Precipitation

Precipitation refers to all the moisture that comes to the earth from atmosphere. This may be in the form of rain, snow, sleet, fog, dew or hail. Precipitation can occur only when the air containing moisture is cooled sufficiently to condense a part of the moisture which is present in the atmosphere. The atmospheric air always contains moisture. Evaporation from the oceans is the major source (about 90%) of the atmospheric moisture for precipitation. Continental evaporation contributes only about 10% of the atmospheric moisture for precipitation. The atmosphere contains the moisture even on days of bright sun shine.

For the occurrence of precipitation, some mechanism is required to cool the atmospheric air sufficiently to bring it to (or near) saturation. This mechanism is provided by either convective systems (due to unequal radiative heating or cooling of the earth’s surface and atmosphere) or by orographic barriers (such as mountains due to which air gets lifted up and consequently undergoes cooling, condensation and precipitation) and results into, respectively, convective and orographic precipitations. Alternatively, the air lifted into the atmosphere may converge into a low pressure area (or cyclone) causing cyclonic precipitation. Artificially induced precipitation requires delivery of dry ice or silver iodide or some other cloud seeding agent into the clouds by aircraft or balloons.

Forms of Precipitation

1) Drizzle

A light steady rain in fine drops (0.5 mm) and intensity <1 mm/hr.

2) Rain

The condensed water vapour of the atmosphere falling in drops (>0.5 mm, maximum size - 6 mm) from the clouds.

3) Glaze

Freezing of drizzle or rain when they come in contact with cold objects.

4) Sleet

Frozen rain drops while falling through air at subfreezing temperature.

5) Snow

Ice crystals resulting from sublimation (i.e., water vapour condenses to ice).

6) Snow flakes

Ice crystals fused together.

7) Hail

Small lumps of ice (>5 mm in diameter) formed by alternate freezing and melting, when they are carried up and down in highly turbulent air currents.

8) Dew

Moisture condensed from the atmosphere in small drops upon cool surfaces.

9) Frost

A feathery deposit of ice formed on the ground or on the surface of exposed objects by dew or water vapour that has frozen.

10) Fog

A thin cloud of varying size formed at the surface of the earth by condensation of atmospheric vapour (interfering with visibility).

11) Mist

A very thin fog.

Classification of Rainfall Based on Rate

Table 1: Classification of Rainfall Based on Rate

Sl. No.	Type of Rainfall	Rate (mm/hr)
1	Light	upto 2.5
2	Moderate	2.5  - 7.5
3	Heavy	>7.5

Types of Precipitation

Adiabatic cooling resulting from the vertical transport of air mass is the primary cause of condensation and hence of precipitation. Depending on the conditions responsible for the vertical motion of the air mass, precipitation can be classified into the following four types.

1) Convective Precipitation

Convective precipitation results from the heating of the earth's surface. The warm ground heats the air over it. As the air warms, the air molecules begin to move further apart. With increased distance between molecules, the molecules are less densely packed. Thus, the air becomes “lighter” and rises rapidly into the atmosphere. As the air rises, it cools. Water vapour in the air condenses into clouds and precipitation.

Fig. 1 Convective Precipitation

2) Orographic Precipitation

Orographic precipitation results when warm moist air moving across the ocean is forced to rise by large mountains. As the air rises, it cools because a higher elevation results in cooler temperatures. Cold air cannot hold as much moisture as warm air. As air cools, the water vapour in the air condenses and water droplets form. Clouds forms and precipitation (rain or snow) occurs on the windward side of the mountain.

This air is now dry and rises over top the mountain. As the air moves back down the mountain, it collects moisture from the ground via evaporation. This side of the mountain is called the leeward side. It receives very little precipitation.

Fig. 2 Orographic Precipitation

3) Cyclonic Precipitation or Frontal Precipitation

Cyclonic or frontal precipitation results when the leading edge of a warm, moist air mass (warm front) meets a cool and dry air mass (cold front). The molecules in the cold air are more tightly packed together (i.e., more dense) and thus, the cold air is heavier than the warm air. The warmer air mass is forced up over the cool air.

As it rises, the warm air cools, the water vapour in the air condenses, clouds are formed and it result in precipitation. This type of system is called Frontal Precipitation because the moisture tends to occur along the front of the air mass. In another words, unequal heating of the earth’s surface creates low and high pressure regions. Movement of air masses from the high pressure regions to low pressure regions displaces the low pressure air upward to cool and cause precipitation. Cyclonic precipitation can be of two types.

Fig. 3 Cyclonic Precipitation

a) Frontal Precipitation

A frontal is called as the hot moist air mass boundary. This precipitation is caused by the expansion of air near the frontal surface.

b) Non-Frontal Precipitation

This is a cold moist air mass boundary that moves and results in precipitation.

There are two main types of cyclones namely Tropical Cyclone (also called hurricane or typhoon) of comparatively small diameter of 300-1500 km causing high wind velocity and heavy precipitation and the Extra-Tropical Cyclone of large diameter up to 3000 km causing wide spread frontal type precipitation.

When two air masses due to contrasting temperatures and densities clash with each other, condensation and precipitation occur at the surface of contact. This surface of contact is called a ‘front’ or ‘frontal surface’. If a cold air mass drives out a warm air mass’ it is called a ‘cold front’ and if a warm air mass replaces the retreating cold air mass, it is called a ‘warm front’. On the other hand, if the two air masses are drawn simultaneously towards a low pressure area, the front developed is stationary and is called a ‘stationary front’. Cold front causes intense precipitation on comparatively small areas, while the precipitation due to warm front is less intense but is spread over a comparatively larger area. Cold fronts move faster than warm fronts and usually overtake them, the frontal surfaces of cold and warm air sliding against each other. This phenomenon is called ‘occlusion’ and the resulting frontal surface is called an ‘occluded front’.

Characteristics of Precipitation in India

India receives more than 75% of its annual precipitation during the monsoon season (June to September). The monsoon (i.e., south-west monsoon) originates in the Indian Ocean and appears in the southern part of Kerala by the end of May or the beginning of June. Monsoon winds, then, advance and cover the entire country by mid-July. The monsoon season is not a period of continuous rainfall. The temporal and spatial variability of the magnitude of rainfall results into regions of droughts and floods. Assam and the north-eastern region are the heavy rainfall regions (with average annual rainfall ranging from 2000-4000 mm) and Uttar Pradesh, Haryana, Punjab, Rajasthan and Gujarat constitute low rainfall regions (with average annual rainfall less than about 1000 mm). Western Ghats receive about 2000-3000 mm of annual rainfall.

Around mid-December, the western disturbances cause moderate to heavy rain and snowfall (about 250 mm) in the Himalayas and Jammu and Kashmir and other northern regions of the country. Low pressure areas formed in the Bay of Bengal during this period cause some rainfall in the south-eastern parts of the country.

Read More

Work, Power, Energy and Force

Work (W)

When force acts on a body and the body undergoes some displacement, then work is said to be done. The amount of work done is equal to the product of force and displacement in the direction of force. Let, ‘P’ be the force acting on the body and ‘s’ be the distance through which the body moves, then, 

Fig.1 Body moves in the direction of application of force

                                         Work done by the force, P = Force × Distance

                                                                               W = P × s

Sometimes, the force P does not act in the direction of motion of the body, or in other words, the body does not move in the direction of the force as shown in figure. In such a case, work done is expressed as the product of the component of the force in the direction of motion and the displacement.

Fig. 2 Body is not moving in the direction of application of force

Hence,

                                                         Work done W = P cos θ × s

If θ = 90⁰, cos θ = 0 and there will be no work done i.e. if force and displacement are at right angles to each other, work done will be zero. Similarly, work done against the force is taken as negative.

When the point of application of the force moves in the direction of motion of the body, work is said to be done by the force. Work done by the force is taken as +ve.

As work is the product of force and displacement, the units of work depend upon the units of force and displacement. Work is expressed in N-m or kN-m. One Newton-meter is the work done by a force of 1N in moving the body through 1m. It is called Joule. 

                                                                   1J = 1 N-m. 

Similarly, 1 kilo Newton-meter is the work done by a force of 1 kN in moving a body through 1m. It is also called kilojoules. 

                                                                  1kJ = 1 kN-m

Power (P)

Power is defined as the rate of doing work. It is thus the measure of performance of engines. For example, an engine doing a certain amount of work, in one second, will be twice as powerful as an engine doing the same amount of work in two seconds. In SI units, the unit of power is watt (W) which is equal to 1 N-m/s or 1 J/s. It is also expressed in Kilowatt (kW), which is equal to 10³ W and Megawatt (MW) which is equal to 10⁶ W. In case of engines, the following two terms are commonly used for power.

                                                                    Power = Work / Time

                                                                            P = W / t

Another unit of power (In British engineering) is Horsepower (hp). Where 

                                                                          1hp = 746 W

Energy (E)

Energy may be defined as the capacity for doing work. Since energy of a machine is measured by the work it can do, therefore unit of energy is same as that of work. In S.I system, energy is expressed in Joules or Kilojoules. It exists in many forms i.e., mechanical, electrical chemical, heat, light etc. There are two types of mechanical energy.

1) Potential Energy(PE or U)

It is the energy possessed by a body by virtue of its position. A body at some height above the ground level possesses potential energy. If a body of mass (m) is raised to a height (h) above the ground level, the work done in rising the body is

                                        Work done = Weight of the body × distance through which it moved

                                                               = (mg) ×h

                                                         PE = mgh

This work (equal to mgh) is stored in the body as potential energy. The body, while coming down to its original level, can do work equal to mgh. Potential energy is zero when the body is on the earth. 

Compressed air also possesses potential energy because it can do some work in expanding, to the volume it would occupy at atmospheric pressure. A compressed spring also possesses potential energy because it can do some work in recovering to its original shape.

2) Kinetic Energy (KE)

It is the energy possessed by a body by virtue of its motion. It is the energy, possessed by a body, for doing work by virtue of its mass and velocity of motion. We can measure kinetic energy of a body by finding the work done by the body against external force to stop it.

Let, m= Mass of the body

u= Velocity of the body at any instant

P= External force applied

a=Constant Retardation of the body

s= distance travelled by the body before coming to rest

As the body comes to rest its final velocity v = 0

Work done, 

                                               W = Force × Distance = P × s ..….... (1)

Now substituting value of (P = m.a) in equation (1),

                                               W = ma × s = m.a.s ...…....(2)

But, v²-u²= -2as (for retardation)

                                                    0 – u²= -2as

                                                          u²= 2as

                                                         as =1/2 u²

Now substituting value of (a.s) in equation (2) and replacing work done with kinetic energy

                                    Kinetic Energy KE = 1/2mu²

If initial velocity is taken as v instead of u then

                                                            KE =1/2 mv²

Force (F)

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 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. The unit of force is N or kgm/s². Mathematically,

                                                       Force = Mass× Acceleration

Where

F-Force, m-Mass and a-Acceleration

Read More

Strain (ε)

When a single force or a system force acts on a body, it undergoes some deformation. This deformation per unit length is known as strain. Strain is a dimensionless unit since it is the ratio of two lengths. But it also a common practice to state it as the ratio of two length units like m/m or mm/mm etc. Strain is represented by 'ε' (Greek lowercase alphabet Epsilon).

No material is perfectly rigid. Under the action of forces it undergoes changes in shape and size. All materials including steel, cast iron, brass, concrete etc. undergo deformation when loaded. But the deformations are very small and hence we cannot see them with naked eye. There are instruments like extensometer and electric strain gauges which can measure this extension. Strain may be of linear strain or lateral strain.

The bars extend under tensile force and shorten under compressive forces along axial direction. The change in length per unit length is known as linear strain/longitudinal strain. Thus, 

When there is a changes in longitudinal direction takes place change in lateral direction also take place. The nature of these changes in lateral direction are exactly opposite to that of changes in longitudinal direction i.e., if extension is taking place in longitudinal direction, the shortening of lateral dimension takes place and if shortening is taking place in longitudinal direction extension takes place in lateral directions. The lateral strain may be defined as changes in the lateral dimension per unit lateral dimension. Thus,

Consider a square bar of length ‘L’ and breadth ‘b’. The linear dimension (length) changes by ‘Δ’ due to the application of tensile or compressive force. The lateral dimension (breadth) changes by b’ due to the application of tensile or compressive force as shown in the figure.

Fig.1 Deformation of a square bar due to axial tensile/compressive force

Shear Strain (ϕ)

This type of strain is produced when the deforming force causes change in the shape of the body. The distortion produced by shear stress on an element or rectangular block is shown in the figure. The shear strain is expressed by angle ‘ϕ’ and it can be defined as the change in the right angle. It is measured in radians and is dimensionless in nature.

Shearing stress has a tendency to distort the element to position AB′C′D from the original position ABCD as shown in figure. This deformation is expressed in terms of angular displacement and is called shear strain. 

Fig.2 Deformation of a rectangular body fixed at bottom due to shear force

Read More

Fundamental Principles of Surveying

There are two fundamental principles of surveying which should be taken into consideration to get good results.

1) Working from whole to part

Working from whole to part is achieved by covering the area to be surveyed with a number of control points called primary control points whose pointing have been determined with a high precision equipment. Based on these points, a number of large triangles are drawn. Secondary control points are then established to fill the gaps with lesser precision than the primary control points. At a more detailed and less precise level, tertiary control points at closer intervals are finally established to fill in the smaller gaps. According to the first principle, the whole survey area is first enclosed by main stations (i.e. control stations) and main survey lines. The area is then divided into a number of divisions by forming well conditioned triangles.

Fig. 1 Working from whole to part - Representation

The main purpose in survey to work from whole to part is to localize the errors. During measurement, if there is any error, then it will not affect the whole work, but if the reverse process is followed then the minor error in measurement will be magnified. In partial terms, this principle involves covering the area to be surveyed with large triangles. These are further divided into smaller triangles and the process continues until the area has been sufficiently covered with small triangles to a level that allows detailed survey to be made in a local level.

2) Using measurements from two control points to fix other points

According to the second principle the points are located by linear or angular measurement or by both in surveying. If two control points are established first, then a new station can be located by linear measurement. Given two points whose length and bearings have been accurately determined, a line can be drawn to join them hence surveying has control reference points. The locations of various other points and the lines joining them can be fixed by measurements made from these two points and the lines joining them. For an example, if A and B are the control points, the following operations can be performed to fix a new point C.

Fig. 2 Location of the third point from the position of two known points

1. The distance AB can be measured accurately and using points A and B as the centers, ascribe arcs using distances d1 and d2, then fix point C (where they intersect).
2. Draw a perpendicular from AB to a point C.
3. Taking one linear measurement from B and one angular measurement as <ABC
4. Taking two angular measurement at A & B as angles < CAB and <ABC.
5. Taking one angle at B as < ABC and one linear measurement from A as AC.

Read More

Density, Mass Density, Specific Weight, Specific Volume and Relative Density

1) Density (r)

The basic definition of the density of a substance is the ratio of the mass of a given amount of the substance to the volume it occupies. Thus, density of a fluid is its mass per unit volume and the SI unit is kg/m³.The density of a fluid, denoted by ‘r’ (lowercase Greek letter ‘rho’).

Fluid density is temperature dependent and to a lesser extent it is pressure dependent. For example the density of water at sea level at 4^oC is 1000 kg/m³ , whilst at 50^oC is 988 kg/m³.

2) Mass Density (r)

The mass density of a fluid is its mass per unit volume, normally stated in kilograms per cubic metre (kg/m³ ). The symbol used for mass density is `rho’ (r).

Typical mass densities are:

Material	Mass density (kg/m3)
Water	1000
Sea water	1024
Mercury	13.6 x 10^3
Oil	800 - 900
Air	1.23

Since a molecule of a substance has a certain mass regardless of its state (solid, liquid or gas), the mass density is proportional to the number of molecules in a unit volume of the fluid. As the molecular activity and spacing increase with temperature, fewer molecules exist in a given volume of fluid as temperature rises. Therefore, the mass density of a fluid decreases with increasing temperature. Further by application of pressure a large number of molecules can be forced into a given volume, it is to be expected that the mass density of a fluid will increase with increasing pressure.

3) Weight Density/Specific Weight (w or g)

The weight density (also called specific weight) of a fluid is its weight per unit volume, with unit of Newton per cubic metre (N/m³). The weight density is calculated by multiplying the mass density by 9.8, the value for the gravitational acceleration. It is denoted by a symbol ‘w’ or ‘g’ (Greek letter ‘gama’). As it represents the force exerted by gravity on a unit volume of fluid, it has units of force per unit volume.

Weight Density = Mass Density x g

The mass density ‘r’ and specific weight ‘w’ are related as indicated below.

where g is acceleration due to gravity.

The specific weight depends on the acceleration due to gravity and the mass density. Since the acceleration due to gravity varies from place to place, the specific weight will also vary. Further the mass density changes with temperature and pressure, hence the specific weight will also depend upon temperature and pressure.

4) Specific Volume (v)

Specific volume of a fluid is the volume of the fluid per unit mass. Thus it is the reciprocal of mass density. It is generally denoted by ‘v’. In SI units specific volume is expressed in cubic meter per kilogram i.e., m³/kg. The specific volume of water is 

                                                   1 /ρ=1/1000 = 0.001 m³ /kg

For liquids the mass density, the specific weight and specific volume vary only slightly with the variation of temperature and pressure. It is due to the molecular structure of the liquids in which the molecules are arranged very compactly (in contrast to that of a gas). The presence of dissolved air, salts in solution and suspended matter will slightly increase the values of the mass density and the specific weight of the liquids.

For gases the values of the above properties vary greatly with variation of either temperature, or pressure, or both. It is due to the molecular structure of the gas in which the molecular spacing (i.e., volume) changes considerably on account of pressure and temperature variations.

5) Relative Density (RD)

The relative density is the ratio of the density of a substance to some standard density. The standard density chosen for comparison with the density of a solid or a liquid is invariably that of water at 4°C. The relative density of a fluid is the mass density of the fluid compared to the mass density of water at 4°C. RD is a pure ratio. So, it has no units. It is also sometimes referred as specific gravity.

Example Question

If a 25 litre volume of oil has a mass of 20 kilograms, determine the oil’s mass density, weight density, relative density and specific volume.

     Mass density = mass/volume

                           = 20/0.025

                           = 800 kg/m³

  Weight density = mass density x g

                           = 800 x 9.8

                           = 7840 N/m

Relative density = mass density of oil/ mass density of water

                           = 800/1000

                           = 0.8

Specific volume = 1/r

                           = 1/800

                           = 1.25 x10 ^ -3 m³ /kg

Read More

Drawing Board

Drawing board is rectangular in shape and is made of four to six strips of well-seasoned soft wood such as pine, fir, oak etc. and about 25 mm thick. The wooden strips are cleated at the back by two battens by means of screws to prevent warping. One of the edges of the board is used as the working edge, on which the T-square is made to slide. It should be perfectly straight. In some boards, this edge is grooved throughout its length and a perfectly straight ebony edge is fitted inside this groove. This provides a true and more durable guide for the T-square to slide on. 

Fig. 1 Bottom Surface of Drawing Board

Fig. 2 Top Surface of Drawing Board

Drawing board is made of soft wooden platens. It is used for supporting the drawing paper/tracing paper for making drawings. Almost perfect planning of the working surface of the drawing board is to be ensured. Drawing board should be softer enough to allow insertion and removal of drawing pins. Drawing board is made in various sizes. Standard drawing boards are designated as follows as per IS: 1444-1989. D2 and D3 size of drawing board is normally recommended for using in schools and colleges.

Table 1. Standard Sizes of Drawing Boards

Sl. No.	Designation	Size (mm)	To be used with sheet sizes
1	D0	1500 x 1000 x 25	A0
2	D1	1000 x 700 x 25	A1
3	D2	700 x 500 x 15	A2
4	D3	500 x 350 x 15	A3

Now-a-days the drawing boards are available with laminated surfaces. The flatness can be checked by placing a straight edge on its surface. If no light passes between them, the surface is perfectly flat. Large size boards are used in drawing offices of engineers and engineering firms. The drawing board is placed on the table in front of the student, with its working edge on his left side. It is more convenient if the table-top is sloping downwards towards the student. If such a table is not available, the necessary slope can be obtained by placing a suitable block of wood under the distant longer edge of the board.

Read More

Coarse aggregate

When the aggregate is sieved through 4.75mm sieve, the aggregate retained is called coarse aggregate. They are obtained by natural disintegration or by artificial crushing of rocks. Gravel, cobble and boulders come under this category. The maximum size of aggregate can be 80 mm. In general, 40mm size aggregate used for plain cement concrete (PCC) and 20mm size is used for reinforced cement concrete (RCC).

The size is governed by the thickness of section, spacing of reinforcement, clear cover, mixing, handling and placing methods. For economy the maximum size should be as large as possible but not more than one-fourth of the minimum thickness of the member. For reinforced sections the maximum size should be at least 5 mm less than the clear spacing between the reinforcement and also at least 5 mm less than the clear cover. Aggregate more than 20 mm size is seldom used for reinforced cement concrete structural members. The size range of various coarse aggregates is given below.

Table 1: Size range of coarse aggregate

Coarse aggregate	Size variation (mm)
Fine gravel	4 – 8
Medium gravel	8 – 16
Coarse gravel	16 – 64
Cobbles	64 – 256
Boulders	>256

Classification of Aggregates as per Shape

The shape is one of the most effective ways of differentiating aggregates. Aggregate is derived from naturally occurring rocks by blasting or crushing etc., so, it is difficult to attain required shape of aggregate. But, the shape of aggregate will affect the workability of concrete. So, we should take care about the shape of aggregate. Aggregates are classified according to shape into the following types.

1) Rounded Aggregate

The rounded aggregates are completely shaped by attrition (the resistance of a granular material to wear) and available in the form of seashore gravel. Rounded aggregates result in the minimum percentage of voids (32 – 33%) hence gives more workability. They require a lesser amount of water-cement ratio. They are not considered for high-strength concrete because of poor interlocking behavior and weak bond strength. It is used mainly in road construction for filling voids between angular aggregates.

Example: River or seashore gravels, desert seashore and windblown sands

Fig. 1 Rounded Aggregate

2) Irregular Aggregates/ Partially Rounded Aggregates

The irregular or partly rounded aggregates are partly shaped by attrition and these are available in the form of pit sands and gravel. Irregular aggregates may result 35- 37% of voids. These will give lesser workability when compared to rounded aggregates. The bond strength is slightly higher than rounded aggregates but not as required for high strength concrete. It is used in low strength or medium-strength concrete, road construction etc.

Example: Pit sands and gravels, land or dug flints, cuboid rock

Fig. 2 Irregular Aggregate

3) Angular Aggregates

The angular aggregates consist of well defined edges formed at the intersection of roughly planar surfaces and these are obtained by crushing the rocks. Angular aggregates result maximum percentage of voids (38-45%) hence gives less workability but this problem is minimized by filling voids with rounded or smaller aggregates. They give 10-20% more compressive strength due to development of stronger aggregate-mortar bond. So, these are useful in high strength concrete manufacturing.

Example: Crushed rocks of all types; talus; screes

Fig. 3 Angular Aggregate

4) Flaky Aggregates

When the aggregate thickness is small when compared with width and length of that aggregate it is said to be flaky aggregate, or on the other, when the least dimension of aggregate is less than the 60% of its mean dimension then it is said to be flaky aggregate or an aggregate is said to be flaky if its least dimension is less than 3/5 (0.6) of the mean dimension. The use of flaky aggregates reduces the flowing capacity of concrete. They lead to segregation in concrete and harshness of concrete. Flaky aggregates also have very low crushing strength so should not be used in high-strength concrete and road construction.

Example: Laminated rocks

Fig. 4 Flaky Aggregate

5) Elongated Aggregates

When the length of aggregate is larger than the other two dimensions then it is called elongated aggregate or the length of aggregate is greater than 180% of its mean dimension or The aggregate is said to be elongated if its greater length is greater than 9/5th of its mean dimension. Elongated aggregates also have very low crushing strength so should not be used in high-strength concrete and road construction.

Fig. 5 Elongated Aggregate

6) Flaky and Elongated Aggregates

When the aggregate length is larger than its width and width is larger than its thickness then it is said to be flaky and elongated aggregates. Flaky, elongated, flaky and elongated aggregates are not suitable for concrete mixing. These are generally obtained from the poorly crushed rocks.

Fig. 6 Flaky and Elongated Aggregate

Classification of Coarse Aggregates Based on Natural or Artificial Formation

Basically, coarse aggregates are classified as either natural or artificial.

1) Natural Aggregates

These are the aggregates that are found from natural sources. Natural aggregates are further divided into two categories as stated below.

a) Gravel

The main origin of gravel is river beds, stream deposits, etc. These aggregates are formed by weathering of bedrock and subsequent transportation and deposition by water, ice, gravity, etc.

b) Crushed Aggregates

Crushed aggregates are obtained from the quarries. They are widely available in the market. Crushed aggregates are small rock fragments that are subjected to mechanical processing such as crushing, washing and sizing.

2) Artificial Aggregates

Artificial aggregates are used because they are in case environment-friendly materials. They are manufactured from various pollutant by-products such as ash, power station solid waste, rice husk ash, furnace slag, granite powder, iron ore slag, over burnt brickbats etc. By using these industrial by-products, we can reduce environmental pollution and protect natural resources.

Read More