rajiv gandhi proudyogiki vishwavidyalaya, bhopal b.tech...
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Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal
B.Tech Syllabus 1st Semester Civil Engineering
Course Content
Subject: Basic Civil Engineering & Engineering Mechanics Code: BT- 2004
1. SURVEYING AND FIELD WORK:
1. Linear measurements : Chain and Tape Surveying, Errors, Obstacles, Booking and
Plotting, Calculation of Areas.
2. Angular Measurements : Bearing, Prismatic Compass, Local Attraction, Bowditch’s
Rule of correction, traverse open and closed, plotting of traverse, accuracy and precision.
3. Levelling : Types of Levels, Levelling Staff, Measurements, recording, curvature and
refraction correction, reciprocal levelling, sensitivity of level.
4. Contours : Properties, uses, plotting of contours, measurement of drainage and volume of
reservoir.
5. Measurement of area by planimeter.
2. BUILDING MATERIALS :
1. Bricks : Manufacturing, field and laboratory test, Engineering properties. 2. Cement
: Types, physical properties, laboratory tests 3. Concrete and Mortar Materials :
Workability, Strength Properties of Concrete, Nominal Proportion of Concrete, Preparation of
Concrete, Compaction Curving. Mortar : Properties and Uses.
Reference Books:
1. S. Ramamrutam & R.Narayanan; Basic Civil Engineering, Dhanpat Rai Pub.
2. Prasad I.B., Applied Mechanics, Khanna Publication.
3. Punmia, B.C., Surveying, Standard book depot.
4. Shesha Prakash and Mogaveer; Elements of Civil Engg & Engg. Mechanics; PHI
5. S.P,Timoshenko, Mechanics of stricture, East West press Pvt.Ltd.
6. Surveying by Duggal – Tata McGraw Hill New Delhi.
7. Building Construction by S.C. Rangwala- Charotar publications House, Anand.
8. Building Construction by Grucharan Singh- Standard Book House, New Delhi
9. Global Positioning System Principles and application- Gopi, TMH
10. R.C. Hibbler – Engineering Mechanics: Statics & Dynamics.
11. A. Boresi & Schmidt- Engineering Mechines- statics dynamics, Thomson’ Books
12. R.K. Rajput, Engineering Mechanics S.Chand & Co.
St. Aloysius Institute of Technology, Jabalpur
Semester: 1st Sem Subject: Basic Civil Engineering Subject Code: BT-2004
SURVEYING:-
UNIT –I: LINEAR MEASUREMENTS
1. Introduction to Surveying
The objective of this lesson is to deal with the introduction and basics of surveying (importance,
objectives, divisions, classifications and principles).
Surveying is defined as the science of making measurements of the earth specifically the surface
of the earth. This is being carried out by finding the spatial location (relative / absolute) of points
on or near the surface of the earth.
Different methods and instruments are being used to facilitate the work of surveying.
The primary aims of field surveying are :
• to measure the horizontal distance between points.
• to measure the Vertical elevation between points.
• to find out the Relative direction of lines by measuring horizontal angles with reference to any
arbitrary direction and to find out Absolute direction by measuring horizontal angles with
reference to a fixed direction. These parameters are utilised to find out the relative or absolute
coordinates of a point / location.
Importance of Surveying to Civil Engineers
The planning and design of all Civil Engineering projects such as construction of highways,
bridges, tunnels, dams etc are based upon surveying measurements.
Moreover, during execution, project of any magnitude is constructed along the lines and points
established by surveying.
Thus, surveying is a basic requirement for all Civil Engineering projects.
Other principal works in which surveying is primarily utilised are
• to fix the national and state boundaries;
• to chart coastlines, navigable streams and lakes;
• to establish control points;
• to execute hydrographic and oceanographic charting and mapping; and
• to prepare topographic map of land surface of the earth.
Objectives of Surveying
• To collect field data;
• To prepare plan or map of the area surveyed;
• To analyse and to calculate the field parameters for setting out operation of actual
engineering works.
• To set out field parameters at the site for further engineering works.
Divisions of Surveying
The approximate shape of the earth can best be defined as an oblate or tri-axial ovaloid. But,
most of the civil engineering works, concern only with a small portion of the earth which seems
to be a plane surface. Thus, based upon the consideration of the shape of the earth, surveying is
broadly divided into two types.
Geodetic Surveying- In this branch of surveying, the true shape of the earth is taken into
consideration.
This type of surveying is being carried out for highly precise work and is adopted for surveying
of large area.
Plane Surveying- In this method of surveying, the mean surface of the earth is considered to be
a plane surface. This type of survey is applicable for small area (less than 200 square kilometer).
Thus for most of the Civil Engineering projects, methods of plane surveying are valid.
Fundamental assumptions in Plane surveying
• All distances and directions are horizontal;
• The direction of the plumb line is same at all points within the limits of the survey;
• All angles (both horizontal and vertical) are plane angles;
• Elevations are with reference to a datum.
Classifications of Surveying
Based on the purpose (for which surveying is being conducted), Surveying has been classified
into:
• Control surveying : To establish horizontal and vertical positions of control points.
• Land surveying : To determine the boundaries and areas of parcels of land, also known as
property survey, boundary survey or cadastral survey.
• Topographic survey : To prepare a plan/ map of a region which includes natural as well as
and man-made features including elevation.
• Engineering survey : To collect requisite data for planning, design and execution of
engineering projects. Three broad steps are
1) Reconnaissance survey : To explore site conditions and availability of infrastructures.
2) Preliminary survey : To collect adequate data to prepare plan / map of area to be used for
planning and design.
3) Location survey : To set out work on the ground for actual construction / execution of the
project.
• Route survey : To plan, design, and laying out of route such as highways, railways, canals,
pipelines, and other linear projects.
• Construction surveys : Surveys which are required for establishment of points, lines, grades,
and for staking out engineering works (after the plans have been prepared and the structural
design has been done).
• Astronomic surveys : To determine the latitude, longitude (of the observation station) and
azimuth (of a line through observation station) from astronomical observation.
• Mine surveys : To carry out surveying specific for opencast and underground mining
purposes.
Principles of Surveying
The fundamental principles upon which the surveying is being carried out are
working from whole to part.
after deciding the position of any point, its reference must be kept from at least two
permanent objects or stations whose position have already been well defined.
The purpose of working from whole to part is
to localise the errors and
to control the accumulation of errors.
This is being achieved by establishing a heirarchy of networks of control points. The less precise
networks are established within the higher precise network and thus restrict the errors. To
minimise the error limit, highest precise network (primary network) of control points are
established using the most accurate / precise instruments for collection of data and rigorous
methods of analysis are employed to find network parameters. This also involves most skilled
manpower and costly resources which are rare and cost intensive.
Operations in Surveying
Operations in surveying consists of :
Planning
Field Observation
Office Works
Setting out works
Exercise 1
Ex.1-1 State two primary divisions of surveying.
Ex.1-2 Enumerate the fundamental parameters of surveying measurement?
Ex.1-3 State the basic principles of surveying.
Ex.1-4 State the basic assumptions of plane surveying.
2. Measurement of Horizontal Distance
Objective of this lesson is to explain the methods, problems and mistakes occuring in direct
measurement of distance.
Introduction
The horizontal distance between points, projected onto a horizontal plane, is required to be
measured in order to prepare plan or map of the area surveyed.
Methods of measurement
In surveying there are several methods for measurement of distance. These are
1. Direct methods;
2. Optical methods; and
3. Electronic method.
In any work, the choice of a method depends on many factors like field condition, accuracy
required, availability of resources (instruments, time, skill, fund etc). Following table
summarizes the principal methods, instrument required, precision, use, errors of measurement
of distance.
Salient Methods of Measuring Distance
Method Instrument Relative Use
Required Precision
(A) Direct Measurement of distance
Taping Tape, pegs, plumb
bob
1 / 3000 to 1 /
5000
Traverse for land surveys and topographic surveys
and during combustion.
(B) Optical Measurement of distance
Stadia Tacheometer 1 / 300 to 1 /
2000
Location of detail for topographic mapping, rough
traverse, checkingmore amount measurement.
(C) Electromagnetic measurement of Distance
EDM EDM Equipment 0.2 mm ± 1
ppm
Traverse, Triangulation and trilateration for control
surveys of all relative precision is defend as the
ratio of the type anf for allowed stand and
deviations to the distance type and for contraction
surveys.
Direct Measurement
When the distance between points / stations are measured directly, usually by using tape, is
known as direct method.
Ranging
When the distance to be measured is more than a tape length, a straight line is required to be laid
between the points/ stations along which measurements are to be carried out. The process of
laying out a straight line between points is known as ranging.
Direct Ranging - When the end stations are inter visible, ranging is being carried out directly.
The intermediate points are placed at distances having interval less than one tape length. The
intermediate points are found by moving a ranging pole in transverse direction and thus, points
are selected in such a way that the end points and the intermediate points lie in a straight line. In
this method, two flags, one ranging pole and a bunch of pegs are required in a team of at least
one surveyor and one assistant.
Indirect Ranging - When the end stations between which a straight line is to be laid, are not inter
visible, indirect method of ranging is being adopted. It is being carried out either by reciprocal
method or by random line method.
.
Taping
Taping involves measurement of the distance with tapes (steel/linen), either by placing it on the
ground or sometimes by getting it suspended between points. Additional equipments employed
during taping are plumb bob, the hand level, pegs/ pins and range pole (or flag or ranging rod)
etc. The precision of distance measured with tapes depends upon the degree of refinement with
which measurements are taken.
Mistakes in Taping
During taping, mistakes generally made by individuals (usually inexperienced) are:
1. Adding or dropping a full length of tape
2. Adding or dropping a part of the length of tape
3. Other points incorrectly taken as 0 or 30 meter marks on tape
4. Reading numbers incorrectly
5. Calling numbers incorrectly or not clearly
3. Errors in Measurement of Distance
Objective of this lesson is to explain the different errors/corrections involved in direct
measurement.
Introduction
The length of a tape is standardized at certain temperature and pull to amend distance be
measured in horizontal along a plane surface. But ideal condition is hardly obtained during field
observation. Thus, it is usual that the observations taken in the field are fraught with errors.
These are of various types depending on the origin and nature. These are required to be
determined and necessary corrections are to be applied before making use of the measurements
for further works.
Types of Errors
Depending on the nature, errors present in the measurement of distance have been classified into two
types: Systematic error and random error.
Systematic Errors
Systematic errors (in taping) are caused due to: non-standard length of tape, slope in terrain,
variations in temperature during measurement, variations in tension, sag, incorrect alignment of the
tape etc.
Random Errors
Distance measured depends on observations and on the determination of quantities such as
temperature t, tension or pull p, slope angle q or elevation difference h. Each of these quantities is
subject to random errors which when propagated through the corresponding relations result in random
errors in the distance. Thus the random errors cause random variation in the distance corrected for
systematic errors. The random errors are of much lower magnitude than the systematic errors. The
different sources of random errors in taping, designated by their standard error and these are: sv
(standard error due to the plumbing of the tape ends), sm (standard error due to the marking the
supported tape ends), sp r(standard error due to uncertainty in the value of the applied pull or tension),
sh (standard error in determining either the slope angle q or elevation difference h), st (standard error
in determining the temperature).
Chaining: Chaining is a term which is used to denote measuring distance either with the help of a chain
or a tape and is the most accurate method of making direct measurements. For work of ordinary
precision, a chain can be used, but for higher precision a tape or special bar can be used. The distances
determined by chaining form the basis of all surveying. No matter how accurately angles may be
measured, the survey can be no more precise than the chaining. Instruments for Chaining: The various
instruments used for the determination of the length of line by chaining are as follows: i. Chain or tape
ii. Arrows iii. Pegs iv. Ranging rods v. Offset rods vi. Plumb bob
Chain: Chains are formed of straight links of galvanized mild steel wire bent into rings at the ends and
joined each other by three small circular or oval wire rings. These rings offer flexibility to the chain.
The ends of the chain are provided with brass handle at each end with revolve joint, so that the chain
can be turned without twisting. Tallies are provided at every 10 or 25 links for facility of counting. The
length of a link is the distance between the centers of two consecutive middle rings, while the length of
the chain is measured from the outside of one handle to the outside of the other handle.
Various Types of Chain Metric Chains: Metric chains are generally available in lengths of 5, 10, 20
and 30 metres. To enable the reading of fractions of a chain without much difficulty, tallies are fixed at
every metre length for chains of 5 m and 10 m lengths and at every five-metre length for chains of 20
m and 30 m lengths. In the case of 20 m and 30 m chains, small brass rings are provided at every metre
length, except where tallies are attached.
Gunter’s Chain or Surveyor Chain: Gunter’s Chain or 66 ft. Chain: Divided into 100 links, each link is
of 0.66 ft. or 7.92 inches. Also called Surveyor’s chain. Engineer’s chain and Gunter’s chain are
commonly used in our country. It was previously used for measuring distance in miles and furlongs (10
Gunter’s chain = 1 furlong 80 Gunter’s chain = 1 mile).
Engineer's Chain: The engineer's chain is 100 ft. long and consists of 100 links, each link being 1 ft.
long. Tallies are provided at every 10 links, then central tally being round. Revenue Chain: The
revenue chain is 33 ft long and consists of 16 links each link being 2 ft long. It is mainly used in
cadastral survey. Steel Band or Band Chain: The steel band consists of a long narrow strip of blue
steel, of uniform width of 12 to 16 mm and thickness of 0.3 to 0.6 mm. Metric steel band are available
in lengths of 20 or 30 metres. It is graduated in meters, decimeters and centimeters on one side and has
0.2 m links on the other. It is used in projects where more accuracy is required.
Tapes: Tapes are available in a variety of materials, lengths and weights. The different types of tape in
general use are discussed below: Cloth or Linen Tape: These are closely woven linen or synthetic
material and are varnished to resist the moisture. These are available in 10 to 30 m in length and 12 to
15 mm in width. The disadvantages of such a tape include: (1) It is affected by moisture and gets
shrunk; (2) Its length gets altered by stretching; and (3) It is likely to twist and does not remain straight
in strong winds.
Metallic Tape: It is a linen tape with brass or copper wires woven into it longitudinally to reduce
stretching. As it is varnished, the wires are not visible. These are available in 20-30 m length. It is an
accurate measurement device and is commonly used for measuring offsets. As it is reinforced with
wires, all the defects of linen tapes are overcome.
Steel Tapes: These are 1 to 50 m in length and are 610 mm wide. At the end of the tape a brass ring is
attached, the outer end of which is zero point of the tape. Invar Tape: This is made of an alloy of
nickel (36%) and steel, having very low coefficient of thermal expansion (0.122 x 10-6 / 0C). These
are available in lengths of 30, 50 and 100 m and in a width of 6 mm.
Pegs: Wooden pegs are used to mark the positions of the stations or terminal points of a survey line.
They are made of stout timber, generally 2.5 cm or 3 cm square and 15 to 60 cm long, tapered at the
end. They are driven in the ground with the help of a wooden hammer and kept about 4 cm projecting
above the surface.
Arrows (Chain pin): Arrows are made of stout steel wire. An arrow is inserted into the ground after
every chain length measured on the ground. Arrows are made of good quality hardened and tempered
steel wire 4 mm in diameter and are black enameled. The length of arrow may vary from 25 cm to 50
cm (generally 40 cm). One end of the arrow is made sharp and other end is bent into a loop or circle for
facility of carrying.
Ranging Rods: Ranging rods have a length of either 2 m or 3 m, the 2 metre length being more
common. They are combined at the bottom with a heavy iron point, and are painted in alternative
bands of either black and white or red and white or black, red and white in succession, each band being
20 cm depth so that on occasion the rod can be used for rough measurement of short lengths. Ranging
rods are used to range some intermediate points in the survey line. They are circular or octagonal in
cross-section of 3 cm nominal diameter, made of well-seasoned, straight grained timber. The rods are
almost invisible at a distance of about 200 metres; hence when used on long lines each rod should have
a red, white or yellow flag, about 30 to 50 cm square, tied on near its top.
Offset Rod: An offset rod is similar to a ranging rod and has a length of 3 m. They are round wooden
rods, shod with pointed iron shoe at one end, and provided with a notch or a hook at the other. The
hook facilitates pulling and pushing the chain through hedges and other obstructions. The rod is mainly
used for measuring rough offsets nearby. It has also two narrow slots passing through the centre of the
section, and set at right angles to one another, at the eye level, for aligning the offset line. Plumbing
Bob: While chaining along sloping ground, a plumb-bob is required to transfer the points to the
ground. It is also used to make ranging poles vertical and to transfer points from a line ranger to the
ground. In addition, it is used as centering aid in theodolites, compass, plane table and a variety of
other surveying instruments.
Types of Errors occurring in Chain Surveying
Types of Errors:
1. Cumulative error
2. Compensative error
Cumulative error
These errors always accumulate in one direction and are serious in nature. They affect the survey work
considerably.
They make measurements too long or too short.
These errors are of two types and are known as systematic errors.
They are classified as follows:
1. Positive error
2. Negative error
Positive error
These errors make the measured length more than the actual length which results into wrong
calculations by the Surveyor.
The following are some of the positive errors:
The length of chain is shorter than the standard length due to bending of links, removal of
connecting rings and knots in links.
The temperature is lower than at which the tape was calibrated.
Not applying sag correction.
Sag takes place due to self weight of the chain.
Incorrect alignment
Negative errors
These errors make the measured length less than the actual length.
Following are some of the negative errors: Length of chain or tape greater than its standard length due to flattening of rings, opening of ring joints
and temperature being higher than at which it was standardised.
Compensative errors
These errors occur in either direction and are likely to compensate.
These occur in following situations:
Incorrect holding of chain
Displacement of arrows
Adding or omitting a full length of chain
Reading wrongly
Booking wrongly
4. OBSTACLES IN CHAIN SURVEYING There are 3 types of obstacles
1. Obstacle to ranging
2. Obstacle to chaining
3. Obstacle to both ranging & chaining.
a) Obstacle to Ranging: The type of obstacle in which the ends are not inter visible is quite common except in flat country. These may be two cases.
i) Both end of the line may be visible form intermediate points on the line
ii) Both ends of the line may not be visible from intermediate points on the line
b) Obstacle to chaining but not ranging
There may be two cases of this obstacle
i) When it is possible to chain round the obstacle ex: a pond
ii) When it is not possible to chain round the obstacle ex: a river
c) Obstacles to both chaining & ranging
A building is the typical example of this type of obstacle the problem lies in prolonging the line beyond the obstacle & determining the distance across it. Method A: Choose two points A & B to one side & Erect perpendicular AC and BD of equal length join CD & prolong it past the obstacle choose two points E and F on CD and erect CG and FH equal to that of AC and BD. Join GH and prolong it. Measure DE, BG = DE.
5. Methods used for the calculation of areas in Surveying:
1. Midpoint Ordinate Rule
2. Average Ordinate Rule
3. Simpson’s rule
4. Trapezoidal rule
Midpoint-ordinate rule
The rule states that if the sum of all the ordinates taken at midpoints of each division multiplied
by the length of the base line having the ordinates (9 divided by number of equal parts).
Midpoint ordinate rule | Method for calculating area in Surveying
In this, base line AB is divided into equal parts and the ordinates are measured in the midpoints
of each division.
Area = ([O1 +O2 + O3 + …..+ On]*L)/n
L = length of baseline
n = number of equal parts, the baseline is divided
d = common distance between the ordinates
Example of the area calculation by midpoint ordinate rule
The following perpendicular offsets were taken at 10m interval from a survey line to an irregular
boundary line. The ordinates are measured at midpoint of the division are 10, 13, 17, 16, 19, 21,
20 and 18m. Calculate the are enclosed by the midpoint ordinate rule.
Given: Ordinates
O1 = 10
O2 = 13
O3 = 17
O4 = 16
O5 = 19
O6 = 21
O7 = 20
O8 = 18
Common distance, d =10m
Number of equal parts of the baseline, n = 8
Length of baseline, L = n *d = 8*10 = 80m
Area = [(10+13+17+16+19+21+20+18)*80]/8
= 1340sqm
Average Ordinate Rule
The rule states that (to the average of all the ordinates taken at each of the division of equal
length multiplies by baseline length divided by number of ordinates).
Average Ordinate Rule
O1, O2, O3, O4….On ordinate taken at each of division.
L = length of baseline
n = number of equal parts (the baseline divided)
d = common distance
Area = [(O1+ O2+ O3+ …. + On)*L]/(n+1)
Here is an example of a numerical problem regarding the calculation of areas using
Average Ordinate Rule The following perpendicular offsets were taken at 10m interval from a survey line to an irregular
boundary line.
9, 12, 17, 15, 19, 21, 24, 22, 18
Calculate area enclosed between the survey line and irregular boundary line.
Area = [(O1+ O2+ O3+ …. + O9)*L]/(n+1)
= [(9+12+17+15+19+21+24+22+18)*8*10]/(8+1)
= 139538sqm
Simpson’s Rule
Statement
It states that, sum of first and last ordinates has to be done. Add twice the sum of remaining
odd ordinates and four times the sum of remaining even ordinates. Multiply to this total sum
by 1/3rd of the common distance between the ordinates which gives the required area.
Where O1, O2, O3, …. On are the lengths of the ordinates d = common distance
n = number of divisions
Note:
This rule is applicable only if ordinates are odd, i.e. even number of divisions.
If the number of ordinates are even, the area of last division maybe calculated separated and
added to the result obtained by applying Simpson’s rule to two remaining ordinates.
Even if first or last ordinate happens to be zero, they are not to be omitted from Simpson’s rule.
The following offsets are taken from a chain line to an irregular boundary towards right side of
the chain line.
Chainage 0 25 50 75 100 125 150
Offset
‘m’
3.6 5.0 6.5 5.5 7.3 6.0 4.0
Common distance, d = 25m
Area = d/3[(O1+O7) + 2 (O3+O5)+4(O2+O4+O6)]
= 25/3[(3.6+4)+2(6.5+7.3)+4(5+5.5+6)]
Area = 843.33sqm
Area Calculation - Trapezoidal Rule
In trapezoidal method, each segment of the section is divided into various trapezoids and
triangles.
Trapezoidal Area A = 1/2 X a X (b1+b2)
Triangle area A = a * b/2
Example 1:
Intersection Point
In the above example, intersection point is between 351 and 354
Filling Height=0.1 @ distance 351
Cutting depth=0.2 @ distance 354
Length from 351 to 354 =3
Distance from 351 to intersection point = 3*[0.1/ (0.1+0.2)] =1 i.e., intersection point is at 352
Cutting Area – Sum of Area of Segment 1, 2, and 3
Sl. No. Easting Initial
Level
Final
Level
Difference Calculation Area (Sq.
meters)
1 345 20.70 20 0.70
2 348 20.50 20 0.50 Segment 1: Area of Trapezoid =
½ * (b1 + b2) * a = ½ * (0.70 +
0.50) * 3
1.80
3 351 20.10 20 0.1 Segment 2: Area of Trapezoid =
½ * (b1 + b2) * a = ½ * (0.50 +
0.10) * 3
0.90
4 352 20.00 20 0 Segment 3: Area of Triangle = ½
* b * h = ½ * 0.1 * 1
0.05
Total 2.75
Filling Area – Sum of Area of Segment 4, 5, 6, and 7
Sl. No. Easting Initial
Level
Final
Level
Difference Calculation Area
(Sq.
meters)
1 352 20.00 20 0.00
2 354 19.80 20 0.20 Segment 4: Area of Triangle = ½
* b * h = ½ * 0.2 * 2
0.20
3 357 19.40 20 0.60 Segment 5: Area of Trapezoid =
½ * (b1 + b2) * a = ½ * (0.20 +
0.60) * 3
1.20
4 360 19.10 20 0.90 Segment 6: Area of Trapezoid =
½ * (b1 + b2) * a = ½ * (0.60 +
0.90) * 3
2.25
5 363 19.00 20 1.00 Segment 7: Area of Trapezoid =
½ * (b1 + b2) * a = ½ * (0.90 +
1.00) * 3
2.85
Total 6.50
UNIT II: ANGULAR MEASUREMENTS
1. Traversing:
In traversing , the frame work consist of connected lines. The length are measured by a chain or a
tape and the direction measured by angle measuring instruments.Hence in compass surveying
direction of survey lines are determined with a compass and the length of the lines are measured
with a tape or a chain. This process is known as compass traversing.
2. Principle of Compass Surveying
The principle of compass surveying is traversing; which involves a series of connected lines.The
magnetic bearing of the lines are measured by prismatic compass.Compass surveying is
recommended when the area is large, undulating and crowded with many details. Compass
surveying is not recommended for areas where local attraction is suspected due to the presence
of magnetic substances like steel structures, iron ore deposits, electric cables , and so on. A
compass is a small instrument essentially consisting of a graduated circle, and a line of sight.
The compass can not measures angle between two lines directly but can measure angle of a line
with reference to magnetic meridian at the instrument station point is called magnetic bearing of
a line.
3. Types of Compass- Prismatic and Surveyor’s Compass
Cylindrical metal box: Cylindrical metal box is having diameter of 8to 12 cm. It
protects the compass and forms entire casing or body of the compass. It protect compass
from dust, rain etc.
Pivot: pivot is provided at the center of the compass and supports freely suspended
magnetic needle over it.
lifting pin and lifting lever: a lifting pin is provided just below the sight vane. When the
sight vane is folded, it presses the lifting pin. The lifting pin with the help of lifting lever
then lifts the magnetic needle out of pivot point to prevent damage to the pivot head.
Magnetic needle: Magnetic needle is the heart of the instrument. This needle measures
angle of a line from magnetic meridian as the needle always remains pointed towards
north south pole at two ends of the needle when freely suspended on any support.
Graduated circle or ring: This is an aluminum graduated ring marked with 0ᴼ to 360ᴼ
to measures all possible bearings of lines, and attached with the magnetic needle. The
ring is graduated to half a degree.
Prism : prism is used to read graduations on ring and to take exact reading by compass. It
is placed exactly opposite to object vane. The prism hole is protected by prism cap to
protect it from dust and moisture.
Object vane: object vane is diametrically opposite to the prism and eye vane. The object
vane is carrying a horse hair or black thin wire to sight object in line with eye sight.
Eye vane: Eye vane is a fine slit provided with the eye hole at bottom to bisect the object
from slit.
Glass cover: its covers the instrument box from the top such that needle and graduated
ring is seen from the top.
Sun glasses: These are used when some luminous objects are to be bisected.
Reflecting mirror: It is used to get image of an object located above or below the
instrument level while bisection. It is placed on the object vane.
Spring brake or brake pin: to damp the oscillation of the needle before taking a reading
and to bring it to rest quickly, the light spring brake attached to the box is brought in
contact with the edge of the ring by gently pressing inward the brake pin
The following procedure should be adopted after fixing the prismatic compass on the tripod for
measuring the bearing of a line.
Centering : Centering is the operation in which compass is kept exactly over the station
from where the bearing is to be determined. The centering is checked by dropping a small
pebble from the underside of the compass. If the pebble falls on the top of the peg then
the centering is correct, if not then the centering is corrected by adjusting the legs of the
tripod.
Leveling : Leveling of the compass is done with the aim to freely swing the graduated
circular ring of the prismatic compass. The ball and socket arrangement on the tripod will
help to achieve a proper level of the compass. This can be checked by rolling round
pencil on glass cover.
Focusing : the prism is moved up or down in its slide till the graduations on the
aluminum ring are seen clear, sharp and perfect focus. The position of the prism will
depend upon the vision of the observer.
Observing Bearing of a line:
Consider a line AB of which the magnetic bearing is to be taken.
By fixing the ranging rod at station B we get the magnetic bearing of needle wrt
north pole.
The enlarged portion gives actual pattern of graduations marked on ring.
Surveyor’s Compass:
It is similar to a prismatic compass except that it has a only plain eye slit instead of eye
slit with prism and eye hole.
NORTH
OBJECT B
A
SOUTH
LINE OF SIGHT
90
180
270
0
This compass is having pointed needle in place of broad form needle as in case of
prismatic compass.
Surveyor’s Compass
Working of Surveyor’s Compass
1) Centering
2) LEVELING
3) OBSERVING THE BEARING OF A LINE
First two observation are same as prismatic compass but third observation differs from
that.
3) OBSERVING THE BEARING OF A LINE : in this compass ,the reading is taken
from the top of glass and under the tip of north end of the magnetic needle directly. No
prism is provided here.
Bearings:
The bearing of a line is the horizontal angle which it makes with a reference
line(meridian).
Depending upon the meridian , there are four type of bearings they are as follows:
1) True Bearing: The true bearing of a line is the horizontal angle between the true
meridian and the survey line. The true bearing is measured from the true north in the
clockwise direction.
2) Magnetic Bearing: the magnetic bearing of a line is the horizontal angle which the
line makes with the magnetic north.
3) Grid Bearing: The grid bearing of a line is the horizontal angle which the line makes
with the grid meridian.
4) Arbitrary Bearing: The arbitrary baring of a line is the horizontal angle which the
line makes with the arbitrary meridian.
Designation of Bearing
The bearing are designated in the following two system:-
1) Whole Circle Bearing System.(W.C.B)
2) Quadrantal Bearing System.(Q.B)
Whole Circle Bearing System:
The bearing of a line measured with respect to magnetic meridian in clockwise direction
is called magnetic bearing and its value varies between 0ᴼ to 360ᴼ.
TRUE MERIDIAN
MAGNETIC MERIDIAN
TRUE BEARING
MAGNETIC BEARING
A
B
MN
TN
The quadrant start from north an progress in a clockwise direction as the first quadrant is
0ᴼ to 90ᴼ in clockwise direction , 2nd 90ᴼ to 180ᴼ , 3rd 180ᴼ to 270ᴼ, and up to 360ᴼ is 4th
one.
Quadrantal Bearing System:
In this system, the bearing of survey lines are measured wrt to north line or south line
which ever is the nearest to the given survey line and either in clockwise direction or in
anti clockwise direction.
Reduced Bearing
When the whole circle bearing is converted into Quadrantal bearing , it is termed as
“REDUCED BEARING”.
Thus , the reduced bearing is similar to the Quadrantal bearing.
Its values lies between 0ᴼ to 90ᴼ, but the quadrant should be mentioned for proper
designation.
Conversion of WCB to RB
Fore Bearing and Back Bearing:
The bearing of a line measured in the forward direction of the survey lines is called the
‘fore bearing’(F.B.) of that line.
The bearing of a line measured in direction backward to the direction of the progress of
survey is called the ‘back bearing’(B.B.) of the line.
Computation of Angles:
Observing the bearing of the lines of a closed traverse, it is possible to calculate the
included angles, which can be used for plotting the traverse.
At the station where two survey lines meet, two angles are formed-an exterior angles and
an interior angles. The interior angles or included angle is generally the smaller
angles(<180ᴼ).
FB of line AB
BB of line AB
A
NORTH
NORTH
Θ1
Θ2
B
FB of AB = Θ1(from A to B) BB of AB= Θ2(from B to A)
Remembering following points: 1) In the WCB system ,the differences
b/n the FB and BB should be exactly 180ᴼ. Remember the following relation :
BB=FB+/-180ᴼ
+ is applied when FB is <180ᴼ
- is applied when BB is >180ᴼ
2) In the reduced bearing system the FB and BB are numerically equal but the quadrants are just opposite.
A
B
C
D
EXAMPLES
A
E
F
BB
/_A
EXTERIOR ANGLE B
FB
A
M
Meridian:
Bearing of a line is always measured clockwise wrt some reference line or direction. This
fixed line is known as meridian.
There three types of meridian:
1) Magnetic meridian: The direction shown by a freely suspended needle which is
magnetized and balanced properly without influenced by any other factors is known as
magnetic meridian.
2) True meridian : True meridian is the line which passes through the true north and
south. The direction of true meridian at any point can be determined by either observing
the bearing of the sun at 12 noon or by sun’s shadow.
3) Arbitrary meridian: In case of small works or in places where true meridian or
magnetic meridian cannot be determined, then ,any direction of a prominent object is
taken as a reference direction called as arbitrary meridian.
4. Local Attraction: A compass shows the direction of the magnetic meridian on the principle of magnetism. Any
magnet attracting material, when is brought near to the compass needle, needle will deflect from
the true magnetic north.
In that case, you will not read the true north direction and if you take the bearings of the lines in
such condition there comes a error in the readings and that error is known as the local attraction.
Materials which are most likely to be present there, while you are doing the compass surveying,
are such as an iron chain, metallic wrist band or ear rings(metallic) that one might be wearing.
Other things such as an electric pole or electric wires may also produce local attraction. The
needle is attracted to these objects, so this will deviate from the true direction of the magnetic
meridian.
If local attraction is available at a station then all the readings taken from that station will have
the same amount of the error, and we have to correct the readings to get the true results.
BB
B
C
There are methods to get the corrections to be applied on the erroneous readings in the
traversing. The two methods which are used in general will be discussed here briefly.
(1) In first method we have to find out the stations where no local attraction exists. To find out
this we have to look for a line where the difference between the fore bearing and the back
bearing is exactly equal to 180 degrees. If we find such line then that means the two end stations
of that line are free from any local attraction. After finding that line we apply the correction to
the bearings of the other lines.
(2) In the second method we find the line where there is no local attraction. We know that even
if the local attraction is present at every station the measured included angles will not be
incorrect and we can calculate them correctly. With the help of the readings from the stations
which are free from local attraction and the correct included angles we can find out the bearings
of all the lines.
If we do not find any line where the both stations are free from the local attraction, we have to
take the line where the error is minimum and then apply the mean correction to both the stations
and then take them as the correct readings.
5. Bowditch Rule
A widely used rule for adjusting a traverse that assumes the precision in angles or directions is
equivalent to the precision in distances. This rule distributes the closure error over the whole
traverse by changing the northings and eastings of each traverse point in proportion to the
distance from the beginning of the traverse. More specifically, a correction factor is computed
for each point as the sum of the distances along the traverse from the first point to the point in
question, divided by the total length of the traverse. The correction factor at each point is
multiplied by the overall closure error to get the amount of error correction distributed to the
point's coordinates. The compass rule is also known as the Bowditch rule, named for the
American mathematician and navigator Nathaniel Bowditch (1773-1838).
The compass rule is based on the assumption that all lengths were measured with equal care
and all angles taken with approximately the same precision
It is also assumed that the errors in the measurement are accidental and that the total error in
any side of the traverse is directly proportional to the total length of the traverse
The compass rule may be stated as follows: The correction to be applied to the latitude (or
departure) of any course is equal to the total closure in latitude (or departure) multiplied by
the ratio of the length of the course to the total length or perimeter of the traverse. These
correction are given by the following equations:
cl = CL (d/D) and cd = CD (d/D)
where:
cl = correction to be applied to the latitude of any course
cd = correction to be applied to the departure of any course
CL = total closure in latitude or the algebraic sum of the north and south latitudes
(NL + SL)
CD = total closure in departure or the algebraic sum of the east and west
departures (ED + WD)
d = length of any course
D = total length or perimeter of the traverse
To determine the adjusted latitude of any course the latitude correction is either added to or
subtracted from the computed latitude of the course
A simple rule to remember is: If the sum of the north latitudes exceeds the sum of the south
latitudes, latitude corrections are subtracted from the north latitudes and added to the
corresponding south latitudes. However, if the sum of the south latitudes exceeds the sum of
the north latitudes, the corrections are applied in the opposite manner
Compute the Coordinates for the traverse defined in Example 29.1 by applying correction to
consecutive coordinates by Bowditch's method.
Solution :
Adjustment of Coordinates of a closed-loop traverse using Bowditch's Rule
Sides
Length
( dij )m
Azimuth
( i )
Consecutive coordinates,
(m) Bowditch's Correction (m)
Adjusted Consecutive coordinates,
m
Departure (
Di ) Latitude ( Li )
Departure,
dij
Latitude,
l ij Departure Latitude
AB 372.222 0° 42' 4.547 372.194 0.375 0.231 4.922 372.425
BC 164.988 94° 42' 164.576 -11.653 0.166 0.102 164.742 -11.551
CD 242.438 183° 04' -12.970 -242.091 0.244 0.151 -12.726 -241.94
DA 197.145 232° 51' -157.136 -119.056 0.198 0.122 -156.938 -118.934
L =
976.793 dD = -0.983 dL = -0.606 = 0.983 = 0.606 = 0.000 = 0.000
6. Open and Closed Traverse
A traverse is a series of connected lines whose lengths and directions are known. A closed traverse is one enclosing a defined area and having a common point for its beginning to end (For Example a close property boundary). An open traverse is one which does not close on the point of the beginning (For example: the line center survey of a highway, railroad, etc). All topgraphical surveys should have a skeleton or network of traverses to serve as horizontal control. To plot a traverse you must have a bearing (Direction) and Length of line (For example: line length from A to B is North 50 degrees 0 degrees East). On a plotting table the reading might look like this (AB=N50 00E X 550.00') Closed Traverse: Boundry is closed
Open traverse: Boundry is not closed.
UNIT III: LEVELLING
1. Types of Levels
Instruments
The instrument primarily used for leveling is the (engineer's) level in association with a
graduated rod known as leveling rod or leveling staff.
Level
A schematic diagram of an engineer's level is shown in Figure. An engineer's level primarily
consists of a telescope mounted upon a level bar which is rigidly fastened to the spindle. Inside
the tube of the telescope, there are objective and eye piece lens at the either end of the tube. A
diaphragm fitted with cross hairs is present near the eye piece end. A focussing screw is attached
with the telescope. A level tube housing a sensitive plate bubble is attached to the telescope (or
to the level bar) and parallel to it. The spindle fits into a cone-shaped bearing of the leveling
head. The leveling head consists of tribrach and trivet with three foot screws known as leveling
screws in between. The trivet is attached to a tripod stand.
Functions of Salient Parts
Telescope : used to sight a staff placed at desired station and to read staff reading distinctly.
Diaphragm : holds the cross hairs (fitted with it).
Eye piece : magnifies the image formed in the plane of the diaphragm and thus to read staff
during leveling.
Level Tube : used to make the axis of the telescope horizontal and thus the line of sight.
Leveling screws : to adjust instrument (level) so that the line of sight is horizontal for any
orientation of the telescope.
Tripod stand : to fix the instrument (level) at a convenient height of an observer
Dumpy Level
A dumpy level is most suitable when from one setting of the instrument, elevations of several
points are to be determined.
(a) (b)
Two Types of Dumpy Levels
Distinctive Features of an Dumpy Level
The optical axis of the telescope of a dumpy is placed perpendicular to the axis of the centre
spindle. The axis of its level tube is permanently placed so that it lies in the same vertical plane
as the optical axis
IOP Level
A IOP level is most suitable when only few readings are to be taken from one setting of the
instrument.
IOP Level
Distinctive Features of an IOP Level
The telescope is mounted on a transverse fulcrum at the vertical axis fitted with a micrometer
screw at the eye-piece end of the telescope.
Instrument is leveled using circular spirit level. The sensitive plate-bubble is to be leveled using
micrometer screw, at the time of taking measurement. Thus, the line of sight is made horizontal
quickly, even though the instrument as a whole may not be exactly level.
Digital level
There are fundamentally two types of automatic levels.
First, the optical one whose distinguishing feature is self-leveling i.e., the instruments gets
approximately leveled by means of a circular spirit level and then it maintains a horizontal line of
sight of its own.
Second, the digital levels whose distinguishing features are automatic leveling, reading and
recording .
Digital Level
The chief features of a digital level are:
A CCD (Charged coupled device) at the plane of diaphragm. It captures an image of the
rod and processes it resulting in a rod reading and a distance to the rod.
A data collector which keeps the level notes, performs checks and keeps a record of every
rod reading and elevation automatically.
A bar-coded rod having a scale represented through a series of bars of different widths.
Bars are spaced constantly or variably. The spacing and width of the bars denote the
code.
Advantages of digital levels include the speed of leveling, the virtual elimination of rod reading
and calculation errors and the accuracy in reading rod.
Limitation of digital level lies in its range. Beyond a certain limit it is to be used in “manual
mode”.
2. Levelling Staff
Leveling Staff
It is a self-reading graduated wooden rod having rectangular cross section. The lower end of the
rod is shod with metal to protect it from wear and usually point of zero measurement from which
the graduations are numbered. Staff are either solid (having single piece of 3 meter height) or
folding staff (of 4 meter height into two or three pieces) . The least count of a leveling staff is 5
mm.
Single Piece 3 m staff
Folded 4 m staff
Temporary Adjustment of Level
At each set up of a level instrument, temporary adjustment is required to be carried out prior to
any staff observation. It involves some well defined operations which are required to be carried
out in proper sequence.
Temporary Adjustment of a Dumpy Level
The temporary adjustment of a dumpy level consists of Setting , Leveling and Focusing .
During Setting, the tripod stand is set up at a convenient height having its head horizontal
(through eye estimation). The instrument is then fixed on the head by rotating the lower part of
the instrument with right hand and holding firmly the upper part with left hand. Before fixing,
the leveling screws are required to be brought in between the tribrach and trivet. The bull's eye
bubble (circular bubble), if present, is then brought to the centre by adjusting the tripod legs.
Next, Leveling of the instrument is done to make the vertical axis of the instrument truly
vertical. It is achieved by carrying out the following steps:
Step 1: The level tube is brought parallel to any two of the foot screws, by rotating the upper part
of the instrument.
Step 2: The bubble is brought to the centre of the level tube by rotating both the foot screws
either inward or outward. (The bubble moves in the same direction as the left thumb.)
Step 3: The level tube is then brought over the third foot screw again by rotating the upper part
of the instrument.
Step 4: The bubble is then again brought to the centre of the level tube by rotating the third foot
screw either inward or outward.
Step 5: Repeat Step 1 by rotating the upper part of the instrument in the same quadrant of the
circle and then Step 2.
Step 6: Repeat Step 3 by rotating the upper part of the instrument in the same quadrant of the
circle and then Step 4.
Step 7: Repeat Steps 5 and 6, till the bubble remains central in both the positions.
Step 8: By rotating the upper part of the instrument through 180 ° , the level tube is brought
parallel to first two foot screws in reverse order. The bubble will remain in the centre if the
instrument is in permanent adjustment.
Focusing is required to be done in order to form image through objective lens at the plane of the
diaphragm and to view the clear image of the object through eye-piece. This is being carried out
by removing parallax by proper focusing of objective and eye-piece. For focusing the eye-piece,
the telescope is first pointed towards the sky. Then the ring of eye-piece is turned either in or out
until the cross-hairs are seen sharp and distinct. Focusing of eye-piece depends on the vision of
observer and thus required whenever there is a change in observer. For focusing the objective,
the telescope is first pointed towards the object. Then, the focusing screw is turned until the
image of the object appears clear and sharp and there is no relative movement between the image
and the cross-hairs. This is required to be done before taking any observation.
Temporary Adjustment of an IOP Level
Temporary adjustment of a tilting level requires the same operations as in case of a dumpy level
except the operations involved in leveling. During leveling, first the IOP instrument is leveled
roughly with the leveling screws till the circular bubble is in the centre. Then, the bubble of the
level tube is brought to the centre by using the tilting screw. In case of IOP level, the bubble is
required to be leveled using tilting screw before each reading is taken.
Exercise
1 Why levels are usually called as “spirit level”?
2 Explain the importance of level tube in a levelling instrument.
3 Explain the chief feature of a digital level.
4 State the differences in the temporary adjustment of a dumpy level and an IOP level
5 State the difference between a dumpy level and a digital level.
3. Measurements and Recording
Basic Principle of Leveling
The fundamental principle of leveling lies in finding out the separation of level lines passing
through a point of known elevation (B.M.) and that through an unknown point (whose elevation
is required to be determined).
Let X represents a point of known elevation (Hx) or a B.M. and Y be a point whose elevation is
required to be determined. To find out the unknown elevation of Y, a level is set up at L in
between X and Y. A leveling staff is first held at X and a reading hx is observed, by sighting the
staff (held vertical to the line of sight of the level). The staff reading at Y, say hy is then
observed. The elevation of the point Y (say Hy) is thus given by Hx + (hx ~ hy) i.e., known
elevation (Hx ) added to the separation of level lines (hx ~ hy) passing through the points.
Methods of Leveling
Direct Leveling : Direct measurement, precise, most commonly used; types:
Simple leveling : One set up of level. To find elevation of points.
Differential leveling : Numbers of set-ups of level. To find elevation of non-intervisible points.
Fly leveling : Low precision, to find/check approximate level, generally used during
reconnaissance survey.
Precise leveling : Precise form of differential leveling.
Profile leveling : finding of elevation along a line and its cross section.
Reciprocal leveling : Along a river or pond. Two level simultaneously used, one at either end.
Indirect or Trigonometric Leveling : By measuring vertical angles and horizontal distance;
Less precise.
Stadia Leveling : Using tacheometric principles.
Barometric Leveling : Based on atmospheric pressure difference; Using altimeter; Very rough
estimation.
Differential Leveling
Applied to determine the elevation of point which is some distant apart from B.M i.e., the
unknown elevation of a point cannot be determined in a single set up of an instrument. Thus, in
this method, instrument gets setup number of times to observe reading along a route in between
observed points. For each set up, staff readings are taken back to a point of known elevation
(first sight from the B.M and forward to a point of unknown elevation) final sight to the terminal
station.
Procedure
Let us consider a station B whose elevation is to be established with reference to a B.M station
A, quite a distant apart. In establishing the station B as B.M., differential leveling is carried out
starting from A and terminating at B. In order to carry out the leveling, first the instrument is set
up at some location, say I1 , in such a way that backsight reading taken on A can be read clearly.
The staffman is then directed to move forward towards B and choose a point, say S1 which is
firm and stable. It is preferable that the distance of S1 from I1be the same as that of station A
from I1. After proper selection of the point S1, staff is held to take the foresight reading for this
instrument set up. The instrument is then shifted to some other position in forward direction, say
I2 towards B and take the backsight reading on S1. Thus, point S1 is used as a turning point. From
I2 foresight reading is taken to another well chosen (as followed in S1) turning point S2. Finally,
from I3 backsight is taken on S2 and last sight at the terminal point B.
Field Book
A field book, also called level book is being used for taking down each staff reading during
leveling and subsequently, used for finding out the elevation of points/ stations. There are two
types of level books (Table.1 and Table 2). Usually, level book contains columns of both the
types together (Table 3) and it is for a surveyor to use only the relevant columns only.
Table 1 Level book note for Rise and Fall method
Staff Reading Difference in Elevation Elevation
Points B.S (m) F.S.(m) Rise (m) Fall (m) R.L (m) Remark
A 2.365 100.000 B.M.
S 1 0.685 1.235 1.130 101.130 T.P.1
S2 1.745 3.570 2.885 98.245 T.P. 2
B 2.340 0.595 97.650
Table 2 Level book note for Height of instrument method
Staff Reading Height of Instrument
(m) R.L. (m) Remarks
Points B.S (m) F.S.(m)
A 2.365 102.365 100.000 B.M.
S 1 0.685 1.235 101.815 101.130 T.P.1
S2 3.570 98.245 T.P.2
B 2.340 97.650
Table 3 Field book for Reduction of level
Staff Reading (m) Difference in
elevation (m) H.I (m) R.L. (m) Remarks
Points B.S. I.S. F.S. Rise Fall
A 2.365 102.365 100.000 B.M.
S 1 0.685 1.235 1.130 101.815 101.130 T.P.1
S2 1.745 3.570 2.885 99.990 98.245 T.P. 2
B 2.340 0.595 102.365 97.650
4.795 7.145 3.480 101.815
Reduction of Level
The observed staff readings as noted in a level book are further required to be manipulated to
find out the elevation of points. The operation is known as reduction of level. There are two
methods for reduction of levels:
1. Rise and Fall method and
2. Height of instrument method.
Rise and Fall Method
For the same set up of an instrument, Staff reading is more at a lower point and less for a higher
point. Thus, staff readings provide information regarding relative rise and fall of terrain points.
This provides the basics behind rise and fall method for finding out elevation of unknown points.
When the instrument is at I1, the staff reading at A (2.365m) is more than that at S1 which
indicates that there is a rise from station A to S1 and accordingly the difference between them
(1.130m) is entered under the rise column in Table 1. To find the elevation of S1 ( 101.130m),
the rise (1.130m) has been added to the elevation of A (100.0m). For instrument set up at I2 , S1
has been treated as a point of known elevation and considered for backsight (having reading
0.685m) . Foresight is taken at S2 and read as 3.570m i.e, S2 is at lower than S1 . Thus, there is a
fall from S1 a nd S2 and there difference (2.885m) is entered under the fall column in Table 1. To
find the elevation of S2 ( 98.245m), the fall (2.885m) has been subtracted from the elevation of
S1 (101.130m). In this way, elevation of points are calculated by Rise and Fall method.
Table 1 Level book note for Rise and Fall method
Staff Reading Difference in Elevation Elevation
Points B.S (m) F.S.(m) Rise (m) Fall (m) R.L (m) Remark
A 2.365 100.000 B.M.
S 1 0.685 1.235 1.130 101.130 T.P.1
S2 1.745 3.570 2.885 98.245 T.P. 2
B 2.340 0.595 97.650
Height of Instrument Method
In any particular set up of an instrument height of instrument, which is the elevation of the line
of sight, is constant. The elevation of unknown points can be obtained by subtracting the staff
readings at the desired points from the height of instrument. This is the basic behind the height of
instrument method for reduction of level.
When the instrument is at I1, the staff reading observed at A is 2.365m. The elevation of the line
of sight i.e., the height of instrument is 102.365m obtained by adding the elevation of A
(100.0m) with the staff reading observed at A (2.365m). The elevation of S1 (101.130m) is
determined by subtracting its foresight reading (1.235m) from the the height of instrument
(102.365m) when the instrument is at I1 . Next, the instrument is set up at I2. S1 is considered as a
point of known elevation and backsight reading ( 0.685m) is taken . The height of the instrument
(101.815 m) is then calculated by adding backsight reading ( 0.685m) with the elevation (R.L.)
of point S1 (101.130m). Foresight is taken at S2 and its elevation (98.245m) is determined by
subtracting the foresight (3.570m) from the height of the instrument (101.815 m). In this way,
elevation of points are calculated by Height of instrument method.
Table 2 Level book note for Height of instrument method
Staff Reading Height of Instrument
(m) R.L. (m) Remarks
Points B.S (m) F.S.(m)
A 2.365 102.365 100.000 B.M.
S 1 0.685 1.235 101.815 101.130 T.P.1
S2 3.570 98.245 T.P.2
B 2.340 97.650
Example
Ex1 Data from a differential leveling have been found in the order of B.S., F.S..... etc. starting
with the initial reading on B.M. (elevation 150.485 m) are as follows : 1.205, 1.860, 0.125,
1.915, 0.395, 2.615, 0.880, 1.760, 1.960, 0.920, 2.595, 0.915, 2.255, 0.515, 2.305, 1.170. The
final reading closes on B.M.. Put the data in a complete field note form and carry out reduction
of level by Rise and Fall method. All units are in meters.
Solution :
B.S. (m) F.S. (m) Rise (m) Fall (m) Elevation (m) Remark
1.205 150.485 B.M.
0.125 1.860 0.655 149.830
0.395 1.915 1.7290 148.040
0.880 2.615 2.220 145.820
1.960 1.760 0.880 144.940
2.595 0.920 1.040 145.980
2.255 0.915 1.680 147.660
2.305 0.515 1.740 149.450
1.170 1.135 150.535 B.M.
Arithmetic Check for Reduction of Level
In case of Rise and Fall method for Reduction of level, following arithmetic checks are applied
to verify calculations.
B.S. - F.S. = Rise - Fall = Last R.L. - First R.L.
With reference to Table 13.3:
B.S. - F.S. = 4.795 - 7.145 = - 2.350
Rise - Fall. = 1.130 - 3.480 = - 2.350
Last R.L. - First R.L.= 97.650 - 100.000 = -2.350
Table 3 Field book for Reduction of level
Staff Reading (m) Difference in
elevation (m) H.I (m) R.L. (m) Remarks
Points B.S. I.S. F.S. Rise Fall
A 2.365 102.365 100.000 B.M.
S 1 0.685 1.235 1.130 101.815 101.130 T.P.1
S2 1.745 3.570 2.885 99.990 98.245 T.P.2
B 2.340 0.595 102.365 97.650
4.795 7.145 3.480 101.815
Example
Ex Carry out the arithmetic checks for Reduction of level of Ex13-1.
Solution :
B.S. = 11.720 m; F.S. = 11.670 m
Therefore B.S - F.S. = 0.050 m
Rise = 5.595 m; Fall = 5.545 m
Therefore Rise - Fall = 0.050 m
Last R.L. - First R.L. = 150.535 - 150.485 = 0.050 m.
B.S - F.S. = Rise - Fall = Last R.L. - First R.L.
Example
Ex Complete the differential-level notes and determine the error of closure of the level circuit
and adjust the elevations of B.M.2 and B.M.3 assuming that the error is constant per set up.
Level book note for Level Net
Staff Reading Height of Instrument
(m)
R.L. (m)
Points B.S (m) F.S.(m)
B.M.1 2.125
T.P.1 1.830 2.945
T.P.2 2.100 3.225
T.P.3 1.650 3.605
B.M.2 2.365 2.805
T.P.4 2.885 2.530
T.P.5 3.065 2.350
B.M.3 3.855 1.100
T.P.6 3.270 1.660
T.P.7 3.865 2.110
B.M.1 3.455
Solution :
Staff Reading Height of Instrument
(m)
R.L. (m)
Points B.S (m) F.S.(m)
B.M.1 2.125 102.125 100.000
T.P.1 1.830 2.945 101.010 99.18
T.P.2 2.100 3.225 99.885 97.785
T.P.3 1.650 3.605 97.93 96.280
B.M.2 2.365 2.805 97.49 95.125
T.P.4 2.885 2.530 97.845 94.960
T.P.5 3.065 2.350 98.56 95.495
B.M.3 3.855 1.100 101.315 97.46
T.P.6 3.270 1.660 102.925 99.655
T.P.7 3.865 2.110 104.680 100.815
B.M.1 3.455 101.225
Error of closure = 101.225 - 100 = + 1.225 m
There are ten (10) set up for the instrument. Thus for each set up, there is an error of 0.1225 m.
Therefore correction for each set up = - 0.1225 m
Adjusted elevation of B.M.2 = 95.125 - 4 x .1225 = 94.635 m
Adjusted elevation of B.M. 3 = 97.46 - 7 x .1225 = 96.603 m
Exercise
Ex.1 State and explain the basic principle of levelling.
Ex.2 Enumerate the difference between rise and fall method (of reduction of level) and height of
instrument method.
Ex.3 Data from a differential leveling have been found in the order of B.S., F.S..... etc. starting
with the initial reading on B.M. (elevation 150.485 m) are as follows : 1.205, 1.860, 0.125,
1.915, 0.395, 2.615, 0.880, 1.760, 1.960, 0.920, 2.595, 0.915, 2.255, 0.515, 2.305, 1.170. The
final reading closes on B.M.. Put the data in a complete field note form and carry out reduction
of level by Height of instrument method. All units are in meters.
4. Reciprocal leveling
Reciprocal Leveling
To find accurate relative elevations of two widely separated intervisible points (between which
levels cannot be set), reciprocal leveling is being used.
To find the difference in elevation between two points, say X and Y , a level is set up at L near X
and readings (X1 and Y1) are observed with staff on both X and Y respectively. The level is then
set up near Y and staff readings (Y2 and X2 ) are taken respectively to the near and distant points.
If the differences in the set of observations are not same, then the observations are fraught with
errors. The errors may arise out of the curvature of the earth or intervening atmosphere
(associated with variation in temperature and refraction) or instrument (due to error in
collimation) or any combination of these.
The true difference in elevation and errors associated with observation, if any, can be found as
follows:
Let the true difference in elevation between the points be h and the total error be e. Assuming,
no error on observation of staff near the level (as the distance is very small)
Then, h = X1 ~ (Y1 - e) [From first set of observation]
and h = (X2 - e) ~ Y2 [From second set of observation]
Thus, the true difference in elevation between any two points can be obtained by taking the mean
of the two differences in observation.
Thus, total error in observations can be obtained by taking the difference of the two differences
in observation. The total error consist of error due to curvature of the earth, atmospheric errors
(due to temperature and refraction) and instrumental errors (due to error in collimation) etc.
Example
Ex1 In order to transfer reduced level across a canyon, a reciprocal leveling campaign was
conducted. Simultaneous readings were observed using two levels one at each side of the
canyon. Each of the levels are having same magnifying power and sensitiveness of level tube.
With instruments interchanged during leveling operation yielded the following average readings:
Instrument
station
Average near
readings, meter
Average distant,
readings, meter
R.L of X = 101.345 m
Distance, XY = 1.025Km
e curvature = 0.0785 XY 2
X 1.780 2.345
Y 2.435 1.870
Find out the R.L. of unknown point. Comment on the errors associated with observations.
Solution :
The difference in elevation between X and Y is
= 0.565 m (Y lower than X)
R.L. of Y (unknown Point) = R.L. of X - h = 101.345 - 0.565 = 100.780 m
Since two leveling rods are used and the elapsed time between reading in a set observation is
little, the error due to change in atmospheric condition can be neglected. Moreover, since
readings were taken with instruments interchanged, instrumental errors get cancelled between
different set of observation. As the observations are repeated and averages of the readings have
been considered for further calculation, it is expected that error associated with observation is
minimized thus removed. Only error present in the observation is that associated with the
curvature of the earth.
Trigonometric Leveling
For rapid leveling or leveling in rolling ground or for inaccessible points, trigonometric method
of leveling is being used. In this method, theodolite (an instrument which can measure angle) is
being generally used as an instrument for taking different measurements.
Let us consider two stations T and X on rolling ground whose difference in elevation is required
to be determined by trigonometric method of leveling. At T, a theodolite instrument is set up. TT
' is the height of the instrument above the point T (to be recorded at the time of observation). A
leveling staff is held at X. At the vertical angle of elevation of the actual line of sight , let x1 is
the observed staff reading. The difference in level between T and X is given by
where xt' xh is deviation of the horizontal line of sight due to curvature of the earth and refraction
of light (given by 0.0675 T' x h2 ). xh x1 is T' x1 sin or T' x h tan , T' x1 is the inclined distance
from the instrument to the staff and T' xh is the horizontal distance between the points, x1 X is the
staff reading at X.
Examples
Ex In order to eliminate the uncertainty due to refraction, observations for vertical angle are
made at both ends of the line as close in point of time as possible. The vertical angle at the lower
of the two peaks to the upper peak is +3° 02' 05"?. The reciprocal vertical angle at the upper peak
is - 3° 12' 55"?. The height of instrument are kept to be same in all observation. The slope
distance between two mountain peaks determined by EDM measurement is 21,345m. Compute
the difference in elevations between the two peaks.
Solution :
Average vertical angle = (3° 02' 05" + 3° 12' 55") / 2 = 6° 15' 00 "
Difference in elevation = 21.345 sin 3° 07' 30 " + 0.0675 (21.345 cos 3° 07' 30 ")2
= (1.163 + 30.662) m
= 31.825 m
Exercise
1The following reciprocal levels were taken on two stations P and Q:
Instrument
station
Average near
readings, meter
Average distant,
readings, meter
R.L of P = 101.345 m
Distance, PQ = 1645 Km
P 2.165 3.810
Q 2.335 0.910
Determine the elevation of Q and the error due to refraction when the collimation error is 0.003m
downward per 100m.
2 In order to reduce the error in measurement of vertical angle a set of measurements are taken
and find the average angle as 9° 02' 05? form a height of instrument as 1.565m to a target height
2.165m. If the elevation of the instrument station is 189.250m above mean sea level, find the
elevation of staff station. Assume any data, if required.
5. Curvature and Refraction Correction
Error due to Earth's Curvature & Refraction
The combined error due to curvature and refraction (ecomb ) is thus given by
ecomb = 0.0675 D2 m where D is the distance in km
It is finally subtractive in nature as the combined effect provides increase in staff reading. Let x l
x a represents the combined error due to curvature and refraction in Figure, it is AL .
In most ordinary leveling operation, the line of sight is rarely more than 2 meter above the
ground (where the variation in temperature causes substantial uncertainties in the refraction
index of air). Fortunately, most lines of sights in leveling are relatively short (< 30 m) and B.S.
& F.S. are balanced. Consequently, curvature and refraction corrections are relatively small thus
insignificant except for precise leveling.
Exercise
Ex.1 A surveyor standing on seashore can just see the top of a ship through the telescope of a
levelling instrument. The height of the line of sight at instrument location is 1.65 meter above
msl and the top of ship is 50 meter above sea level. How far is the ship from the surveyor?
The following notes refer to the reciprocal levels taken with one level:
Instrument Station Staff Readings on Remarks
Near Station Further station
P 1.03 1.630 Distance PQ = 800 m
Q 2.74 0.950 R.L. of P = 450 m
Find (i) the true R.L. of Q;
combined correction for curvature and refraction
the error in collimation adjustment of the instrument.
UNIT IV- CONTOURS
1. Properties of Contours
Contour
A contour is defined as an imaginary line of constant elevation on the ground surface. It can also
be defined as the line of intersection of a level surface with the ground surface. For example, the
line of intersection of the watersurface of a still lake or pond with the surrounding ground
represents a contour line.
Definition
A line joining points of equal elevations is called a contour line. It facilitates depiction of the
relief of terrain in a two dimensional plan or map
Contour Interval
The difference in elevation between successive contour lines on a given map is fixed. This
vertical distance between any two contour lines in a map is called the contour interval (C.I.) of
the map. Figure 1(a) shows contour interval of 1m whereas Figure 1(b) shows 10m.
The choice of suitable contour interval in a map depends upon four principal considerations.
These are:
Nature of the Terrain
Nature of Terrain
The contour interval depends upon the nature of the terrain (Table 1). For flat ground, a small
contour interval is chosen whereas for undulating and broken ground, greater contour interval is
adopted.
Table 1 Contour Interval ( CI) for different types of Survey
Sl. No Purpose of survey Scale CI (m)
1 Building site 1/1000 or less 0.2 to 0.5
2 Town planning,
reservoir etc. 1/5,000 to 1/10,000 0.5 to 2
3 Location Survey,
earthwork, etc. 1/10,000 to 1/20,000 1 to 3
Scale of the Map
Scale of the Map
The contour interval normally varies inversely to the scale of the map i.e., if the scale of map is
large, the contour interval is considered to be small and vice versa (Table 2).
Table 2 CI for different scales and types of Ground
SI.NO Map Scale Type of
Terrain CI(m)
1
Large
(1:1000 or
less)
Flat 0.2 to 0.5
Rolling 0.5 to 1
Hilly 1 to 2
2
Intermediate
(1:1000 to
1: 10,000)
Flat 0.5 to 1.5
Rolling 1.5 to 2
Hilly 2 to 3
3
Small
(1: 10,000
or more)
Flat 1 to 3
Rolling 3 to 5
Hilly 5 to 10
Accuracy
Accuracy
Accuracy need of surveying work also decide the contour interval. Surveying for detailed
design work or for earthwork calculations demands high accuracy and thus a small contour
interval is used. But in case of location surveys where the desired accuracy is less, higher
contour interval should be used.
Time of Cost
Time and Cost
If the contour interval is small, greater time and funds will be required in the field survey, in
reduction and in plotting the map. If the time and funds available are limited, the contour
interval may be kept large.
Horizontal Equivalent
The horizontal distance between two points on two consecutive contour lines for a given slope is
known as horizontal equivalent. For example, in Figure 1 (b) having contour interval 10m, the
horizontal equivalent in a slope of 1 in 5 would be 50 m. Thus, horizontal equivalent depends
upon the slope of the ground and required grade for construction of a road, canal and contour
interval.
Characteristics of Contour
The principal characteristics of contour lines which help in plotting or reading a contour map are
as follows:
1. The variation of vertical distance between any two contour lines is assumed to be
uniform.
2. The horizontal distance between any two contour lines indicates the amount of slope and
varies inversely on the amount of slope. Thus, contours are spaced equally for uniform
slope ; closely for steep slope contours and widely for moderate slope .
3. The steepest slope of terrain at any point on a contour is represented along the normal of
the contour at that point . They are perpendicular to ridge and valley lines where they
cross such lines.
4. Contours do not pass through permanent structures such as buildings .
5. Contours of different elevations cannot cross each other (caves and overhanging cliffs are
the exceptions).
6. Contours of different elevations cannot unite to form one contour (vertical cliff is an
exception).
7. Contour lines cannot begin or end on the plan.
8. A contour line must close itself but need not be necessarily within the limits of the map.
9. A closed contour line on a map represents either depression or hill . A set of ring contours
with higher values inside, depicts a hill whereas the lower value inside, depicts a
depression (without an outlet).
10. Contours deflect uphill at valley lines and downhill at ridge lines. Contour lines in U-
shape cross a ridge and in V-shape cross a valley at right angles. The concavity in
contour lines is towards higher ground in the case of ridge and towards lower ground in
the case of valley.
11. Contours do not have sharp turnings.
2. Plotting of Contours
Contouring
The method of establishing / plotting contours in a plan or map is known as contouring. It
requires planimetric position of the points and drawing of contours from elevations of the plotted
points. Contouring involves providing of vertical control for location of points on the contours
and horizontal control for planimetric plotting of points. Thus, contouring depends upon the
instruments used (to determine the horizontal as well as vertical position of points). In general,
the field methods of contouring may be divided into two classes:
Direct methods
Direct Method
In the direct method, the contour to be plotted is actually traced on the ground. Points which
happen to fall on a desired contour are only surveyed, plotted and finally joined to obtain the
particular contour. This method is slow and tedious and thus used for large scale maps, small
contour interval and at high degree of precision. Direct method of contouring can be employed
using Level and Staff as follows:
Vertical control : In this method, a benchmark is required in the project area. The level is set
up on any commanding position and back sight is taken on the bench mark. Let the back sight
reading on the bench mark be 1.485 m. If the reduced level of the bench mark is 100 m, the
height of instrument would be 100 + 1.485 = 101.485 m. To locate the contour of 100.5 m
value, the staff man is directed to occupy the position on the ground where the staff reading is
101.485 -100.500 = 0.985 m. Mark all such positions on the ground where the staff reading
would be 0.985 m by inserting pegs. Similarly locate the points where the staff reading would
be 101.485 -101 = 0.485 m for 101m contour. The contour of 101.5 m cannot be set from this
setting of the instrument because the height of instrument for this setting of the instrument is
only 101.485 m. Therefore, locating contours of higher value, the instrument has to be shifted to
some other suitable position. Establish a forward station on a firm ground and take fore sight on
it. This point acts as a point of known elevation, for shifting the position of the instrument to
another position, from where the work proceeds in the similar manner till the entire area is
contoured.
Horizontal control : The horizontal control is generally provided by method of plane table
surveying or locating the positions of points by other details in which will be discussed in later
module .
Indirect methods
Indirect Methods
In this method, points are located in the field, generally as corners of well-shaped geometrical
figures such as squares, rectangles, and spot levels are determined. Elevations of desired
contours are interpolated in between spot levels and contour lines are drawn by joining points of
equal elevation.
Indirect methods are less expensive, less time consuming and less tedious as compared to the
direct method. These methods are commonly employed in small scale surveys of large areas or
during mapping of irregular surface or steep slope. There are two different ways usually
employed for indirect method of contouring:
Grid method and
Radial line method
A Comparison between Direct and Indirect Methods of Contouring
Direct Method Indirect Method
1 Very accurate but slow and tedious Not very accurate but quicker and less
tedious.
2 Expensive Reasonable cost
3
Appropriate for small projects
requiring high accuracy, e.g., layout
of building, factory, structural
foundations, etc.
Suitable for large projects requiring
moderate to low accuracy, e.g., layout of
highway, railway, canal, etc.
4 More suitable for low undulating
terrain. Suitable for hilly terrain.
5 Calculations need to be carried out in
thefield Calculation in the field is not mandatory.
6 After contouring, calculation cannot
be checked.
Calculations can be checked as and when
needed
Drawing of Contours
Points of desired elevation, at which contours are desired to be drawn, are interpolated in
between observed points. Then, contours are drawn by joining points of equal elevation by
smooth curves keeping in mind the principal characteristics of contour. They are then inked in,
preferably in brown to distinguish them from other features. The contour value is written down
in a gap in the line provided for the purpose. Every fifth contour is drawn bolder to make it
distinguishable from the rest.
Exercise
Ex.1 On the basis od spot elevations in meters given in Fig. 1 draw contours at 20 m interval.
Exercise Figure -1
Ex.2 Fig. 2 shows the same area with stream courses in addition to the spot elevations. Draw the
contours, in this case also, at 20 m interval.
Exercise Figure 2
3. Uses of Contours
Nature of Ground
To visualize the nature of ground along a cross section of interest, a line say XY is being
considered through the contour map . The intersection points between the line and contours are
projected at different elevations of the contours are projected and joined by smooth curve. The
smooth curve depicts the nature of the ground surface along XY.
To Locate Route
Contour map provides useful information for locating a route at a given gradient such as
highway, canal, sewer line etc.
Let it be required to locate a route from P to Q at an upward gradient of 1 in 100. The contour
map of the area is available at a contour interval of 5 meter at a scale of 1:10000. The horizontal
equivalent will therefore be equal to 100 meter. Then with centre at P with a radius of 2 cm draw
an arc to cut the next higher contour, say at q. With q as centre, mark the next higher contour by
an arc of radius 2 cm say at r. Similarly, other points such as s,t,u…. etc are obtained and joining
the points provides the location of route. (Figure 2)
Intervisibility between Stations
When the intervisibility between two points can not be ascertained by inspection of the area, it
can be determined using contour map. The intervisibility is determined by drawing a line joining
the stations / points say PQ and plot the elevations of the points and contours intersected by PQ
as shown in Figure 3. If the intervening ground is found to be above A'B' line, the intervisibility
is obstructed. In the figure, the ground is obstructing the line of sight.
To Determine Catchment Area or Drainage Area
The catchment area of a river is determined by using contour map. The watershed line which
indicates the drainage basin of a river passes through the ridges and saddles of the terrain
around the river. Thus, it is always perpendicular to the contour lines. The catchment area
contained between the watershed line and the river outlet is then measured with a planimeter
(Figure 4).
Storage capacity of a Reservoir
The storage capacity of a reservoir is determined from contour map. The contour line indicating
the full reservoir level (F.R.L) is drawn on the contour map. The area enclosed between
successive contours are measured by planimeter (Figure 5). The volume of water between F.R.L
and the river bed is finally estimated by using either Trapezoidal formula or Prismoidal formula.
4. Measurement of Drainage and Volume of Reservoir
Examples
Ex.1 In a hydro-electric project, the reservoir provides a storage of 5.9 million cubic meter
between the lowest draw down and the top water level. The areas contained within the stated
contours and the upstream face of the dam are as follows :
Contour (m) 200 195 190 185 180 175 170 165
Area (104 sq m) 44 34 28 23 20 16 11 8
If the R.L. of the lowest draw down is 167 m, find the reduced level of water at the full storage
capacity of the reservoir.
Solution :
The area contained in lowest draw down level i.e. at 167 m is as follows :
Given, contour interval = 5 m
The area contained between 165 m and 170 m level is (11 - 8) x 104 = 3 x 104 sq m
i.e., For a height of 5 m, difference in area = 3 x 104 sq m
Therefore between 165 m and 167 m, i.e. for a height drift of 2 m, the area difference
= 1.2 x 104 sq m
The area contained in 167 m contour = (8 + 1.2 ) x 104 sq m = 9.2x 104 sq m
Now from given and calculated data and using trapezoidal rule
Contour Area contained
(104)
Volume contained
between (104)
Volume contained
by (104)
167 9.2
30.3
170 11.0 30.3
67.5
175 16.0 97.8
90.0
180 20.0 187.8
107.5
185 23.0 295.3
127.5
190 28.0 422.8
155.0
195 34.0 577.8
195.0
200 44.0 772.8
So, at full storage capacity, the height of water level lies between 195 m and 200 m.
The volume of water beyond 195 m height is
(5.9 x 106 - 5.778 x 106) = 1.22 x 105 cu.m
Let h be the height of water level above 195 m height. Then area contained in (195 + h) m
contour is
= 34 x 104 +
The volume between 195 m and (195 + h) m contour is
or, h2 + 34 h -12.2 = 0
Solving, we get h = 0.355 m
Thus the reduced level of water at the full reservoir capacity is (195 + 0.355) = 195.355 m
Exercise
Ex.1 The areas enclosed by contours on the upstream face of dam in a hydro-electric project as
Contour (m) 800 790 780 770 760 750 740 730
Area (hectares) 31.41 26.74 24.89 22.23 19.37 17.74 12.91 5.35
The lowest draw down level is 733 m. compute the full reservoir capacity.
UNIT V- MEASUREMENT OF AREA BY PLANIMETER
A linear planimeter. Wheels permit measurement of long areas without restriction
Polar Planimeter
The working of the linear planimeter may be explained by measuring the area of a rectangle
ABCD (see image). Moving with the pointer from A to B the arm EM moves through the yellow
parallelogram, with area equal to PQ×EM. This area is also equal to the area of the parallelogram
A"ABB". The measuring wheel measures the distance PQ (perpendicular to EM). Moving from
C to D the arm EM moves through the green parallelogram, with area equal to the area of the
rectangle D"DCC". The measuring wheel now moves in the opposite direction, subtracting this
reading from the former. The movements along BC and DA are the same but opposite, so they
cancel each other with no net effect on the reading of the wheel. The net result is the measuring
of the difference of the yellow and green areas, which is the area of ABCD.
The images show the principles of a linear and a polar planimeter. The pointer M at one end of
the planimeter follows the contour C of the surface S to be measured. For the linear planimeter
the movement of the "elbow" E is restricted to the y-axis. For the polar planimeter the "elbow" is
connected to an arm with its other endpoint O at a fixed position. Connected to the arm ME is the
measuring wheel with its axis of rotation parallel to ME. A movement of the arm ME can be
decomposed into a movement perpendicular to ME, causing the wheel to rotate, and a movement
parallel to ME, causing the wheel to skid, with no contribution
to its reading.
Linear Planimeter Polar Planimeter
BUILDING MATERIALS:-
UNIT-I: BRICKS
1. Constituents of a good brick earth:
Bricks are the most commonly used construction material. Bricks are prepared by moulding clay
in rectangular blocks of uniform size and then drying and burning these blocks.
Silica
o Brick earth should contain about 50 to % of silica.
o It is responsible for preventing cracking, shrinking and warping of raw bricks.
o It also affects the durability of bricks.
o If present in excess, then it destroys the cohesion between particles and the brick becomes
brittle.
Alumina
o Good brick earth should contain about 20% to 30% of alumina.
o It is responsible for plasticity characteristic of earth, which is important in moulding operation.
o If present in excess, then the raw brick shrink and warp during drying.
Lime
o The percentage of lime should be in the range of 5% to 10% in a good brick earth.
o It prevents shrinkage of bricks on drying.
o It causes silica in clay to melt on burning and thus helps to bind it.
o Excess of lime causes the brick to melt and brick looses its shape.
Iron oxide
o A good brick earth should contain about 5% to 7% of iron oxide.
o It gives red colour to the bricks.
o It improves impermeability and durability.
o It gives strength and hardness.
o If present in excess, then the colour of brick becomes dark blue or blakish.
o If the quantity of iron oxide is comparatively less, the brick becomes yellowish in colour.
Magnesia
o Good brick earth should contain less a small quantity of magnesia about1%)
o Magnesium in brick earth imparts yellow tint to the brick.
o It is responsible for reducing shrinkage
o Excess of magnesia leads to the decay of bricks. Harmful Ingredients in Brick:
Undesirable Ingredients in Bricks
Lime
o A small quantity of lime is required in brick earth. But if present in excess, it causes the brick
to melt and hence brick loses its shape.
o If lime is present in the form of lumps, then it is converted into quick lime after burning. This
quick lime slakes and expands in presence of moisture, causing splitting of bricks into pieces.
Iron pyrites
o The presence of iron pyrites in brick earth causes the brick to get crystallized and disintegrated
during burning, because of the oxidation of the iron pyrits.
o Pyrites discolourise the bricks.
Alkalis
o These are exist in the brick earth in the form of soda and potash. It acts as a flux in the kiln
during burning and it causes bricks to fuse, twist and warp. Because of this, bricks are melted
and they loose their shape.
o The alkalis remaining in bricks will absorb moisture from the atmosphere, when bricks are
used in masonry. With the passage of time, the moisture gets evaporated leaving grey or white
deposits on the wall surface (known as efflorescence). This white patch affects the appearance of
the building structure.
Pebbles
o Pebbles in brick earth create problem during mixing operation of earth. It prevents uniform and
through mixing of clay, which results in weak and porous bricks
o Bricks containing pebbles will not break into shapes as per requirements.
Vegetation and Organic Matter: The presence of vegetation and organic matter in brick earth
assists in burning. But if such matter is not completely burnt, the bricks become porous. This is
due to the fact that the gasses will be evolved during the burning of the carbonaceous matter and
it will result in the formation of small pores.
2. Manufacturing of Bricks
Manufacturing of bricks In the process of manufacturing bricks, the following distinct operations
are involved.
• Preparation of clay
The clay for brick is prepared in the following order.
• Unsoiling : The top layer of the soil, about 200mm in depth, is taken out and thrown away. The
clay in top soil is full of impurities and hence it is to be rejected for the purpose of preparing
bricks.
• Digging : The clay is then dug out from the ground. It is spread on the levelled ground, just a
little deeper than the general level. The height of heaps of clay is about 600mm to 1200mm.
• Cleaning : The clay as obtained in the process of digging should be cleaned of stones, pebbles,
vegetable matters. If these particles are in excess, the clay is to be washed and screened. Such a
process naturally will prove to be troublesome and expensive.
• Weathering : The clay is then exposed to atmosphere for softening and mellowing. The period
varies from few weeks to full season.
• Blending : The clay is made loose and any ingredient to be added to it , is spread out at its top.
The blending indicates intimate or harmonious mixing. It is carried out by taking a small amount
of clay every time and turning it up and down in vertical direction. The blending makes clay fit
for the next stage of tempering.
• Tempering : In the process of tempering, the clay is brought to a proper degree of hardness and
it is made fit for the next operation of moulding .Kneaded or pressed under the feet of man or
cattle .The tempering should be done exhaustively to obtain homogeneous mass of clay of
uniform character. For manufacturing good bricks on a large scale, tempering is done in pug
mill. A typical pug mill capable of tempering sufficient earth for a daily output of about 15000 to
20000 bricks. A pug mill consists of a conical iron tub with cover at its top .It is fixed on a
timber base which is made by fixing two wooden planks at right angle to each other. The bottom
of tub is covered except for the hole to take out pugged earth. The diameter of pug mill at bottom
is about 800mm and that at top is about 1 m. The provision is made in top cover to place clay
inside pug mill .A vertical shaft with horizontal arms is provided at center of iron tub. The small
wedge-shaped knives of steel are fixed at arms. The long arms are fixed at vertical shaft to attach
a pair of bullocks .The ramp is provided to collect the pugged clay .The height of pug mill is
about 2m. Its depth below ground is 600m to800mm lessen the rise of the barrow run and to
throw out the tempered clay conveniently. In the beginning, the hole for pugged clay is closed
and clay with water is placed in pug mill from the top. When vertical shaft is rotated by a pair of
bullock, the clay is thoroughly mixed up by the action of horizontal arms and knives and
homogeneous mass is formed. The rotation of vertical shaft can also be achieved by using steam,
diesel or electrical power. When clay has been sufficiently pugged, the hole at the bottom of the
tub, is opened out and pugged earth is taken out from the ramp by barrow i.e. a small cart with
wheels for next operation of moulding. The pug mill is then kept moving and feeding of clay
from top and taking out of pugged clay from bottom are done simultaneously. If tempering is
properly carried out, the good brick earth can then be rolled without breaking in small threads of
3mm diameter.
A Pug Mill
• Moulding
• Drying
• Burning
Moulding: The clay which is prepared as above is then sent for the text operation of moulding.
Following are two types of moulding:
i. Hand Moulding
ii. Machine Moulding
Hand moulding: In hand moulding, the bricks are moulded by hand i.e.; manually. It is adopted
where manpower is cheap and is readily available for the manufacturing process of bricks on a
small scale. The moulds are rectangular boxes which are open at top and bottom. They may be
of wood or steel. It should be be prepared from well-seasoned wood. The longer sides are kept
slightly projecting to serve as handles. The strips of brass or steel are sometimes fixed on the
edges of wooden moulds to make them more durable. It is prepared from the combination of
steel plate and channel. It may even be prepared from steel angles and plates. The thickness of
steel mould is 6mm.They is used for manufacturing bricks on a large scale. The steel moulds are
more durable than wooden one and turn out bricks of uniform size. The bricks shrink during
drying and burning .Hence the moulds are therefore made larger than burnt bricks (812%). The
bricks prepared by hand moulding are of two types: Ground moulded and Table moulded
Ground moulded bricks: The ground is first made level and fine sand is sprinkled over it. The
mould is dipped in water and placed over the ground. The lump of tempered clay is taken and is
dashed is the mould. The clay is pressed in the mould in such a way that it fills all the corners of
mould. The surplus clay is removed by wooden strike or framed with wire. A strike is a piece of
wood or metal with a sharp edge. It is to be dipped in water every time. The mould is then lifted
up and raw brick ids left on the ground. The mould is dipped in water and it is placed just near
the previous brick to prepare another brick. The process is repeated till the ground is covered
with raw bricks. The lower faces of ground moulded bricks are rough and it is not possible to
place frog on such bricks. A frog is mark of depth about 10mm to 20mm which is placed on raw
brick during moulding. It serves two purposes.
1.It indicates the trade name of the manufacturer
2.In brick work, the bricks are laid with frog uppermost. It thus affords a key for mortar when the
next brick is placed over it.
The ground moulded bricks of better quality and with frogs on their surface are made by using a
pair of pallet boards and a wooden block. A pallet is a piece of thin wood. The block is bigger
than the mould and it has projection of about 6mm height on its surface. The dimensions of
projection correspond to internal dimensions of mould. The design of impression or frog is made
on this block. The wooden block is also known as the moulding block or stock board.
The mould is placed to fit in the projection of wooden block and clay is then dashed inside the
mould. A pallet is placed on the top and the whole thing is then turn upside down. The mould is
taken out and placed over the raw brick and it is conveyed to the drying sheds. The bricks are
placed to stand on their longer sides in drying sheds and pallet boards are brought back for using
them again. As the bricks are laid on edge, they occupy less space and they dry quicker and
better.
Table Moulded Bricks:
i) The process of moulding of bricks is just similar as above. But in this case, the
mould stands near a table size 2m x 1m. The bricks are moulded on the table
and send for further process of drying.
ii) However the efficiency of the moulder gradually decreases because of
standing at some place for a longer duration. The cost of brick is also
increases when table moulding is adopted.
Machine Moulding:
This type of moulding is carried out by two processes:
i) Plastic clay machine
ii) Dry clay machine
Plastic Clay Moulding
i) Such machine consists of a rectangular opening having length and width is equal to an
ordinary bricks. The pugged clay is placed in the machine and it comes out through the
rectangular opening.
ii) These are cut into strips by the wire fixed at the frame. The arrangement is made in such
a way that the strips thickness is equal to that of the bricks are obtained. So it is also
called as WIRE CUT BRICKS.
Dry Clay Machine moulding
i)In these machines, the strong clay is finally converted in to powered form. A small quantity of
water is then added to form a stiff plastic paste.
ii) Such paste is placed in mould and pressed by machine to form dry and well-shaped bricks.
They do not require the process of drying.
Drying
The damp bricks, if brunt, are likely to be cracked and distorted. Hence the moulded bricks are
dried before they are taken for the next operation of burning. For the drying the bricks are laid
longitudinally in the stacks of width equal to two bricks, A stack consists of ten or eight tiers.
The bricks are laid along and across the stock in alternate layers. All the bricks are placed on
edges. The bricks are allowed to dry until the bricks are become leather hard of moisture content
about 2%.
Burning
Bricks are burned at high temperature to gain the strength, durability, density and red color
appearance. All the water is removed at the temperature of 650 degrees but they are burnt at an
temperature of about 1100 degrees because the fusing of sand and lime takes place at this
temperature and chemical bonding takes between these materials after the temperature is cooled
down resulting in the hard and dense mass.
Bricks are not burnt above this temperature because it will result in the melting of the bricks and
will result in a distorted shape and a very hard mass when cooled which will not be workable
while brickwork. Bricks can be burnt using the following methods:
(a) Clamp Burning
(b) Kiln Burning
Clamp Burning:
Clamp is a temporary structure generally constructed over the ground with a height of about 4 to
6 m. It is employed when the demand of the bricks is lower scale and when it is not a monsoon
season. This is generally trapezoidal in plan whose shorter edge among the parallel sides is
below the ground and then the surface raising constantly at about 15 degrees to reach the other
parallel edge over the ground. A vertical brick and mud wall is constructed at the lower edge to
support the stack of the brick. First layer of fuel is laid as the bottom most layer with the coal,
wood and other locally available material like cow dung and husk. Another layer of about 4 to 5
rows of bricks is laid and then again a fuel layer is laid over it. The thickness of the fuel layer
goes on with the height of the clamp.
After these alternate layers of the bricks and fuel the top surface is covered with the mud so as to
preserve the heat.Fire is ignited at the bottom, once fire is started it is kept under fire by itself for
one or two months and same time period is needed for the cooling of the bricks.
Disadvantages of Clamp burning:
1. Bricks at the bottom are over-burnt while at the top are under-burnt.
2. Bricks lose their shape, and reason may be their descending downward once the fuel layer is
burnt.
3. This method cannot employ for the manufacturing of large number of bricks and it is costly in
terms of fuel because large amount of heat is wasted.
4. It cannot be employed in monsoon season.
Kiln Burning:
Kiln is a large oven used for the burning of bricks. Generally coal and other locally available
materials like wood, cow dung etc. can be used as fuel. They are of two types:
• Intermittent Kilns.
• Continuous Kilns.
Fig of a typical kiln
Intermittent Kilns:
These are also the periodic kind of kilns, because in such kilns only one process can take place at
one time. Various major processes which takes place in the kilns are: Loading, unloading,
Cooling, and Burning of bricks.
There are two kind of intermittent kilns: (i) Up-draught Intermittent Kilns (ii) Down draught
Intermittent Kilns
Down draught kilns are more efficient because the heat is utilized more by moving the hot gases
in the larger area of the kiln. In up draught kilns the hot gases are released after they rise up to
chimney entrance.
Continuous Kilns:
These kilns are called continuous because all the processes of loading, unloading, cooling,
heating, pre-heating take place simultaneously. They are used when the bricks are demanded in
larger scale and in short time. Bricks burning are completed in one day, so it is a fast method of
burning.
There are two well-known continuous kilns:
Bull's Trench Kiln: Bull’s trench kiln consists of a rectangular, circular or oval plan shape. They
are constructed below the ground level by excavating a trench of the required width for the given
capacity of brick manufacturing. This Trench is divided generally in 12 chambers so that 2
numbers of cycles of brick burning can take place at the same time for the larger production of
the bricks. Or it may happen that one cycle is carried out at one time in all the 12 chambers by
using a single process in the 2-3 chambers at the same time. The structure is under-ground so the
heat is conserved to a large extent so it is more efficient. Once fire is started it constantly travels
from one chamber to the other chamber, while other operations like loading, unloading, cooling,
burning and preheating taking place simultaneously. Such kilns are generally constructed to have
a manufacturing capacity of about 20,000 bricks per day. The drawback of this kiln is that there
is not a permanent roof, so it is not easy to manufacture the bricks in the monsoon seasons.
Hoffman's Kiln: The main difference between the Bull's trench kiln and the Hoffman kilns are:
1. Hoffman's kiln is an over the ground structure while Bull's Trench Kiln is an underground
structure.
2.Hoffman's kiln have a permanent roof while Bull's trench Kiln do not have so it former can be
used in 12 months a year to manufacture bricks but later is stopped in the monsoon season.
Hoffman's kiln is generally circular in plan, and is constructed over the ground. The whole
structure is divided into the 12 chambers and the entire processes takes place simultaneously like
in Bull's trench Kiln.
3. Classification of Bricks
Classification of Bricks as per common practice
Bricks, which are used in construction works, are burnt bricks. They are classified into four
categories on the basis of its manufacturing and preparation, as given below.
1. First class bricks
2. Second class bricks
3. Third class bricks
4. Fourth class bricks
First Class Bricks: These bricks are table moulded and of standard shape and they are burnt in
kilns. The surface and edges of the bricks are sharp, square, smooth and straight. They comply
with all the qualities of good bricks. These bricks are used for superior work of permanent
nature.
Second Class Bricks: These bricks are ground moulded and they are burnt in kilns. The surface
of these bricks is somewhat rough and shape is also slightly irregular. These bricks may have
hair cracks and their edges may not be sharp and uniform. These bricks are commonly used at
places where brick work is to be provided with a coat of plaster.
Third Class Bricks: These bricks are ground moulded and they are burnt in clamps. These
bricks are not hard and they have rough surfaces with irregular and distorted edges. These bricks
give dull sound when struck together. They are used for unimportant and temporary structures
and at places where rainfall is not heavy.
Fourth Class Bricks: These are over burnt bricks with irregular shape and dark colour. These
bricks are used as aggregate for concrete in foundations, floors, roads etc., because of the fact
that the over burnt bricks have a compact structure and hence they are sometimes found to be
stronger than even the first class bricks.
Classification of Bricks as per constituent materials
There are various types of bricks used in masonry.
• Common Burnt Clay Bricks
• Sand Lime Bricks (Calcium Silicate Bricks)
• Engineering Bricks
• Concrete Bricks
• Fly ash Clay Bricks
Common Burnt Clay Bricks
Common burnt clay bricks are formed by pressing in moulds. Then these bricks are dried and
fired in a kiln. Common burnt clay bricks are used in general work with no special attractive
appearances. When these bricks are used in walls, they require plastering or rendering.
Sand Lime Bricks
Sand lime bricks are made by mixing sand, fly ash and lime followed by a chemical process
during wet mixing. The mix is then moulded under pressure forming the brick. These bricks can
offer advantages over clay bricks such as: their colour appearance is grey instead of the regular
reddish colour. Their shape is uniform and presents a smoother finish that doesn’t require
plastering. These bricks offer excellent strength as a load-bearing member.
Engineering Bricks
Engineering bricks are bricks manufactured at extremely high temperatures, forming a dense and
strong brick, allowing the brick to limit strength and water absorption. Engineering bricks offer
excellent load bearing capacity damp-proof characteristics and chemical resisting properties.
Concrete Bricks
Concrete bricks are made from solid concrete. Concrete bricks are usually placed in facades,
fences, and provide an excellent aesthetic presence. These bricks can be manufactured to provide
different colours as pigmented during its production.
Fly Ash Clay Bricks
Fly ash clay bricks are manufactured with clay and fly ash, at about 1,000 degrees C. Some
studies have shown that these bricks tend to fail poor produce pop-outs, when bricks come into
contact with moisture and water, causing the bricks to expand.
4. Test on Bricks
To know the quality of bricks following 7 tests can be performed. In these tests some are
performed in laboratory and the rest are on field.
• Compressive strength test - This test is done to know the compressive strength of brick. It is
also called crushing strength of brick. Generally 5 specimens of bricks are taken to laboratory for
testing and tested one by one. In this test a brick specimen is put on crushing machine and
applied pressure till it breaks. The ultimate pressure at which brick is crushed is taken into
account. All five brick specimens are tested one by one and average result is taken as brick’s
compressive/crushing strength.
• Water Absorption test - In this test bricks are weighed in dry condition and let them immersed
in fresh water for 24 hours. After 24 hours of immersion those are taken out from water and wipe
out with cloth. Then brick is weighed in wet condition. The difference between weights is the
water absorbed by brick. The percentage of water absorption is then calculated. The less water
absorbed by brick the greater its quality. Good quality brick doesn’t absorb more than 20% water
of its own weight.
• Efflorescence test - The presence of alkalis in bricks is harmful and they form a grey or white
layer on brick surface by absorbing moisture. To find out the presence of alkalis in bricks this
test is performed. In this test a brick is immersed in fresh water for 24 hours and then it’s taken
out from water and allowed to dry in shade. If the whitish layer is not visible on surface it proofs
that absence of alkalis in brick. If the whitish layer visible about 10% of brick surface then the
presence of alkalis is in acceptable range. If that is about 50% of surface then it is moderate. If
the alkalis’ presence is over 50% then the brick is severely affected by alkalis.
• Hardness test - In this test a scratch is made on brick surface with a hard thing. If that doesn’t
left any impression on brick then that is good quality brick.
• Size, Shape and Colour test - In this test randomly collected 20 bricks are staked along
lengthwise, width wise and height wise and then those are measured to know the variation of
sizes as per standard. Bricks are closely viewed to check if its edges are sharp and straight and
uniform in shape. A good quality brick should have bright and uniform colour throughout.
• Soundness test - In this test two bricks are held by both hands and struck with one another. If
the bricks give clear metallic ringing sound and don’t break then those are good quality bricks.
• Structure test - In this test a brick is broken or a broken brick is collected and closely observed.
If there are any flows, cracks or holes present on that broken face then that isn’t good quality
brick.
UNIT II- CEMENT
1. Introduction and Use of Cement
Cement is a binder, a substance that sets and hardens and can bind other materials together.
Cements used in construction can be characterized as being either hydraulic or non-hydraulic,
depending upon the ability of the cement to be used in the presence of water. Non-hydraulic
cement will not set in wet conditions or underwater, rather it sets as it dries and reacts with
carbon dioxide in the air. It can be attacked by some aggressive chemicals after setting.
Hydraulic cement is made by replacing some of the cement in a mix with activated aluminium
silicates, pozzolanas, such as fly ash. The chemical reaction results in hydrates that are not very
water-soluble and so are quite durable in water and safe from chemical attack. This allows
setting in wet condition or underwater and further protects the hardened material from chemical
attack (e.g., Portland cement).
Use
1. Cement mortar for Masonry work, plaster and pointing etc.
2. Concrete for laying floors, roofs and constructing lintels, beams, weather-shed, stairs,
pillars etc.
3. Construction for important engineering structures such as bridge, culverts, dams, tunnels,
light house, clocks, etc.
4. Construction of water, wells, tennis courts, septic tanks, lamp posts, telephone cabins etc.
5. Making joint for joints, pipes, etc.
6. Manufacturing of precast pipes, garden seats, artistically designed wens, flower posts,
etc.
7. Preparation of foundation, water tight floors, footpaths, etc.
2. Types of Cements
Many types of cements are available in markets with different compositions and for use in
different environmental conditions and specialized applications. A list of some commonly used
cement is described in this section:
Portland cement
Ordinary Portland cement is the most common type of cement in general use around the world.
This cement is made by heating limestone (calcium carbonate) with small quantities of other
materials (such as clay)to 1450°C in a kiln, in a process known as calcination, whereby a
molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or
quicklime, which is then blended with the other materials that have been included in the mix.
The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into
a powder to make 'Ordinary Portland Cement'(often referred to as OPC). Portland cement is a
basic ingredient of concrete, mortar and most non-specialty grout. 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.
Portland cement may be grey or white.
• This type of cement use in construction when there is no exposure to sulphates in the soil
or ground water.
• Lime saturation Factor is limited between i.e. 0.66 to 1.02.
• Free lime-cause the Cement to be unsound.
• Percentage of (AL2O3/Fe2O3) is not less than 0.66.
• Insoluble residue not more than 1.5%.
• Percentage of SO3 limited by 2.5% when C3A < 7% and not more than 3% when C3A
>7%.
• Loss of ignition -4%(max)
• Percentage of Mg0-5% (max.)
• Fineness -not less than 2250 cm2/g.
Rapid hardening Portland cement
• It is firmer than Ordinary Portland Cement
• It contains more C3S are less C2S than the ordinary Portland cement.
• Its 3 days strength is same as 7 days strength of ordinary Portland cement.
Low heat Portland cement
• Heat generated in ordinary Portland cement at the end of 3days 80 cal/gm. While in low
heat cement it is about 50cal/gm of cement.
• It has low percentage of C3A and relatively more C2S and less C3S than O.P. Cement.
• Reduce and delay the heat of hydration. British standard ( B S. 1370 : 1974 ) limit the
heat of hydration of this cement.
Sulphate resisting Portland cement
• Maximum C3A content by 3.5% and minimum fineness by 2500 cm'/g.
• Firmer than ordinary pot land cement.
• Sulphate forms the sulpha-aluminates which have expensive properties and so causes
disintegration of concrete.
Sulphate resisting Portland cement
• For this cement, the silage as obtained from blast furnace is used
• The clinkers of cement are ground with about 60 to 65 percent of slag.
• Its strength in early days is less and hence it required longer curing period. It proves to be
economical as slag, which is a Waste product, is used in its manufactures.
Pozzolanic cement
• As per Indian standard, the proportions of Pozzolana may be 10 to 25 % by weight. e.g.
Burnt clay, shale, Fly ash.
• This Cement has higher resistance to chemical agencies and to sea water because of
absence of lime.
• It evolves less heat and initial strength is less but final strength is 28 days onward equal
to ordinary Portland cement.
• It possesses less resistance to the erosion and weathering action.
• It imparts higher degree of water tightness and it is cheap.
White Portland cement
• Grey colour of O.P. cement is due to presence of Iron Oxide. Hence in White Cement
Fe,,O, is limited to 1 %. Sodium Alumina Ferrite (Crinoline) NavAlF6 is added to act as
flux in the absence of Iron-Oxide. •:
• It is quick drying, possesses high strength and has superior aesthetic values and it also
cost lee than ordinary Cement because of specific requirements imposed upon the raw
materials and the manufacturing process.
• White Cement are used in Swimming pools, for painting garden furniture, moulding
sculptures and statues etc.
Coloured Portland
• The Cement of desired colour may be obtained by mixing mineral pigments with
ordinary Cement.
• The amount of colouring material may vary from 5 to 10 percent. If this percentage
exceeds 10percent, the strength of cements is affected.
• The iron Oxide in different proportions gives brown, red or yellow colour. The
coloured Cement are widely used for finishing of floors, window sill slabs, stair
treads etc.
Expansive cement
This type of cement is produced by adding an expanding medium like sulphoaluminate and a
stabilizing agent to the ordinary cement.
• The expanding cement is used for the construction of water retaining structures and
for repairing the damaged concrete surfaces.
High alumina cement
• This cement is produced by grilling clinkers formed by calcining bauxite and lime. It
can stand high temper lures.
• If evolves great heat during setting. It is therefore not affected by frost.
3. Composition of Cement clinker
The various constituents combine in burning and form cement clinker. The compounds formed
in the burning process have the properties of setting and hardening in the presence of water.
They are known as Bogue compounds after the name of Bogue who identified them. These
compounds are as follows: Alite (Tricalcium silicate or C3S), Belite (Dicalcium silicate or C2S),
Celite (Tricalciumalluminate or C3A) and Felite (Tetracalciumalumino ferrite or C4AF).
Tricalcium silicate
It is supposed to be the best cementing material and is well burnt cement. It is about 25-50%
(normally about 40 per cent) of cement. It renders the clinker easier to grind, increases resistance
to freezing and thawing, hydrates rapidly generating high heat and develops an early hardness
and strength. However, raising of C3S content beyond the specified limits increases the heat of
hydration and solubility of cement in water. The hydrolysis of C3S is mainly responsible for 7
day strength and hardness. The rate of hydrolysis of C3S and the character of gel developed are
the main causes of the hardness and early strength of cement paste. The heat of hydration is 500
J/g.
Dicalcium silicate
It constitutes about 25-40% (normally about 32 per cent) of cement. It hydrates and hardens
slowly and takes long time to add to the strength (after a year or more). It imparts resistance to
chemical attack. Rising of C2S content renders clinker harder to grind, reduces early strength,
decreases resistance to freezing and thawing at early ages and decreases heat of hydration. The
hydrolysis of C2S proceeds slowly. At early ages, less than a month, C 2S has little influence on
strength and hardness. While after one year, its contribution to the strength and hardness is
proportionately almost equal to C3S. The heat of hydration is 260 J/g.
Tricalciumalluminate
It is about 5-11% (normally about 10.5 per cent) of cement. It rapidly reacts with water and is
responsible for flash set of finely grounded clinker. The rapidity of action is regulated by the
addition of 2-3% of gypsum at the time of grinding cement. Tricalciumalluminate is responsible
for the initial set, high heat of hydration and has greater tendency to volume changes causing
cracking. Raising the C3A content reduces the setting time, weakens resistance to sulphate attack
and lowers the ultimate strength, heat of hydration and contraction during air hardening. The
heat of hydration of 865 J/g.
Tetracalciumalumino ferrite
It constitutes about 8–14% (normally about 9 per cent) of cement. It isresponsible for flash set
but generates less heat. It has poorest cementing value. Raising theC4AF content reduces the
strength slightly. The heat of hydration is 420 J/g.
4. Hydration of Cement
In the anhydrous state, four main types of minerals are normally present: Alite, Belite, Celite and
Felite. Also present are small amounts of clinker sulfate (sulfates of sodium, potassium and
calcium) and gypsum, which was added when the clinker was ground up to produce the familiar
grey powder.
When water is added, the reactions which occur are mostly exothermic, that is, the reactions
generate heat. We can get an indication of the rate at which the minerals are reacting by
monitoring the rate at which heat is evolved using a technique called conduction
calorimetry.Almost immediately on adding water some of the clinker sulphates and gypsum
dissolve producing an alkaline, sulfate-rich, solution. Soon after mixing, the (C3A) phase (the
most reactive of the four main clinker minerals) reacts with the water to form an aluminate-rich
gel (Stage I on the heat evolution curve above). The gel reacts with sulfate in solution to form
small rod-like crystals of ettringite. (C3A) reaction is with water is strongly exothermic but does
not last long, typically only a few minutes, and is followed by a period of a few hours of
relatively low heat evolution. This is called the dormant, or induction period (Stage II).The first
part of the dormant period, up to perhaps half-way through, corresponds to when concrete can be
placed. As the dormant period progresses, the paste becomes too stiff to be workable. At the end
of the dormant period, the Alite and Belite in the cement start to react, with the formation of
calcium silicate hydrate and calcium hydroxide. This corresponds to the main period of hydration
(Stage III), during which time concrete strengths increase. The individual grains react from the
surface inwards, and the anhydrous particles become smaller. (C3A) hydration also continues, as
fresh crystals become accessible to water. The period of maximum heat evolution occurs
typically between about 10 and 20 hours after mixing and then gradually tails off. In a mix
containing OPC only, most of the strength gain has occurred within about a month. Where OPC
has been partly-replaced by other materials, such as fly ash, strength growth may occur more
slowly and continue for several months or even a year. Ferrite reaction also starts quickly as
water is added, but then slows down, probably because a layer of iron hydroxide gel forms,
coating the ferrite and acting as a barrier, preventing further reaction.
Products of Hydration: During Hydration process several hydrated compounds are formed
most important of which are, Calcium silicate hydrate, calcium hydroxide and calcium
aluminium hydrates which is important for strength gain.
Calcium silicate hydrate:
This is not only the most abundant reaction product, occupying about 50% of the paste volume,
but it is also responsible for most of the engineering properties of cement paste. It is often
abbreviated, using cement chemists' notation, to "C-S-H," the dashes indicating that no strict
ratio of SiO2 to CaO is inferred. C-S-H forms a continuous layer that binds together the original
cement particles into a cohesive whole which results in its strong bonding capacity. The Si/Ca
ratio is somewhat variable but typically approximately 0.45-0.50 in hydrated Portland cement
but up to perhaps about 0.6 if slag or fly ash or micro silica is present, depending on the
proportions.
Calcium hydroxide:
The other products of hydration of C3S and C2S are calcium hydroxide. In contrast to the C-S-
H, the calcium hydroxide is a compound with distinctive hexagonal prism morphology. It
constitutes 20 to 25 per cent of the volume of solids in the hydrated paste. The lack of durability
of concrete is on account of the presence of calcium hydroxide. The calcium hydroxide also
reacts with sulphates present in soils or water to form calcium sulphate which further reacts with
C3A and cause deterioration of concrete. This is known as sulphate attack. To reduce the
quantity of Ca (OH)2 in concrete and to overcome its bad effects by converting it into
cementitious product is an advancement in concrete technology. The use of blending materials
such as fly ash, silica fume and such other pozzolanic materials are the steps to overcome bad
effect of Ca(OH)2 in concrete. However, Ca(OH)2 is alkaline in nature due to which it resists
corrosion in steel.
Calcium aluminium hydrates:
These are formed due to hydration of C3A compounds. The hydrated aluminates do not
contribute anything to the strength of concrete. On the other hand, their presence is harmful to
the durability of concrete particularly where the concrete is likely to be attacked by sulphates. As
it hydrates very fast it may contribute a little to the early strength.
5. Various tests on cement:
Basically two types of tests are under taken for assessing the quality of cement. These are either
field test or lab tests. The current section describes these tests in details.
Field test:
There are four field tests may be carried out to as certain roughly the quality of cement.There are
four types of field tests to access the colour, physical property, and strength of the cement as
described below.
Colour
• The colour of cement should be uniform.
• It should be typical cement colour i.e. grey colour with a light greenish shade.
Physical properties
• Cement should feel smooth when touched between fingers.
• If hand is inserted in a bag or heap of cement, it should feel cool.
Presence of lumps
• Cement should be free from lumps.
• For a moisture content of about 5 to 8%,this increase of volume may be much as 20 to 40
%,depending upon the grading of sand.
Strength
• A thick paste of cement with water is made on a piece of thick glass and it is kept under
water for 24 hours.It should set and not crack.
Laboratory tests:
Six laboratory tests are conducted mainly for assessing the quality of cement. These are: fineness, compressive strength, consistency, setting time, soundness and tensile strength.
Fineness
• This test is carried out to check proper grinding of cement.
• The fineness of cement particles may be determined either by sieve test or permeability
apparatus test.
• In sieve test ,the cement weighing 100 gm. is taken and it is continuously passed for 15
minutes through standard BIS sieve no. 9.The residue is then weighed and this weight
should not be more than 10% of original weight.
• In permeability apparatus test, specific area of cement particles is calculated. This test is
better than sieve test. The specific surface acts as a measure of the frequency of particles
of average size.
Compressive strength
• This test is carried out to determine the compressive strength of cement.
• The mortar of cement and sand is prepared in ratio 1:3.
• Water is added to mortar in water cement ratio 0.4.
• The mortar is placed in moulds. The test specimens are in the form of cubes and the
moulds are of metals. For 70.6 mm and 76 mm cubes ,the cement required is 185gm and
235 gm. respectively.
• Then the mortar is compacted in vibrating machine for 2 minutes and the moulds are
placed in a damp cabin for 24 hours.
• The specimens are removed from the moulds and they are submerged in clean water for
curing.
• The cubes are then tested in compression testing machine at the end of 3days and 7 days.
Thus compressive strength was found out.
Consistency
• The purpose of this test is to determine the percentage of water required for preparing
cement pastes for other tests.
• Take 300 gm of cement and add 30 percent by weight or 90 gm of water to it.
• Mix water and cement thoroughly.
• Fill the mould of Vicat apparatus and the gauging time should be 3.75 to 4.25 minutes.
• Vicat apparatus consists of a needle is attached a movable rod with an indicator attached
to it.
• There are three attachments: square needle, plunger and needle with annular collar.
• The plunger is attached to the movable rod. the plunger is gently lowered on the paste in
the mould.
• The settlement of plunger is noted. If the penetration is between 5 mm to 7 mm from the
bottom of mould, the water added is correct. If not process is repeated with different
percentages of water till the desired penetration is obtained.
Setting time
• This test is used to detect the deterioration of cement due to storage. The test is
performed to find out initial setting time and final setting time.
• Cement mixed with water and cement paste is filled in the Vicat mould.
• Square needle is attached to moving rod of Vicat apparatus.
• The needle is quickly released and it is allowed to penetrate the cement paste. In the
beginning the needle penetrates completely. The procedure is repeated at regular intervals
till the needle does not penetrate completely.(upto 5mm from bottom)
• Initial setting time =<30min for ordinary Portland cement and 60 min for low heat
cement.
• The cement paste is prepared as above and it is filled in the Vicat mould.
• The needle with annular collar is attached to the moving rod of the Vicat apparatus.
• The needle is gently released. The time at which the needle makes an impression on test
block and the collar fails to do so is noted.
• Final setting time is the difference between the time at which water was added to cement
and time as recorded in previous step, and it is =<10hours.
Soundness
• The purpose of this test is to detect the presence of uncombined lime in the cement.
• The cement paste is prepared.
• The mould is placed and it is filled by cement paste.
• It is covered at top by another glass plate. A small weight is placed at top and the whole
assembly is submerged in water for 24 hours.
• The distance between the points of indicator is noted. The mould is again placed in water
and heat is applied in such a way that boiling point of water is reached in about 30
minutes. The boiling of water is continued for one hour.
• The mould is removed from water and it is allowed to cool down.
• The distance between the points of indicator is again measured. The difference between
the two readings indicates the expansion of cement and it should not exceed 10 mm.
Tensile strength
• This test was formerly used to have an indirect indication of compressive strength of
cement.
• The mortar of sand and cement is prepared.
• The water is added to the mortar.
• The mortar is placed in briquette moulds. The mould is filled with mortar and then a
small heap of mortar is formed at its top. It is beaten down by a standard spatula till water
appears on the surface. Same procedure is repeated for the other face of briquette.
• The briquettes are kept in a damp for 24 hours and carefully removed from the moulds.
• The briquettes are tested in a testing machine at the end of 3 and 7 days and average is
found out.
UNIT-III CONCRETE AND MORTAR MATERIALS
1. Introduction
Concrete is a composite material composed mainly of water, aggregate, and cement. Often,
additives and reinforcements are included in the mixture to achieve the desired physical
properties of the finished material. When these ingredients are mixed together, they form a fluid
mass that is easily molded into shape. Over time, the cement forms a hard matrix which binds the
rest of the ingredients together into a durable stone-like material with many uses.
The aim is to mix these materials in measured amounts to make concrete that is easy to:
Transport, place, compact, finish and which will set, and harden, to give a strong and durable
product. The amount of each material (ie cement, water and aggregates) affects the properties of
hardened concrete.
2. Production of concrete
A good quality concrete is essentially a homogeneous mixture of cement, coarse and fine
aggregates and water which consolidates into a hard mass due to chemical action between the
cement and water. Each of the four constituents has a specific function. The coarser aggregate
acts as a filler. The fine aggregate fills up the voids between the paste and the coarse aggregate.
The cement in conjunction with water acts as a binder. The mobility of the mixture is aided by
the cement paste, fines and nowadays, increasingly by the use of admixtures. The stages of
concrete production are: Batching or measurement of materials, Mixing, Transporting, Placing,
Compacting, Curing and Finishing.
Batching
It is the process of measuring concrete mix ingredients either by volume or by mass and
introducing them into the mixture. Traditionally batching is done by volume but most
specifications require that batching be done by mass rather than volume. The proportions of
various ingredients are determined by proper mix design.
A concrete mix is designed to produce concrete that can be easily placed at the lowest cost. The
concrete must be workable and cohesive when plastic, then set and harden to give strong and
durable concrete. The mix design must consider the environment that the concrete will be in; ie
exposure to sea water, trucks, cars, forklifts, foot traffic or extremes of hot and cold.
Proportioning concrete is a mixture of cement, water, coarse and fine aggregates and admixtures.
The proportion of each material in the mixture affects the properties of the final hardened
concrete. These proportions are best measured by weight. Measurement by volume is not as
accurate, but is suitable for minor projects.Cement content: as the cement content increases, so
does strength and durability. Therefore to increase the strength, increase the cement content of a
mix. Water Content: adding more water to a mix gives a weaker hardened concrete. Always use
as little water as possible, only enough to make the mix workable. Water to cement ratio: as the
water to cement ratio increases, the strength and durability of hardened concrete decreases. To
increase the strength and durability of concrete, decrease the water-cement ratio. Aggregates: too
much fine aggregate gives a sticky mix. Too much coarse aggregate gives a harsh or boney mix.
Mixing: concrete must be mixed so the cement, water, aggregates and admixtures blend into an
even mix. Concrete is normally mixed by machine. Machine mixing can be done on-site or be a
pre-mixed concrete company. Pre-mixed concrete is batched (proportioned) at the plant to the
job requirements. Truck mixing the materials are normally added to the trucks at batching plants
and mixed for required time and speed at the plant. The trucks drum continues to rotate to agitate
the concrete as it is delivered to the site. Site mixing when site mixing begin by loading a
measured amount of coarse aggregate into the mixer drum. Add the sand before the cement, both
in measured amounts.
Mixing
The mixing operation consists of rotation or stirring, the objective being to coat the surface the
all aggregate particles with cement paste, and to blind all the ingredients of the concrete into a
uniform mass; this uniformity must not be disturbed by the process of discharging from the
mixer. The mixing may done by manually or by mechanical means like, Batch mixer, Tilting
drum mixer, Non tilting drum mixer, Pan type mixer, Dual drum mixer or Continuous mixers.
There are no general rules on the order of feeding the ingredients into the mixer as this
depend on the properties of the mixer and mix. Usually a small quantity of water is fed first,
followed by all the solids materials. If possible greater part of the water should also be fed
during the same time, the remainder being added after the solids. However, when using very dry
mixes in drum mixers it is necessary to feed the coarse aggregate just after the small initial water
feed in order to ensure that the aggregate surface is sufficiently wetted.
3. Compaction
The operation of placing and compaction are interdependent and are carried out simultaneously.
They are most important for the purpose of ensuring the requirements of strength,
impermeability and durability of hardened concrete in the actual structure. As for as placing is
concerned, the main objective is to deposit the concrete as close as possible to its final position
so that segregation is avoided and the concrete can be fully compacted. The aim of good concrete
placing can be stated quite simply.It is to get the concrete into position at a speed, and in a
condition, that allow it to be compacted properly. To achieve proper placing following rules
should be kept in mind:
1. The concrete should be placed in uniform layers, not in large heaps or sloping layers.
2. The thickness of the layer should be compatible with the method of vibration so that
entrapped air can be removed from the bottom of each layer.
3. The rate of placing and of compaction should be equal. If you proceed too slowly, the
mix could stiffen so that it is no longer sufficiently workable. On no account should
water ever be added to concrete that is setting. On the other hand, if you go too quickly,
you might race ahead of the compacting gang, making it impossible for them to do their
job properly.
4. Each layer should be fully compacted before placing the next one, and each subsequent
layer should be placed whilst the underlying layer is still plastic so that monolithic
construction is achieved.
5. Collision between concrete and formwork or reinforcement should be avoided.
6. For deep sections, a long down pipe ensures accuracy of location of concrete and
minimum segregation. You must be able to see that the placing is proceeding correctly,
so lighting should be available for large, deep sections, and thin walls and columns.
Once the concrete has been placed, it is ready to be compacted. The purpose of compaction is to
get rid of the air voids that are trapped in loose concrete.
It is important to compact the concrete fully because: Air voids reduce the strength of the
concrete. For every 1% of entrapped air, the strength falls by somewhere between 5 and 7%.
This means that concrete containing a mere 5% air voids due to incomplete compaction can lose
as much as one third of its strength. Air voids increase concrete's permeability. That in turn
reduces its durability. If the concrete is not dense and impermeable, it will not be watertight. It
will be less able to withstand aggressive liquids and its exposed surfaces will weather badly.
Moisture and air are more likely to penetrate to the reinforcement causing it to rust. Air voids
impair contact between the mix and reinforcement (and, indeed, any other embedded metals).
The required bond will not be achieved and the reinforced member will not be as strong as it
should be. Air voids produce blemishes on struck surfaces. For instance, blowholes and
honeycombing might occur. There are two methods for compaction which includes: vibration by
vibrators or by tamping using tamping rods.
4. Curing
Curing is the process of making the concrete surfaces wet for a certain time period after placing
the concrete so as to promote the hardening of cement. This process consists of controlling the
temperature and the movement of moisture from and into the concrete.
Curing of concrete is done for the following purposes. Curing is the process of controlling the
rate of moisture loss from concrete to ensure an uninterrupted hydration of Portland cement after
concrete has been placed and finished in its final position. Curing also helps maintain an
adequate temperature of concrete in its early stages, as this directly affects the rate of hydration
of cement and eventually the strength gain of concrete or mortars.
Curing of concrete must be done as soon as possible after placement and finishing and must
continue for a reasonable period of time, for the concrete to achieve its desired strength and
durability. Uniform temperature should be maintained throughout the concrete depth to avoid
thermal shrinkage cracks.Material properties are directly related to micro-structure. Curing
assists the cement hydration reaction to progress steadily and develops calcium silicate hydrate
gel, which binds aggregates leading to a rock solid mass, makes concrete denser, decreases the
porosity and enhances the physical and mechanical properties of concrete.
Some other purposes of curing can be summed up as: curing protects the concrete surfaces from
sun and wind, the process of curing increase the strength of the structure, the presence of water is
essential to cause the chemical action which accompanies the setting of concrete. Generally there
is adequate quantity of water at the time of mixing to cause the hardening of concrete, but it is
necessary to retain water until the concrete is fully hardened.
If curing is efficient, the strength of concrete gradually increases with age. This increase in
strength is sudden and rapid in early stages and it continues slowly for an indefinite period. By
proper curing, the durability and impermeability of concrete are increased and shrinkage is
reduced. The resistance of concrete to abrasion is considerably increased by proper curing.
Curing period:
For ordinary Portland cement, the curing period is about 7 days to 14 days. If rapid hardening
cement is used the curing period can be considerably reduced.
Disadvantages of improper curing:
Following are the disadvantages of improper curing of concrete:
The chances of ingress of chlorides and atmospheric chemicals are very high. The compressive
and flexural strengths are lowered. The cracks are developed due to plastic shrinkage, drying
shrinkage and thermal effects. The durability decreases due to higher permeability. The frost and
weathering resistances are decreased. The rate of carbonation increases. The surfaces are coated
with sand and dust and it leads to lower the abrasion resistance. The disadvantages are more
prominent in those parts of surfaces which are directly exposed or which have large surfaces
compared to depth such as roads, canal, bridges, cooling towers, chimneys etc.
Factors affecting evaporation of water from concrete:
The evaporation of water depends upon the following 4 factors: Air temperature, Fresh concrete
temperature, Relative humidity and Wind velocity.
From the above mentioned factors it can be concluded environment directly influences the
process of evaporation, hence only the fresh concrete temperature can be monitored or
supervised by the concrete technologists. The evaporation of water in the first few hours can
leave very low amount of water in the concrete hydration, this leads to various shrinkage cracks.
Under normal condition the average loss of water varies from 2.5 to 10 N per m2 per hour. The
major loss occurs in the top 50 mm layer over a period of 3 hours, the loss could be about 5% of
the total volume of that layer.
Methods of curing:
While selecting any mode of curing the following two factors are considered:
• The loss of water should be prevented.
• The temperature should be kept minimum for dissipation of heat of hydration.
Methods of curing can be categorized into the following:
Water curing- preventing the moisture loss from the concrete surface by continuously wetting the
exposed surface of concrete.
Membrane curing- minimizing moisture loss from concrete surface by covering it with an
impermeable membrane.
Steam curing- keeping the surface moist and raising the temperature of concrete to accelerate the
rate of strength gain.
Water curing is of the following types:
Ponding: most inexpensive and common method of curing flat slabs, roofs, pavements etc. A
dike around the edge of the slab is erected and water is filled to create a shallow pond. Care must
be taken to ensure that the water in the pond does not dry up, as it may lead to an alternate
drying and wetting condition.
Sprinkling: fogging and mist curing- using a fine spray or fog or moist of water to the concrete
can be efficient method of supplying water to concrete during hot weather, which helps to reduce
the temperature of concrete.
Wet coverings: water absorbent fabrics may be used to maintain water on concrete surfaces.
They must be continuously kept moist so as to prevent the fabrics from absorbing water from the
body of concrete, due to capillary action.
Impermeable membrane curing is of following types:-
Formwork: leaving the form work in place during the early age of concrete is an efficient
method of curing.
Plastic sheeting: plastic sheets form an effective barrier to control the moisture losses from the
surface of concrete, provided they are secured properly and protected from damage. The
efficiency of this system can be enhanced by flooding the concrete surface with water, under the
plastic sheet.
Membrane curing compounds: Curing compounds are wax, acrylic and water based liquids are
spread over the freshly finished concrete to form an impermeable membrane that minimizes the
loss of moisture from the concrete surfaces. These are cost effective methods of curing where
standard curing procedures are difficult to adopt. When applied to cure concrete the time of the
application is critical for maximum effectiveness. Too early application dilutes the membrane,
whereas too late application results in being absorbed into
the concrete. They must be applied when the free water on the surface has evaporated. For
concrete with low w/c ratio, this is not a suitable process.
Steam curing: Steam curing is the process of accelerating the early hardening of concrete and
mortars by exposing it to steam and humidity. These types of curing systems are adopted for
railway sleepers, concrete blocks, pipes, manhole covers, poles etc. Precast iron is cured by this
method under pressure. Curing in hot and cold weather requires additional attention.
Hot weather: During hot weather, concrete must be protected from excessive drying and from
direct wind and sun. Curing materials which reflect sunlight to reduce concrete temperature must
be used.
Cold weather: Some problems associated with temperature below 400C are:
• Freezing of concrete before strength is developed.
• Slow development of concrete strength.
• Thermal stresses induced by the cooling of warm concrete to cooler ambient
temperatures
Chemical curing: In this method water is sprinkled over the surface, after adding certain amount
of some hygroscopic material (e.g. sodium chloride or calcium chloride). The hygroscopic
materials absorb moisture from the atmosphere and thus keep the surface damp.
Alternating current curing: Concrete can be cured by passing alternating current through freshly
laid concrete.
5. Water cement ratio and compressive strength
A cement of average composition requires about 25% of water by mass for chemical reaction. In
addition, an amount of water is needed to fill the gel pores. Nearly 100 years ago, Duff Abrams
discovered the direct relationship between water-to-cement ratio and strength, i.e., lesser the
water used higher the strength of the concrete, since too much water leaves lots of pores in the
cement past. According to Abram’s law, the strength of fully compacted concrete at a given age
and normal temperature is inversely proportional to the water – cement ratio. Here the water-
cement ratio is the relative weight of water to the cement in the mixture. For most applications,
water-to-cement ratio should be between 0.4 and 0.5 lower for lower permeability and higher
strength. In concrete, the trade off, of course, is with workability, since very low water content
result in very stiff mixtures that are difficult to place.
6. Worability
Workability is one of the physical parameters of concrete which affects the strength and
durability as well as the cost of labor and appearance of the finished product. Concrete is said to
be workable when it is easily placed and compacted homogeneously i.e. without bleeding or
Segregation. Unworkable concrete needs more work or effort to be compacted in place, also
honeycombs &/or pockets may also be visible in finished concrete. Definition of Workability
“The property of fresh concrete which is indicated by the amount of useful internal work
required to fully compact the concrete without bleeding or segregation in the finished product.”
Factors affecting workability:
• Water content in the concrete mix
• Amount of cement & its Properties
• Aggregate Grading (Size Distribution)
• Nature of Aggregate Particles (Shape, Surface Texture, Porosity etc.)
• Temperature of the concrete mix
• Humidity of the environment
• Mode of compaction
• Method of placement of concrete
• Method of transmission of concrete
How to improve the workability of concrete
• Increase water/cement ratio
• Increase size of aggregate
• Use well-rounded and smooth aggregate instead of irregular shape
• Increase the mixing time
• Increase the mixing temperature
• Use non-porous and saturated aggregate
• With addition of air-entraining mixtures
Workability tests:
There are 4 types of tests for workability. They are slump test, compacting factor test, flow test,
and Vee bee test
Slump test
The slump test result is a slump of the behavior of a compacted inverted cone of concrete under
the action of gravity. It measures the consistency or the wetness of concrete. Metal mould, in the
shape of the frustum of a cone, open at both ends, and provided with the handle, top internal
diameter 4 in (102 mm), and bottom internal diameter 8 in (203 mm) with a height of 1 ft (305
mm). A 2 ft (610 mm) long bullet nosed metal rod, (16 mm) in diameter. Apparatus Required:
Compacting Factor apparatus, Trowels, Graduated cylinder, Balance and Tamping rod and iron
bucket.
The test is carried out using a mould known as a slump cone. The cone is placed on a hard non-
absorbent surface. This cone is filled with fresh concrete in three stages, each time it is tamped
using a rod of standard dimensions. At the end of the third stage, concrete is struck off flush to
the top of the mould. The mould is carefully lifted vertically upwards, so as not to disturb the
concrete cone. Concrete subsides. This subsidence is termed as slump, and is measured in to the
nearest 5 mm if the slump is <100 mm and measured to the nearest 10 mm if the slump is >100
mm.The slumped concrete takes various shapes, and according to the profile of slumped
concrete, the slump is termed as true slump, shear slump or collapse slump. If a shear or collapse
slump is achieved, a fresh sample should be taken and the test repeated. A collapse slump is an
indication of too wet a mix. Only a true slump is of any use in the test. A collapse slump will
generally mean that the mix is too wet or that it is a high workability mix, for which slump test is
not appropriate. Very dry mixes; having slump 0 – 25 mm are used in road making, low
workability mixes; having slump 10 – 40 mm are used for foundations with light reinforcement,
medium workability mixes; 50 - 90 for normal reinforced concrete placed with vibration, high
workability concrete; > 100 mm.
This test is usually used in laboratory and determines the workability of fresh concrete when size
is about 40 mm maximum. The test is carried out as per specification of IS: 1199-1959.
Compacting factor test:
Steps for performing the experiment:
• keep the apparatus on the ground and apply grease on the inner surface of the cylinders.
• Measure the mass as w1 kg by weighing the cylinder accurately and fix the cylinder on
the base in such a way that the central points of hoppers and cylinder lie on one vertical
line and cover the cylinder with a plate.
• For each 5 kg of aggregate mixes are to be prepared with water-cement ratio by weight
with 2.5 kg sand and 1.25 kg of cement and then add required amount of water
thoroughly until and unless concrete appears to be homogeneous.
• With the help of hand scoop without compacting fill the freshly mixed concrete in upper
hopper part gently and carefully and within two minutes release the trap door so that the
concrete may fall into the lower hopper such that it bring the concrete into standard
compaction.
• Fall the concrete to into the cylinder by bringing the concrete into standard Compaction
immediately after the concrete has come to rest and open the trap door of lower hopper
and then remove the excess concrete above the top of the cylinder by a pair of trowels,
one in each hand will blades horizontal slide them from the opposite edges of the mould
inward to the center with a sawing motion.
• Clean the cylinder from all sides properly. Find the mass of partially compacted concrete
thus filled in the cylinder and say it W2 kg. After this refill the cylinder with the same
sample of concrete in approximately 50 mm layers, by vibrating each layer heavily so as
to expel all the air and obtain full compaction of the Concrete.
• Struck off level the concrete and weigh and cylinder filled with fully compacted concrete.
Let the mass be W3 kg.
• Calculate compaction factor by using the formula: C.F = W2 – W1 / W3 – W1
Flow Table Test:
The flow table test or flow test is a method to determine the consistence of fresh concrete.
Flow table with a grip and a hinge, 70 centimeters (28 in) square. Abrams cone, open at the top
and at the bottom - 30 centimeters (12 in) high, 17 centimeters (6.7 in) top diameter, 25
centimeters (9.8 in) base diameter. Water bucket and broom for wetting the flow table. Tamping
rod-60 centimeters (24 in) long. Conducting the test: The flow-table is wetted. The cone is
placed in the center of the flow-table and filled with fresh concrete in two equal layers. Each
layer is tamped 10 times with tamping rod. Wait 30 seconds before lifting the cone. The cone is
lifted, allowing the concrete to flow. The flow-table is then lifted up 40mm and then dropped 15
times, causing the concrete to flow. After this the diameter of the concrete is measured.
Vee-Bee Test:
This test is useful for concrete having low and very low workability. In this test the concrete is
moulded into a cone in a cylinder container and the entire set up is mounted on a vibrating table.
When vibrator starts, concrete placed on the cone starts to occupy the cylindrical container by
the way of getting remoulded. Remolding is complete when the concrete surface becomes
horizontal. The time required for completion of remoulding since start of vibrator is measured
and denoted as Vee-bee seconds. This provides a measure for workability. Lesser is the Vee-bee
seconds more is the workability.
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