechanics) with its scope.

Answer 6

Any building, bridge, dam, retaining
wall etc. consist of components like foundations. Foundation is laid from a certain depth
below the ground surface till hard layer is reached. The soil should be thoroughly checked for
its suitability for construction purposes. The study dealing with the properties &behavior of
soil under loads & changes in environmental conditions is called geo-technical engineering.
The knowledge of the geology of an area is also very much necessary.

SCOPE OF GEOTECHNICAL ENGINEERING

1. Foundation design and construction
2. Highway pavement design
3. Design and construction of tunnels underground structure and drainages structures
4. Design of retaining structures
5. Design of earthen dams and embankment

Question 7

What is Structural Engineering? Describe its scope.

Answer 7

A building or a bridge or a dam consists of various elements
like foundations, columns, beams, slabs etc. These components are always subjected to
forces. It becomes important to determine the magnitude & direction the nature of the forces
and acting all the time. Depending upon the materials available or that can be used for
construction, the components or the parts of the building should be safely & economically
designed.
A structured engineer is involved in such designing activity. The use of computers in
designing the members, is reducing the time and also to maintain accuracy.

SCOPE OF STRUCTURAL ENGINEERING
1. Responsible for creation of structural system in accordance with the needs of the
client and architect.
2. Plays an important role to build industrial production and manufacturing unit.
3. Keys main for total planning and designing of nuclear power plants.
4. Take the responsibility about the safety and serviceability of the structure for its
lifetime.

Question 8

What is Transportation Engineering? Give its scope.

Answer 8

The transport system includes roadways, railways, air & waterways. Here the role of civil engineers is to construct facilities related to each one.
Sometimes crucial sections of railways & roads should be improved. Roads to remote places
should be developed. Ports &harbors should be designed to accommodate, all sizes of
vehicles. For an airport, the runway & other facilities such as taxiways, terminal buildings,
control towers etc. should be properly designed.

SCOPE OF TRANSPORTATION ENGINEERING

1. Traffic management
2. Parking facilities
3. Rapid transportation
4. Urbanization and industrialization
5. Accident study for safe and comfort transport system

Question 9

What are Irrigation& Water resources engineering? Describe their scopes respectively.

Answer 9

Irrigation is the process of supplying water by artificial means to agricultural fields for raising crops.
Since rainfall in an area is insufficient or unpredictable in an area, water flowing in a river can be stored by constructing dams and diverting the water into the canals & conveyed to the agricultural fields. Apart from dams & canals other associated structures like canals
regulators, aqua ducts, weirs, barrages etc. are also necessary. Hydroelectric power generation facilities are also included under this aspect.

SCOPE OF WATER RESOURCE ENGINEERING

1. Flood mitigation
2. Irrigation
3. Hydroelectric power
4. Domestic and industrial water supply
5. Aquatic animal management

SCOPE OF IRRIGATION ENGINEERING

6. Diversion of stored water to canal for distribution
7. Lifting of water by digging wells and fed to small channels
8. Development of hydroelectric power
9. Increase in flood production
10. Protection from famine
11. Ground water storage improvement

Question 10

What is Water Supply and Sanitary Engineering? Give their scopes respectively.

Answer 10

People in every village, town & city need potable water. The water available (surface water
& ground water) may not be fit for direct consumption. In such cases, the water should be
purified and then supplied to the public. For water purification, sedimentation tanks, filter
beds, etc. should be designed. If the treatment plants are for away from the town or city,
suitable pipelines for conveying water & distributing it should also be designed. In a town or
city, a part of the water supplied returns as sewage. This sewage should be systematically
collected and then disposed into the natural environment after providing suitable treatment.

The solid waste that is generated in a town or locality should be systematically collected and
disposed off suitably. Before disposal, segregation of materials should be done so that any
material can be recycled & we can conserve our natural resources.

Scope of Environmental Engineering

1. Protection and conservation of environment
2. Good water supply
3. Waste water treatment
4. Pollution treatment
5. Solid waste management.

Question 11

What are building materials? What is the importance of building materials and construction technology?

Answer 11

Any engineering structure requires a wide range of materials known as building materials. The choice of the materials is wide & open. It becomes important for any construction engineer to be well versed with the
properties & applications of the different materials. Any construction project involves many activities and also required many materials, manpower, machinery & money.
The different activities should be planned properly; the manpower, materials & machinery should be
optimally utilized, so that the construction is completed in time and in an economical manner.
In case of large construction projects management techniques of preparing bar charts & network diagrams, help in completing the project orderly in time.

Question 12

Give the Classification of Building Materials.

Answer 12

Traditional materials:
Stones, timber, bricks, lime ,cement ,tar ,bitumen, mortar ,ferrous and non ferrous metals,
ceramic materials ,etc.

Alternative Building Materials:
Mud –blocks, concrete-blocks, plastics, glass, aluminum, paints, fly ash, etc.

Composite Materials:
RCC, fiber reinforcement concrete, ferro-cement, composite laminate doors, plastic
laminates, asbestos sheets, fiber reinforced glass, etc.
Smart Materials or Intelligent Materials
Optic fiber, piezoelectric material, electro-strictive and magneto-strictive materials, etc.

Question 13

What are bricks?

Answer 13

Brick is the most commonly used building materials. It is light, easily available, uniform
shape and size, and relatively cheaper except in hilly areas. Bricks are easily mould from
plastic clays, also known as brick clay or brick earth.

Question 14

Draw and label the parts of a brick.

Answer 14

*insert drawing here*
Parts:
Frog/indent
Stretcher face
Arris or angle
Header face

Question 15

State any 5 qualities of good bricks.

Answer 15

Qualities of good bricks
The good bricks which are to be used for the construction of important structures should
possess the following qualities

1. The bricks should be table moulded, well-burnt in kilns, copper- colored, free from
   cracks and with sharp and square edges. The color should be uniform and bright.
2. The bricks should be uniform in shape and it should be of standard size.For India, a
   brick of standard size 190 mm x 90 mm x 90 mm is recommended by the BIS. With
   mortar thickness, the size of such a brick becomes 200 mm x 100 mm x 100 mm and it
   is known as the nominal size of the modular brick.
3. The brick should give a clear metallic ringing sound when struck with each other.
4. The bricks when broken or fractured should show a bright homogeneous and uniform
   compact structure free from voids.
5. The brick should not absorb water more than 20% by weight for first class bricks and
   22% by weight for second class bricks, when soaked in cold water for a period of 24
   hours.
6. The brick should be sufficiently hard. No impression should be left on brick surface,
   when it is scratched with finger nail.
7. The bricks should not break into pieces when dropped flat on hard ground from a
   height of about one meter.
8. The brick should have low thermal conductivity. They should be sound proof.
9. The bricks, when soaked in water for 24 hours should not show deposits of white salts
   when allowed to dry in shade.
10. No brick should have the crushing strength below 5.50N/mm2.

Question 16

Give the Classification of Bricks Based on their Quality.

Answer 16

The bricks used in construction are classified as:
1. First class bricks: These bricks are of standard shape and size. They are burnt in kilns.
They fulfill all desirable properties of bricks.

2. Second class bricks: These bricks are ground moulded and burnt in kilns. The edges may not be sharp and uniform. The surface may be somewhat rough. Such bricks are commonly used for the construction of walls which are going to be plastered.
3. Third class bricks: These bricks are ground moulded and burnt in clamps. Their edges are somewhat distorted. They produce dull sound when struck together. They are used for temporary and unimportant structures.
4. Fourth class bricks: These are the over burnt bricks. They are dark in colour. The shape is irregular. They are used as aggregates for concrete in foundations, floors and roads.

Question 17

List the engineering application of bricks.

Maybe a 2m qustn

Answer 17

Bricks are used in the following civil works:
1. As structural unit, since the clay bricks or burnt bricks are strong, hard, durable and
resistive to abrasion and fire.
2. As aesthetic unit/ surface finish: Bricks can be used in different colour, sizes and
orientation to get different surface design. As an aesthetic material brick can be used
in pavements, facing work and architectural purposes.
3. For lining of ovens, furnaces and chimneys as it shows good fire resistance.
4. For protecting steel columns from fire.
5. As aggregates in providing water proofing to R.C.C. roofs.
6. For pavers for footpaths and cycle tracks.
7. For lining sewer lines.

Question 18

Application of bricks based on quality of bricks.

Answer 18

First class and second class bricks are widely used for all sorts of sound work especially of permanent nature. These structures include buildings, dams, roads,  sewers, bridge piers, tunnels, pitching works etc.
1. Use of first class bricks are specified for obtaining the architectural effects on faces
of structures where they are to be kept exposed for beauty.
2. Masonry with second class bricks is generally plastered to make the smooth surface
obtained due to the irregular shape and size of bricks. Mortar required in brick
masonry using second class bricks will also be more.
3. Third class and sun-dried bricks are used for construction work of temporary nature.
These bricks are not used in damp situations or at places subjected to heavy rains.
4. Forth class bricks are used as road metal and as aggregates in the foundation concrete.

Question 19

Advantages and Disadvantages of bricks

Answer 19

Advantages of Bricks
1. Economical (Raw material is easily available)
2. Hard and durable
3. Compressive strength is good enough for ordinary construction
4. Different orientations and sizes give different surface textures
5. Very low maintenance cost is required
6. Demolishing of brick structures is very easy, less time consuming and hence
economic
7. Reusable and Recyclable
8. Highly fire resistant

Disadvantages of Bricks

1. Time consuming construction
2. Cannot be used in high seismic zones
3. Since bricks absorb water easily, it causes fluorescence when not exposed to air
4. Very less tensile strength
5. Rough surfaces of bricks may cause mold growth if not properly cleaned.
6. Cleaning brick surfaces is a hard job.
7. Color of low quality brick changes when exposed to sun for a longer period of time

Question 20

What is a stone?

Answer 20

Stone is a ‘naturally available building material’ which has been used from the early age
of civilization. It is available in the form of rocks, which is cut to required size and
shape and used as building block.

Question 21

List and explain the properties of stones

Answer 21

The following properties of the stones should be looked into before selecting them for
engineering works:

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.

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

Density: Denser stones are stronger. Light weight stones are weak. Hence stones with
specificgravity less than 2.4 are considered unsuitable for buildings.

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.

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.

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.

Percentage wear: It is measured by attrition test

Porosity and Absorption: All stones have pores and hence absorb water. The reaction of
water with material of stone causes disintegration. Absorption test is specified as percentage
of water absorbed by the stone when it is immersed under water for 24 hours

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

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

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

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.

Seasoning: The stones obtained from quarry contain moisture in the pores. The strength oft he
stone improves if this moisture is removed before using the stone. The process of removing
moisture from pores is called seasoning.

Question 22

What are the Requirements of Good Building Stones?

Answer 22

Strength: The stone should be able to resist the load coming on it. Ordinarily this is not of
primary concern since all stones are having good strength. However in case of large structure,
it may be necessary to check the strength.

Durability: Stones selected should be capable of resisting adverse effects of natural forces
like wind, rain and heat.

Hardness: The stone used in floors and pavements should be able to resist abrasive forces
caused by movement of men and materials over them.

Toughness: Building stones should be tough enough to sustain stresses developed due to
vibrations. The vibrations may be due to the machinery mounted over them or due to the
loads moving over them. The stone aggregates used in the road constructions should be
tough.

Specific Gravity: Heavier variety of stones should be used for the construction of dams,
retaining walls, docks and harbors. The specific gravity of good building stone is between 2.4
and 2.8.

Porosity and Absorption: Building stone should not be porous. If it is porous rain water
enters into the pour and reacts with stone and crumbles it. In higher altitudes, the freezing of
water in pores takes place and it results into the disintegration of the stone.

Dressing: Giving required shape to the stone is called dressing. It should be easy to dress so
that the cost of dressing is reduced. However the care should be taken so that, this is not be at
the cost of the required strength and the durability.
Appearance: In case of the stones to be used for face works, where appearance is a primary
requirement, its color and ability to receive polish is an important factor

Seasoning: Good stones should be free from the quarry sap. Laterite stones should not be
used for 6 to 12 months after quarrying. They are allowed to get rid of quarry sap by the
action of nature. This process of removing quarry sap is called seasoning.

Cost: Cost is an important consideration in selecting a building material. Proximity of the
quarry to building site brings down the cost of transportation and hence the cost of stones
comes down

Question 23

What are the Engineering application of Stones?

Answer 23

Stones are used in the following civil engineering constructions:
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.
8. Crushed stones are used in the following works also:
8.1. As a basic inert material in concrete
8.2. For making artificial stones and building blocks
8.3. As railway ballast.

Question 24

What is cement?

Answer 24

One material which has completely revolutionized the construction industry is cement. It was in 1824, a mason of England by name Joseph Aspidin developed cement by burning at high temperature a mixture of lime and clay and then grinding it into fine powder.
This is known as Ordinary Portland Cement.
Cement is a binder, a substance used in construction that sets and hardens and can bind other materials together.
The most important types of cement are used as a component in the production of mortar in masonry, and of concrete, which is a combination of cement and
an aggregate to form a strong building material.

Question 25

Physical properties of cement?

Answer 25

Properties of Cement

Physical Properties:

1. Fineness: Finer cement particles impart better quality. It is measured in terms of percentage of weight retained after sieving the cement through 90 micron sieve or by surface area. According to IS code specification weight retained on the sieve should not be more than 10 per cent. In terms of specific surface should not be less than 2250
   cm2/gm.
2. Soundness: Once the concrete has hardened it is necessary to ensure that no volumetric changes takes place. The cement is said to be unsound, if it exhibits
   volumetric instability after hardening. It is determined by the Le Chatelier test.
3. Setting of cement: When water is added to cement it forms a thick paste. Gradually as time passes, it transforms into a non-plastic rigid mass. The setting time is influenced by the amount of water added to the cement, the temperature at which the cement paste is allowed to set and the humidity of the atmosphere. The setting of cement is identified in two stages, initial setting and final setting. The setting time is
   determined in the laboratory by Vicat Needle Apparatus As per Bureau of Indian Standards (BIS), for ordinary cement , the initial setting time shall not be less than 30 minutes and the final setting time should not be more than 10 hours.

Question 26

Mechanical properties of cement.

Answer 26

1. Compressive strength: Cement mortar cubes of size 7.06 cm are made out of mortar of 1: 3 composition (1 part of cement to 3 parts of sand) and tested in a Universal compressive testing machine. Normally the tests are done after 3, 7 and 28 days.
2. Tensile strength: Test pieces (briquettes) are made out of cement sand mortar 1: 3 and tested in a standard tensile testing machine after 3, 7 and 28 days.

Question 27

List any 3 types of cement and their applications.

Answer 27

Portland Cement: The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and
once hardened, can become a structural (load bearing) element. Concrete can be used in the construction of structural elements like panels, beams, street furniture, or may make cast-in situ concrete for building superstructures like roads and dams. These may be supplied with concrete mixed on site, or may be provided with “ready-mixed” concrete made at permanent mixing sites.

White Cement: The cement when made free from coloring oxides of iron, manganese and chlorine results into white cement. In the manufacture of this cement, the oil fuel is used instead of coal for burning. White cement is used for the floor finishes, plastering, ornamental works etc. In swimming pools white cement is used to replace glazed tiles. It is used for
fixing marbles and glazed tiles.

Colored Cement: The cements of desired colors are produced by intimately mixing pigments with ordinary cement. The chlorium oxide gives green colour. Cobalt produce blue colour. Iron oxide with different proportion produce brown, red or yellow colour. Addition of manganese dioxide gives black or brown colored cement. These cements are used for giving
finishing touches to floors, walls, window sills, roofs etc.

Quick Setting Cement: Quick setting cement is produced by reducing the percentage of gypsum and adding a small amount of aluminium sulphate during the manufacture of cement.
Finer grinding also adds to quick setting property. This cement starts setting within 5 minutes after adding water and becomes hard mass within 30 minutes. This cement is used to lay concrete under static or slowly running water.

Rapid Hardening Cement: This cement can be produced by increasing lime content and burning at high temperature while manufacturing cement. Grinding to very fine is also necessary. Though the initial and final setting time of this cement is the same as that of portland cement, it gains strength in early days. This property helps in earlier removal of
form works and speed in construction activity.

Low Heat Cement: In mass concrete works like construction of dams, heat produced due to hydration of cement will not get dispersed easily. This may give rise to cracks. Hence in such constructions it is preferable to use low heat cement.

Pozzolana Cement: Pozzolana is a volcanic power found in Italy. It can be processed from shales and certain types of clay also. In this cement pozzolana material is 10 to 30 per cent.
It can resist action of sulphate. It releases less heat during setting. It imparts higher degree of water tightness. Its tensile strength is high but compressive strength is low. It is used for mass concrete works like dam, tall structures etc. It is also used in sewage line works.

Expanding Cement: This cement expands as it sets. This property is achieved by adding
expanding medium like sulpho-aluminate and a stabilizing agent to ordinary cement. This is
used for filling the cracks in concrete structures.

High Alumina Cement: It is manufactured by calcining a mixture of lime and bauxite. It is more resistant to sulphate and acid attack. It develops almost full strength within 24 hours of adding water. It is used for under water works.

Blast Furnace Cement: In the manufacture of pig iron, slag comes out as a waste product.
By grinding clinkers of cement with about 60 to 65 per cent of slag, this cement is produced.
The properties of this cement are more or less same as ordinary cement, but it is cheap, since it utilize waste product. This cement is durable but it gains the strength slowly and hence needs longer period of curing concrete.

Acid Resistant Cement: This cement is produced by adding acid resistant aggregated such as quartz, quartzite, sodium silicate or soluble glass. This cement has good resistance to action of acid and water. It is commonly used in the construction of chemical factories.

Sulphate Resistant Cement: By keeping the percentage of tricalcium aluminate C3A below five per cent in ordinary cement this cement is produced. It is used in the construction of structures which are likely to be damaged by alkaline conditions. Examples of such structures
are canals, culverts etc

Question 28

What is plain concrete?

Answer 28

Plain concrete, commonly known as concrete, is an intimate mixture of binding material, fine aggregate, coarse aggregate and water. This can be easily mould to desired shape and size before it loses plasticity and hardens.
Plain concrete is strong in compression
but very weak in tension. The tensile property is introduced in concrete by inducting different
materials and this attempt has given rise to RCC, PSC, FRC, cellular concrete and Ferro cement.

Question 29

List the major ingredients of concrete.

Answer 29

Major ingredients of concrete are:
1. Binding material (like cement, lime, polymer)
2. Fine aggregate (sand)
3. Coarse aggregates (crushed stone, jelly)
4. Water.
5. A small quantity of admixtures like air entraining agents, water proofing agents,
workability agents etc. may also be added to impart special properties to the plain
concrete mixture.

Question 30

Briefly mention and explain the steps involved in preparation of concrete.

Answer 30

The following steps are involved in the concreting:

1. Batching
2. Mixing
3. Transporting and placing and
4. Compacting.
5. Curing

Batching: The measurement of materials for making concrete is known as batching. The
following two methods of batching is practiced:
1. Volume batching
2. Weight batching.

Mixing: To produce uniform and good concrete, it is necessary to mix cement, sand and coarse aggregate, first in dry condition and then in wet condition after adding water.
Transporting and Placing of Concrete. After mixing, concrete should be transported to the final position. In small works it is transported in iron pans from hand to hand of a set of workers. Wheel barrow and hand carts also may be employed. In large scale concreting
chutes and belt conveyors or pipes with pumps are employed.

Compaction of Concrete: In the process of placing concrete, air is entrapped. The entrapped air reduces the strength of concrete up to 30%. Hence it is necessary to remove this entrapped air. This is achieved by compacting the concrete after placing it in its final position. Compaction can be carried out either by hand or with the help of vibrators.

Curing of Concrete: Curing may be defined as the process of maintaining satisfactory moisture and temperature conditions for freshly placed concrete for some specified time for proper hardening of concrete. Curing in the early ages of concrete is more important. Curing is done for 28 days. If curing is not done properly, the strength of concrete reduces. Cracks
develop due shrinkage. The durability of concrete structure reduces. The following curing
methods are employed:
1. Spraying of water
2. Covering the surface with wet gunny bags, straw etc.
3. Ponding
4. Steam curing

Question 31

Explain the Properties of green/fresh concrete.

Answer 31

Workability: This is defined as the ease with which concrete can be compacted fully without segregating and bleeding. It can also be defined as the amount of internal work required to fully compact the concrete to optimum density. The workability depends upon the quantity of water, grading, shape and the percentage of the aggregates present in the concrete.

Segregation: Separation of coarse particles from the green concrete is called segregation.
This may happen due to lack of sufficient quantity of finer particles in concrete or due to throwing of the concrete from greater heights at the time of placing the concrete. Because of the segregation, the cohesiveness of the concrete is lost and honey combing results. Ultimately it results in the loss of strength of hardened concrete. Hence utmost care is to be taken to avoid segregation.

Bleeding: This refers to the appearance of the water along with cement particles on the surface of the freshly laid concrete. This happens when there is excessive quantity of water in the mix or due to excessive compaction. Bleeding causes the formation of pores and renders the concrete weak. Bleeding can be avoided by suitably controlling the quantity of water in the concrete and by using finer grading of aggregates.

Harshness: Harshness is the resistance offered by concrete to its surface finish. Harshness is due to presence of lesser quantity of fine aggregates, lesser cement mortar and due to use of poor graded aggregates. It may result due to insufficient quantity of water also. With harsh concrete it is difficult to get a smooth surface finish and concrete becomes porous.

Question 32

Explain the Properties of Hardened Concrete.

Answer 32

Strength: The characteristic strength of concrete is defined as the compressive strength of
150 mm size cubes after 28 days of curing below which not more than 5 per cent of the test
results are expected to fail. The unit of stress used is N/mm2. It is represented as M20 where,
M stands for design mix and 20 stands for strength of concrete.

Dimensional Change: Concrete shrinks with age. The total shrinkage depends upon the constituents of concrete, size of the member and the environmental conditions. Total shrinkage is approximately 0.0003 of original dimension Durability: Environmental forces such as weathering, chemical attack, heat, freezing and
thawing try to destroy concrete. The period of existence of concrete without getting adversely
affected by these forces is known as durability. Generally dense and strong concretes have better durability. The cube crushing strength alone is not a reliable guide to the durability.
Concrete should have adequate cement content and should have low water cement ratio.

Impermeability: This is the resistance of concrete to the flow of water through its pores.
Excess water during concreting leaves a large number of continuous pores leading to the permeability. Since the permeability reduces the durability of concrete, it should be kept very low by using low water cement ratio, dense and well graded aggregates, good compaction and continuous curing at low temperature conditions.

Question 33

Give the Applications of Concrete

Answer 33

1. As bed concrete below column footings, wall footings, on wall at supports to beams
2. As sill concrete
3. Over the parapet walls as coping concrete
4. For flagging the area around buildings
5. For pavements
6. For making building blocks

Question 34

What is RCC? Give a brief explanation

Answer 34

Concrete is good in resisting compressive stress but it is very weak in resisting tensile stress. Hence reinforcement is provided in the concrete wherever tensile stress is expected.
The best reinforcement is steel, since the tensile strength of steel is quite high and the bond between steel and concrete is good. As the elastic modulus of steel is as high as concrete, the force developed in steel is high. However in tensile zone, hair cracks in concrete are unavoidable. Reinforcement are usually in the form of mild steel or ribbed steel bars of
diameter 6 to 32 mm diameter. A cage of reinforcements, kept in a form work and then green
concrete is poured. After the concrete hardens, the form work is removed. The composite material of steel and concrete, now called R.C.C. acts as structural member and can resist tensile as well as compressive stress efficiently.

Question 35

Properties and uses of R.C.C.

Answer 35

Properties of concrete:
1. It should be capable of resisting tensile, compressive, bending or shear stresses.
2. It should not show excessive deflections to the serviceability requirement.
3. There should be proper cover to reinforcement so that corrosion of steel is prevented
4. The hair cracks developed should be with permissible limit.
5. R.C.C is a good fire resistant 6. It can be moulded to desired shape and size.
6. Durability of R.C.C. is very good. 8. R.C.C. structure can be designed to take any
load.

Uses of R.C.C.:

1 R.C.C is used as a structural element, wherever direct tension or bending tension is expected. The common structural elements in a building where R.C.C is used are footing, columns, beams, lintels, chejjas, roof slabs, curved roofs etc, and stairs.

2 R.C.C. is used for the construction of storage structures like water tanks, dams, bins, silos and bunkers they are used for the construction of big structures like bridges, retain walls, docks and harbors, and under water structures

3. R.C.C. is used for pre-casting rail sleepers, elective poles
4. R.C.C is use for tall buildings like multistoried buildings, chimneys and towers
5. R.C.C is used for paving highways, city roads and airport