Basic Terminologies in Mechanics

1) Mass (m)

The quantity of the matter possessed by a body is called mass. The mass of a body will not change unless the body is damaged and part of it is physically separated. If the body is taken out in a space craft, the mass will not change but its weight may change due to the change in gravitational force. The body may even become weightless when gravitational force vanishes but the mass remain the same.

2) Weight (w)

Weight of a body is the force with which the body is attracted towards the centre of the earth. The weight of the body is equal to the product of mass and the acceleration due to gravity. This quantity of a body varies from place to place on the surface of the earth.

Mathematically,

w=mg

Where ‘w’ is the weight of the body, ‘m’ is the mass of the body and ‘g’ is the acceleration due to gravity.

Table 1 Difference between Mass and Weight

Mass	Weight
Mass is the total quantity of matter contained in a body.	Weight of a body is the force with which the body is attracted towards the centre of the earth.
Mass is a scalar quantity, because it has only magnitude and no direction.	Weight is a vector quantity, because it has both magnitude and direction.
Mass of a body remains the same at all places. Mass of a body will be the same whether the body is taken to the centre of the earth or to the moon.	Weight of body varies from place to place due to variation of ‘g’ (i.e., acceleration due to gravity.
Mass resists motion in a body.	Weight produces motion in a body.
Mass of a body can never be zero.	Weight of a body can be zero.
Using an ordinary balance (beam balance), the mass can be determined.	Using a spring balance, the weight of the body can be measured.
The SI unit of the mass is the kilogram (kg).	The SI unit of the weight is Newton (N).

3) Time

The time is the measure of succession of events. The successive event selected is the rotation of earth about its own axis and this is called a day. To have convenient units for various activities, a day is divided into 24 hours, an hour into 60 minutes and a minute into 60 seconds. Clocks are the instruments developed to measure time. To overcome difficulties due to irregularities in the earth’s rotation, the unit of time is taken as second, which is defined as the duration of 9192631770 period of radiation of the cesium-133 atom.

4) Space

The geometric region in which study of body is involved is called space. A point in the space may be referred with respect to a predetermined point by a set of linear and angular measurements. The reference point is called the origin and the set of measurements as coordinates. If the coordinates involved are only in mutually perpendicular directions, they are known as cartesian coordination. If the coordinates involve angles as well as the distances, it is termed as Polar Coordinate System.

5) Length

It is a concept to measure linear distances. Meter is the unit of length. However depending upon the sizes involved micro, milli or kilo meter units are used for measurements. A meter is defined as length of the standard bar of platinum-iridium kept at the International Bureau of weights and measures. To overcome the difficulties of accessibility and reproduction now meter is defined as 1690763.73 wavelength of krypton-86 atom.

5) Continuum

A body consists of several matters. It is a well known fact that each particle can be subdivided into molecules, atoms and electrons. It is not possible to solve any engineering problem by treating a body as conglomeration of such discrete particles. The body is assumed to be a continuous distribution of matter. In other words the body is treated as continuum.

6) Particle

A particle may be defined as an object which has only mass and no size. Theoretically speaking, such a body cannot exist. However in dealing with problems involving distances considerably larger compared to the size of the body, the body may be treated as a particle, without sacrificing accuracy.

For example:

• A bomber aeroplane is a particle for a gunner operating from the ground.
• A ship in mid sea is a particle in the study of its relative motion from a control tower.
• In the study of movement of the earth in celestial sphere, earth is treated as a particle.

7) Rigid Body

A body is said to be rigid, if the relative positions of any two particles do not change under the action of the forces acting on it i.e., the distances between different points of the body remain constant. No body is perfectly rigid. Rigid body is ideal body.

Fig. 1 Rigid Body due to the action force F

8) Deformable Body

When a body deforms due to a force or a torque it is said deformable body. Material generates stresses against deformation. All bodies are more or less elastic.

Fig. 2 Deformable Body due to the action force F

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Force and System of Forces

Force is that which changes or tends to change the state of rest of uniform motion of a body along a straight line. It may also deform a body by changing its dimensions. The force may be broadly defined as an agent which produces or tends to produce, destroys or tends to destroy motion. It has a magnitude and direction.

Mathematically,

                                                            Force = Mass× Acceleration

                                                                   F = m a

Where, F - Force

            m - Mass

             a - Acceleration

Characteristics of Force

1) Magnitude: Magnitude of force indicates the amount of force (expressed as N or kN) that will be exerted on another body

2) Direction: The direction in which it acts

3) Nature: The nature of force may be tensile or compressive

4) Point of Application: The point at which the force acts on the body is called point of application

Units of Force

1) In C.GS. System

In this system, there are two units of force: (i) Dyne and (ii) Gram force (gmf). Dyne is the absolute unit of force in the C.G.S. system. One dyne is that force which acting on a mass of one gram produces in it an acceleration of one centimeter per second².

2) In M.K.S. System

In this system, unit of force is kilogram force (kgf). One kilogram force is that force which acting on a mass of one kilogram produces in it an acceleration of 9.81 m/ sec².

3) In S.I. Unit

In this system, unit of force is Newton (N). One Newton is that force which acting on a mass of one kilogram produces in it an acceleration of one m /sec².

                                                                1 Newton = 10⁵ Dyne

Effect of Force

A force may produce the following effects in a body, on which it acts.

1. It may change the motion of a body. i.e. if a body is at rest, the force may start its motion and if the body is already in motion, the force may accelerate or decelerate it.
2. It may retard the forces, already acting on a body, thus bringing it to rest or in equilibrium.
3. It may give rise to the internal stresses in the body, on which it acts.
4. A force can change the direction of a moving object.
5. A force can change the shape and size of an object

Principle of Physical Independence of Forces

It states, “If a number of forces are simultaneously acting on a particle, then the resultant of these forces will have the same effect as produced by all the forces.”

System of Forces

When two or more forces act on a body, they are called to form a system of forces. Force system is basically classified into the following types.

1) Coplanar Forces

The forces, whose lines of action lie on the same plane, are known as coplanar forces.

Fig. 1 Coplanar Forces

2) Collinear Forces

The forces, whose lines of action lie on the same line, are known as collinear forces.

Fig. 2 Collinear Forces

3) Concurrent Forces

The forces, which meet at one point, are known as concurrent forces. The concurrent forces may or may not be collinear.

Fig. 3 Concurrent Forces

4) Coplanar Concurrent Forces

The forces, which meet at one point and their line of action also lay on the same plane, are known as coplanar concurrent forces.

Fig. 4 Coplanar Concurrent Forces

5) Coplanar Non-Concurrent Forces

The forces, which do not meet at one point, but their lines of action lie on the same plane, are known as coplanar non-concurrent forces.

Fig. 5 Coplanar Non-Concurrent  Forces

6) Non-Coplanar Concurrent Forces

The forces, which meet at one point, but their lines of action do not lie on the same plane, are known as non-coplanar concurrent forces.

Fig. 6 Non-Coplanar Concurrent  Forces

7) Non-Coplanar Non-Concurrent Forces

The forces, which do not meet at one point and their lines of action do not lie on the same plane, are called non-coplanar non-concurrent forces.

Fig. 7 Non-Coplanar Non-Concurrent  Forces

8) Parallel Forces

The forces, whose lines of action are parallel to each other, are known as parallel forces.

Fig. 8 Parallel Forces

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Workability of Fresh Concrete

Workability of concrete is defined in ASTM C125 as “the property determining the effort required to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity (uniform)”. The term manipulate includes the early age operations of placing, compacting and finishing. Another definition of workability of fresh concrete is “the amount of mechanical work or energy, required to produce full compaction of the concrete without segregation.” Road Research laboratory, U.K., who has extensively studied the field of compaction and workability, defined workability as “the property of concrete which determines the amount of useful internal work necessary to produce full compaction.” Another definition is that the “ease with which concrete can be compacted hundred per cent having regard to mode of compaction and place of deposition.”

Workability is a parameter in which a mix designer is required to specify in the mix design process, with full understanding of the type of work, distance of transport, loss of slump, method of placing and many other parameters involved. Assumption of right workability with proper understanding backed by experience will make the concreting operation economical and durable. The effort required to place a concrete mixture is determined largely by the overall work needed to initiate and maintain flow, which depends on the rheological properties of the cement paste and the internal friction between the aggregate particles. Workability is completely depending upon the properties and quantity of various ingredients of concrete. The properties of fresh concrete affect the choices of handling, consolidation and construction sequence. They may also affect the properties of the hardened concrete.

The properties of fresh concrete are short term requirements in nature and should satisfy the following requirements.

• It must be easily mixed and transported.
• It must be uniform throughout a given batch and between batches.
• It must keep its fluidity during the transportation period.
• It should have flow properties such that it is capable of completely filling the forms.
• It must have the ability to be fully compacted without segregation.
• It must set in a reasonable period of time.
• It must be capable of being finished properly, either against the forms or by means of trowel or other surface treatment.

Workability of fresh concrete consists of two aspects: consistency and cohesiveness. Consistency describes how easily fresh concrete flows, while cohesiveness describes the ability of fresh concrete to hold all the ingredients together uniformly. Traditionally, consistency can be measured by a slump cone test, the compaction factor or a ball penetration compaction factor test as a simple index for fluidity of fresh concrete. Cohesiveness can be characterized by a Vee-Bee test as an index of both the water holding capacity (the opposite of bleeding) and the coarse aggregate holding capacity (the opposite of segregation) of a plastic concrete mixture. The flowability of fresh concrete influences the effort required to compact concrete. The easier the flow, the less work is needed for compaction. A liquid like self compacting concrete can completely eliminate the need for compaction. However, such a concrete has to be cohesive enough to hold all the constituents, especially the coarse aggregates in a uniform distribution during the process of placing.

A concrete which has high consistency and which is more mobile, need not be of right workability for a particular job. Every job requires a particular workability. A concrete which is considered workable for mass concrete foundation is not workable for concrete to be used in roof construction. Concrete, which is considered workable when vibrator is used, is not workable when concrete is to be compacted by hand. Similarly a concrete considered workable when used in thick section is not workable when required to be used in thin sections. Therefore, the word workability assumes full significance of the type of work, thickness of section, extent of reinforcement and mode of compaction. Workability is not a fundamental property of concrete and it must be related to the type of construction and methods of placing, compacting and finishing.

Hundred per cent compaction of concrete is an important parameter for contributing to the maximum strength. Lack of compaction will result in air voids whose damaging effect on strength and durability is equally or more predominant than the presence of capillary cavities. To enable the concrete to be fully compacted with given efforts, normally a higher water/cement ratio than that calculated by theoretical considerations may be required. That is to say the function of water is also to lubricate the concrete so that the concrete can be compacted with specified effort forthcoming at the site of work. Compaction plays an important role in ensuring the long term properties of the hardened concrete, as proper compaction is vital in removing air from concrete and in achieving a dense concrete structure. Subsequently, the compressive strength of concrete can increase with an increase in the density. Traditionally, compaction is carried out using a vibrator. Nowadays, the newly developed self compacting concrete can reach a dense structure by its self weight without any vibration.

Factors Affecting Workability

The factors helping concrete to have more lubricating effect to reduce internal friction for helping easy compaction are given below.

1) Water Content and Water-Cement Ratio

Water-cement ratio is one of the most important factors which influence the concrete workability. Generally, a water cement ratio of 0.45 to 0.6 is used for good workable concrete without the use of any admixture. Higher the water/cement ratio, higher will be the water content per volume of concrete and concrete will be more workable. Higher water-cement ratio is generally used for manual concrete mixing to make the mixing process easier. For machine mixing, the water/cement ratio can be reduced. This generalized method of using water content per volume of concrete is used only for nominal mixes. For designed mix concrete, the strength and durability of concrete is of utmost importance and hence water cement ratio is mentioned with the design. Generally designed concrete uses low water-cement ratio so that desired strength and durability of concrete can be achieved.

2) Mix Proportions

Aggregate-cement ratio is an important factor influencing workability. Higher the aggregate-cement ratio, the leaner is the concrete. In lean concrete, less quantity of paste is available for providing lubrication, per unit surface area of aggregate and hence the mobility of aggregate is restrained. On the other hand, in case of rich concrete with lower aggregate-cement ratio, more paste is available to make the mix cohesive and fatty to give better workability. The more cement is used, concrete becomes richer and aggregates will have proper lubrication for easy mobility or flow of aggregates. The low quantity of cement with respect to aggregates will make the less paste available for aggregates and mobility of aggregates is restrained.

3) Size of Aggregate

The bigger the size of the aggregate, the less is the surface area and hence less amount of water is required for wetting the surface and less matrix or paste is required for lubricating the surface to reduce internal friction. For a given quantity of water and paste, bigger size of aggregates will give higher workability. Surface area of aggregates depends on the size of aggregates. For a unit volume of aggregates with large size, the surface area is less compared to same volume of aggregates with small sizes. When the surface area increases, the requirement of cement quantity also increases to cover up the entire surface of aggregates with paste. This will make more use of water to lubricate each aggregate. Hence, lower sizes of aggregates with same water content are less workable than the large size aggregates.

4) Shape of Aggregates

The shape of aggregates influences workability. Angular, elongated or flaky aggregate makes the concrete very harsh when compared to rounded aggregates or cubical shaped aggregates. Contribution to better workability of rounded aggregate will come from the fact that for the given volume or weight it will have less surface area and less voids than angular or flaky aggregate. Being round in shape, the frictional resistance is also greatly reduced. The river sand and gravel provide greater workability to concrete than crushed sand and aggregate.

5) Surface Texture

The influence of surface texture on workability is due to the total surface area of rough textured aggregate is more than the surface area of smooth rounded aggregate of same volume. It can be seen that rough textured aggregate will show poor workability and smooth or glassy textured aggregate will give better workability. A reduction of inter particle frictional resistance offered by smooth aggregates also contributes to higher workability.

6) Grading of Aggregates

This is one of the factors which will have maximum influence on workability. A well graded aggregate is the one which has least amount of voids in a given volume. Other factors being constant, when the total voids are less, excess paste is available to give better lubricating effect. With excess amount of paste, the mixture becomes cohesive and fatty which prevents segregation of particles. Aggregate particles will slide past each other with the least amount of compacting efforts. Well graded aggregates have all sizes in required percentages and low water cement ratio is sufficient for properly graded aggregates.

7) Use of Admixtures

There are many types of admixtures used in concrete for enhancing its properties. There are some workability enhancer admixtures such as plasticizers and superplasticizers which increase the workability of concrete even with low water-cement ratio. They are also called as water reducing concrete admixtures. They reduce the quantity of water required for same value of slump. Air entraining concrete admixtures is used in concrete to increase its workability. This admixture reduces the friction between aggregates by the use of small air bubbles which acts as the ball bearings between the aggregate particles. Similarly, the fine glassy pozzolanic materials, increases the surface area and offer better lubricating effects for giving better workability.

8) Cement Content of Concrete

Cement content affects the workability of concrete in good measure. More the quantity of cement, the more will be the paste available to coat the surface of aggregates and fill the voids between them. This will help to reduce the friction between aggregates and smooth movement of aggregates during mixing, transporting, placing and compacting of concrete. Also, for a given water-cement ratio, the increase in the cement content will also increase the water content per unit volume of concrete increasing the workability of concrete. Thus, increase in cement content of concrete also increases the workability of concrete.

9) Ambient Temperature

In hot weather, if temperature increases, the evaporation rate of mixing water also increases and hence fluid viscosity increases. This phenomenon affects the flowability of concrete and due to fast hydration of concrete; it will gain strength earlier which decreases the workability of fresh concrete.

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Method of Folding of Drawing Sheets

When drawings sheets are in more numbers, they have to be folded and kept in order to save the trace required for preserving them. Folding of drawings applies to only the drawings which are released for shop floor for manufacturing of components/reference. Original drawings will never be taken out of drawing office and they should be kept under safe custody. Drawings which are prepared on tracing sheets/transparencies like cloth, polymer, acrylic polymer transparencies should never be folded. They should be kept in polythene folders and kept in filing cabinets. Sometimes the blue prints/photo copies of drawings which are released to shop floor are also laminated for extending their life. While folding the drawings following care should be taken.

• It is required to the fold the drawings such that, they should not get defaced damaged.
• Drawing sheet to be folded such that the title block is easily visible to retrieve it and keeping it back.

Folding Principle of Drawings

The following is the method of folding printed drawing sheets for drawing sheet of size A1, A2 and A3 as recommended by as per IS 11664 - 1986. There are two methods of folding of drawing prints. The first method is intended for drawing prints to be filed or bound, while the second method is intended for prints to be kept individually in filing cabinet. Depending on the method of folding adopted, suitable folding marks are to be introduced in the tracing sheets as guide.

The basic principles in each of the above methods are to ensure that

• All large prints of sizes higher than A4 are folded to A4 sizes.
• The title blocks of all the folded prints appear in topmost position
• The bottom right corner shall be outermost visible section and shall have a width not less than 190 mm.

Fig. 1 Method of Folding of Drawing Prints

Fig.2 Folding of Prints for Sorting in Filing Cabinet as per IS 11664 - 1986

Fig.3 Folding of Prints for Filing or Binding as per IS 11664 - 1986

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Drawing sheet

Different qualities of drawing sheets are available in the market. Depending upon the nature of the drawing, the qualities of drawing papers are selected. The drawing paper should be of uniform thickness and of such quality that erasing should not have leave any impression on it. For ordinary pencil drawings, the paper selected should be tough and strong. It should be uniform in thickness and as white as possible. One of the sides of the drawing paper is usually rough and the other smooth. The smooth surface is the side for the drawing work. Good quality of paper with smooth surface should be selected for drawings which are to be inked and preserved for a long time. It should be such that the ink does not spread. These are of two types.

1) Hand-Made Paper

Hand-made papers have rough surfaces, pale in colour and not used for regular work, but meant for charts.

2) Mill-Made Paper

Mill-made papers are most commonly used for regular work, and are available in different sizes and rolls. They are specified by their weight in kg per ream or density in grams per square meter.

Designation of sheets

The drawing sheets are designated by symbols such as A0, A1, A2, A3, A4 and A5. A0 being the largest. Table 1 gives the length and breadth of the above sizes of sheets. For class work use of A2 size drawing sheet is preferred.While working or handling, the papers are liable to tear on the edges. So slightly large size (untrimmed) sheets are preferred. They are trimmed afterwards. IS: 10811:1983 give the designation of preferred trimmed and untrimmed sizes.

Table 1: Standard Sizes of Trimmed and Untrimmed Drawing Sheets

Sl. No.	Designation size in mm	Trimmed size in mm (Width x Length)	Untrimmed size in mm (Width x Length)
1	A0	841 x 1189	800 x 1230
2	A1	594 x 841	625 x 880
3	A2	420 x 594	450 x 625
4	A3	297 x 420	330 x 450
5	A4	210 x 297	240 x 330
6	A5	148 x 210	165 x 240

Fig. 1 Standard Size of Drawing Sheets 

Fig. 2 General Features of a Drawing Sheet

Basic Principles

Surface area of A0 size is one square meter. Successive format sizes (from A0 to A5) are obtained by halving along the length or doubling along the width. The areas of the two subsequent sizes are in the ratio 1:2. The basic principles involved in arriving at the sizes are:

(a) x:y = 1: √2

(b) xy =1

Where y and x are the sides and having a surface area of l m² so that x=0.841 m and. y =l.l89 m.

Fig. 3 Relationship between Two Sides

Quality Drawing Paper

The drawing papers should have sufficient teeth or grain to take the pencil lines and withstand repeated erasing. A backing paper is to be placed on the drawing board before fixing drawing/tracing paper, to get uniform lines. Before starting the drawing, the layout should be drawn. White drawing papers which do not become yellow on exposure to atmosphere are used for finished drawings, maps, charts and drawings for photographic reproductions. For pencil layouts and working drawings, cream colour papers are best suited.

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Construction Engineering

Construction Engineering is a professional discipline that deals with the designing, planning, construction and management of infrastructures such as roads, tunnels, bridges, airports, railroads, facilities, buildings, dams, utilities and other projects. Construction engineering is similar to civil engineering, which also focuses on infrastructure design and development, but with more emphasis on managing the construction process on project sites. It is an important field because it ensures structures are safe, well-made and dependable. It also makes sure construction projects get finished by a set date and according to strict plans and building codes.

Construction engineers are involved in nearly every step of a construction project, from its design to its implementation. They manage building projects and maintenance, often being present to oversee workers and activities on-site. Projects and infrastructure that construction engineers might work on include:

• Roads and highways
• Bridges
• Tunnels
• Railroads
• Housing projects
• Airports
• Energy sources like dams
• Facilities such as wastewater treatment plants
• Utilities
• Drainage and sewage systems
• Public buildings such as hospitals and sports stadiums

The typical duties of a construction engineer include:

• Calculating the cost of inspections, testing, materials, equipment and labor to create a budget for each project
• Managing funds appropriately to stay within budget
• Using computer software and simulations to create project designs and 3D models
• Performing risk analysis
• Surveying potential construction sites and planning their layouts
• Preparing bids from contractors and managing the contracting firms they hire
• Choosing and acquiring materials and equipment
• Hiring and overseeing workers and setting their schedules
• Making sure projects follow environmental laws, government regulations and building codes
• Designing and overseeing the construction of temporary structures needed on-site
• Using engineering and business skills to solve any problems that might occur during construction
• Staying up-to-date on the latest technology, building laws and construction processes 

Successful construction projects require a highly coordinated team effort. Builders and skilled trade’s people are required to lay brick, construct frames, install plumbing and electrical systems and ensure completion of a long list of other elements. With a large-scale construction project, construction engineers play an essential role in designing and implementing complicated building plans. They may also oversee the development or maintenance of critical infrastructure, ranging from roads and bridges to dams and water supplies.

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Water

Water is mainly used for construction purposes, preparation and curing of concrete and mortar, preparation of cement paste etc. Water is an important ingredient of concrete as it actively participates in the chemical reaction with cement. Since it helps to form the strength giving cement gel, the quantity and quality of water required must be checked.

Quality of Water

It should be noted that if water is fit for drinking it is fit for making concrete. This does not appear to be a true statement for all conditions. Some waters containing a small amount of sugar would be suitable for drinking but not for mixing concrete and conversely water suitable for making concrete may not necessarily be fit for drinking. Some specifications require that if the water is not obtained from source that has proved satisfactory, the strength of concrete or mortar made with questionable water should be compared with similar concrete or mortar made with pure water.

Some specification also accept water for making concrete if the pH value of water lies between 6 and 8 and the water is free from organic matter. Instead of depending upon pH value and other chemical composition, the best course to find out whether a particular source of water is suitable for concrete making or not, is to make concrete with this water and compare its 7 days and 28 days strength with companion cubes made with distilled water. If the compressive strength is upto 90%, the source of water may be accepted. This criterion may be safely adopted in places like coastal area of marshy area or in other places where the available water is brackish in nature and of doubtful quality.

Carbonates and bi-carbonates of sodium and potassium effect the setting time of cement. While sodium carbonate may cause quick setting, the bi-carbonates may either accelerate or retard the setting. The other higher concentrations of these salts will materially reduce the concrete strength. If some of these salts exceed 1000 ppm, tests for setting time and 28 days strength should be carried out. In lower concentrations they may be accepted. Brackish water contains chlorides and sulphates. When chloride does not exceed 10,000 ppm and sulphate does not exceed 3,000 ppm the water is harmless, but water with even higher salt content has been used satisfactorily.

Salts of Manganese, Tin, Zinc, Copper and Lead cause a marked reduction in strength of concrete. Sodium iodate, sodium phosphate and sodium borate reduce the initial strength of concrete to an extra ordinarily high degree. Silts and suspended particles are undesirable as they interfere with setting, hardening and bond characteristics. A turbidity limit of 2000 ppm has been suggested. Algae in mixing water may cause a marked reduction in strength of concrete either by combining with cement to reduce the bond or by causing large amount of air entrainment in concrete. Algae which are present on the surface of the aggregate have the same effect as in that of mixing water.

The initial setting time of the test block made with a cement and the water proposed to be used shall not differ by ±30 minutes from the initial setting time of the test block made with same cement and distilled water.

Table 1 Permissible limit for solids as per IS 456 of 2000

Material	Tested as per	Permissible limit Max.
Organic	IS 3025 (pt 18)	200 mg/l
Inorganic	IS 3025 (pt 18)	3000 mg/l
Sulphates (as SO3)	IS 3025 (pt 24)	400 mg/l
Chlorides (as Cl)	IS 3025 (pt 32)	2000 mg/l for concrete work not containing embedded steel and 500 mg/l for reinforced concrete work
Suspended	IS 3025 (pt 17)	2000 mg/l

Use of Sea Water for Mixing Concrete

Sea water has a salinity of about 3.5%. In that about 78% is sodium chloride and 15% is chloride and sulphate of magnesium. Sea water also contains small quantities of sodium and potassium salts. This can react with reactive aggregates in the same manner as alkalies in cement. Therefore sea water should not be used even for PCC if aggregates are known to be potentially alkali reactive. It is reported that the use of sea water for mixing concrete does not appreciably reduce the strength of concrete although it may lead to corrosion of reinforcement in certain cases.

Sea water slightly accelerates the early strength of concrete. But it reduces the 28 days strength of concrete by about 10 to 15%. However, this loss of strength could be made up by redesigning the mix. Water containing large quantities of chlorides in sea water may cause efflorescence and persistent dampness. When the appearance of concrete is important, sea water may be avoided. The use of sea water is also not advisable for plastering purpose which is subsequently going to be painted.

Divergent opinion exists on the question of corrosion of reinforcement due to the use of sea water. Some research workers cautioned about the risk of corrosion of reinforcement particularly in tropical climatic regions, whereas some research workers did not find the risk of corrosion due to the use of sea water. Experiments have shown that corrosion of reinforcement occurred when concrete was made with pure water and immersed in pure water when the concrete was comparatively porous, whereas, no corrosion of reinforcement was found when sea water was used for mixing and the specimen was immersed in salt water when the concrete was dense and enough cover to the reinforcement was given. From this it could be inferred that the factor for corrosion is not the use of sea water or the quality of water where the concrete is placed. The factors effecting corrosion is permeability of concrete and lack of cover. However, since these factors cannot be adequately taken care of always at the site of work, it may be wise that sea water be avoided for making reinforced concrete.

For economical or other passing reasons, if sea water cannot be avoided for making reinforced concrete, particular precautions should be taken to make the concrete dense by using low water/cement ratio coupled with vibration and to give an adequate cover of at least 7.5 cm. The use of sea water must be avoided in prestressed concrete work because of stress corrosion and undue loss of cross section of small diameter wires. The latest Indian standard IS 456 of 2000 prohibits the use of sea water for mixing and curing of reinforced concrete and prestressed concrete work. This specification permits the use of sea water for mixing and curing of plain cement concrete (PCC) under unavoidable situation.

(Ref : Concrete Technology Theory and Practice by M.S. Shetty)

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Highway Planning in India

Excavations in the sites of Indus valley, Mohenjo-dero and Harappan civilizations revealed the existence of planned roads in India as old as 2500 - 3500 BC. The Mauryan kings also built very good roads. Ancient books like Arthashastra written by Kautilya, a great administrator of the Mauryan times, contained rules for regulating traffic, depths of roads for various purposes and punishments for obstructing traffic.

During the time of Mughal period, roads in India were greatly improved. Roads linking North-West and the Eastern areas through Gangetic plains were built during this time. After the fall of the Mughals and at the beginning of British rule, many existing roads were improved. The construction of Grand Trunk road connecting North and South is a major contribution of the British. However, the focus was later shifted to railways, except for feeder roads to important stations.

Modern Developments

The First World War period and that immediately following it found a rapid growth in motor transport. So, the need for better roads became a necessity. For that, the Government of India appointed a committee called Road Development Committee with Mr. M.R. Jayakar as the chairman. This committee came to be known as Jayakar committee.

1) Jayakar Committee (1927)

In 1927 Jayakar committee for Indian road development was appointed. The major recommendations and the resulting implementations were given below.

• Committee found that the road development of the country has become beyond the capacity of local governments and suggested that Central government should take the proper charge considering it as a matter of national interest.
• They gave more stress on long term planning programme, for a period of 20 years (hence called twenty year plan) that is to formulate plans and implement those plans within the next 20 years.
• One of the recommendations was the holding of periodic road conferences to discuss about road construction and development. This paved the way for the establishment of a semi official technical body called Indian Road Congress (IRC) in 1934.
• The committee suggested imposition of additional taxation on motor transport which includes duty on motor spirit, vehicle taxation and license fees for vehicles plying for hire. This led to the introduction of a development fund called Central Road Fund in 1929. This fund was intended for road development.
• A dedicated research organization should be constituted to carry out research and development work. This resulted in the formation of Central Road Research Institute (CRRI) in 1950.

2) Nagpur Road Congress (1943)

The Second World War saw a rapid growth in road traffic and this led to the deterioration in the condition of roads. To discuss about improving the condition of roads, the government convened a conference of chief engineers of provinces at Nagpur in 1943. The result of the conference is the Nagpur plan.

• A twenty year development programme for the period (1943-1963) was finalized.
• It was the first attempt to prepare a coordinated road development programme in a planned manner.
• The roads were divided into four classes:
• National Highways which would pass through states, and places having national importance for strategic, administrative and other purposes.
• State Highways which would be the other main roads of a state.
• District Roads which would take traffic from the main roads to the interior of the district.
• According to the importance, some are considered as Major District Roads and the remaining as Other District Roads.
• Village Roads which would link the villages to the road system.
• The committee planned to construct 2 lakh kms of road across the country within 20 years.
• They recommended the construction of star and grid pattern of roads throughout the country.
• One of the objectives was that the road length should be increased so as to give a road density of 16kms per 100 sq.km

3) Bombay Road Congress (1961)

The length of roads envisaged under the Nagpur plan was achieved by the end of it, but the road system was deficient in many respects. The changed economic, industrial and agricultural conditions in the country wanted a review of the Nagpur plan. Accordingly, a 20 year plan was drafted by the Roads wing of Government of India, which is popularly known as the Bombay plan. The highlights of the plan were

• It was the second 20 year road plan (1961-1981)
• The total road length targeted to construct was about 10 lakhs.
• Rural roads were given specific attention. Scientific methods of construction were proposed for the rural roads.
• The necessary technical advice to the Panchayath should be given by State PWD's.
• They suggested that the length of the road should be increased so as to give a road density of 32kms/100 sq.km
• The construction of 1600 km of expressways was also then included in the plan.

4) Lucknow Road Congress (1984)

This plan has been prepared by keeping in view of the growth pattern envisaged in various fields by the turn of the century. Some of the salient features of this plan are as given below.

• This was the third 20 year road plan (1981-2001). It is also called Lucknow road plan.
• It aimed at constructing a road length of 12 lakh kilometers by the year 1981 resulting in a road density of 82kms/100 sq.km
• The plan has set the target length of NH to be completed by the end of seventh, eighth and ninth five year plan periods.
• It aims at improving the transportation facilities in villages, towns etc. such that no part of country is farther than 50 km from NH.
• One of the goals contained in the plan was that expressways should be constructed on major traffic corridors to provide speedy travel.
• Energy conservation, environmental quality of roads and road safety measures were also given due importance in this plan.

Current Scenario

About 60% of freight and 87% passenger traffic is carried by road. Although National Highways constitute only about 2% of the road network, it carries 40% of the total road traffic. Easy availability, adaptability to individual needs and cost savings are some of the factors which go in favour of road transport. Road transport also acts as a feeder service to railway, shipping and air traffic. The number of vehicles has been growing at an average pace of around 10% per annum. The share of road traffic in total traffic has grown from 13.8% of freight traffic and 15.4% of passenger traffic in 1950-51 to an estimated 62.9% of freight traffic and 90.2% of passenger traffic by the end of 2009-10. The rapid expansion and strengthening of the road network, therefore, is imperative, to provide for both present and future traffic and for improved accessibility to the hinterland.

Road Development Plan Vision: 2021

The Government of India takes up the development works of National Highways through five year plans. However, the Ministry in 2001 had prepared, through Indian Roads Congress (IRC), `Road Development Plan VISION: 2021’ for a period of 20 years (2001-2021). This document provides the vision for the next 20 years for development and maintenance of all categories of roads i.e. National Highways, State Highways, Major District Roads and Rural Roads. The urban roads as well as the roads for specific need e.g. tourism, forestry, mining and industrial areas etc. have also been considered. The research and development, mobilization of resources, capacity building and human resources development, quality system, environment and energy considerations for the highway sector and highway safety are also included in this document which serves as only a valuable guide to the Centre and the State Governments for planning purpose. Salient features of Vision: 2021 are given below.

• To construct National Highway such that, it forms 100 sq.km network.
• To construct Express Highway for fast moving vehicle and Four-lane road having maximum traffic density.
• To connect District Head quarter by four lane, Taluk head quarters, Industrial centre, Tourist centre by two lane State Highways.
• To connect Village having population more than 1500 by MDR (Major District Road).
• To connect Village having population 1000 to 1500 by ODR (Other District Road).
• To connect remote Village by all weather road.

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