CE409/16 1 TRANSPORTATION ENGINEERING UNIT - 1 HIGHWAY PLANNING AND DEVELOPMENT IN INDIA CONTENTS: Aims / Objectives: 1.1. Introduction 1.2. Different Modes of Transportation 1.3. Characteristics of Road Transportation 1.4. Highway Planning and Development in India 1.5. Summary 1.6. Self Assessment Questions 1.7. Books for Reference. Aims / Objectives: Transportation system is required for carrying passengers and goods from one place to the other. The different modes of transport are Roads , Railways , Airways and Water ways. Of all communications , highway or road is the nearest communication to man and is the only means of transportation that offers to the whole community alike. Merits and demerits of roads as a means of transport are presented. Due to lack of rational and scientific planning road development in India has suffered a major set back. This set back has become a major hurdle in Nation’s march towards progress and prosperity. The government of India formed a Road Development Committee , under the chairman ship of Mr. M.R. Jayakar , in 1927 to examine the desirability of developing the road system of India and the means by which such development could be achieved. The committee submitted its report in 1928 which may be considered as a major land mark in the planned development of roads in our country. The recommendations of the Jayakar Committee and their impact on the planning and development of roads in modern India have been explained. 1.1. Introduction: Transportation contributes to the economic , industrial and cultural development of any region or country. Transportation is also essential for strategic movement in emergency for the defence of the country and to maintain better law and order. A study of the economic , industrial and cultural development of the advanced nations like the United State , United Kingdom , Japan , Germany and others indicate that the progress and prosperity of any
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CE409/16 1
TRANSPORTATION ENGINEERING
UNIT - 1 HIGHWAY PLANNING AND DEVELOPMENT IN INDIA
CONTENTS:
Aims / Objectives:
1.1. Introduction
1.2. Different Modes of Transportation
1.3. Characteristics of Road Transportation
1.4. Highway Planning and Development in India
1.5. Summary
1.6. Self Assessment Questions
1.7. Books for Reference.
Aims / Objectives:
Transportation system is required for carrying passengers and goods from one place to
the other. The different modes of transport are Roads , Railways , Airways and Water ways.
Of all communications , highway or road is the nearest communication to man and is the
only means of transportation that offers to the whole community alike. Merits and demerits of
roads as a means of transport are presented.
Due to lack of rational and scientific planning road development in India has suffered
a major set back. This set back has become a major hurdle in Nation’s march towards
progress and prosperity. The government of India formed a Road Development Committee ,
under the chairman ship of Mr. M.R. Jayakar , in 1927 to examine the desirability of
developing the road system of India and the means by which such development could be
achieved. The committee submitted its report in 1928 which may be considered as a major
land mark in the planned development of roads in our country. The recommendations of the
Jayakar Committee and their impact on the planning and development of roads in modern
India have been explained.
1.1. Introduction:
Transportation contributes to the economic , industrial and cultural development of
any region or country. Transportation is also essential for strategic movement in emergency
for the defence of the country and to maintain better law and order. A study of the economic ,
industrial and cultural development of the advanced nations like the United State , United
Kingdom , Japan , Germany and others indicate that the progress and prosperity of any
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country or nation may be linked up with the efficiency and adequacy of its transportation
systems.
1.2. Different Modes of Transport:
The three media surrounding us , Land , Water and Air , have been used effectively
for the development of transportation modes. Land has given scope for the development of
road and rail transport. Water and air have developed water ways and air ways. Water ways
include seas , rivers , canals and lakes for movement of ships and boats.
The choice of a transportation system depends upon (i) length of haul (ii) weight and
size of consignment (iii) traffic density (iv) nature of route and (v) quality of service.
1.3. Characteristics of Road Transport:
Some of the important characteristics of this mode of transport are as follows:
(i) Of all communications , road communication is the nearest to men.
(ii) Road transport is the only means of transport that offers itself to the whole community
alike.
(iii) Roads are used by various modes of transport , that is , by-cycles , rickshaws , animal
drawn carts and carriages , automobiles , etc. ; but railways , airways and waterways are used
by rolling stock , aeroplanes and by ships and boats respectively.
(iv) Construction and maintenance cost of roads is cheaper than that of railway tracks , docks
and harbours and airports.
(v) Stage Construction is feasible for roads.
(vi) Roads can be constructed to penetrate interior of any region and to connect villages. This
advantage becomes particularly evident when planning the communication system in hilly
regions and scarcely populated areas. Provision of railways in such areas become
uneconomical.
(vii) Road transport offers a complete freedom to the road users to transfer the vehicle from
one lane to another and from one road to another according to the need and convenience.
(viii) Road transport offers a flexible service , free from fixed schedules.
(ix) In particular for short distance travel and short hauls road transport saves time and is
economical.
(x) Road transport offers door to door service.
(xi) Road Transport has a high employment potential.
(xii) Road Transport causes parking problems of serious proportions in city streets.
(xiii) One of the serious disadvantages of road transport in its poor record of safety.
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(xiv) Road transport has been one of the major causes of environmental pollution. Noise ,
fumes , vibrations , loss of aesthetics , ribbon development. Cluster of advertisements along
highways - are some of the ill-effects.
1.4.0. High-way Planning:
Planning is a pre-requisite for any development programme. This is particularly
necessary when long range comprehensive plans have to be drawn.
Before going to the stage of planning , one should fix up the main objectives of a
programme. Following are some of the main objectives of highway planning.
(i) To provide for efficient , safe , economical , comfortable and speedy movement of goods
and people.
(ii) To plan anticipated future developments.
(iii) To plan for a road system having maximum utility within available resources.
(iv) To phase the road development programme from financial considerations.
(v) To evolve a financial system.
1.4.1. Planning and Development in India:
The history of roads dates back to the period before the advent of recorded history.
The various civilisations of the world that are known for their excellence and attainments
have left traces of their art of road building.
In Mauryan age , considerable importance began to be attached to roads as trade ,
agriculture and cultural activities flourished. Rajapaths (main highways) and vanijapathas
(trade routes) were constructed. Kautilya , Prime minister of Emperor Chandragupta Maurya ,
laid down rules for the construction of roads for different types of traffic in his book
‘Arthashasthra’. During the Pathan and Mughal periods , roads were greatly improved. Some
of the highways either built or maintained by Mughals and other rulers received great
appreciation from the foreign visitors who visited India during the reign. Roads were built
running from North-West to Eastern areas through Gangetic plains , linking also the coastal
and central parts. Later the fall of the Mughal empire led to scant attention to
communications ; and the conditions of the roads deteriorated considerably. At the beginning
of the British rule , roads were constructed by British Military Engineers on the remains of
old roads which existed. These roads connected important military and business centres.
Military maintenance of roads was not quite adequate and in 1865 Lord Dalhousie ,
the then Governor General , formed the public works department in more or less the same
form that exists today. Engineering Colleges were established to train civil engineers.
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Important roads were provided with metalled beds and were bridged. Specifications were
formed for construction of roads. By the end of 19th century , these efforts resulted in the
establishment of a good system of trunk roads in the country. With the development of
railways (in the latter part of 19th century) a set back to the rapid development of roads
occurred. Government of India act 1919 put a further damper on road development as the
subject of roads was purely a provincial charge and central government remained concerned
with roads of strategic importance.
After world war I , motor vehicle traffic on roads increased. The existing roads were
not capable to withstand both bullock-cart traffic and motor vehicles. This demanded better
road network which can carry the mixed traffic. In November 1927 , Government of India
appointed a committee called the Road Development Committee under the chairmanship of
Mr. M.R. Jayakar. The committee , known popularly as the Jayakar committee was required
to:
(i) examine the desirability of developing the road system of India and the means by which
such development could be achieved.
(ii) examine the possibility , having regard to the distribution of functions between the centre
and state governments , of co-ordinating the activities of the different governing authorities in
the country by the formation of a central road board or otherwise.
1.4.2. Recommendations of Jayakar Committee: The committee’s report (1928) may be
considered as a major landmark in the planned development of roads in our country. The
most important recommendations made by the committee are:
(i) The road development in the country should be considered as a national interest as it has
become beyond the capacity of state governments and local bodies.
(ii) An extra tax should be levied on petrol from the road users to develop a road
development fund called ‘Central Road Fund’.
(iii) A semi-official technical body should be formed to pool the technical knowledge from
various parts of the country and to act as an advisory body on various aspects of roads.
(iv) A research organisation should be instituted to carry research and development work and
to be available for consultation.
Most of the recommendations of Jayakar committee were accepted by Government of
India and were implemented subsequently.
1.4.3. Central Road Fund: Following the recommendations of Jayakar Committee for
funding the roads , CENTRAL ROAD FUND was created in 1929 with additional duty
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levied on petrol and was intended for road development. Twenty percent of the same will be
retained by the central government for meeting the expenses of road development of the
country and the remaining will be distributed among the states in the ratio of actual
consumption of petrol or revenue collected.
1.4.4. Indian Roads Congress (IRC): A semi-official technical body known as the Indian
Roads Congress (IRC) was formed in 1934 by the government of India. This , it may be
recalled , was one of the recommendations of the Jayakar Committee.
Now IRC is an active body of national importance controlling standardisation ,
specifications and recommendations as regards design and construction of roads and bridges.
The IRC publishes journals , research publications and standard specifications on various
aspects of Highway and Traffic engineering. The IRC works in collaboration with the Roads
wing of the Ministry of Shipping and Transportation , Government of India. It is responsible
for the various highway development plans of our country.
1.4.5. Motor Vehicles Act:
In-order to have control over the driver , vehicle ownership and vehicle operation on
roads , the Government of India broughtout for the first time the Motor Vehicles Act in 1939.
This act has been thoroughly revised in the year 1988.
1.4.6. Nagpur Conference:
At the initiative of IRC , a conference of the chief engineers of all states was held at
Nagpur in 1943 to finalise the road development plan for the country as a whole. This may be
considered as a landmark in the history of road development in India , as it was the first
attempt to prepare a co-ordinated road development programme in a comprehensive and
scientific manner. In this conference a 20 year plan , for the period 1943-63 , popularly
known as Nagpur Plan , was finalised. All roads were classified into five categories and a
target of 16 KM of road per 100 sq. km area of the country was aimed at.
1.4.7. Central Road-Research Institute (C.R.R.I):
One of the recommendations of the Jayakar Committee was to set up a central
organisation of research. Accordingly , an institute for carrying out research in various fields
of highway engineering , called the Central Road Research Institute (CRRI) was started at
New-Delhi in 1950. This institute is mainly engaged in applied research and offers technical
advice to state governments , other organisations and industries on various problems
concerning highways.
1.4.8. National Highway Act:
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The National Highway Act was passed in the year 1956. According to this act , the
development and maintenance of National Highways is the responsibility of the Central
government. The Central government is empowered to declare any other highway as National
Highway or to omit any of the existing National Highway from the list.
1.4.9. Border Roads Development Board:
This board was set up in March 1960 under the chairmanship of the prime minister. A
General Reserve Engineering Force (GREF) consisting of unskilled and skilled labour ,
supervisors and engineers from all parts of India was raised. This organisation is to take up
construction of roads at high altitudes in extremely varied , difficult and hostile terrain under
unfavourable climatic conditions.
1.4.10. Second Road Development Plan (1961 ‘ 81):
The second twenty year road development plan for the period 1961 - 81 was initiated
by the IRC and was finalised in 1959 and is also known as the Bombay Road Plan. The plan
gave due considerations to the developments those are taking place and developments that
have to take place in our country in various fields during the plan period. The target of road
length contemplated during this plan period was 32 per 100 Sq. Km of area covered.
Though the road length envisaged in this plan has been exceeded , the standards to
which these roads have been brought , leave scope for considerable improvement. The
position of rural roads is far from satisfactory , Constraint of resources have been the major
bottleneck for this state of affairs.
1.4.11. Highway Research Board:
Recognising the need for faster research on highway matters , the Indian Roads
Congress has established a Highway Research Board on October 24 , 1973. Its main
functions are to advise the government about the road research programme required for the
conditions prevailing in our country , correlate the research information from various
organisation in India and recommend priorities about various road research problems. It will
also obtain feedback of research findings and evaluate the same , collect and disseminate the
results of research.
1.4.12. National Transport Policy Committee (NTPC):
This committee was formed in the year 1978 to prepare a comprehensive national
transport policy for the country , keeping in view the objectives and priorities set out in the
Five Year Plans. This Committee submitted its report in 1980 and most of the
recommendations of the Committee have been accepted by Government of India. Some of the
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important recommendations include (i) Liberalisation of transport sector , inclusion of
transportation in priority sector and optimal inter-modal mix between railway and road
transport based on resource - cost consideration and energy conservation.
(ii) Development of roads in rural , hilly and tribal areas ; strengthening of national highways
; increasing the funds for maintenance of roads ; to connect all the villages with all weather
low-cost roads within the next twenty years , and
(iii) Separate recommendations for various factors connected with development and growth
of road transport by the year 2001.
1.4.13 Third Twenty Year Road Development Plan (1981 - 2001): This plan is also called
‘Lucknow Road Plan’ and has been prepared keeping in view the growth pattern envisaged in
various fields by the turn of this century. Some of the points which were given due
consideration while formulating the plan are improvement of transportation facilities in
villages , towns and small cities , conservation of energy , preservation of environmental
quality and improvement in road safety.
1.4.14. National Highway Authority: National Highway Authority was constituted by the
Ministry of Surface Transport with effect from June , 15 , 1989 with the following objectives:
(1) National Highways carry 1/3 of the total road traffic and to cope up with the increasing
demands of traffic widening of existing sections to four lanes and construction of express
ways on the high traffic density corridors are required. The funds for this are met with from
external financing institutions like the World Bank and Asian Development Bank.
Construction , maintenance and operation of National Highways , hither to done by State
P.W.D’s will ultimately be taken over by National Highway authority.
(2) Construction of toll based expressways having grade separated , divided carriage ways
will serve as a vailable alternative facilities. These require initial budgetary provision. Within
10 to 15 years the cost of the facilities along with interest is recovered through tolls ; then the
revenues generated through tolls will be very high in comparison with maintenance and
operation costs. As such ultimately the authority will have enough internal resources of its
own for construction of an expressway net work.
(3) With the National Highways Authority of India , taking over execution of National
Highway Projects , it will be possible to ensure uniformity and continuity in the improvement
to National Highway system , introduction of modern management and operation techniques ,
and optimum mechanisation and new technology in road construction besides deployment of
modern equipment for energy saving and pollution control.
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(4) Because of economics better equipment will be deployed and a continuous flow of large
scale projects would be feasible with one executing agency handling National Highway
Projects.
1.5. Summary:
The basic function of a transportation system is to carry passengers and goods from
one place to another. Social , cultural and economic development of a region or country
depends upon its transportation system. An efficient transportation system is necessary for
maintaining law and order with in the country and for boarder security.
The different modes of transport are roads , railways , airways and waterways. Out of
these roads are the most popular and major means of transport and are considered as vital
means of communication.
The Jayakar Committees report may be considered as a major land mark in the
planned development of roads in our country. Various phases of planning and development of
highways in India , during the 20th century , have been dealt with in detail.
1.6. Self Assessment Questions:
(1) Briefly out line the historical development of highways in India.
(2) Discuss the merits and limitations of roads as transportation means.
(3) Write notes on
(a) Jayakar Committee’s Recommendations
(b) Indian Roads Congress
(c) National Transportation Policy Committees
(d) Objectives of highway planning.
1.7. Books of Reference:
(1) Bindra , S.P. (1977) - A course in Highway Engineering , Dhanpat Rai and Sons , New -
Delhi.
(2) Kadiyali , L.R. (1984) - Principles and Practice of Highway Engineering - Khanna Tech
Publications , New - Delhi.
(3) Khanna , Dr. S.K. and Justo , Dr. C.R.G. (1991) - Highway Engineering , Nem chand and
Bro., Roorkee.
***
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TRANSPORTATION ENGINEERING
UNIT - 2
ROAD DEVELOPMENT PLANS OF INDIA CONTENTS:
Aims / Objectives:
2.1. Introduction
2.2. Classification of Roads
2.3. Road Development plans
2.4. Rural Road Patterns
2.5. Master Plan Preparation
2.6. Summary
2.7. Self Assessment Questions
2.8. Reference
Aims / Objectives:
Highways have been universally recognised as vital means of transport every where.
Three long term plans have been drawn for the development of roads in India for the period
1943 to 2001. Important features of these three plans - Nagpur Plan , Bombay Plan and
Lucknow Plan have been explained. Classification of roads based on a rational basis is quite
essential for planning of highways in a region or country. Classification of roads based on
their location and importance , adopted in the Nagpur Plan , and the modified system of
classification of roads adopted in the third 20 year development plan have been discussed.
Road patterns generally adopted for rural roads have been included in all long term planning
programmes. ‘Master Plans’ play a very important role. Various stages in the preparation of
master plans are also indicated in this unit.
2.1. Introduction:
Nagpur Plan is the first plan prepared in India on scientific principles , for the
development of highways for the period 1943 - 63. The targets of this plan have been
achieved by the end of the second five year plan i.e., by 1961. As such a perspective plan for
the period 1961 - 81 , known as ‘Second Twenty Year Plan’ was drafted by the Roads wing
of Government of India. The roads in these two plans have been divided into five groups
based on their location and importance. Star and Grid pattern of roads have been adopted.
Transport planners realised that prosperity of the country takes place only when
transportation facilities are extended to rural and undeveloped areas. Further , aspects like
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environmental protection , energy conservation and improvement in road safety have also to
be included because of the expected very high rate of growth of road traffic by the turn of this
century. The Lucknow plan for the period 1981 - 2001 has been drafted including all the
above aspects.
2.2. Classification of Roads:
Roads are classified based on a number of considerations , some of the important
consideration are ;
(a) Structural Behaviour:
Based on their structural behaviour roads are classified as Flexible pavements and
Rigid pavements. These are discussed in units 9 and 10.
(b) Material of Construction:
Based on the materials of construction roads are classified as Earth roads , Gravel
roads , Water Bound Macadam roads , Bituminous roads and Cement Concrete roads. These
are discussed in Units - 11 and
(c) Service Conditions:
Based on their service conditions during different seasons of a year , roads are divided
into two categories - all weather roads and fair weather roads.
(d) Traffic Volume or Load transported or Location and Function:
Classification systems based on the traffic volume or the load transported have been
arbitrarily fixed by different agencies and there is no common agreement regarding the limits
for each classification group. However , in the system based on location and function ,
different categories may be defined clearly.
The Nagpur plan and the Lunknow plan have classified the roads based on their
location and importance. In the Nagpur plan roads have been classified into five major
categories as follows:
(i) National Highways (NH) (ii) State Highways (SH) (iii) Major District Roads (MDR) (iv)
Other District Roads (ODR) and (v) Village Roads (VR).
The above system of classification of roads has been modified in the Lunknow plan
(1981 - 2001) and the roads in the country have been classified into three groups.
(i) Primary System: - This system consists of two categories of roads (a) Express ways and
National Highways (NH).
(ii) Secondary System:- The secondary system consists of two categories of roads , namely ,
State Highways (SH) , Major District Roads (MDR).
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(iii) Tertiary System or rural roads:- This system includes Other District Roads (ODR) and
Village Roads (VR).
Each of the above categories are explained below.
2.2.1. Express Ways:
Express ways are separate class of highways with superior facilities and design
standards and are meant as through routes having very high volume of traffic. The express
ways are to be provided with divided carriage ways , controlled access , grade separations at
cross roads and fencing. These highways should permit only fast moving vehicles. Express
ways may be owned by the Central government or a State government depending on whether
the route is a national highway or state highway.
2.2.2. National Highways:
Main highways running through the length and breadth of India , connecting foreign
highways , capitals of large states , ports and including roads required for strategic
movements for the defence of India are classified as National Highways. They constitute the
frame on which the entire road communication system of the country based. They must give
uninterrupted road communication throughout the year and should be of fairly high grade
construction. All National Highways vest in the union Government of India as per the
National Highway Act 1956 and is the responsibility of the centre to develop and maintain
properly all national highways.
2.2.3. State Highways:
These highways are other main trunk or arterial roads of a state , connecting up with
the National Highways or highways of adjacent states and linking the district head quarters
and important cities within the state. The state highways are the main arteries of traffic within
a state. They are to be of the same standards as National Highways.
2.2.4. District Roads:
District roads are roads traversing each district serving areas of production and
marketing and connecting these with each other or with national and state highways or
railways or important navigational routes. They should be capable of taking road traffic into
the heart of rural areas throughout the year with only minor interruptions. District roads are
divided into two classes on the basis of traffic.
(i) Major District Roads (M.D.R) for higher order of traffic.
(ii) Other District Roads (O.D.R) for lower order of traffic.
2.2.5. Village Roads:
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Village roads are roads connecting villages or groups of villages with each other and
to the nearest district , state or national highway or railway or navigational routes. They are in
essence roads from villages to a market or to a main route.
The road systems within the Urban areas are classified as ‘Urban Roads’ and will
form a separate category of roads to be taken up by the respective urban authorities.
2.3. Long Term Road Plans:
Selient features of the three plans are presented briefly.
2.3.1. Nagpur Plan:
This is the first plan prepared on scientific principles for the development of highways
in India. At the initiative of the IRC , chief engineers of the various states met at Nagpur for
drafting a highway development plant for the period 1943-63. According to this plan the road
net work in the country was divided into five categories:
(i) National Highways (ii) State Highways (iii) Major District roads (iv) Other district roads
and (v) Village roads. Requirements of each of these categories of roads are given in article
2.2.
The target for the total length of the roads was fixed as 16 km per 100 Sq. Km of the
area covered. Based on ‘Star and Grid pattern’ of road network two sets of formulae have
been developed. One for the total length of NH , SH and MDR and another for the length of
ODR and VR. These formulae have been developed taking into consideration the
geographical , agriculture and population conditions.
2.3.2. Second Twenty Year Road Plan:
The length of roads envisaged under the Nagpur plan was found to have been
achieved by the end of the second plan i.e., by 1961 , but the road system was deficient in
may respects. The changed economic , industrial and agricultural conditions in the country
warranted a review of the country’s rapidly growing economy. Accordingly roads wing of
Government of India received the situation and drafted a perspective plan for road
development for the period 1961 - 81 , known as second twenty year road plan.
Five different formulae based on the ‘star and Grid’ pattern of roads have been
formulated for the five categories of roads proposed in Nagpur plan. The target of this plan
has been fixed as 32 km of total length of road per 100 Sq. km of area covered.
Comparison of Nagpur Road Plan and Second 20-Year Road Plan:
(i) The Nagpur plan has a target length of 16 km per 100 Sq. Km area covered where as the
second 20 year plan has double this length.
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(ii) Nagpur road plan gives two formulae. One for total length of fast category of roads ,
namely N.H , S.H and M.D.R and the second formula for finding the total length of O.D.R.
and V.R. Hence it is not possible to get the road length for each category of the roads
separately. In the second 20 - year plan it is possible to find out the length of each category of
roads as five different formulae are available for the five different categories.
(iii) The Nagpur plan formulae for the road lengths divide the area into two categories -
Agricultural area and Non-Agricultural area. In the second road plan , the area is divided into
three categories - developed and agricultural area , semi-developed area and undeveloped and
uncultivated area.
(iv) In developing formulae for the different categories of roads in the Nagpur plan , villages
and towns are divided into six groups based on population. All towns with population greater
than 5000 , are grouped together. In the second 20 year plan , villages and towns have been
divided into nine different population groups. All towns with population greater than
1,00,000 are kept in one group.
(v) In Nagpur plan the length of railway track in the area was deducted from the total length
of road required. Such a deduction was not allowed in the second 20 year formulae , as it was
realised that the highway system should develop independently.
(vi) In the second 20 year plan , a development factor of 5% only is allowed where as in the
Nagpur plan this factor is 15%.
(vii) In the second 20 year road plan , provision was made for express highways. (Highways
provided for the movement of heavy volumes of motor traffic at higher speeds and have
atleast four lanes).
(viii) In general it may be said that the second 20 - year road plan has been developed on a
more rational and scientific basis than the Nagpur road plan.
Deficiencies of the Road Plans:
The two plans are mainly centered around planning a network of roads. These plans
are hardly based on and evolved from principles of transport planning. The plans are not
correlated to transport needs and are not based on systematic transport surveys.
The plan formulae for evolving the road length indicate that greater length was
apportioned for developed areas than semi-developed and underdeveloped area. The back-
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wardness tended to be perpetuated rather than conditions of communications and accessibility
improved.
2.3.3. Third Twenty Year Road Development Plan (1981 - 2001):
Salient features of the Lunknow plan are as follows:
(i) The future road development should be based on the modified classification consisting of
primary , secondary and tertiary road systems as mentioned in Article 2.2.
(ii) The road network should be developed so as to preserve the rural oriented economy and
to develop small towns with all essential facilities. All villages with population over 500
(based on 1981 census) should be connected by all weather roads by the end of this century.
(iii) The N.H. net work should be expanded to form square grids of 100 km sides so that no
part of the country is more than 50 km away from a N.H.
(iv) The over all road density in the country should be increased to 82 km per 100 Sq km area
by the year 2001.
(v) The lengths of SH and MDR required in a state or region should be decided based on both
the area and the number of towns with population above 5,000 in the state or region.
(vi) Express ways should be constructed along major traffic corridors to provide fast travel.
(vii) All the towns and villages with population over 1500 should be connected by MDRs and
villages with population 1000 to 1500 by ODRs. There should be a road within a distance of
3.0 km in plain and 5.0 km in hilly terrain connecting all villages or groups of villages with
population less than 500.
(viii) Roads should be constructed in less industrialised areas to attract growth of industries.
(ix) Long term plans for road development should be prepared at various levels. The road
network should be scientifically decided to provide maximum utility.
(x) The existing roads should be improved by rectifying the defects in road geometrics ,
improving the riding quality of the pavement surface and strengthening of the pavement
structure to save vehicle operation cost and thus to conserve energy.
(xi) There should be improvements in environmental quality and road safety.
Determination of Road Lengths:
I. Primary System:
(i) Express ways of total length 2000 Km to be developed for fast travel based on traffic
requirements.
(ii) Total length of NH in the country or in a state in Km = Total Area of the country or state
in Sq. Km / 50.
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II Secondary System:
(i) Length of State Highways (SH) in Km.
(a) By total area: S.H , Km = Area of the State in Sq . Km / 25
(b) By total number of towns and area in the state ,
SH , Km = 62.5 x no. of towns in the state - area of state , sq . km
50
(ii) Length of MDR in a State in Km.
(a) By total area , MDR Km = Area of State in Sq. Km / 12.5
(b) By no. of towns in the State , MDR , Km = 90 x no. of towns in the state.
(III) Tertiary System or Rural Roads:
(i) Length of Rural Roads (ODR and VR) in each state
= Total length of roads in the State - Length of (NH + SH + MDR) in the state.
Note:
Total length of roads in a state = Area of the State in Sq Km
10082×
2.4. Road Patterns:
The following are the road patterns (fig 2.1) used for rural roads.
(i) Grid or Rectangular or Block pattern.
(ii) Radial pattern
(a) star and Block
(b) star and circular
(c) star and grid.
(iii) Hexagonal pattern
(iv) Minimum travel pattern.
The choice of a road pattern depends upon: layout of town showing industrial ,
agricultural and production centres , terrain and topography and choice of the planner.
2.4.1. Grid pattern:
In this type (fig 2.1A) roads are perpendicular to each other. It is easy to set out this
pattern and is suitable for flat countries without any predominant natural features. This
system has been adopted in the city roads of Chandigarh , This pattern produces
monotonously long sets flanked by dull blocks of buildings. It encourages an even spread of
traffic over the entire grid. It is easy for the through traffic to bypass a definite control area in
the middle of the grid. This pattern is not quite convenient from traffic operation point of
view.
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2.4.2. Radial pattern:
Fig 2.1 B , 2.1 C and 2.1 D show the various systems of radial road patterns.
In this system a number of roads radiate from central core known as focal point. This
system of roads lead to congestion of centre (fig 2.1B)
The ring roads (figs 2.1C and 2.1D) are circumferential highways to permit traffic to
avoid centre of town. The location , number and design of ring roads depend upon the
population of the town , size , layout and usage of central area.
The inner ring road deflects traffic which has no need to traverse the central area and
the outer ring road is used by through traffic of the town as distribution between radials. The
outer ring roads are located within the outer fringe of present and future development.
The Connaught place in New-Delhi has radial and circular pattern of road network.
The Nagpur Road Plan (1943 - 63) and the II Road Plan (1962 - 81) were formulated on the
basis of star and grid pattern.
The advantages of this pattern are not much because (i) Towns are not circular (ii) It
is not possible to join a ring route at any point and (iii) the relative advantages of routes are
different.
2.4.3. Hexagonal Pattern:
In this pattern the roads are arranged to form a hexagonal shape (fig 2.1 E). Each
system has one of its road common with another system of hexagon.
2.5. MASTER PLAN:
Master plan is the final road development plan for the area under study - a city or a
district or a state or a country. It is an ideal plan showing the full development of the area at a
future data. It serves as a guide to the planner to improve some of the existing roads and plan
net work of new roads. Master plan of an area helps in controlling the industrial picture of the
fully developed area in a planned and scientific manner.
The various stages in preparation of a master plan are
(a) Data collection: This include data regarding existing land use , population , industrial and
agricultural growth , traffic flow , topography and future trends.
(b) Preparation of draft plan based on future trends and invite suggestion from public and
experts.
(c) Revision of draft plan in the light of discussions and comment from public and experts ,
and
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(d) Compare the various alternate proposals of road system and determine the sequence in
which the master plan will be implemented.
In India , in the various development plans considered , targets for the lengths of
roads have been fixed based on population , area , number of towns , agricultural and
industrial growth. Similar system may be adopted in preparing master plan also.
2.6. Summary:
For the development of roads in our country , three long term plans have been drawn.
The first plan , popularly known as Nagpur plan , drawn for the period 1943 - 63 may be
considered as a land mark in the development of roads in our country.
Depending on the development of the area and population served , roads have been
divided into five groups - National Highways , State Highways , Major District Roads , Other
District Roads and Village Roads. A target of 16 Km of road for every 100 Sq.Km of area
covered was fixed for this plan period. As the targets of Nagpur plan could be achieved by
1961 , a second road development plan for the period 1961 to 1981 , also known as Bombay
plan , was formulated. The targets of this plan were double that of the Nagpur plan. In both of
these plans star and gird pattern of roads has been used for developing the formulae for the
different categories of roads proposed in the Nagpur Plan.
Both the Nagpur plan and Bombay plan have been hardly based on and evolved from
principles of transportation planning. The plan formulae for evolving the road length indicate
that greater length was apportioned for developed areas than for semi-developed or under
developed areas. The backwardness tended to be perpetuated rather than conditions of
communications and accessibility improved. Taking care of these short coming and keeping
in view the growth pattern envisaged in the various fields by the turn of the century , a third
road development plan for the period 1981-2001 has been prepared. Attention was paid while
drafting the plant to present the quality of environment , to improve road safety and to
conserve energy.
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Fig 2.1 ROAD PATTERNS
Roads have been classified into three groups - primary system consisting of the Express ways
and National Highways , Secondary System comprising of State Highways and Major
CE409/16 19
District Roads and Tertiary system or Rural roads which include other district roads and
village roads for the purpose of the Lucknow plan.
Road patterns adopted in rural roads have also been discussed in this unit. Data to be
collected and the various steps in the preparation of Master Plans for highway development
have also been dealt with in detail.
2.7. Self Assessment Questions:
1. Compare the I and II - 20 year Road development plans clearly bring out the deficiencies
in these two plans.
2. Discuss important aspects of Lucknow plan indicating how the total lengths of different
categories of roads can be calculated ?
3. Write notes on
(a) Rural Road Patterns
(b) Master plans for Roads
(c) Classification of Roads.
2.8. BOOKS FOR REFERENCE:
1. Bindra , S.P. (1977) - A course of Highway Engineering.
Dhanpath Rai & Sons , New Delhi.
2. Kadiyali L.R. (1984) - Principles and practice of Highway Engineering -
Khanna Tech. Publications , New Delhi.
3. Khanna , Dr. S.K., and Justo , Dr. CEG - Highway Engineering ,
1. Wheel load = 5100 kg; equivalent circular are of 15 cm
2. Tyre pressure = 6.3 to 7.3 kg/cm2
3. Traffic value may be projected to for 20 years. Based on traffic intensity corrections have
to be carried out to the designed thickness. These corrections are given in IRC : 58 - 1974,
Guidelines for Design of Rigid pavements.
4. Temperature differentials for calculating the warping stresses have been recommended
based on thickness of slab end region and are available in IRC: 58-1974.
5. Modulus of sub-grade reaction K is to be determined using standard plate of 75cm
diameter at 0.125 cm deflection. The minimum K - value of 5.5. kg/cm3 is specified for
laying cement concrete pavement. In clayey sub-grades a suitable sub-base course may be
provided to increase the K -value.
6. The flexural strength of concrete used in the pavement should not be less than 40 kg/cm2.
µ = 0.15 α = 10 × 10-5 per 0C.
E = 3 × 10+5 kg/cm2
10.5.2. CALCULATION OF STRESSES :
1. The wheel load stresses at the edge and corner regions are calculated using the equations
(10.8) and (10.9), respectively.
2. Temperature stresses are calculated using the equations (10.11) and (10.13).
3. The critical combination of stresses in summer is obtained and the flexural stress so
obtained should be less than 40 kg/cm2 for the designed thickness of slab.
4. The design thickness is adjusted for traffic intensity as explained in 10.4.1. above.
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10.5.3. SPACING OF JOINTS :
The following maximum spacing are recommended.
Nature of
Joint
Maximum spacing
metres
Remarks
1)Expansion
Joints
2) Contrac-
tion Joint
140
90
120
50-60
4.5
Foundation is rough for slabs of all thickness for
25mm wide expansion joint
For smooth foundation surfaces of slabs constructed
in summer for slab thickness upto 20 cm.
For slabs up to thickness of 25 cm.
When the construction is carried out in winter
For unreinforced slabs of all thickness
10.6. JOINTS IN CONCRETE PAVEMENTS :
Joints may be broadly divided into transverse and longitudinal joints. Transverse
joints may be conveniently classified into four groups - expansion joints, contraction joints,
warping joints, and construction joints. Longitudinal joints are required in concrete roads
more than 4.5 m wide to allow for transverse warping and to allow for uneven settlement of
the sub-grade.
10.6.1. SPACING OF EXPANSION JOINTS :
The width of the gap in the expansion joint depends upon the length of slab.
Expansion joint spacing is designed based on the maximum temperature variations expected
and width of the joint. Dowel bars are provided at expansion joints for load transfer form one
slab to the other. It is recommended not to have a gap more than 2.5 cm for an expansion
joint. If δ’ is the maximum expansion in a slab of length Le with a temperature rise from t1 to
t2 in degrees centigrade, then the spacing of the expansion joints is given by
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Le(metres) = ( )δ1
1100 C t2 − t10.17
where C is the coefficient of expansion of concrete δ’ expansion of the slab in cm. It is
assumed that the joint filler may be compressed upto 50% of its thickness and therefore the
expansion joint gap should be twice the allowable expansion in concrete (i.e.,). 2 δ’.
Fig 10.3. TYPICAL EXPANSION JOINT
10.6.2. SPACING OF CONTRACTION JOINTS :
The slab contracts due to the fall of slab temperature below the construction
temperature. This movement is resisted by the sub-grade drag or friction between the bottom
fiber of the slab and the sub-grade. Length of slab to resist the frictional drag, that is spacing
of contraction joints,
LC = 2 104ScWf
× 10.18
Here
LC = spacing between the contraction joints, m.
f = Coefficient of friction (1.5)
W = Unit weight of slab, kg/m3 (2400 kg/m3)
Sc = Allowable stress in tension in cement concrete.
10.6.3. WARPING JOINTS :
If expansion and contraction joints are properly designed and constructed there is no
need of providing warping joints in addition.
Construction aspects of these joints are discussed n Unit No.12.
10.7. SELF - ASSESSMENT QUESTIONS :
1) Find out the spacing of expansion and contraction joints given the following data.
Expansion gap. 2.5 cm.
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Laying temperature of concrete = 100C
Slab temperature in summer = 540C.
Coefficient of thermal expansion of concrete = 10 × 10-6 / 0C.
Coefficient of friction = 1.5
Ultimate tensile stress in concrete = 1.6 kg/cm2
Factor of safety = 2.
NOTE : δ1 in the formula = 2.5 / 2 = 1.25 cm.
(Ans : Spacing of Expansion joint = 28.5m, spacing of contraction joint = 4.44m).
2) Explain the terms (a) Modulus of sub-grade reaction (b) Radius of relative stiffness
and (c) radius of resisting section.
3) Distinguish between warping stresses and frictional stresses.
10.8. SUMMARY :
Stresses are set up in concrete road slabs by wheel loading and by changes in
temperature. The wheel load stresses are calculated for three critical load positions, namely,
interior, edge and corner positions of the road slab, based on Westergaurds theory. The
equations given by Estergaurd require considerable amount of trails in their solution, if the
slab thickness has to be determined. Bradbury suggested a simplified procedure in terms of
stress coefficients. The IRC considers the edge and corner loading positions only and
recommends the use of Westergaurds edge load formula modified by Teller and Sutherland
and the Westergaurd corner load formula modified by Kelley for calculating these stresses.
Temperature tends to produce two types of stresses in a concrete road slab. They are
warping stresses and frictional stresses. Whenever the top and bottom surfaces of a concrete
pavement simultaneously possess different temperatures, the slabs tends to warp downwards
or upwards inducing warping stresses. These warping stresses are calculated by the equations
developed by Bradbury. The increase or decrease of pavement average temperature causes
expansion or contraction of pavement slab. When these movements are restrained frictional
stresses are developed in the slabs. For designing the pavement slab critical combination of
these stresses have to be obtained. For Indian conditions, critical combination of tresses take
place on a summer mid-day at the edges.
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Joints are provided in concrete roads to allow for the movements of the slab due to
changes in temperature and moisture content, but the number of joints should be a minimum.
This lesson discusses spacing of expansion and contraction joints.
10.9. REFERENCES :
1. Bindra, S.P. (1977) - A Course in High Way Engineering - Dhanpathy Rai and Sons,
Delhi.
2. Khanna, Dr. S.K. and Justo, Dr. C.E.G. (1991) - Highway Engineering - Nem Chand and
Bros, Roorkee.
3. - (1955) Concrete Roads, H.M.S.O. Publication.
***
TRANSPORTATION ENGINEERING
UNIT - 11
CONSTRUCTION OF FLEXIBLE PAVEMENTS
CONTENTS :
Aims / Objectives
11.1. Introduction
11.2. Earth Roads
11.3. Gravel Roads
11.4. Maintenance of Earth and Gravel Roads.
11.5. Water Bound Macadam Roads
11.6. Maintenance of Water Bound Macadam Roads
11.7. Types of Bituminous pavements
11.8. Surface Treatments
11.9. Grouted or Penetration mecadam
11.10. Pre-mix Methods
11.11. Maintenance of Bituminous Roads
11.12. Self - Assessment Questions
11.13. Summary
11.14 References
AIMS / OBJECTIVES :
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Materials required, principles of construction of and equipment and plants needed for
the construction of earth, gravel, water bound Macadam (WBM) and different types of
bituminous roads are presented in this lesson. Proper maintenance of a road is a must for
realising the best serviceability throughout its life. Usual causes of damage and maintenance
methods of each type of the above roads are also discussed in detail.
11.1. INTRODUCTION :
In our country there is need to construct wide net work of roads to meet the large
demand of transportation expansion. Since funds available for the construction of large
mileage of roads are also quite meager, it is necessary to have roads which cost less not only
from the construction point of view, but also from the maintenance considerations. Such
types of roads are popularly known as ‘Low-cost Roads’. These Low-cost road should be
amenable for stage construction. Making improvement to the existing roads according to the
traffic needs is called ‘Stage Construction’ or ‘Phased development of the roads’. Earth
roads, gravel roads and the water bound Macadam (W.B.M.) roads fall under this category.
Bituminous or tar roads , which are popularly known as ‘Black Top Roads’ in which
bitumen or tar and mineral aggregates are used are also quite popular in our country. Roads
are constructed with varying aggregate sizes and compositions and with different types of
bituminous binders. Hence there are varying techniques of their construction.
Materials used, their requirements and specifications, equipment and plant needed and
construction procedure for each of the above types of flexible pavements are presented in
detail.
A well designed and constructed road must be maintained well in order to reduce the
operation cost and increase the serviceability of the pavement. A detailed note on the
maintenance aspects of each type of construction is also included.
11.2. EARTH ROADS :
An earth road is the lowest form of the surface. It is the first stage in the development
of a road which is to be further developed as increasing traffic requires. These roads are
generally dusty and form ruts quickly thereby destroying the road crown. The camber
provided to the earth roads is very steep and ranges between 1 in 25 (4.0%) to 1 in 33. (3%)
in order to drain off rain water quickly.
11.2.1. MATERIALS : Soils of the following properties are considered satisfactory for
constructing earth roads.
Base course Wearing course
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Clay content
Silt content
Sand content
Liquid Limit
plasticity Index
5%
9-32%
60-80%
25%
6%
10-18%
5-15%
65-80%
35%
4 to 10%
Highly expansive clays exhibiting marked swell and shrinkage properties should not
be used. The different construction operations are briefly discussed below,
11.2.2. CONSTRUCTION OPERATIONS : The soil survey is carried out and suitable
borrow pits are located. The trees, shrubs, grass, roots and other organic matter including top
soil are removed before excavating the earth for construction.
The centre line and road edges are marked on the ground along the alignment, by
driving wooden pegs. Reference pegs are also driven to help in following the desired vertical
profile of the road during construction.
The sub-grade is then prepared by cleaning the site, excavating and construction of
fills to bring the road to the desired grade and shaping the sub-grade to the desired camber.
The site clearance may be carried out manually using appliances like spade, pick and hand
shovel. Mechanical equipment like dozer, scraper and ripper may also be used for the
purpose. Construction of fills and excavation of cuts to bring the road to the desired profile
may also be done either manually or using excavation, hauling and compaction equipment.
The borrowed soil is balanced, if necessary and dumped on the prepared sub-grade
and water is added, if necessary to bring it to the optimum moisture content. Then the soil is
rolled in layers such that the compacted thickness of each layer does not exceed 10cm. The
type of roller for compaction is decided based on soil type, desired amount of compaction,
and availability of equipment. At least 95% of dry density of I.S. light compaction is
considered desirable. The camber of the finished pavements surface is checked and corrected,
if necessary.
The compacted earth road will be opened to traffic after it is allowed to dry out for a
few days.
11.2.3. TREATED EARTH ROADS : The earth roads can be improved considerably by
treatment with bituminous material or calcium chloride. Clayey and silty soil roads which are
extremely dusty in dry weather and soften readily in wet weather can be treated by
application of bituminous materials. Calcium chloride when used to treat the earth roads,
keeps them slightly damp by absorbing moisture from the air. It has been observed that
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calcium chloride as a dust palliative is only effective when relative humidity of the
atmosphere is above 31%.
11.3. GRAVEL ROADS :
These roads consist of a carriage way constructed with gravels. These roads are fairly
resistant and are suitable to cater an average dial traffic between 350 to 400 vehicles. The
carriage way of this type of road is provided with a camber ranging between 1 in 33 (3.0%) to
1 in 40 (2.5%).
11.3.1. MATERIALS : Hard variety of crushed stone or gravel of specified gradation is
used. Rounded stones and river gravel are not preferred as there is poor interlocking.
Gravel to be used for construction is stacked along the sides of the proposed road.
11.3.2. TYPES OF CONSTRUCTION : Two types of construction methods are generally
available. They are the ‘Feather Type’ and the ‘Trench Type’ (Fig. 11.1.). In the trench type
the sub-grade is prepared by excavating a shallow trench. Since there is better confinement of
the gravel, the trench type is preferred. The feather type is constructed over the sub-grade
with varying thickness, so as to obtain the desired cross slope for the road surface.
Fig. 11.1. Feather type
Fig. 11.1. Trench type
11.2.3. CONSTRUCTION PROCEDURE : Site is cleared and fills and cuts are completed.
Trench is formed to the desired depth of construction, the trench is brought to the desired
grade and compacted.
The gravel aggregates are placed carefully in the trench so as to avoid segregation and
such that the desired camber is obtained. The layer is rolled using a smooth wheel roller
starting from the edges and proceeding towards the centre, with an overlap of atleast half the
width of the roller in the longitudinal direction. Some quantity of water is sprickled and
rolling is done again so that the compaction is effective. The camber is checked and corrected
CE409/16 185
from time to time using a template. A few days after the final rolling, the road is opened for
traffic.
11.4. MAINTENANCE OF EARTH AND GRAVEL ROADS :
In these roads, the usual damages needing frequent maintenance are:
(1) Formation of dust in dry weather.
(2) Formation of longitudinal ruts along the wheel path of vehicles, and
(3) Formation of cross-ruts along the surface after the monsoons due to surface water.
The dust nuisance may be reduced by frequent sprinkling of water or by use of dust
palliatives like calcium chloride. periodical maintenance by spreading moist soil along ruts
and reshaping the camber is necessary.
11.5. WATER BOUND MACADAM ROADS :
In India, Water Bound Macadam (W.B.M) has been the most popular base course
material. Macadam construction means the base course is made of crushed or broken
aggregates bound together by the action of rolling. Water bound macadam construction
should consist of clean, crushed broken aggregates mechanically interlocked by rolling and
bound together with screenings and binding material where necessary with water, laid on a
prepared sub-grade, sub-base, of an existing pavement as the case may be. Generally,
W.B.M. is constructed in thickness ranging from 8 c.m. to 30 c.m. The camber provided is 1
in 33 (3.0%) to 1 in 40 (2.5%).
When used as surface course WBM gets deteriorated rapidly under mixed traffic
condition and so this construction is used as base course and is covered with either
bituminous surfacing or cement concrete surfacing.
11.5.1. MATERIALS : The materials required for WBM roads are coarse aggregates,
screenings and filler material. The crushed or broken stones should be hard and durable and
free from excess of flaky, elongated, soft and disintegrated particles and dirt. The aggregates
should meet the following requirements.
Los-Angeles abrasion value (500 revolutions ) 40% max.
Flaking Index 15 % max.
The coarse aggregate is either of 90 to 40mm size or 63 to 40mm size or 50 to 20mm size, fulfilling the specified gradation requirement. The maximum size to be used depends on the type of aggregate available and the total compacted thickness of the layers. The specified gradation requirements of coarse aggregate are given in Table No. 11.1. Table - 11.1
Specified Gradation Requirements of Coarse Aggregates Used in WBM Construction
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Grading No. Size range mm. Sieve size mm. Percentage by weight passing the sieve
1. 90-40 100 80 63 40 20
100 65-85 25-60 0-15 0-5
2. 63 to 40 80 63 50 40 20
100 90-100 30-70 0-15 0-5
3. 50-20 63 50 40 20 10
100 95-100 35-70 0-10 0-5
The screening and other filler materials used to fill up the voids in the coarse
aggregate should meet the grading requirements given in Table No. 11.2.
Table 11.2.
Grading Requirements For Screenings Used in W.B.M. Construction
Type of screening Sieve size mm Percentage by weight passing
the sieve
12.5 mm (for gradings 1 or 2) 12.5
10.0
4.75
0.15
100
90-100
10-30
0-8
10 mm (for gradings 2 or 3) 10.0
4.75
0.15
100
85-100
10-30
Filler material should contain sufficient clay content to prevent revelling of the surface course
of W.B.M layers. Hence it is recommended that the plasticity index of filler material may be
upto 9.
11.5.2. CONSTRUCTION PROCEDURE : Materials of the required grading for
construction are stacked on the road side.
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The site is cleared and either a trench is cut to the required camber or earth bunds are
made in order to provide the required confinement to the loose aggregates for compaction by
rolling. The weak spots are corrected and rolled before the coarse aggregates are placed. On
clay sub-grades a blanket of granular material like sand is spread to a thickness of about 10
cm.
The coarse aggregates are spread upon the prepared surface from the stock piles such
that the required profile is obtained. The thickness of each layer should be such that the
compacted thickness normally doesn’t exceed 7.5cm. The aggregates are spread evenly to the
required profile by using templates placed across the road about 6m apart. The surface is
checked from time to time ensuring proper grade and camber.
After spreading the aggregates, the same are compacted to a full width by rolling. For
this purpose, a three wheel power roller of 6 to 10 tonnes capacity or tandem roller or
equivalent vibratory roller is used. The rolling is done at edges with roller running forward
and backward, until the edges are firmly compacted. Then the roller is moved from the edges
to the centre, parallel to the centre line such that sufficient overlapping is there.
After the coarse aggregates are thoroughly keyed and set by rolling, the screenings are
spread uniformly to fill the interstices. Dry rolling and brooming is carried out. After dry
rolling, the surface is sprinkled with water; swept and rolled. Hand brooms are used to place
the wet screenings into the voids.
The filler material with plasticity index not more than 9 is applied in two successive
thin layers. After the application, the surface is sprinkled with water. the slurry is allowed to
fill up the voids. Rolling is then done.
The road section is allowed to dry overnight and a layer of sand or earth about 6 mm
thick is speed on the surface, lightly sprinkled with water and rolled.
The shoulders are formed to the same cross slope of the pavement and compacted by
rolling. The traffic is allowed on the WBM when the road is properly dried and set.
11.6. MAINTENANCE OF W.B.M. ROAD :
These roads are damaged rapidly due to heavy mixed traffic and adverse climatic
conditions. In dry weather dust is formed and during rains mud is formed. The steel tired
bullock carts cause severe wear and tear to the WBM surface. The fast moving vehicles raise
dust in dry weather and churn up the mud in wet conditions. Due to the combined effects of
the traffic and the rain water, washing away of the soil binder from the surface takes place,
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resulting in the stone aggregates protruding out or getting loose from the surface layer. Pot
holes and ruts are formed in weak spots.
To prevent the aggregates from getting loosened from the surface course, thin layer of
moist soil binder is spread on the surface, particularly after the monsoon. Dust nuisance can
be effectively prevented by providing a bituminous surface dressing course over the WBM
pavement. Temporary measures include spraying of dust palliatives are taken.
Pot holes and ruts formed should be patched up,. The patch repair work is carried out
by first cutting out to a rectangular shape the defective area to remove the stones unto the
effected depth. Then with the coarse aggregates of the same size, the patch is filled up and
compacted well by ramming, such that the patches area is abut 1cm above the general
pavement surface. This allows for further compaction of this patched portion, under traffic.
Wet soil binder is then applied on the surface of the patched area to fill up the interstices and
the surface is rammed again.
11.7. TYPES OF BITUMINOUS PAVEMENTS :
Based on the methods of construction bituminous pavements may be classified under
the following categories :
I) Surface Treatments. They include
a) Prime Coat
b)Tack Coat
c) Surface Dressing and
d) Seal Coat
II) Grouted or Penetration Macadam.
III) Premix which may be any of the following :
a) Bituminous Bound Macadam
b) Carpet
c) Bituminous Concrete
d) Sheet Asphalt or Rolled Asphalt and
e) Mastic Asphalt.
IV) Bituminous pavements are also classified on the basis of mixing and construction
techniques. They are a) Road mix and b) Central Plant mix.
V) Bitumen and tar require heating to bring them to a proper viscosity for their use. Then
the construction technique is termed as ‘HOT MIX METHOD’. Cut backs and emulsions
when used are applied cold and the technique is known as ‘COLD MIX’.
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11.8. SURFACE TREATMENTS :
These are the works carried out to alter the qualities of a wearing surfaces. The
different types of surface treatments are briefly described below.
11.8.1. PRIME COAT :
This consists of application of a less viscosity cut back eg. RC-O, MC-1 or SC-1 on
an existing base of pervious texture like WBM base. Various functions of a prime coat are :
(I) It plugs capillary voids and water proofs the existing base. Otherwise the binder used for
wearing course is likely to go into the void spaces of the existing base and little binder
quantity will be left for binding the aggregate pieces in the surfacing.
11.8.2. TACK COAT :
When the interface treatment is done for an existing bituminous or concrete pavement
it is called a tack coat. Since in this case the base is comparatively impervious, the quantity of
binder required may be less than the primer. However, the tack coat serves the same purpose
as the a primer.
The surface on which the tack coat is to be applied should be thoroughly swept and
cleaned of dust and other foreign matter. The rate of spread of straight run bitumen should be
5kg/10m2 area for an existing bitumen treated surface and 10 kg/10m2 area for an untreated
WBM surface.
11.8.3. SURFACE DRESSING :
Mixed traffic is likely to destroy the WBM road in a very short time. Bituminous
surface dressing prevents the removal of binding material between the stones in WBM road.
The main functions of surface dressing may be (i) to provide dust free surface over a base
course (ii) to provide water proof layer to prevent infiltration of surface water, and (iii) to
protect the base course.
The surface dressing is done in one or two layers and accordingly called single-coat or
two-coat surface dressing. It includes the application of a thin layer of bitumen followed by
cover material of stone chips or coarse sand, which is then rolled. The grades of bitumen used
are 80-100 and 180-200. The surface dressing work is done only in dry and cleaned weather.
Coarse aggregates should be clean, strong and durable, fairly cubical in shape. The
first coat will be 12 mm thick with aggregate of 12 mm nominal maximum size. When
second coat is used it will be 9mm nominal maximum size aggregates and will be of 9mm
thick.
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For good surface dressing, the base course is well prepared to its profile and is made
free from pot holes and ruts. The base course should be made free from all dust, loose soil
etc. The aggregates should be exposed to a depth of 1.25cm, but at the same time should not
be loosened. This is done by the use of wire brushes and final dusting is done with jute bags.
On the prepared surface using a mechanical sprayer or pouring can, uniform spraying
of prime coat is done. Then the bituminous binder is sprayed uniformly at a specified rate,
care is taken that excessive binder is not applied to localized areas as this would cause
bleeding. After the application of the binder, the cover material of sonte chips is spread to
cover the surface uniformly and rolled with a 6 to 8 tonnes tandem roller. Rolling is done
from the edges proceeding towards the centre longitudinally with over lapping not less than
1/3 of the roller tread. Rolling is continued until the particles are firmly interlocked. This is
the final rolling if the surface dressing is in single coat. If the second coat is applied, then the
rolling is done again after the treatment is done for the second coat.
The surface is checked for its cross - slope and the road section is opened to traffic
after 24 hours.
11.8.4. SEAL COAT :
Seal coat is usually recommended as a final cover over certain bituminous surfaces
which are not impervious. They are open graded bituminous constructions which include
grouted macadam, bitumen bound macadam and premixed carpet. Seal coat is also provided
over an existing bituminous pavement which is worn-out. Seal coat is thus a single coat
surface dressing which is usually applied over the exiting black top surfaces to seal the
surfacing against ingress of water, to develop skid resistance texture and to enliven an
existing weathered surface.
Surface treatments are shown in Fig. 11.2.
Fig. 11.2. Surface Treatments
11.9. GROUTED OR PENETRATION MACADAM :
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In penetration macadam construction, the bitumen is sprayed after the aggregates are
spread and compacted in dry state. The bitumen penetrates into the voids from the surface of
the compacted aggregates, thus filling up a part of the voids and binding some stone
aggregates together. Depending upon the quantity of bitumen spread, and the extent of
penetration it is called ‘Full-Grout’ when the bitumen penetrates to the full depth of
compacted aggregates and ‘Semi-Grout’ when it penetrates upto half the depth. Full grout is
adopted in regions of heavy rainfall and semi-grout is adopted in regions of moderate rain fall
and traffic, results in an open graded structure, its use is some times recommended for base
course construction only.
11.9.1. CONSTRUCTION PROCEDURE :
The construction of a penetration macadam is recommended for thickness of 5cm and
7.5cm. The materials used are as a specified below:
a) BITUMEN/TAR : IRC recommends to use any grade of bitumen from 80-100, 60-70
and 30-40; Road tars, RT-4 and RT-5 could also be used. The quantity of bitumen required
depends on the depth of penetration of bitumen into the compacted aggregate layer desired.
b) AGGREGATES : The physical requirements of stone aggregates are specified by the
following values.
Los - Angeles abrasion value 40% max.
Aggregate impact value 30% max.
Flakiness index 25% max.
Stripping at 40°C after 24 hours immersion 25% max.
The gradings of aggregates as recommended by the IRC are given below in table 11.3
and Table 11.4.
Plant and Equipment : Various equipment needed are bitumen heating device,
bitumen distributors, aggregate spreader, and roller for compaction.
Construction Steps :
The underlying course is prepared and conditioned to uniform grade. The surface is
lightly scarified, brushed and prime or tack coat is applied.
Table 11.3 Grading of Coarse Aggregates for penetration Macadam
Percentage passing sieve size mm. Compacted Thickness mm
50 75
63 -- 100
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50 100 --
38 -- 35 - 70
25 35 - 70 --
19 -- 0 - 15
12 0 - 15 --
9 -- --
4.75 -- --
2.36 0 - 5 0 - 5
Table 11.4 Key Aggregates for Penetration Macadam.
Percentage passing sieve size mm. Compacted Thickness mm
50 75
25 -- 100
19 100 35 - 70
12 35 - 70 --
9 -- 0 - 15
4.75 0 - 15 --
2.36 0 - 15 0 - 5
The coarse aggregates of the desired grading depending on the thickness of
construction, are spread with proper edge protection. The profile is checked for the desired
camber. The rolling is done on the dry aggregates with 10 tonnes roller until the aggregates
are compacted and interlocked. Rolling is commenced from the edges and proceeded to the
centre, the overlap recommended being 30 cm. The dry compacted aggregates are checked
for the desired profile and corrected when necessary.
Over the dry and compacted coarse aggregate the binder is applied uniformly either
with pressure distributor or a hand sprayer. The quantity of bitumen required for this purpose
is 50 and 68 kg per 10m2 for 5cm and 7.5cm compacted thickness respectively.
After the application of bitumen, the key aggregates (Table 11.4) are spread and
rolled. The cross profile is again checked.
The seal coat is applied either immediately or after a few days. The pavement section
is again rolled. Excessive rolling, however, should be avoided. The finished surface is then
opened to traffic after at least 24 hours.
11.10. PRE-MIX METHODS :
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In this group of methods, the aggregate and the binder are pre-mixed prior to placing
and spreading the mix. Each aggregate particle gets coated with uniform thickness of binder
film. Another advantage associated with the premix construction is the increased stability of
the mix. In the premix, the aggregate gradation is carefully selected to give a dense mass
possessing minimum voids.
This method includes bituminous macadam. bituminous carpet, bituminous concrete,
sheet asphalt and mastic asphalt. Construction techniques of these pavements are explained.
11.10.1. BITUMEN BOUND MACADAM :
This bitumen bound macadam, also some times called bituminous macadam, is a
premix immediately laid after mixing and then compacted. It is an open graded construction
suitable only as a base course. When this layer is exposed as a surface course, at least a seal
coat is necessary. This is laid in finished thickness of 5cm or 7.5cm.
MATERIALS :
a) BITUMEN OR ROAD TAR :
The grades of bitumen are 30/40, 60/70 and 80/100 and Road Tar RT-4. Cut back and
emulsions can also be used in cold mix construction technique. The binder content used
varies from 3.0 to 4.5% by weight of the mix.
b) AGGREGATES :
Aggregates used are of low porosity fulfilling the following requirements for base
course.
Los-Angeles abrasion value 50% max.
Aggregate impact value 35% max.
Flakiness index 15% max.
Stripping at 400C after 24 hrs immersion 25% max.
The IRC specifies the following grading of aggregates for base course construction.
Percentage passing
sieve size, mm
Base Course Compacted Thickness, mm
50 75
I II I II
63
50
40
--
100
--
--
100
90-100
100
--
35-70
100
90-100
35-65
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25
20
12
10
4.75
2.36
0.075
25-70
--
0-15
--
--
0-5
0-3
50-80
--
10-30
--
--
--
0-5
--
0-15
--
---
--
0-5
0-3
20-40
--
5-20
--
--
--
0-5
c) STABILITY REQUIREMENT :
Satisfactory requirements of bituminous mix are specified in terms of Marshall
stability and flow values. A Marshall stability value of 200 kg is recommended for light and
medium traffic, where as a value of 300 kg is recommended for heavy and very heavy
traffic. Flow value should be between 10-40 in terms of 0.1 mm units.
PLANTS AND EQUIPEMENTS :
Various plants and equipment required for the job include : sprayer, mechanical or
improvised hand mixer, spreader and roller.
CONSTRUCTION STEPS :
The underlying course is prepared and conditioned to uniform grade. The surface is
lightly scarified, brushed and tack coat or prime coat of thin layer of bitumen binder is
applied on the existing layer either using the sprayer or a pouring can.
The bitumen binder, and aggregates as per recommended grading are separately
heated to the specified temperature and are then placed in the mixer chosen for the job and
mixed thoroughly to get a homogenous mixture. The mixture is then conveyed to the site,
placed on the desired location and is spread with rakes to a predetermined thickness. The
camber of the profile is checked with a template. It may also be noted that the compacting
temperature also influences the strength characteristics of the resultant pavement structure. It
is therefore required that a minimum time is spent between the placement of the mix and the
rolling operations.
Soon after the spreading of the mix rolling is done with 8 to 10 tonnes tandem roller.
The rolling is commenced from the edges of the pavement and proceeded towards the centre
and uniform overlapping is provided. The roller wheels should be kept damp to avoid the
bituminous material form sticking to the wheels. The pavement surface should be checked for
longitudinal and cross profile.
11.10.2. BITUMINOUS CARPET :
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Bituminous carpet is a premix prepared from stone chips of 10mm to 12mm size, sand
and bitumen binder. The thickness of such a carpet may vary form 2cm to 2.5cm . The
construction is usually recommended for a surface course layer. The carpet is finally covered
with a seal coat.
MATERIALS REQUIRED :
a) BITUMEN / TAR :
The bitumen binder of 80-100 grade or road tar of grade RT-3 is used.
b) STONE CHIPS :
For the carpet of 2cm thick the stone chips of 12mm and 10mm nominal size are
required. The stone chips should be angular, clean, hard, tough and durable. Medium coarse
sand passing 1.7mm sieve and retained on 1.18mm sieve, which is clean, hard and durable is
also required.
The aggregate fulfilling the following requirements are selected.
Los-Angeles abrasion value 35% max.
Aggregate impact value 30% max.
Flakiness index 30% max.
Stripping at 400C after 24 hrs immersion 25% max.
EQUIPMENT :
Various equipment and plants required for the job include Sprayer, mixer, spreader
and roller.
CONSTRUCTION STEPS:
The underlying course is prepared and conditioned to uniform grade. The surface is
lightly scarified, brushed cleaned and tack coat or prime coat is applied on the existing layer
either using the sprayer or a pouring can. The tack coat or prime coat is applied just before
spreading the pre-mix.
The aggregates and bitumen are heated separately upto the required temperature and
then mixed into a thorough and homogeneous mixture in a mixer - mechanical or improvised
hand mixer. The pre-mix is taken out and carried to the site for spreading and rolling. The
spreading is done with suitable rakers. The cross profile of the laid material is checked with
suitable templates.
Soon after the spreading of the mix, rolling is done with a 6 to 9 tonnes tandem or
pneumatic roller. At one operation 15 metre of the premix is laid and rolled. the roller wheels
CE409/16 196
should be kept damp to avoid the bituminous material from sticking to wheels. The rolling is
done until there is no further movement of aggregates in the mix layer.
In areas of low rainfall, a premixed - sand seal coat is applied over the carpet. In areas
of high rainfall (over 125cm per year) a liquid seal is sprayed and covered with a layer of
chippings applied over the carpet. The stone chips are of 6mm size. This layer is rolled by a
light tandem roller to give a smooth finished surface. After the application of seal coat, the
pavement so constructed is opened to traffic after a period of 24 hours.
11.10.3. BITUMINOUS CONCRETE :
The bituminous concrete is the highest quality of construction in the group of black
top surfaces This is a carefully proportioned mixture of coarse aggregate, fine aggregate and
mineral filler coated with bitumen binder. In this both the aggregates and the bituminous
binder are heated to the required temperature prior to mixing. The mixes are properly
designed to satisfy the design requirement of stability and durability. Mineral filler is used to
fill up the voids in the fine aggregate and consists of inert materials (Lower than 600 micron
sieve) stone-dust, cement, hydrated lime, fly ash or other non-plastic materials.
MATERIALS REQUIRED :
a) AGGREGATES :
Aggregates used for bituminous concrete should satisfy the following gradation
requirements.
Table : 11.6. Gradation of Aggregates for Bituminous concrete.
Sieve Size mm Percent by Weight
Limit I Limit II
20.0
12.50
10.00
4.75
2.36
--
100
80 - 100
55 - 75
35 - 50
100
80 - 100
70 - 90
50 - 70
35 - 50
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0.60
0.30
0.15
0.075
18 - 29
13 - 23
8 - 16
4 - 0
18 - 29
13 - 23
8 - 16
4 - 10
Physical requirements of course and fine aggregates are specified as under
Los-Angeles abrasion value 40% max.
Aggregate impact value 30% max.
Flakiness index 25% max.
Stripping at 400C after 24 hrs immersion 25% max.
b) BITUMEN :
The grade of bitumen depends upon the climatic conditions of a given region.
However grades 30-40, 60-70 or 80-100 are usually recommended for use. The binder
content used ranges form 5.0 to 7.5% by weight of the mix. The exact binder content required
depends upon the results of Marshall test carried out in a laboratory.
c) STABILITY REQUIREMENTS :
The requirements of the mix based on the traffic intensity are presented in Table 11.7.
Table 11.7. Requirements of Bituminous Concrete
Requirements Traffic
Heavy Medium Light
Stability, Kg(min). 340 227 227
Flow Value, 0.1mm units 20-40 20-45 20-50
Voids in mix % 3-5 3-5 3-5
Number of compaction
blows of each end of
Marshall test specimen
75 50 35
PLANTS AND EQUIPMENT :
In order to achieve high quality in construction mechanized construction should be
used.
CONSTRUCTION STEPS :
The underlying course is prepared and conditioned to uniform grade. It is desirable to
lay bituminous concrete surface course on a binder course instead of directly laying it on a
WBM.
CE409/16 198
The premix is prepared in a hot mix plant. The hot mixed material is collected form
the mixer by the transporters, carried to the location and is spread by mechanical paver. The
camber and the thickness of the layer are accurately verified. The control of temperature
during mixing and compaction are of great significance in the strength of the resulting
pavement structure.
Soon after the spreading of mix by paver, the surface should be thoroughly compacted
by rolling with a set or rollers moving at a speed not more than 5 kmph. The initial rolling is
done by 8 to 12 tonnes roller and intermediate rolling is done with a fixed wheel pneumatic
roller of 15-30 tonnes having a tyre pressure of 7 kg/cm2. The wheels of the roller are kept
damp wit water. The number of passes required depends on the thickness of the layer. In
warm weather rolling on the next day helps to increase the density if the initial rolling was
not adequate.
QUALITY CONTROL :
The various field controls include (i) aggregate grading control (ii) binder grade
control (iii) temperature control for aggregates and (iv) temperature control for mix during
mixing and compaction. It is recommended that at least one test for the above quality controls
must be carried out for every 100 tones of mix discharged by plant. The field density should
be checked for every 1000m2 of compacted surface.
11.10.4. SHEET ASPHALT OR ROLLED ASPHALT :
Sheet Asphalt contains high percentage of mortar consisting of sand, filler and
bitumen and is quite dense and impervious. The characteristics of durability, imperviousness
and load transmission are excellent in the sheet asphalt. It has been observed that the elastic
modulus of this layer is equivalent to that of cement concrete under transient stress. This
sheet asphalt is used only in wearing courses.
11.10.5. MASTIC ASPHALT :
This is superior to the other types of surfacing because of its ability to take up very
heavy shear stress without deformation. This is hence recommended for very heavy traffic
cities and placed where the braking and accelerating stresses are very heavy - bus stops and
roundabouts. This is a mixture of bitumen, fine aggregate and filler in suitable proportions
which yield avoidless and impermeable mass. The filler, bitumen binder and fine aggregate
are taken in suitable proportions and they are heated in sequence, and cooked at a temperature
of 2000C; then mastic asphalt has a consistency that it can flow. At this temperature the
mastic asphalt is spread to thickness between 2.5cm to 5cm. On cooling it hardens to a
CE409/16 199
semisolid or solid state. No rolling is required. Mastic asphalt has not found any importance
in our country because of its high cost and non-availability of the grade of asphalt required.
11.11. MAINTENANCE OF BITUMINOUS SURFACES :
Maintenance works of bituminous surfacing mainly consists of (i) Patch repairs, (ii)
Pot hole repairs (iii) Surface treatments and (iv) Resurfacing. These are briefly discussed
here.
11.11.1. PATCH REPAIRS :
Inadequate or defective binding material causes removal of aggregates during
monsoons. Patching may be done on affected isolated areas or sections using a cold premix.
11.11.2. POT HOLES :
Pot holes are cut to rectangular shape and the affected materials in the section is
removed until sound material is encountered. The excavated holes are cleaned and applied
with primer. A premixed material is placed in the sections. The material so placed in the Pot
holes is well compacted by ramming to avoid any raveling. The finished level of the patches
is kept slightly above the original level to allow for subsequent compaction under traffic.
Generally cut-back or emulsion is used as binder.
11.11.3. SURFACE TREATMENT :
Excess of bitumen in the surface material bleeds and the pavement becomes slippery.
Corrugations or rutting or shoving develop in such pavement surfaces. Blotting material such
as stone chips of maximum size 1.25mm or coarse sand is spread and rolled to develop
permanent bond between the existing surface and the new materials.
The binders in the black top surface also get oxidized due to aging. This develops
minute cracks in the pavement surface. Such pavements surfaces are applied with a renewal
coat or seal coat. It may be necessary to apply more than one layer of surface treatments, if
the surface has been seriously damaged.
11.11.4. RE SURFACING :
When the pavement surface is totally worn out and develops a poor riding surface, it
may be economical to provide an additional surface course on the existing surface.
11.12. SELF-ASSESSMENT QUESTIONS :
1. Enumerate the steps for the preparation of sub-grade.
2. Specify the materials required for the construction of WBM roads. Give also a
detailed account of the construction and maintenance procedure.
3. Distinguish between the following :
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a) Bituminous Macadam and Penetration Macadam.
b) Seal Coat and Bituminous Carpets.
c) Fine aggregate and Mineral filler.
4. Give a detailed specification for a two coat surface dressing over an existing WBM
road.
11.12. SUMMARY :
Earth and gravel roads are the lowest type of roads used in our country and may be
used successfully when the traffic intensity is between 30 to 200 tonnes per day. The usual
damages needing frequent maintenance of these roads are formation of dust and formation of
longitudinal and cross ruts. Materials and their requirements, construction and maintenance
aspects of these roads are presented in detail.
Another type of construction that is popular in our country is the Water Bound
Macadam (WBM) road. Water bound macadam construction consist of clean crushed coarse
aggregate mechanically inter locked by rolling and the voids in which are filled with
screenings and binding material with the aid of water on a prepared sub-grade, sub-base or
base of an existing pavement as the case may be. In the case of WBM roads the damage is
caused by the removal of the binding material from the surface resulting in pot holes and ruts.
Construction and maintenance aspects of the WBM roads in discussed in detail.
Bituminous roads when properly constructed maintained and used, have long and
economic lives. Based on the methods of construction these pavements are classified as
surface treatments, grouted or penetration macadam and premix types.
The following aspects of construction are discussed under each category of the black
top roads.
MATERIALS USED :
a) Bitumen / Tar : Grades
b) Aggregates : Physical requirements and grading
c) Plants and Equipment, and :
d) Construction procedure :
Maintenance works of bituminous surfacing mainly consists of patch repairs, pot hole
repairs, surface treatments and resurfacing. Important aspects of these have been discussed.
11.14. REFERENCES :
CE409/16 201
1. Bindra, S.P. (1977) - A Course in High Way Engineering - Dhanpathy Rai and Sons,
Delhi.
2. Khanna, Dr. S.K. and Justo, Dr. C.E.G. (1991) - Highway Engineering - Nem Chand and
Bros, Roorkee.
3. - Bituminous Materials in Road Construction, HMSO. Publication.
***
TRANSPORTATION ENGINEERING
UNIT - 12
CONSTRUCTION OF CONCRETE PAVEMENTS
CONTENTS :
Aims / Objectives :
12.1. Introduction
12.2. Construction of Pavement Slab
12.3. Construction of Joints
12.4. Joint Filler and Sealer Materials
12.5. Maintenance of Concrete Pavements
12.6. Self - Assessment Questions
12.7. Summary
12.8. Reference
AIMS / OBJECTIVES :
Cement concrete pavements are very much preferred because they provide an
excellent riding surface and have much longer life than any other type of construction. These
merits of cement concrete pavements can be realised only when they are well designed,
constructed and maintained. Design of rigid pavements is already dealt with. In this lesson,
methods of construction and maintenance of concrete roads are explained.
12.1. INTRODUCTION :
Cement concrete roads are very high standard roads which are the costliest of all other
types of roads. They provide excellent riding surface and pleasing appearance. Though
initially the cement concrete roads are very costly, because of their long span of life,
excellent riding surface and negligible maintenance cost, these roads prove to be cheaper than
the bituminous roads. The cement concrete material exhibits its characteristics which can be
CE409/16 202
predicted by theory and as such a structure made using this material can well be designed on
a rational basis. This indirectly saves cost as the resultant structure gives an excellent
performance.
A few of the draw backs of the cement concrete pavements are :
1) The transversal and longitudinal joints which are unavoidable in construction are
planes of weakness; they also delay the construction and increase the cost of maintenance of
these roads. As such, the number of joints should be a minimum.
2) A minimum period of 28 days curing is required before the cement concrete pavement
could be opened to traffic.
3) Cement concrete pavements require very high initial investment and are not suitable
for stage construction;
Three types of pavement construction are available:
(i) Cement Grouted Layer
(ii) Rolled Concrete Layer, and
(iii) Cement Concrete Slab.
In ‘Cement Grouted Layer’, open graded aggregate mix with minimum size of
aggregates as 18 to 25mm is laid on the prepared sub - grade and the aggregates are dry
rolled. A grout made of coarse sand cement and water is applied on the surface and is allowed
to seep through the aggregate matrix. The technique can be compared with bituminous
grouted or penetration type construction.
In ‘Rolled Concrete Layer’, a lean mix of aggregate, sand, cement and water is
prepared and laid on the prepared sub-grade or sub-base course. Then the surface is rolled by
a ‘Tandem Roller’. The rolling should be completed before the final setting time of cement.
Curing is done as per conventional methods.
The cement grout layer and rolled concrete layer are suitable for base course only.
However the cement concrete slabs serve as both base and surface courses. Construction of
cement concrete slab pavements includes (i) construction of pavement slab and (ii) design
and placement of joints.
12.2. CONSTRUCTION OF CEMENT CONCRETE PAVEMENT SLAB :
There are two methods f construction of cement concrete slab: They are (a) Alternate
Bay Method and (b) Continuous Bay Method.
CE409/16 203
(a) ALTERNATE BAY METHOD :
In this method, the cement concrete slabs (bays) are constructed in alternate
succession having the next bay to follow up after a time lapse of one week when normal
cement is used and atleast two days later, in the case of rapid hardening cement. In this
method of construction, the bays are constructed in x.y,z etc leaving gaps of bay x’, y’ and z’
(Fig. 12.1).
Fig. 12.1. Construction Method of Cement Concrete Road
This method has the following advantages and disadvantages :
ADVANTAGES :
(i) Provides additional working space for laying slabs.
(ii) Provides ease in joint construction.
DISADVANTAGES :
(i) Larger number of transverse joints are to be provided, and this increases the cost of
construction and maintenance. It also results in bad riding surface.
(ii) During rainy season, Iran water may get collected in the incomplete bays.
(iii) Needs traffic diversion during construction because the construction is spread over the
complete road way width.
b) CONTINUOUS BAY CONSTRUCTION :
In this method all the bays of one traffic lane are laid continuously (i.e.,) x, y’ z etc. or
x’, y, z’ etc. (Fig. 12.1) without any break. The construction joints are however provided at
the end of the days work. The main dis-advantage of this method is the difficulty of providing
joints. This method is still preferred because during construction half the traffic lane width
could be utilised by the diverted traffic.
CE409/16 204
12.2. MATERIALS FOR CEMENT CONCRETE PAVEMENTS :
The various materials used in the construction of cement concrete pavements are
cement, coarse - aggregate, fine aggregate and water. For joints materials required are dowel
bars, joint filler and sealer.
a) CEMENT :
Ordinary portland cement is generally used. When the road has to be opened for
traffic early, rapid hardening cement may be used.
b) COARSE AGGREGATE :
Good quality aggregates should be used and should be free from harmful materials
such as iron, pyrites, coal, mica, clay, alkali, organic impurities etc., It is always desireable to
use round gravel aggregates. The largest size of aggregate in a mix should not exceed one
quarter of the thickness of the slab. The best combination of strength and workability is to be
obtained. The physical requirements of aggregates suitable for cement concrete construction
are as follows :
Aggregate crushing value 30% (max.)
Aggregate impact value 30% (max.)
Los - Angeles value 16% (max.)
Soundness, (average loss in weight after 10 cycles ) 12% (max) in Sodium Sulphate
18% (max) in Magnesium Sulphate
(c) FINE AGGREGATE :
Natural sand should be preferred as fine aggregate, though crushed stone may be
used.
(d) MIX DESIGN OF CONCRETE :
The concrete may be proportioned so as to obtain a minimum modulus of ruptuore of
35 kg/cm2 on field specimens after 28 days curing or to develop a minimum compressive
strength of 280 kg/cm2 at 28 days, or higher value as desired in the design.
12.2.2. EQUIPMENT :
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The equipment needed for the construction of concrete slabs are for batching, mixing,
placing, finishing and curing the concrete pavement. These are explained under construction
steps for cement concrete pavement slab.
12.2.3. CONSTRUCTION STEPS FOR CEMENT CONCRETE PAVEMENT SLAB :
The concrete pavement construction should be done only during dry weather where
the temperature is between 4 to 400C. The various construction stages involved are described
below :
a) PREPARATION OF SUB-GRADE OR SUB-BASE : The foundation layer should
be graded and compacted to obtain a smooth hard surface. In case the cement concrete
pavement is to be laid on the sub-grade, then it should be dressed to the required profile and
cross-section. Generally the sub-grade or sub-base is prepared to a width of atleast 30cm
beyond the edge of the pavement to be constructed. The minimum value of the modules of
sub-grade reaction obtained with a plate bearing test should be 5.54kg/cm3 for the foundation
material.
b) FIXING OF FORM WORK :
In past timber forms were used exclusively in concrete road works. These forms get
warped after having been in contact with wet concrete on very few occasions. Present trend
is, therefore, to use steel forms at least of 3m, length, except on curves of less than 45m
radius where shorter sections are used. These steel forms are of M.S. channel and of depth
equal to the thickness of the pavements. When set to grade, the maximum deviation of the top
surface of any section from a straight line is not exceeded by 3 mm.
c) BATCHING AND MIXING OF MATERIALS :
The coarse aggregates, fine aggregate and cement are proportioned by weight in a
weight - batching plant and placed into the hopper. The cement may be measured by bag, the
weight of which is taken 50 kg.
The mixing of concrete should be done in a power driven batch mixer to ensure
uniform distribution of materials throughout the mass. The minimum mixing time should be
fixed in relation to the mixer type and capacity. The workability of concrete should be
checked by performing slump test.
d) TRANSPORTING AND SPREADING OF CONCRETE :
Soon after mixing, the concrete should be transported and placed on the prepared base
between the form work in such a manner as to avoid seggregation and uneven compaction.
CE409/16 206
The concrete should not be dropped from a height greater than 90 cm and should be deposited
within 20 minutes from the time of discharge from the mixer.
e) COMPACTION :
The concrete should be compacted fully using vibrating screed and / or internal
vibrators or hand tampers, known as “Hand Tamping Beam” (Fig. 12.2). Compaction should
be so controlled as to prevent excess mortar working on to the top due to over-compaction.
Any low or high spots should be made good by adding or removing concrete. The slab should
be tested for trueness.
Fig. 12.2. Tamping beam
f) FLOATING AND STRAIGHT EDGING :
The concrete is further compacted by means of the longitudinal float (Fig. 12.3). The
longitudinal float is held in a position parallel to the carriage way centre line and passed
gradually from one side to the other. After this, the excess water gets disappeared, the slab
surface is tested for its grade and level with straight edge (Fig. 12.4).
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Fig. 12.3. Float
Fig. 12.4. Straight Edge
g) FINISHING :
Soon after correcting the surface for profile and just before the concrete becomes
hard, the surface should be finished by belting , brooming and edging. For belting, short
strokes are applied with a two-ply canvas belt (Fig. 12.5) transversely to the pavement
surface. Brooming is always done perpendicular to the centre line of the pavement. The
edging tools are used to carefully finish the edges.
Fig. 12.5
h) CURING :
The initial curing is started soon after the finished pavement surface is able to take the
weight of wet jute mats without leaving any marks thereon. The mats are thoroughly
saturated with water and should extend beyond the pavement edges at least by 0.5m. The
initial curing should be continued for a period of 24 hours.
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During final curing after the removal of the mats, wet earth is banked in the form of a
soil berms. A layer of sandy soil is spread and is kept thoroughly saturated with water for 14
days. In places where water is scarce or pavement is on a steep gradient, impervious
membrane curing method should be used.
The concrete pavement is generally opened to the traffic after 28 days of curing.
12.3. JOINTS IN PAVEMENTS:
Joints are provided in concrete roads to allow for expansion, contraction and warping
of the slab caused by the changes of temperature and moisture content. They are also
necessary to allow for the break in construction at the end of the day and to allow the road to
be laid in lanes of convenient width. Design of spacing of various types of joins is dealt with
n detail in article 10.5. Construction aspects of these joints is discussed here.
12.3.1. REQUIREMENTS OF A GOOD JOINT :
1. A joint must be water - proof at all times
2. A joint should not permit ingress of stone grits.
3. Joint must be permitted to move freely at all times.
4. A joint should not detract from the riding quality of a carriage way.
5. A joint should interfere as little as possible in concreting.
6. A joint should not be cause of an expected structural weakness in a pavement.
12.3.2. EXPANSION JOINTS :
These joints are provided to allow for the expansion of slabs due to rise in slab
temperature above the construction temperature of the cement concrete. Expansion joints also
permit the construction of slabs. These joints are provided in our country at an interval of 18
to 21 metres. A typical expansion joint is shown in Fig. 12.6. The approximate gap width for
this joint is from 2.0 to 2.5 cm.
It may be stated that the break in the continuity of a slab forming a joint adds a
weaker plane in the cement concrete pavement. The stresses induced due to the wheel loads
at such joints are of very high order at the edges and corner regions. In order to strengthen
these locations load transfer devices are used.
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Fig. 12.6. Expansion Joint with Dowel bar
This is done through a system of reinforcement provided at suitable intervals
projecting in the concrete in longitudinal direction upto 60 cm length. Such a device is called
‘DOWEL BAR’. Dowel bars are embedded and fixed in concrete at one end and the other
end is kept free to expand or contract by providing a thin coating of bitumen over it. Metal
cap is provided at this end to offer a space of about 2.5. cm for movements during expansion.
Spacing between the dowel bars generally adopted is 30 cm. The size of the dowel bars will
be about 2 cm to 3 cm.
12.3.3. CONTRACTION JOINTS :
These joints are provided to permit the contraction of the slabs. These joints are
spaced closer than expansion joins. Load transfer at these joints is provided through the
physical interlocking by the type of aggregates employed in the construction and with the
average soil and temperature conditions, the recommended spacing for construction joints are
given in Table 12.1. Since it is recommended to provide contraction joints at closer spacing,
there seems to be no need of providing any load transference, as mainly this will be done by
aggregate interlocking. For added safety some agencies recommend use of dowel bars which
are fully bound in the concrete. (Fig. 12.7).
Table 12.1 : Spacing of Contraction Joints
Type of coarse aggregate Joint spacing in metres
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Granite
Limestone
Gravel
a) Calcareous
b) Siliceous
Slag
7.5
7.5
7.5
4.5
4.5
A) Dummy Joint
B) Construction Joint with Dowel Bow
Fig. 12.7. Construction Joints
12.3.4. WARPING JOINTS OR HINGED JOINTS :
These joints are provided to relieve the stresses induced due to warping. These joints
are rarely needed if the suitably designed expansion and contraction joints are provided to
prevent cracking. Longitudinal joints with tie bars are in this class of joint.
12.3.5. LONGITUDINAL JOINTS :
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These joints are provided in wide cement concrete pavements to prevent longitudinal
cracking. They are provided with the bars and these bars help to maintain the two slabs at the
same level. They are not designed to transfer load from one slab to the other. These “tie bars”
are generally 75 cm long and spaced at 60cm apart. Their sizes depend upon the traffic
intensity, that is, 25mm, 20mm, and 12.5 mm diameter bars are used for very heavy, heavy
and medium traffic intensity respectively. IRC recommends to use plain butt or butt with tie
bar (Fig. 12.8) type of joints.
a) Plain Butt Joint
b) Butt Joint with Tie - bar.
Fig. 12.8. Longitudinal joints
12.3.6. ARRANGEMENT OF JOINTS :
Arrangement of transverse joints are as follows :
a) Staggered arrangement
b) Uniform arrangement, and
c) Skew arrangement
Fig. 12.9. shows these arrangements. It is observed that where transverse joints are
arranged staggered on either side of the longitudinal joint as shown in fig. 12.9A, sympathetic
cracks are often formed in line with transverse joints. It is recommended to provide joints
across the longitudinal joint in the same transverse alignment as shown in Fig. 12.9.B.
It is always attempted to avoid the skew alignment of the joints, but in some typical
layouts at intersections it may be required to provide skew arrangements. At places where
these arrangements cannot be avoided, the acute corners so formed are strengthened with
reinforcement as shown in Fig. 12.10.
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a) Staggered Transverse Joint
b) Uniform Joint
c) Skew Arrangement
Fig. 12.9. Arrangement of Joints
Fig. 12.10. Strengthening of Corner Region
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12.4. JOINT FILLER AND SEALER MATERIALS :
Joint spaces are first filled with compressible filler materials to fill up the gap between
the adjacent slab and the top of joints are sealed using a sealer to prevent infiltration of water.
12.4.1. JOINT FILLER :
Joint fillers should be compressible, elastic and durable. Various types of joint filler
materials usually used are soft wood, impregnated fibre board and cork or cork bound with
bitumen. These pre-formed fillers are made from fibres of soft board, fibre board, coir fibre,
or cork. It is required that the performed strips of these materials are properly bonded
together with bitumen. The bitumen content specified by the IRC is 35% by weight. Various
properties required for the satisfactory filler materials are as follows : (As per IRC)
a) COMPRESSION :
The pressure required to compress the specimen to 50% of its original thickness
should be between 7 to 53 kg/cm2. Loss of weight should not be more than 3%.
b) RECOVERY :
At the end of three cycles of load application, specimen should recover by at least 70
percent.
EXTENSION : When compressed to 50% the extension of one edge, should not be
more than 6.5mm where other edges are rest ran.
12.4.2. JOINT SEALER :
For effective sealing of the joint for a long period, it is essential that the sealing
compound possess the following properties:
a) Adhesion to cement concrete edges,
b) Extensibility without fracture,
c) Resistance to the ingress of grit, and
d) Durability.
Different types of sealing compounds are in use. Bitumen is used either along or with
mineral filler as a sealing compound. Rubber - bitumen compounds are also used for this
purpose. Air blown bitumens are also used with advantage, as they are less susceptible to the
temperature changes.
12.5. MAINTENANCE OF CONCRETE PAVEMENTS :
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A well designed and constructed cement concrete road requires very little
maintenance. Main defects in this type of road is the formation of cracks. It is therefore,
necessary to examine the cracks and causes ascertained before any remedial measure is
adopted.
12.5.1 TREATMENT OF CRACKS :
As fine cracks do not harm the pavements, they may be left without any treatment. If
the cracks are wide enough to allow infiltration of water, grit etc., they should be attended
immediately to avoid further damage to the pavement.
The cracks are thoroughly cleaned of all dirt and any other loose particles. This is
done by using a sharp tool and blowing with air blower. The surface is then applied with a
coat of kerosene to facilitate the bond of the sealing material. The cracks are then filled with
suitable grade of bitumen in liquid form. The sealing material is provided 3 mm extra over
the height required. Sand is spread over it.
12.5.2. MAINTENANCE OF JOINTS :
The joints are the weakest spots and the efficiency of the pavement would be
determined by the proper functioning’s of joints. Large number of failure are observed at or
near the joints. Care should be taken to see that filler and sealer materials are in-tact in the
joints. In the event the joints have lost or damaged, either filler or sealer material or both, the
replacement is immediately done. Vertical edges of the joint are also very essential as
inclined faces get very seriously damaged.
12.6. SELF - ASSESSMENT QUESTIONS :
1. In narrow lanes cement concrete pavements are used. Can you justify this practice ?
2. Contraction joints are provided at closer spacing than Expansion joints in concrete
pavements, Why?
3. a) Compare alternate bay and continuous bay methods of construction of cement
concrete roads.
b) With the aid of neat sketches show the different types of joints and their positions .
12.7. SUMMARY :
Cement concrete pavements are preferred because of their excellent riding surface,
very high life and little maintenance. Construction of concrete slab pavements include
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construction of pavement itself and design and placement of the joints. There are two
methods of construction of cement concrete slab pavements: alternate bay method and
continuous bay method. Each method of construction has its applications and limitations.
Steps involved in the construction of pavement slabs are dealt with in detail. The efficiency
of a cement concrete pavement is largely determined by the spacing and efficient functioning
of the various joints. Usual spacing of the joints and constructional details of different types
of joints are presented in detail.
A well designed and constructed cement concrete road requires very little
maintenance. Maintenance of cement concrete roads include treatment of cracks and
maintenance of joints.
12.8. REFERENCES :
1. Bindra, S.P. (1977) - A Course in High Way Engineering - Dhanpathy Rai and Sons,
Delhi.
2. Khanna, Dr. S.K. and Justo, Dr. C.E.G. (1991) - Highway Engineering - Nem Chand and
Bros, Roorkee.
3. - (1955) Concrete Roads, H.M.S.O. Publication.
***
TRANSPORTATION ENGINEERING
UNIT-13
SOIL STABILISED ROADS
Aims / Objectives :
13.1. Introduction
13.2. Mechanical Stabilisation
13.3. Soil-Cement Stabilisation
13.4. Soil-Lime stabilisation
13.5. Bituminous Stabilisation
13.6. Summary
13.7. Self-Assessment Questions
13.8. References
AIMS / OBJECTIVES :
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Soil stabilization means the improvement of the stability or bearing power of the soil
by the use of compaction, proportioning and/ or the addition of suitable admixtures or
stabilisers. Roads which are constructed using these techniques are called ‘Stabilized Roads’
and are gaining popularity in developing countries because of their susceptibility for stage
construction. In this chapter, common methods of stabilisation of road beds like mechanical
stabilisation in which soil and aggregate are proportioned to get a dense mixture and methods
in which admixtures like cement, lime and bituminous materials are used to improve the
stability of locally available soil are discussed.
13.1. INTRODUCTION :
In the construction of roads, cost of construction can be brought down by selecting
locally available aggregates and soil, and correctly proportioning them for maximum density.
If such a soil - aggregate mixture is adequately compacted to get a mechanically stable layer,
the process is ‘Mechanical Stabilisation’.
If the locally available soil is very poor and can not withstand the expected traffic
loads, it can be improved through compaction after the addition of an inexpensive admixture,
the ‘stabilising Agent’. A number of stabilising agents have been used in highway
construction. The more important of these may be classified as cementing agents, modifiers
or water proofing agents. The more common cementing agents are Portland cement, lime and
lime fly ash mixtures. They act through the formation of cementitious compounds that more
or less permanently bind together individual particles or aggregates of particles. Lime is also
a powerful soil modifier that serves to decrease the plasticity, reduce water content and
increase workability of wet clay prior to compaction. Bitumen is used as a water proofing
agent as well as a cementing compound.
Stabilising agents are selected according to the type of soil, stability problem at hand
and the economics of their use.
13.2. MECHANICAL STABILISATION :
When a granular structure, such as a road base or surfacing has the property of
resistance to lateral displacement under load, it is said to be ‘Mechanically Stable’. In
mechanically stabilized soils, the resistance is provided by the natural forces of cohesion and
internal friction in the soil. Cohesion is mainly associated with the silt and clay content of the
material while internal friction is a characteristic of coarser particles. Mechanical stabilization
is still the stabilization method that is most widely used in road construction throughout the
CE409/16 217
world. Its popularity is based on the fact that it makes possible maximum usage of locally
available materials in highway construction. In this process, aggregates and soils are properly
proportioned and the resulting mixture is adequately compacted to get a stable layer.
Factors affecting mechanical stabilisation of soil-aggregate stabilisation include the
following .
a) Quality and quantity of the soil binder.
b) Strength and gradation of aggregates, and
c) Compaction.
13.2.1. Quality and Quantity of the Soil Binder :
A Stabilised soil - aggregate mass is analogous to cement concrete in that the coarse
aggregate content plays the role similar to that of coarse aggregate in concrete and the soil,
sometimes called the binder soil, with water acts as mortar. The main use of this form of
stabilisation is for sub-base construction of high type of roads and road bases and surface
courses of secondary type of roads. The quality and quantity of the binder soil plays a very
important role on the characteristics of soil-aggregate mixture.
Plasticity characteristics of binder soil effect the performance of the soil-aggregate
mix considerably. Soil with high plasticity index, results in poor stability under soaked
conditions. hence, it is desirable to limit the plasticity index of the soil constituents. salts like
sulphates and presence of mica are also undesirable. But presence of salts like calcium
chloride are considered to be beneficial. Liquid limit for binder soil for base course may be
upto 25% and for surface course upto 35%. Similarly plasticity index value for base course
should not exceed 6% and for surface courses should be between 5 and 10%.
The influence of the quantity of soil in soil-aggregate mixture is illustrated in Fig.
13.1. When the aggregate is without fines (Fig.13.1a) the mass will be stable only when
confined, highly permeable, practically no variation in volume or stability with moisture
variation.
CE409/16 218
Fig. 13.1. Typical States of Soil - Aggregates
In fig. 13.1.b, the voids in the compacted aggregate are just filled with compacted
binder, without disturbing the grain to grain contact of the aggregates. In this state, the
density of the mix will be maximum with increased stability even when unconfined due to
higher cohesion, but the mix is less permeable and variation in volume and stability due to
moisture variations much depend on the property of the binder soil. The state when the
aggregates are mixed with excess of fines and compacted is shown in fig.13.1.c. In this state,
there is no contact between the aggregates and they float in the binder soil, the stability is
decreased and mix is considered less desirable with poor drainage, more variation in stability
and volume with moisture variation. Thus proportioning of the mix effects the properties of
soil-aggregate mixtures considerably.
13.2.2. Strength and Gradation of Aggregates :
From the above discussion, it will be appreciated that maximum stability is obtained
for a soil-aggregate mixture when the voids in the compacted aggregate are just filled up,
with the binder - soil (Fig.13.1.b). In this case, the load transfer takes place through the
contact points of the aggregates and in such circumstances aggregates with high crushing
strength are to be used. However, weak aggregates have also been successfully used in
mechanical stabilization work (see article 13.2.5). Grain size distribution of the combined
mix would determine the maximum stability of the mix. A well graded aggregate-soil mix
results in a mix with high dry-density and stability values.
Dense mixtures may be obtained when their particle size distributions follow Fuller’s
Law which is expressed as
p = 100 (d/D)0.5 ---- (13.1)
Where p = percent by weight of the total mixture passing any given sieve size.
d = aperture size of that sieve.
CE409/16 219
and D = size of the largest particle in the mixture.
However, this grading does not define the practical limits for useful grading of
aggregates. Considering the various practical requirements to be satisfied, number of standard
specifications for aggregate gratings have been brought out by different agencies like,
AASHO, I.R.C. etc. Table 13.1. presents British recommendations for the gradation of
granular stabilised sub-bases.
Table 13.1
BS, Sieve Size, mm percentage by weight passing
76.0
38.1
9.52
4.76
0.6000
0.075
100
85-100
45-100
25-85
8-45
0-10
The clay content of soil-aggregate stabilised road - base must be very carefully
controlled. Where as in surface course, a non-porous layer is required inorder to prevent
water infiltration, the very opposite is normally true in a road base. Plasticity characteristics
specified for binder soil have already been discussed.
13.2.3. Blending Soils and Aggregate :
In some localities deposits of naturally occurring soils will be found which meet the
soil - aggregate specifications. More often than not, however, two or more soils will have to
be blended in proper proportions to produce mixtures meeting these requirements. Methods
for determining the proportions to blend are still essentially by trail and error. They involve
either estimating trail gradations, preparing test mixtures and testing for gradation and
plasticity, or else estimating the proportions which gives the desired plasticity index,
preparing trail mixtures, and testing them for gradation and plasticity. Some of the more
commonly used guide-procedures for blending soils are discussed below.
a) Proportioning of Materials by Rothfutch’s Method :
This method may be used when a number of materials have to be mixed together for
obtaining a desired gradation. The actual procedure will be apparent from the following
example. First the design gradation is decided based on the recommended grain size
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distribution charts or tables. Such a gradation is presented in columns 1, 2 and 3 of Table
13.2. The grain size distribution of a crusher run stone (A) sand (B) and silty-clay (C) that is
required to be mixed to produce a mechanically stable surface within the limits specified in
column 3, are presented in columns 4,5 and 6 in Table 13.2.
(i) The required grain-size distribution is represented by the diagonal oo’ of a rectangle
(Fig.13.2). The vertical ordinates of the rectangle are graduated for percentages from 0 to 100
on a linear scale. The horizontal scale for sieve aperture size is graduated by drawing for each
sieve size a vertical line that intersects the diagonal at a point where the ordinate equals the
percentage passing that sieve, (i.e.,) 100 percent for 25 mm sieve, 92% for 20mm sieve and
so on.
(ii) The size distribution of the aggregates to be mixed (Table 13.2 columns 4, 5, and 6
are plotted on this scale of sieve size (Fig.13.2) giving the lines BAO’ (Crusher run BFE
(Sand) and OG (silty clay).
(iii) The nearest straight line to these size distributions are drawn with the aid of a
transparent straight edge, by the ‘minimum balanced areas’. They are the dotted lines CO,
BO and OG (the last being coincident with the actual size distribution).
(iv) The opposite ends of these lines are joined, giving the chain lines CD and BG (In this
case, the later coincides with the 0.075 mm sieve size ordinates). The points where these lines
cross the required size- distribution line are marked by the circles L and M. The proportions
in which these three aggregates should be mixed are obtained from each difference between
the ordinates of these points, and are shown on the right hand side of Fig. 13.2.
Sieve Sizes (mm)
Fig. 13.2 : Determination of mixture for stabilised surfacings
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The particle-size distribution that will result form mixing the aggregates in these
proportions is given in column 7 of Table 13.2. The size distribution obtained is within the
limits (column-3).
b) Blending two materials by Plasticity Index :
The proportion is to be blended to give the required plasticity index can be estimated
from the following equations :
a = 100 SB ( )
( ) ( )p p
S p p S p pB
B B A A
−− − −
---- (13.2)
b = 100-a
Where a = percentage of material A in final mixture.
b = percentage of material B in final mixture.
p = Required plasticity index of final mixture.
pA = Plasticity index of material A
pB = Plasticity index of material B
SA = Percentage passing 425 µ sieve in material A.
SB = Percentage passing 425 µ sieve in material B.
Table 13.2
Example of Rothfutch’s Method for Proportioning Mixture of Aggregate (See Fig. 13.2).
I S Sieve
size mm
Percentage passing
Required size
distribution.
Aggregates available Mixture
37% A
45% B
18% C
Limits Average (A)
Crushed
stone
(B)
Sand
(C)
Silty Clay
25
20
10
100
85-100
65-100
100
92
82
95
70
21
--
--
--
--
--
--
98
89
71
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4.75
2.00
0.6
0.075
55-85
40-70
25-45
10-25
70
55
35
18
11
7
2
Trace
100
85
55
Nil
--
--
--
100
67
58
43
18
13.2.4. Construction Method :
The construction materials are collected from the selected borrow pits and stacked
along the sides of the road in the desired proportions.
The equipment needed are for excavation upto shallow depth, haulage for short
distance and for compaction. Machinery or Manual labour may be used for excavation and
haulage. For compaction roller of suitable type and weight is necessary depending on the
materials to be compacted. Construction steps are as follows :
(i) The sub-grade is prepared.
(ii) The materials are mixed in the desired proportions as per the design. Generally the
proportions are converted on volume basis.
(iii) Moisture is added if necessary and the materials are thoroughly remixed.
(iv) The wet mix is spread to the desired grade and compacted by rollers. Rolling is started
form the edges, and with adequate longitudinal overlap, it is continued upto the center.
Rolling is continued till adequate compaction is achieved.
(v) Field control tests are to check moisture content and density after compaction.
(vi) The Stabilized road is opened to traffic often the compacted layer hardens by
drying.
13.2.5. Stabilization using Soft-Aggregates :
When hard variety of aggregates are not available locally, the local soft aggregates
may have to be used for construction in order to keep the construction cost as low as possible.
These aggregates have low crushing strength and low aggregate impact value. If the load
transfer takes place through points of contact between aggregates Fig.13.1.b, they get crushed
due to high stresses at points of contract. This problem can be avoided by using the soft
aggregates with excess of binder soil so that the aggregate to aggregate contact is lost and the
aggregate float in a matrix of binder soil (Fig.13.1.c). This principle has been utilised in the
method of stabilization suggested by ‘MEHRA’ for construction of low-cost roads using soft-
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aggregates like kankar, brick bats laterite etc. The soil and aggregate are mixed in 2:1 ratio
and I.R.C. standardized the procedure of construction.
Mehra’s Method of Stabilization :
Base course material consists of compacted soil with sand content (of size less than
0.425 mm and greater than 0.075 mm) being not less than 50% and plasticity index 5 to 7.
Wearing course material consists of brick aggregates and soil mixed in the ration 1:2.
The sand content (of size less than o.425 mm and greater than 0.075 mm) in the soil should
not be less 33% and plasticity index 9.5 to 12.5. However, when bituminous surface
treatment is desired, the plasticity index is limited to 8-10.
The Mehra’s Method of conduction is briefly as follows :
(i) Soil is collected from approved borrow pits and stacked on road side.
(ii) Water is added upto OMC, and soil is mixed and spread to desired camber and grade.
(iii) 11 1/2 cm thick loose base course material is spread and rolled by 8 tonnes
power roller to a compacted thickness of 7 1/2 cm.
(iv) Surface course material (brick aggregate + soil in the ratio 1:2) mixed with
adequate water is spread to 11 1/2 cm loose thickness and the layer is rolled by 8
tonnes power roller to a compacted thickness of about 7 1/2 cm.
(v) After rolling, the surface is watered and left over night. The surface is again
rolled and finished.
(vi) The road is closed to traffic for four to five days and kept sprinkled with water. For
next few days only rubber tired traffic is allowed and after about 2 weeks the road is
opened to all traffic.
This method of constriction can carry 50 tonnes per day of mixed traffic in places
with light rainfall. With bituminous surface treatment the road can give satisfactory service
upto about 200 tonnes per day even in places with heavy rainfall.
13.3. SOIL-CEMENT STABILISATION :
Of all the methods of soil stabilization now in use, that which utilizes cement as the
stabilizing agent is second only to mechanical stabilization in importance and usage,. Factors
which have helped to make use of portland cement so popular as a soil stabilizer in nearly
every other country in the world, are as follows :
(i) Cement is available readily in most countries as a home product.
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(ii) Cement is manufactured on such a large scale that its price is comparatively
less.
(iii) Use of cement generally involves less care and control than may other method of
stabilisation.
(iv) More information is generally available on cement treated soil mixtures than on other
types of soil stabilisation.
(v) Almost any soil can be stabilised with portland-cement if enough cement is
used in combination with the right amount of water and proper compaction and
curing.
There are three different types of cement treated soil mixtures. The engineer should
distinguish among these so that he will know how and when each may be used most
advantageously.
13.3.1. Types of Cement - Treated Soil Mixtures :
a) Soil-Cement :
In this, sufficient cement is added to the soil to harden it and the moisture content of
the mixture is adequate for compaction purposes and hydrating the cement. This soil -cement
mixture should be capable of meeting the particular criteria resulting to strength or durability.
Most-important applications of soil-cement are as sub-base or/and base course in road ways
and parking areas, airport runways, taxiways and aprons. Soil-cement is not used in road
surfacings as it has poor resistance to abrasion. Another super-imposed material, eg.: a
concrete pavement or bituminous surfacing must be used to protect it from wheels of traffic.
b) Cement - Modified Soil :
In certain situations cement may be used to decrease soil plasticity. Cement generally
brings about a decrease in liquid limit and an increase in plastic limit with a corresponding
decrease in plasticity index. The increase in plastic limit is accompanied by a corresponding
increase in optimum moisture content. Situations which indicate the use of modified soil
include construction over wet plastic sub-grades.
c) Plastic - Soil Cement :
This is an intimate mixture of pulverised soil, cement and enough quantity of water to
produce a mortar like consistency at the time of mixing and placing. This is used primarily as
an erosion control material for lining on the sides of ditches and canals. In general, these
CE409/16 225
mixtures require about 4% or more cement than soil-cement mixture in order to meet the
same criteria.
13.3.2 Mechanism of Stabilisation :
In granular soils, the stabilisation is due to bond between the cementitious
components of hydrated cement and compacted soil particles at the points of contact. In
plastic soils, the free lime given out during hydration plays a prominent part in the reactions.
It brings about cation exchange on the surface of soil particles resulting in changes in the
plasticity characteristics. The soil then becomes friable and the cementitious products then
bind the lump of clay particles.
13.3.3. Factors Influencing Properties of Soil Cement :
The factors which primarily affect soil-cement properties are as follows :
(a) Type of soil
(b) Type and amount of Cement.
(c) Water content
(d) Degree of mixing
(e) Compaction
(f) Curing and
(g) Chemical additives.
(a) Type of soil :
The properties and durability of soil-cement depend upon gradation clay content,
Atterberg limits, specific surface, organic matter and sulphate content of the soil. The cement
requirement of fine grained soils is higher than that of well graded coarse grained soils. It is
because of the fact, the fine grained soils have higher specific surface area. The presence of
organic matter and sulphate retards the chemical action of cement. Generally a soil having
more than 50% passing, 4.75 mm sieve, less than 50% passing 0.075 mm sieve and having
liquid limit less than 40% and plasitc limit less than 18% is considered suitable for cement
stabilization.
(b) Type and Amount of Cement :
The greater the cement content the stronger is the resulting soil-cement properties. It
is now practice (in India and Britain) to specify the desired stabilities of soil-cement mixtures
CE409/16 226
in terms of minimum unconfined strength and not in terms of cement content. However in
U.S. the desired cement content is normally selected to meet durability requirements.
(c) Water Content :
Water is necessary in soil-cement mixture in order to hydrate the cement, to improve
the workability and to facilitate compaction. This water should be relatively clean and free
from harmful amounts of alkalies, acids or organic matter. In the case of soil-cement
mixtures it is important to realise that the optinum moisture for maximum density is not the
same as that for strength. In general, the optimum moisture content for maximum strength
tends to be on the dry side of optimum for maximum density for sandy soils and on the wet
side for clayey soils. The location of optimum value for strength is dependent not only on the
amount of clay present in the soil, but also on the type of clay mineral.
(d) Degree of Mixing :
High mixing efficiencies will result in lower cement content in order to achieve a
given soil-cement field strength. Increasing the moist mixing time and/or delaying
compaction after ending the moist mixing, generally results in an increase in the optimum
moisture content for maximum dry unit weight of soil-cement mixture, while its durability
and unconfined compressive strength are decreased. For these reasons, many specifications
place an upper limit on the length of the time between when moisture is added to the mixture
and when compaction is completed. This upper limit of time is about 2 hours as per many
specifications.
(e) Compaction :
Higher amount of compaction results in increased strength and durability.
(f) Curing :
The soil cement must be moist - cured during the initial stages of its life so that
moisture sufficient to meet the hydration needs of cement can be maintained in the mix.
Higher strength is obtained at higher curing temperatures.
(g) Chemical Additives :
Laboratory studies have shown that when trace chemicals like sodium carbonate,
sodium silicate, calcium chloride etc., have been used as additives to soil-cement moistures,
dramatic improvements in strengths can be obtained. It is a common practice to premix a
small quantity of lime with highly plastic soils to facilitate pulverization. It has been reported
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that a significant reduction in cement content, without loss of long-term strength, could be
obtained by adding fly-ash to the cement-soil mixture.
13.3.4. Design of Soil-Cement Mix :
There are various mix design methods: The most commonly known being British and
P.C.A. Methods.
(a) British Method :
In this method, design is based on the unconfined compressive strength of 5 cm dia
and 10 cm long specimens cured for seven days. The cement content corresponding to a
strength of 17.5 Kg/cm2 (Fig.13.3.) is taken as design cement content for base courses of
highway pavements with light to medium traffic. However for heavy traffic, a higher strength
of 28 to 35 kg/cm2 may be adopted.
Fig. 13.3. Compressive strength (7-days) and max. Dry Density at different Cement
Contents.
(b) P.C.A. Method :
In this, the design criterion is based on durability of the soil-cement specimens to
withstand the specified wet-dry and freeze-thaw cycles, Durability is decided based on
resistance to loss in weight due to brushing the surface, volume change and moisture content
during the specified durability cycles.
13.3.5. Construction Method :
The following three methods are used for construction of stabilized soil roads.
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(a) Mix-in-place method.
(b) Travelling plant method.
(c) Stationary plant method.
The major construction operations for soil-cement road are :
(i) Preparation of sub-grade.
(ii) Thorough pulverisation of the soil.
(iii) Thorough mixing of soil with the required quantity of cement.
(iv) Addition of water and its thorough incorporation in the mix.
(v) Spreading and Compacting
(vi) Curing by placing a suitable protective cover to prevent surface evaporation
losses of water.
The compaction of soil-cement mix is done soon after placing the wet mix. The joint
between old and new work should be laid carefully. Following field control tests have to be
carried out to control the quality of the work.
(i) Cement-content test
(ii) Moisture content test prior to compaction
(iii) Density of compacted layer.
It is also desirable to check depth of the processed layer and surface irregularities of
finished surface.
13.4. SOIL - LIME STABILISATION :
Lime as a soil additive, brings several beneficial changes to soil containing silt and
clay particles. The use of lime in construction of high ways is not new. Romans used
pozzonlana with lime for improving its cementing action and used in their roads about 2000
years ago. As in the case of soil-cement, soil-lime is not suitable for the surface courses of
pavements because of its very poor resistance to abrasion and impact. This process has
gained popularity now-a-days in view of its simplicity, efficiency and economy.
13.4.1. Mechanism of Stabilisation :
When lime is mixed with plastic soil, three stages of reaction can be recongnised.
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(i) An early stage that occurs within a few minutes to an hour and is marked by a
flocculation, agglomeration and granulation of soil particles, a reduction in plasticity and
swelling potential and considerable improvement in the workability.
(ii) A subsequent stage in which a compacted mixture slowly develops strength as a result
of pazzolanic reactions and the formation of new compounds over a period as long as several
years, and
(iii) A third stage in which lime reacts with carbon-dioxide from the atmosphere and form
carbonates of calcium and magnesium. These carbonates are weak cements and the strength
gain due to carbonation is minimal in comparison with detrimental effects resulting from it.
The first stage may be identified as soil modification or amelioration effects, the
second as soil cementation or pozzolanic reactions and the third stage as carbonation. Both
the first two stages are important to stabilization process, since for wet, plastic sub-grade soils
it is the modification that yields proper soil conditions for the mixing and compaction