1.introduction to highway engineering
TRANSCRIPT
1.Introduction to Highway Engineering
Overview
Road transport is one of the most common mode of transport. Roads in the form
of trackways, human pathways etc. were used even from the pre-historic times.
Since then many experiments were going on to make the riding safe and comfort.
Thus road construction became an inseparable part of many civilizations and
empires. In this chapter we will see the different generations of road and their
characteristic features. Also we will discuss about the highway planning in India.
Functions of IRC, CRRI, and Roads wing of Surface Transportation.
1. Appointment of the Jayakar Committee:
In 1927 central Govt. appointed an Indian Road development committee under the
chairmanship of
M.R. Jayakar to report on the existing road conditions, and suggestion for their future
developments.
The Jayakar committee submitted its report on 1928 with the
recommendations that since the provincial governments and the local
bodies are not able to look after all the roads; the road development in the
country should be taken up by the Central Government.
2. Indian Roads Congress (I.R.C.):
The Indian Roads Congress was established by the Central Government in 1934 as
per the recommendations of the Jayakar Committee. The I.R.C. was constituted to
provide a forum for the regular pooling the technical ideas, experiences and
knowhow for the panning of the development of the roads throughout the country.
I.R.C. provides the recommended specifications regarding the design and
construction of the roads in the country.
IRC has collaborated with the road wing of the ministry of the surface
transportation of Govt. of India. It publishes journals, standard specifications and
guidelines on various aspects of highway engineering.
- Functions of Indian Roads Congress (IRC):
IRC a body of professional highway engineers provides the following services:
(i) It provides a forum for expression of collective opinion of its members for all
matters affecting the construction and maintenance of roads in India.
(ii) It promotes the use of the standard specifications and practices.
(iii) It provided with the suggestions for the better methods of planning,
designing, construction, administration and maintenance of roads.
(iv) It conducts periodical meetings to discuss technical problems regarding roads.
(v) It makes the laws for the development, improvement and protection of the roads.
(vi) It furnishes and maintains libraries and museums for encouraging the science of road
making.
Functions of Central Road Research Institute (CRRI):
CRRI was started by the Central Government in 1950, for the research work in the
highway engineering. CRRI is a series of laboratories under the council of
scientific and industrial research in India. It offers the following services:
(1) Carries basic and applied research for the design, construction and maintenance of the
highways.
(2) Carries research on traffic safety and transport economics.
(3) Carries research on economical utilization of locally available materials
for construction and maintenance of roads.
(4) Research for the development of the new machinery, tools equipment
and instruments for highway engineering.
(5) To provide technical advice and consultancy services to various organizations.
(6) To provide library and documentation services.
3. Roads wing of ministry of surface transport:
The roads wing of the ministry of Surface Transport handles the road matters of
the Central Govt. It is headed by a Director General.
The Director General is assisted by two additional Director Generals(one for
roads and one for bridges), a numbers of Chief Engineers, Superintending
Engineers, Executive Engineers and Asst.
Executive Engineers. The roads wing has a chief Engineer for the North-East
region posted at Guwahati and a Liaison-cum-Inspectorate organization consisting
of S.E’s and E.E’s in the various states. The functions of the roads wing of
Surface Transport are:
(a) To control funds approved by Central Government for the development of National
Highways.
(b) To control the central road fund.
(c) To prepare plans for development and maintenance of National Highways in
consultation with state PWD’s.
(d) To oversee technically the quality of works executed by the agencies.
(e) To administer matters regarding road research.
(f) To examine technically the projects of roads and bridges prepared by the PWD
4. National Highways Authority of India
The National Highways Authority of India (NHAI) is an autonomous agency of the
Government of India, responsible for management of a network of over 50,000 km
of National Highways out of 1,15,000 km in India.[5] It is a nodal agency of the
Ministry of Road Transport and Highways. NHAI has signed a memorandum of
understanding (MoU) with the Indian Space Research Organisation for satellite
mapping of highways.[6].
Abbreviation -
NHAI
Formation -
1988
Type -Autonomous government agency
Purpose -Development and maintenance of
National Highways Chairman -Yudhvir Singh
Malik, IAS
Parent organisation -Ministry of Road Transport and Highways
# Classification or Types of Roads
The roads are classified based on many
factors as follows. 1 Materials
2 Location &
function 3
Traffic volume
4 Width
5 Economy
6 Traffic type
7 Rigidity
8 Topography
Types of Roads Based on
Materials Earthen roads
Gravel roads
Murrum roads
Kankar roads
WBM roads
Bituminous
roads
Concrete road
1 Earthen Roads
Earthen roads are laid with soil. They are cheaper of all types of roads. This type
of road is provided for less traffic areas and or for countryside areas. Good drainage
system should be required which reflects good performance for longer period.
2. Gravel Roads
Gravel roads are also low quality roads but they are good when compared to earthen
roads. Compacted mixture of gravel and earth is used as pavement material in this
case.
3. Murrum Roads
Murrum is a matter obtained from the disintegration of igneous rocks by
weathering agencies. This is used to make roads called as murrum roads.
4. Kankar Roads
Kankar is nothing but impure form of lime stone. Kankar roads are provided
where lime is available in good quantity. These are also low quality and
performance wise they are similar to gravel and murrum roads.
5. WBM Roads
Water Bound Macadam (WBM) roads contain crushed stone aggregate in
its base course. The aggregates are spread on the surface and these are
rolled after sprinkling water.
WBM roads provides better performance compared to earthen, gravel, murrum and kankar
roads.
roads are laid as layers about 10cm thickness of each layer. They are very rough
and maid disintegrate immediately under traffic.
6. Bituminous Roads
Bituminous roads are very popular roads around the world. They are most used
roads in the world. They are low in cost and good for driving conditions. They are
flexible and thickness of bituminous roads depends upon the subgrade soil
conditions.
7. Concrete Roads
Cement concrete is used to construct the pavements in case of concrete roads.
These are very popular and costlier than all other types of roads. They are not
flexible so, they require less maintenance.
Concrete roads are suitable for high traffic areas. Concrete roads are laid
with joints and time of construction is more.
Types of Roads Based on Location
and Function National highways
State
highways
District
roads
Rural roads or village roads
1.National Highways
National highways are main roads of a particular country. They connects all major
cities to the capital of the country. They run throughout the length and breadth of
the country. Minimum two lane road is provided for national highways.
2 State Highways
State highways are second main roads which connect major parts of state with
in it. State highway ultimately connects to the national highways.
3. District Roads
District roads are provided with in the cities and connects markets and
production places to state and national highways. Two types of district roads are
there namely,
4. Major district roads
Major district roads connect headquarters of neighboring district with main parts
of district while minor district roads are laid with in the district.
5. Rural Roads or Village Roads
Village roads connects the nearby villages with each other. They lead to nearby
town or district roads. Usually low quality roads are provided as village roads
because of low traffic.
Unit 2 road geometry
The geometric design of roads is the branch of highway engineering concerned
with the positioning of the physical elements of the roadway according to
standards and constraints. The basic objectives in geometric design are to
optimize efficiency and safety while minimizing cost and environmental damage.
Right of way
of Way (ROW) can be simply defined as a rite of passage to another person's
land or property. This is a common term often used by land surveyors and civil
engineers and is usually associated in land usage rights.
Formation width
Width of formation. Width of formation or roadway width is the sum of the
widths of pavements or carriage way including separators and shoulders. This
does not include the extra land in formation/cutting.
Shoulder
shoulder is an emergency stopping lane by the verge of a road or motorway, on
the right in countries which drive on the right, or on the left side in India, Japan,
the UK, Australia, and other left-side driving countries. Wikipedia
Carriage Way:
It is the width of the road which is used by the traffic for moving on it. It is
generally central portion of the total land width and is paved and surfaced with the
bituminous concrete for service to the road users. Width of the carriage way
depends on the number of the lanes in the road which again depends on the class
of the highway. If it is higher level road like NH then it will need more numbers of
lanes and therefore the carriageway width will be more.
Camber:
Camber is the transverse slope provided to the road surface for the drainage of
the rainwater for the better performance of the road. Camber can be written as 1
in n or x%.
Drainage of the rainwater is necessary
(1) To maintain the safe value of the friction between the road surface and the tyres
(2) To maintain the strength and durability of the surface concrete
(3) To maintain the durability and strength of the sub-grade soil which can be
harmed if the infiltration of the water takes place to it.
There are generally three types of the cambers: (a) Straight Camber (b) Parabolic
Camber (c) Mixed Camber.
Types of Camber
(a) Straight Camber: This type of camber is provided by meeting two straight
surfaces at the crown. Crown is the central and top most point on the surface of
the road. The edge shape produces inconvenience to the traffic so it is not used
in general.
(b) Parabolic Camber: Parabolic camber is provided by providing a parabolic shape
to the surface of the road. It is also not used in general because it has steep slopes
towards the edges, which can create the outward thrust to the vehicles.
(c) Mixed Camber: Mixed camber is formed by use of the straight surfaces at the
edges but parabolic surface at the centre. It is mostly used for the road construction
because both the problem of the earlier two are solved if we use this camber.
Gradient: It is the slope provided to the surface of the road in the longitudinal
direction for the vertical alignment of the road. There are three kinds of gradients:
A vehicle on ascending gradient
(a) Ruling Gradient (b) Limiting Gradient (c) Exceptional Gradient (d) Minimum Gradient.
Ruling gradient is the design gradient, so it is used to design the road in the vertical alignment.
Limiting and exceptional gradients are provided in the limited stretch of the roads where necessary and
in case of the emergencies or exceptional cases when such need arises respectively.
Minimum gradient is the gradient which is required as the minimum from the drainage point of view in
case of the plane areas.
Sight Distance: Sight distance at any instance is the distance along the centerline of the road which is
visible to the eye of a driver at an height of 1.2 m from the road surface such that an obstruction of
height 0.15 m is visible to him. The heights of the eye of the driver and the obstruction is standardized
by the Indian Roads Congress.
Sight Distance
Most important sight distance which are necessary to be studied here in the design point of view are:
(a) Stopping Sight distance
(b) Overtaking sight Distance
Stopping sight distance(SSD): SSD is the sight distance which is necessary for a driver to stop a vehicle
from the design speed to the 0 speed without any collision with the obstruction on the road. It is also
known as the absolute minimum sight distance so this much sight distance is provided at all the cross
section of the road.
Overtaking Sight Distance(OSD): OSD is the sight distance which is necessary for a vehicle running at the
design speed to overtake a slower moving vehicle without collision with the vehicles coming from the
opposite direction. Generally It is not possible to provide the OSD at every cross section of the road so, it
is provided after a stretch of the road.
Super- Elevation: The outer edge of the road with respect to the inner edge of the road is raised in case
of the horizontal curves, this is called super-elevation. Super-elev
Curves
Road curves are regular bends in roads to bring a gradual change of direction.
Similar curves are on railways and canals.
Curves provided in the horizontal plane are known as horizontal curves and are
circular or parabolic.
-Four types of circular curves are on roads:
Simple curve
Compound curve
Reverse or serpentine curve
Deviation curve
Unit 3
Highway survey and plan
The aim of location survey is to select a route with the following points kept in
mind.
With reasonable economy it should meet the minimum requirement regarding
curvature and grades.
To produce an easy riding (traveling), free flowing traffic artery that has a high
capacity and it meets all the safety standards.
The location survey should recognize and evaluate the routes impact on already
existing industries, business, and residential values and on future development.
Before field survey for any highway location is started, tentative decision,
regarding the design speed of the route, its cross-section, and the maximum
grade must be made. These decision made are based on the;
Estimated of amount, character and hourly distribution of traffic, along with
Knowledge of the area is traversed.
And available funds.
RESULTING ROUTE: After comparison of the different alternative design, the route
is selected which has cheapest overall cost, considering capital investment,
maintenance, expense and saving to the road user.
ENGINEERING DATA:
All details of the topography, soil and problems like drainage and maintenance,
should be investigated before a scientific plan programmed can be suggested. The
engineering data includes following things;
Topographic and geological maps.
Stream and drainage basin maps.
Climatic records.
Preliminary survey maps of previous projects.
Traffic surveys and capacity studies.
RECONNAISSANCE SURVEY REPORT:
This report must consist of;
Total length of line.
The elevation of main and intermediate summit
All adverse grades.
Stream crossing.
Nature of construction.
Right of way circumstances.
Soil conditions.
Unusual or troublesome condition.
Approximate estimate of cost.
PRELIMINARY LOCATION SURVEY:
After the preferred location has been established, the preliminary location survey
serves as basis for fixing the actual highway location.
Conventionally the baseline of preliminary survey i.e. P-line should follow as
closely as possible to the expected final line.
The surrounding are then related to this P-line.
Elevations - At 100ft and at breaks in the ground provide data for profile and
serve as starting point for cross-sections that covers a strip of land on each side of
P-line.
Cross-section - are of width 100’ to 800’, depending upon;
Standard of accuracy
Speed of work and instrument used.
However accurate measurements are used for checking the accuracy of final
location.
The next step is to plot plan and profile of the preliminary line.
FINAL LOCATION SURVEY:
Final location is essentially fixing of the details of the projected highway. It serves
the dual purpose of
Permanently establishing the center-line.
Collecting information necessary for preparation of plans for construction.
The line should be established as closely as is practical to the line drawn on the
preliminary map. It should conform the major and minor control points and the
alignment that was previously determined.
Staking out on the ground of the center line of the projected road provides
opportunity for minor correction like small shift of the line.
It is useful to make a new profile and accurate cross-section from which
excavation and embankment quantities can be measured.
Sufficient points of curvature and tangency, BMs at relatively close interval and in
position free from disturbance by construction activities.
Direction of all property lines, distance to property corners and location of
building, fences and other improvements.
It is important to keep notes on alignment and levels i.e. notes taken in field
during the final location survey usually becomes part of permanent record.
The final location survey is complete when all necessary information in available
and ready for designer to use. It in insured that all information required
preparation of complete construction.
All information pertaining to
Alignment
Topography
Bench mark levels
Cross sections
Section corner ties and other land ties
Drainage and utilities
Unit 4
Road materials
The various MATERIALS used for the construction of road pavement are termed as road materials.
Different types of road materials
1. Soil
2. Aggregates
3. Binders.
1. Soil - Types of soil tests for road construction project requires the site
investigation to be carried out to understand the soil profile. For road
construction works, the properties of soil at subgrade level are required.
The common soil test for road construction includes classification of soil, particle
size distribution, moisture content determination, specific gravity, liquid limit
and plastic limit tests. Moisture content, particle size and specific gravity tests
on soils are used for the calculation of soil properties such as degree of
saturation.
The soil tests can be laboratory tests or in-situ tests. The laboratory tests
should be carried out on every sample taken for determination of particle size
and moisture content.
The most common soils are
Clay, silt , sand, loam, marl, shale
Clay 10-20%
Silt 5 -15%
Sand 65 -75%
2. Aggregates
Types of soil tests for road construction project requires the site investigation to
be carried out to understand the soil profile. For road construction works, the
properties of soil at subgrade level are required.
The common soil test for road construction includes classification of soil, particle
size distribution, moisture content determination, specific gravity, liquid limit
and plastic limit tests. Moisture content, particle size and specific gravity tests
on soils are used for the calculation of soil properties such as degree of
saturation.
The soil tests can be laboratory tests or in-situ tests. The laboratory tests
should be carried out on every sample taken for determination of particle size
and moisture content.
Natural aggregates- 1 crushed rocks
2- gravels
3- sand
Artificial aggregates
1.Brick aggregates
2.Blast furnace slag
3.Fly ash
3- Binders-
The material used in binding the road aggregates and providing the smooth and impermeable
surface for movement of vehicles is called binders
Common binders are --
Cement , bitumen , tar
1. Bitumen –
Asphalt, also known as bitumen is a sticky, black, and highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asphaltum was also used.[2] The word is derived from the Ancient Greek ἄσφαλτος ásphaltos.
The primary use (70%) of asphalt is in road construction, where it is used as the glue or binder mixed with aggregate particles to create asphalt concrete. Its other main uses are for bituminous waterproofing products, including production of roofing felt and for sealing flat roofs.[3]
The terms "asphalt" and "bitumen" are often used interchangeably to mean both natural and manufactured forms of the substance. In American English, "asphalt" (or "asphalt cement") is commonly used for a refined residue from the distillation process of selected crude oils. Outside the United States, the product is often called "bitumen", and geologists worldwide often prefer the term for the naturally occurring variety. Common colloquial usage often refers to various forms of asphalt as "tar", as in the name of the La Brea Tar Pits.
Naturally occurring asphalt is sometimes specified by the term "crude bitumen". Its viscosity is similar to that of cold molasses[4][5] while the material obtained from the fractional distillation of crude oil boiling at 525 °C (977 °F) is sometimes referred to as "refined bitumen". The
2. cement –
cement is a binder, a substance used for construction that sets, hardens, and adheres to
other materials to bind them together. Cement is seldom used on its own, but rather to bind sand
and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry,
or with sand and gravel, produces concrete.
Cements used in construction are usually inorganic, often lime or calcium silicate based, and can
be characterized as either hydraulic or non-hydraulic, depending on the ability of the cement to
set in the presence of water (see hydraulic and non-hydraulic lime plaster).
Non-hydraulic cement does not set in wet conditions or under water. Rather, it sets as it dries
and reacts with carbon dioxide in the air. It is resistant to attack by chemicals after setting.
Hydraulic cements (e.g., Portland cement) set and become adhesive due to a chemical
reaction between the dry ingredients and water. The chemical reaction results in
mineral hydrates that are not very water-soluble and so are quite durable in water and safe from
chemical attack. This allows setting in wet conditions or under water and further protects the
hardened material from chemical attack. The chemical process for hydraulic cement found by
ancient Romans used volcanic ash (pozzolana) with added lime (calcium oxide).
The word "cement" can be traced back to the Roman term opus caementicium, used to
describe masonry resembling modern concrete that was made from crushed rock with burnt
lime as binder. The volcanic ash and pulverized brick supplements that were added to the burnt
lime, to obtain a hydraulic binder, were later referred to as cementum, cimentum, cäment,
and cement. In modern times, organic polymers are sometimes used as cements in concrete.
3- Tar
Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat.[1] Production and trade in pine-derived tar was a major contributor in the economies of Northern Europe[2] and Colonial America. Its main use was in preserving wooden sailing vessels against rot. The largest user was the Royal Navy. Demand for tar declined with the advent of iron and steel ships.
Tar-like products can also be produced from other forms of organic matter, such as peat. Mineral products resembling tar can be produced from fossil hydrocarbons, such as petroleum. Coal tar is produced from coal as a byproduct of coke production.
-Cut back -
Cutback Bitumen ( Liquid Bitumen ) is Bitumen that is dissolved in a solvent . Typical
solvents include Naptha, gasoline and kerosene, white spirit etc. The type of solvent
controls the curing time while the amount determines the viscosity of the Cutback
Bitumen.
The advantage Cutbacks have over Emulsions is a much higher residual Bitumen
percent, typically over 80% compares with over 40-65% for Bitumen emulsions. The
result is more Bitumen left on the roadway after curing, for the same volume of binder
applied.
Cutback Classification
Cutbacks are divided into two classifications, Rapid-Curing (RC) and Medium-Curing
(MC) depending on the solvent used. They are further defined by a number which
indicates the minimum kinematic viscosity (fluidity) of the cutback.
Grades & Properties
Grade Curing Speed Viscosity Penetration of Residue
MC 30 Medium 30-60 120- 150
MC 70 Medium 70-140 120- 150
MC 250 Medium 250- 500 120- 150
MC 800 Medium 800- 1600 120- 150
MC 3000 Medium 3000- 6000 120- 150
RC 70 Rapid 70-140 80- 120
RC 250 Rapid 250-500 80- 120
RC 800 Rapid 800- 1600 80- 120
RC 3000 Rapid 3000- 6000 80- 120
*Kinematic Viscosity at 140 deg F ( 60 deg C), in Centistokes , Penetration of Residue at 77 deg F (25 deg C) , 100 grams, 5 seconds.
Application
Cutback bitumen’s suitable for primer sealing can also be used in the manufacture
ofpre-mix asphalt, which is used in patch repairs.Cutback bitumen’s are used
extensively in sprayed sealingapplications, particularly in cooler weather where
theyprovide improved initial stone retention due to their lower viscosity. Typically, a
single application of the appropriate cutback bitumen is sprayed onto the primed
pavement ontowhich aggregate is laid.
What is Bitumen Emulsion?
Bitumen emulsion is a mixture of fine droplets of bitumen and water. But as the
bitumen is a petroleum product it doesn’t mix with water and as it is sticky in
nature, it doesn’t easily gets disintegrated into fine droplets. To overcome this
problem an emulsifier is used.
Emulsifier can be defined as a surface-active agent. Emulsifier keeps the
bitumen in its fine droplet state by disallowing it to mix with other droplets. As
the droplets are very fine they suspend in water.
“Therefore, bitumen emulsion is a dispersed liquid consisting of three
products, i.e. water, bitumen and emulsion”.
a) Slow setting emulsion
In this type of emulsion, a special type of emulsifier is used to slow the process
of water evaporation. This type of emulsifier are relatively stable.
b) Medium setting emulsion
This type of bitumen emulsion doesn’t break as when applied on aggregate. The
process of evaporation starts when the fine dust of mineral are mixed with the
aggregate emulsion mix.
c) Rapid setting emulsion
This type of bitumen emulsion breaks down rapidly as it comes with contact
with aggregate helping in fast setting and rapid curing.
# Tests of road materials-
1. Test for soil subgrade
California Bearing Ratio Test on Subgrade Soil -
The California Bearing Ratio(CBR) test is a measure of resistance of a material
to penetration of standard plunger under controlled density and moisture
conditions. It was developed by the California Division of Highways as a method
of classifying and evaluating soil- subgrade and base course materials for
flexible pavements.
CBR test may be conducted in remoulded or undisturbed sample. Test consists
of causing a cylindrical plunger of 50mm diameter to penetrate a pavement
component material at 1.25mm/minute.
The loads for 2.5mm and 5mm are recorded. This load is expressed as a
percentage of standard load value at a respective deformation level to obtain
CBR value.
Table of Contents
California Bearing Ratio Test on Subgrade Soil
The aim of this test is the determination of California Bearing Ratio value of the
subgrade soil.
Apparatus for CBR Test
Loading machine-any compression machine can operate at constant rate of
1.25mm per minute can be used. Cylindrical moulds- moulds of 150mm
diameter and 175mm height provided with a collar of about 50mm length and
detachable perforated base.
Compaction rammer, surcharge weight-annular weights each of 2.5kg and
147mm diameter. IS sieve 20mm, Coarse filter paper, balance etc.
Procedure of California Bearing Ratio Test
Sieve the sample through 20mm IS sieve. Take 5 kg of the sample of soil
specimen. Add water to the soil in the quantity such that optimum moisture
content or field moisture content is reached.
Then soil and water are mixed thoroughly. Spacer disc is placed over the base
plate at the bottom of mould and a coarse filter paper is placed over the spacer
disc.
The prepared soil water mix is divided into five. The mould is cleaned and oil is
applied. Then fill one fifth of the mould with the prepared soil. That layer is
compacted by giving 56 evenly distributed blows using a hammer of weight
4.89kg.
The top layer of the compacted soil is scratched. Again second layer is filled and
process is repeated. After 3rd layer, collar is also attached to the mould and
process is continued.
After fifth layer collar is removed and excess soil is struck off. Remove base
plate and invert the mould. Then it is clamped to baseplate.
Surcharge weights of 2.5kg is placed on top surface of soil. Mould containing
specimen is placed in position on the testing machine.
The penetration plunger is brought in contact with the soil and a load of
4kg(seating load) is applied so that contact between soil and plunger is
established. Then dial readings are adjusted to zero.
Load is applied such that penetration rate is 1.25mm per minute. Load at
penetration of 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 7.5, 10 and 12.5mm are noted.
Standard Load Values for CBR Test
Penetration(mm) Standard Load(kg) Unit Standard Load(kg/cm2)
2.5 1370 70
5 2055 105
2- tests for aggregates
1. Los Angeles Abrasion Test on Aggregates -Values for
Pavements and Roads
Los Angeles abrasion test on aggregates is the measure of aggregate toughness
and abrasion resistance such as crushing, degradation and disintegration. This
test is carried out by AASHTO T 96 or ASTM C 131: Resistance to Degradation
of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles
Machine.
The aggregate used in surface course of the highway pavements are subjected
to wearing due to movement of traffic.
When vehicles move on the road, the soil particles present between the
pneumatic tyres and road surface cause abrasion of road aggregates. The steel
rimmed wheels of animal driven vehicles also cause considerable abrasion of the
road surface.
Therefore, the road aggregates should be hard enough to resist abrasion.
Resistance to abrasion of aggregate is determined in laboratory by Los Angeles
test machine.
The principle of Los Angeles abrasion test is to produce abrasive action by use
of standard steel balls which when mixed with aggregates and rotated in a drum
for specific number of revolutions also causes impact on aggregates.
The percentage wear of the aggregates due to rubbing with steel balls is
determined and is known as Los Angeles Abrasion Value.
2. Specific Gravity and Water Absorption Tests on Aggregates Specific gravity test of aggregates is done to measure the strength or quality of
the material while water absorption test determines the water holding capacity
of the coarse and fine aggregates.
The main objective of these test is to,
1. To measure the strength or quality of the material.
2. To determine the water absorption of aggregates.
Aggregate Sample
Specific Gravity is the ratio of the weight of a given volume of aggregate to
the weight of an equal volume of water. It is the measure of strength or quality
of the specific material. Aggregates having low specific gravity are generally
weaker than those with higher specific gravity values.
Table of Contents
Procedure of Water Absorption and Specific
Gravity Test on Aggregates
There are three methods of testing for the determination of the specific gravity
of aggregates, according to the size of the aggregates larger than 10 mm, 40
mm and smaller than 10 mm. For Samples larger than 10 mm, 40 mm, the
below given test method is used and for samples smaller than 10 mm
Pycnometer test is done.
3. Determination of Aggregate Impact Value – Impact Test on
Aggregates Determination of Aggregate Impact Value – Impact Test on Aggregates is done
to carry out to:
Determine the impact value of the road aggregates,
Assess their suitability in road construction on the basis of impact
value.
Table of Contents
Aggregate Impact Value on Coarse Aggregates
Apparatus for Aggregate Impact Test
The apparatus as per IS: 2386 (Part IV) – 1963 consists of:
(i) A testing machine weighing 45 to 60 kg and having a metal base with a
painted lower surface of not less than 30 cm in diameter. It is supported on
level and plane concrete floor of minimum 45 cm thickness. The machine should
also have provisions for fixing its base.
(ii) A cylindrical steel cup of internal diameter 102 mm, depth 50 mm and
minimum thickness 6.3 mm. .
(iii) A metal hammer or tup weighing 13.5 to 14.0 kg the lower end being
cylindrical in shape, 50 mm long, 100.0 mm in diameter, with a 2 mm chamfer
at the lower edge and case hardened. The hammer should slide freely between
vertical guides and be concentric with the cup. Free fall of hammer should be
within 380±5 mm.
(iv) A cylindrical metal measure having internal diameter 75 mm and depth 50
mm for measuring aggregates.
(v) Tamping rod 10 mm in diameter and 230 mm long, rounded at one end.
(vi) A balance of capacity not less than 500g, readable and accurate up to 0.1
g.
Theory of Aggregate Impact Test
The property of a material to resist impact is known as toughness. Due to
movement of vehicles on the road the aggregates are subjected to impact
resulting in their breaking down into smaller pieces.
The aggregates should therefore have sufficient toughness to resist their
disintegration due to impact. This characteristic is measured by impact value
test.
The aggregate impact value is a measure of resistance to sudden impact or
shock, which may differ from its resistance to gradually applied compressive
#.Tests for bitumen
Various Lab Tests on Bitumen for Pavement Construction
Various laboratory tests on bitumen is conducted to check quality and different
properties of bitumen for pavement construction. Bitumen is a black or brown
mixture of hydrocarbons obtained by partial distillation of crude petroleum.
Bitumen is insoluble in water. It composes 87% carbon, 11% hydrogen and 2%
oxygen by weight. It is obtained in solid or semi-solid state. It is generally used
as surface coarse for roads, roof coverings etc.
Table of Contents
Tests on Bitumen to Check Quality and
Properties for Pavement
To ensure the quality of bitumen several tests are performed which are as
follows.
Ductility test
Flash and Fire point test
Float test
Loss on heating test
Penetration test
Softening point test
Specific gravity test
Viscosity test
Water content test
Ductility Tests on Bitumen
The property of bitumen which allows it to undergo deformation or elongation is
called ductility of bitumen. The ductility of bitumen is measured by the distance
in Cm (centimeter), to which the bitumen sample will elongate before breaking
when it is pulled by standard specimen at specified speed and temperature.
Firstly the bitumen sample is heated to 75-100oC and melted completely. This is
poured into the assembled mold which is placed on brass plate. To prevent
sticking the mold and plate are coated with glycerin and dextrin. After filling the
mold, placed it in room temperature for 30-40 minutes and then placed it in
water for 30 minutes.
Then take it out and cut the excess amount of bitumen with the help of hot
knife and level the surface. Then place the whole assembly in water bath of
ductility machine for 85 to 95 minutes. Then detach the brass plate and the
hooks of mold are fixed to machine and operate the machine.
The machine pulls the two clips of the mold horizontally and then bitumen
elongates. The distance up to the point of breaking from the starting point is
noted as ductility value of bitumen. The minimum value should be 75cm.
Flash and Fire Point Tests on Bitumen
Flash point of bitumen is defined as the point of lowest temperature at which
bitumen catches vapors of test flame and fires in the form of flash. Fire point of
bitumen is defined as the point of lowest temperature at which the bitumen
ignites and burns at least for 5 second under specific conditions of test.
Flash and fire point test helps to control fire accidents in bitumen coated areas.
By this test we can decide the bitumen grade with respect to temperature for
particular areas of high temperatures.
Float Tests on Bitumen
Float test is used to determine the consistency of bitumen. But we generally use
penetration test and viscosity test to find out the consistency of bitumen except
for certain range of consistencies. The float test apparatus consists of aluminum
float and brass collars as shown in below figure.
These collars are filled with melted bitumen sample and cooled to 5oC and then
attached them into aluminum floats and this assembly is placed in water bath at
a temperature of 50oC. Note down the time in seconds from the instant the float
is put on the water bath until the water breaks the material and enters the float.
Loss on Heating Tests on Bitumen
When the bitumen is heated, water content present in the bitumen is
evaporated and bitumen becomes brittle which can be damaged easily. So, to
know the amount of loss ness we will perform this test. In this test, take the
bitumen sample and note down its weight to 0.01gm accuracy at room
temperature.
Then place the sample in oven and heat it for 5 hours at 163oC. After that take
out the sample and cooled it to room temperature and take the weight to
0.01gm accuracy and note down the value. Then for the two values of weight
before and after heating we can compute the loss of mass. The loss should be
less than 5% of total weight otherwise it is not preferred for construction.
Penetration Test on Bitumen
The penetration value of bitumen is measured by distance in tenths of mm that
a standard needle would penetrate vertically into bitumen sample under
standard conditions of test. By this test we can determine the hardness or
softness value of bitumen.
In this test, firstly heat the bitumen above its softening point and pour it into a
container of depth attest 15mm. bitumen should be stirred wisely to remove air
bubbles. Then cool it to room temperature for 90 minutes and then placed it in
water bath for 90 minutes.
Then place the container in penetration machine adjust the needle to make
contact with surface of sample. Make dial reading zero and release the needle
for exactly 5 seconds and note down the penetration value of needle for that 5
seconds. Just repeat the procedure thrice and note down the average value.
Softening Point Test on Bitumen
Softening point of bitumen indicates the point at which bitumen attains a
particular degree of softening under specified conditions of the test. Take small
amount of bitumen sample and heat it up to 75-100oC. Ring and ball apparatus
is used to conduct this test. Heat the rings and apply glycerin to prevent from
sticking. Fill this rings with bitumen and remove the excess material with hot
sharp knife.
Assemble the apparatus parts, balls are arranged in guided position that is on
the top of bitumen sample. And fill the beaker with boiled distilled water. Then
apply temperature @ 5oC per minute. At certain temperature bitumen softens
and ball slowly move downwards and touches the bottom plate, this point is
noted as softening point.
Specific Gravity Test on Bitumen
Specific gravity of bitumen is the ration of mass of given volume of bitumen to
the mass of equal volume of water at specified temperature. Specific gravity is
the good indicator of quality of binder. It can be determined by pycnometer
method.
In this method, take clean and dry specific gravity bottle and take its
weight(w1).in the 2ndcase, fill the bottle with distilled water and dip it in water
bath for 30 minutes and note down the weight(w2). Next, fill half the bottle with
bitumen sample and weigh (w3).
Finally fill the bottle with half water and half portion with bitumen and weigh
(w4). Now we can find out specific gravity from the formulae.
Viscosity Test on Bitumen
Viscosity is the property of bitumen which influences the ability of bitumen to
spread, penetrate into the voids and also coat the aggregates. That is it
influences the fluid property of bitumen. If viscosity of bitumen is higher,
compactive effort of bitumen reduces and heterogeneous mixture arises.
If viscosity is lower, then it will lubricate the aggregate particles. Viscosity is
determined by using tar viscometer. The viscosity of bitumen is expressed in
seconds is the time required for the 50 ml bitumen sample to pass through the
orifice of a cup, under standard conditions of test and at specified temperature.
Water Content Test on Bitumen
When bitumen is heated above the boiling point of water, sometimes foaming of
bitumen occurs. To prevent this bitumen should have minimum water content in
it. Water content in bitumen is determined by dean and stark method. In this
method, the bitumen sample is kept in 500ml heat resistant glass container.
Container is heated to just above the boiling point of water. The evaporated
water is condensed and collected. This collected water is expressed in terms of
mass percentage of sample. It should not more than 0.2% by weight.