rigid pavement
TRANSCRIPT
A seminar report on
Rigid pavements as alternative specification for
Expressway by
SONI PRAGNESH B.
(Roll No. 11)
Guide
Miss.R.N.Shukla
CIVIL ENGINEERING DEPARTMENT
L. D. COLLEGE OF ENGINEERING
AHMEDABAD – 380 015
MAY 2006
Certificate
This is to certify that the seminar entitled “RIGID PAVEMENTS AS
ALTERNATIVE SPECIFICATION FOR EXPRESSWAY” which is
submitted by Soni Pragnesh B. Roll No.11 for partial fulfillment of the
requirement for the degree of Master of Engineering Sem:II (Civil) in
Transportation engineering within four walls of L.D.College of Engineering to
Gujarat University, Ahmedabad is a record of work supervision and guidance of
Miss.R. N. Shukla.
(Guide)
Date: Miss. R. N. Shukla.
Lecturer,Civil Engg. Dept.
L.D.College of engineering.
Ahmedabad – 380 015
Examiner: Prof. K.M.Shah
Head of the Department
Civil Engg. Dept.
L.D.College of engineering.
Ahmedabad – 380 015
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Acknowledgement
I take this opportunity to thank Miss.R.N.Shukla. Faculty-Civil Engineering
Department, L.D.College of Engineering, Ahmedabad for organizing the concept
of seminar presentation and also for his valuable guidance and formation of
methodology and compilation of this seminar report.
I would like to express my deep sense of gratitude towards the faculty members of
Civil Engineering Department and my colleagues for giving the guidance and
support.
May, 2006 Soni Pragnesh B.
M.E. CIVIL (TRANSPORTATION ENGG.)
ROLL NO: 11
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Abstract
Report focuses on considerations of rigid pavements for their requirements of
expressway such as traffic safety, travel comfort, durability e.t.c.It contains
precautions and pre requisites for effective utilization of rigid pavement.
Report shows comparison of characteristics of flexible and rigid pavement,
construction methods of cement concrete pavement and economics of
cement concrete and flexible pavement.
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Contents
Certificate 2
Acknowledgement 3
Abstract 4
Content 5
List of figure 7
List of table 8
Chapter Description Page
No. No.
1 Introduction
1.1 General 9
1.2 India’s road modernization need 9
1.3 Pavement choice 10
2 Consideration of rigid pavement from the point of special
requirement of expressway
2.1 Traffic safety 11
2.2 Travel comfort 11
2.3 Durability 12
2.4 Maintenance need 12
3 Precautions and pre requisites for effective utilization
3.1 General 13
3.2 Structural mechanism of cement concrete pavement 13
3.3 Special environmental condition for concrete 14
3.4 Rigidity of concrete pavement 14
3.5 Consideration relevant to structural and functional aspect 15
4 Comparison of characteristics of flexible and cement concrete
pavements for expressway 17
5
5 Construction of cement concrete pavement
5.1 Construction of Pavement slab 25
5.2 Construction of joints 30
6 Economics of concrete and flexible pavement
6.1 Comparison of initial cost 35
6.2 Life-cycle coats 38
7 Conclusion 39
8 References 40
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List of figure
Figure Description Page
No. No.
1 Construction method of cement concrete road 26
2 Expansion joint 33
3 Warping joint 33
4 Longitudinal joint 34
5 Contraction joint 34
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List of Table
Table Description Page
No. No.
1 Pavement thickness 36
2 Cost of materials 36
3 Formulae for costs of expressway pavements 37
4 Comparison of initial cost of flexible and rigid pavements for 37
expressway
5 Comparison of life-cycle cost of flexible and rigid pavements for 38
expressway
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Chapter 1
Introduction
1.1 General
Need of express way system;
Invention of wheel was a giant step in the history of mankind. Then onward the man applied all
his resources to move these wheels faster and faster. Now a days speed, comfort and safety are
vital in transport sector. The national highway system is designed to cater for traffic with 100
km speed. However the actual operating are never more than 40kmph due to rapid increase in
vehicular traffic and carriage way being shared by both slow and fast traffic. The appropriate
solution lies in construction of expressway with control of access and allowing only fast moving
vehicles. The first national expressway between Ahmedabad and Vadodara has been taken up
for construction in India.
1.2 India’s road modernization need
As India’s economy growing fast, road transport demand rises. The present network of arterial
road is un able to cope up with even present need for transport, let alone the future demands.
Modernization of India’s road, and particularly the construction of a system of super fast
expressways, is long overdue. Plans are being drown up for expressway.
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1.3 Pavement choice
Expressways are costly to build and maintain. Because of a substantial volume of commercial
vehicles likely to use facility, the pavement structure has to receive careful consideration in
design and choice of materials forming the pavement. Pavement costs constitute a significant
proportion of total cost of highway facility. Hence, great care is needed in selecting right type
of pavement and specification for the various courses that make up the pavement. In
expressway schemes, a matter that should not be lost sight of is the cost of maintaining the
pavement, including routine repairs, periodic renewals and overlays. Maintenance operations
in expressway routes can cause considerable in convenience and annoyance to users,
especially if the facility is toll based. An entrepreneur who invests money on a toll based
expressway would prefer to minimize his involvement with maintenance operation to the
barest level. The choice of pavement type, whether flexible or cement concrete, therefore, has
to be very carefully exercised.
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Chapter 2
Consideration of rigid pavement from the point of special
requirement of expressway
2.1 Traffic safety
Pavement associated traffic safety factors include skid resistance, drainability against
hydroplaning, and night visibility. Cement concrete pavement has distinct initial advantage
over bitumen pavement in this regard, as surface texturing forms integral part of the normal
construction practice for such pavements. They also have superior night visibility by virtue
of their lighter colour. Durable surface texture with long life , not difficult to ensure, though
it calls for attention to number of factors. Restoration of lost texture /retexturing however
calls for special technology and can be quite costly. In area of low rainfall intensity,
hydroplaning not being the governing consideration, it a possible to design the concrete mix
for adequate skid resistance even after the loss of textured surface finish, subject to
availability of appropriate quality material.
2.2 Travel comfort
Travel comfort is governed by level of surface evenness of the pavement which governs its
riding quality. The concrete pavement can provide a very even surface with manual finishing
operations, within stipulated tolerance of 3 mm under a 3 m straight edge. Subject to
adoption of appropriate precautions during construction to ensure wear resistance, they retain
their profile by virtue of their inherent rigidity, and provide a fairly constant riding quality
over long periods. Having high shear resistance, are not prone to shoving or potholing
associated with flexible pavements. Ensuring good initial surface profile and proper
construction and maintenance joints need particular attention in this regard.
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2.3 Durability
Poorly designed and constructed concrete pavements are known to have very long
service life. The cement concrete road constructed in the country in the past, though
extremely limited in length, have an excellent service track, having given good service
under condition much sever than those for which they are originally intended. The
thinner once among these ultimately succumbed as much under bitumen repair
technology which is not appropriate to them, as under heavy traffic. Adequate design and
good construction practice with needed quality control can together provide durable
concrete pavements with long service life and needed levels of traffic safety and travel
comfort.
2.4 Maintenance need
The routine maintenance needs of concrete pavements are limited to ensuring a good
joint seal. Use of superior synthetic joint seal could substantially cut down the frequency
and extent of needed periodic resealing. For any local defects or inadequacies developing
over long use, appropriate and expeditious technologies are available, which can be
utilized effectively in preference to bituminous repairs. With some maintenance and
repair needs, concrete pavements also have the potential advantage of practically no
disturbance or dislocation to traffic for attending to related operations.
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Chapter 3
Precautions and pre requisites for effective utilization of rigid
pavement for expressways
3.1 General
The special requirements for effective utilization of rigid pavement are emanate from
following factors;
(a) The structural mechanism of concrete and concrete pavements.
(b) Special environmental conditions of paving concrete.
(c) The rigidity of concrete pavements.
3.2 Structural mechanism of concrete and concrete pavements
Cement concrete develops very fine, small, discontinuous micro-cracks in initial stages
due to hydrothermal changes. Under increasing or repetitive loading, the micro-cracks
tend to extend and join, resulting in fracture and failure. To minimize them inherent
micro-cracking, only minimally essential water for ensuring full compaction of concrete
should be used. Full of saturation concrete during the 28 days curing period is also
imperative, as capillary pores in concrete with low water cement ratio are not continuous,
and if once dried, subsequent immersion dose not result in penetration of water therein,
resulting in lower strength and fatigue resistance.
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3.3 Special environmental conditions of paving concrete.
Concrete pavements have a large surface to volume ratio, era exposed to atmosphere on
one face, with the lower face being in contact with the ground. Such condition lead to
higher susceptibility to shrinkage, calling for adoption of minimum feasible water and
cement compatible with the required strength and its realization, as also for due attention
to curing to obviate early shrinkage cracking. The temperature differential and the
resultant warping resistant stresses to which concrete pavements are subject, due to
different espouser conditions of its two faces, considerable reduce the concrete strength
available for supporting the traffic load and catering to their fatigue effects, calling for
high strength concrete.
3.4 Rigidity of concrete pavement
The rigidity inherent in concrete as a structural material enables concrete pavements to
maintain an excellent functional stability over long period in terms of their surface
profile. While such stability is a great asset in case of pavements constructed to correct
profile, it can become a serious liability in the correction of a substandard surface, the
methods available for the purpose not being simple, expeditious or economical.
Emphasis on quality assurance initially is, therefore, very important, weather through
appropriate mechanization or strict supervision and control of manual surface finishing
operations.
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3.5 Considerations relevant to structural and functional aspect of rigid
pavements
3.5.1 Pavement design
While concrete pavement makes more efficient use of constructional material,
particularly aggregates, as compared to bituminous pavement, they are much more
sensitive to overloading in terms of damage to the pavement structural strength. The
concept of equivalent standard axel loads (ESALs), which is based on functional criteria,
does not adequately their structural response and is not the appropriate criteria for their
design.
3.5.2 Concrete mix design
Concrete mix design for expressway should based on both the structural and functional
requirements of such pavements. It should not have the requisites flexural strength, but
should also provide needed wear resistance and skid resistance. While kid resistance of
new pavement would mainly depend upon the texturing of the surface, the materials –
particularly the aggregate would be so selected as to ensure adequate skid resistance even
after the initial texture wears off. Where such materials are not readily available, two
layer bonded construction may be considered, with the more wear and skid resistant mix
design adopted for upper layer.
3.5.3Quality control of construction
For expeditious construction of substantial lengths of express way, highly mechanized
construction technology would need to be adopted. Central mixing and batching plant,
transit mixtures, and paving and finishing trains can obviate much of the variability
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associated with manual or semi-mechanized construction. How ever constant check on
the supplies of fresh material, and the strength and workability of concrete would need to
be ensured, expeditiously introducing any modification to the mix design by the test
check. Computerization of the quality control data, and software and the export systems
for analysis and interpretation of the data and arriving at the needed adjustments
/corrective action should form an integral part of such quality control system.
3.5.4 Maintenance and rehabilitation
As indicated earlier, cement concrete need very little routine maintenance, while
confined practically renewal of the joint seal. Any joint spalls or contraction cracks are
best maintained using resin repair technology. For surfacing or over laying of sound
concrete pavements to improve their riding quality or enhance their structural strength,
bonded concrete technology is available, provided it is feasible to close the lane under
such renovation to traffic for the requisite construction period including curing.
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Chapter 4
Comparison of characteristics of flexible and cement concrete
pavements for expressway
(a) Desirable Properties of a good Pavement
A highway pavement is designed to support wheel loads imposed on it from traffic
moving over it. Additional stresses are also imposed by changes in the environment. For
satisfactorily performing these functions, the pavement should have many desirable
characteristics. These are:
1) The pavement should have a long life.
2) During its design life, it should perform satisfactorily, without suffering excessive
deformations and rutting.
3) The pavement should be structurally sound to withstand the stresses imposed on
it.
4) It should be sufficiently thick to distribute the loads and stresses to a safe value
on the subgrade soil.
5) It should provide a reasonably hard wearing surface, so that the abrading action
of wheels (pneumatic and irontyred) does not damage surface.
6) Its riding quality should be good. It should be smooth enough to provide comfort
to the road users at the high speeds at which modern vehicles are driven.
7) The energy consumption should be low.
8) The surface of the pavement should have a skidding resistance texture.
9) The surface should be impervious so that water does not get into lower layer of
the pavement and the subgrade and cause deterioration.
10) The pavement should have good reflectivity properties.
11) The pavement should conserve the nature’s resources; the use of binder should
not involve drain of foreign exchange.
12) Maintenance cost of pavement should be low.
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13) The initial cost the pavement should not be excessively high. The life-cycle-cost
of the pavement should be low.
14) The analyses of stresses and strain in a pavement should be simple and well-
understood, making the design precise.
15) The pavement should permit easy repairs to utilize that may be laid underneath it.
16) The pavement should not be affected by occasional spillage of petroleum
products.
17) Technology of construction must be available in the country.
In the succeeding paragraphs, the two pavement types will be assessed against each
of the above desired characteristics.
(b) Life of pavement
It is well known that an adequately designed and constructed cement concrete pavement
has a life of 30-40 years. This is proved from experiences abroad. Even the thin concrete
slabs constructed by manual means years ago in India have given 30-40 years of
satisfactory life. Against this, flexible pavements have a much shorter life. They are
really, if ever, designed for a life greater than 20 years. This is because the various layer
of the pavement suffer densification under traffic, lose their elastic properties over bay
period of time and tend to disintegrate. Thus, after the design life, flexible pavements
need to be rehabilitated and strengthen substantially. For a super fast facility, an assured
long life is a greater advantage, as it saves the discomfort to traffic during periodic
renewals and rehabilitation.
(c) Performance during design life
As a loads pass over a flexible pavement, it deflects, returning back to its original
position after the passage of the load. When the pavement is new, its behavior is
perfectly elastic, and the recovery of the deflection is perfectly elastic, and the recovery
is not full, the pavement suffering a permanent deflection each time a load goes over it.
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The cumulative effect of this time a load goes over it. The cumulative effect of this
phenomenon results in rutting and cracking in the wheel-paths, causing deterioration in
the performance of the pavement. It can well be said that the –deterioration of the
flexible pavement starts right away with its being thrown open to traffic. The rate of
deterioration is governed by the volume and nature of traffic and the initial quality of
construction it self. But, in the case of a concert e pavement, deterioration is hardly
perceptible and one can expect a consistently uniform performance through out its life.
(d) Structural soundness
Well designed pavements, whether flexible or rigid, are able to withstand the stresses
imposed on them. No superiority can be claimed for a particular pavement type on this
score.
(e) Adequacy for load Distribution:
Though each of the two types of pavements act in a different way their thickness are so
adjusted that the loads get distributed to a safe value on the sub grade soil. The flexible
pavement has only to have a much higher thickness than the concrete pavement to
accomplish this task.
(f) Hard wearing surface
Wearing surfaces of pavements are subjected to hard abrading action of wheels. Severe
abrasion takes place, particularly on curves, and junctions. Concrete is a much superior
material than bituminous surface in this regard.
(g)Riding quality
A good riding quality is a prime requirement of roads surfaces from various
considerations. A smooth surface ensures rider comfort, particularly, at high speeds.
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Vehicle operating costs are low on smooth roads, fuel consumption being one of the
components of these costs. Concrete roads and bituminous surfaces, constructed to
modern specifications provide a smooth riding quality when constructed. But, whereas a
concrete pavement maintains its initial quality throughout its life, a bituminous surface
deteriorates in riding quality as traffic moves over it. In quantitative terms, both
pavements types when initially constructed can have a roughness value of around 2000
mm / km as measured with a bump integrator. On a concrete road, one can expect the
same surface smoothness to continue over its life. In contrast, the roughness increases on
a bitumen surface and rutting cased by densification of the layer forming the pavement.
Consequently, with in a short period of 2 – 5 year, roughness values can reach vales as
high as 5000 mm / km, necessitating the provision of a light bitumen treatment to restore
original riding quality. The effect is that riding comfort suffers and vehicle operating cost
increase on a flexible pavement
(h) Energy conservation
Under the prevailing world wide concern for energy conservation, a road surface that
leads to energy saving must get precedence. Concrete surface results in less fuel
consumption than bitumen surface in two ways. Firstly, the consistently smooth surface
of a concrete road gives a fuel economy of up to 5%. Secondly, concrete surfaces are
rigid and do not deflect to bowl shapes as a flexible does under a heavy load. When a
deflection bowl is caused, the wheel has to climb over the depression, absorbing energy
losses in the process. It has been found from a recent study in U.S.A. that a saving in fuel
up to 20% is possible by adopting concrete roads in place of flexible pavements. Using
these study results, it has been shown that a concrete pavement pays for it self through
full saving alone in a short period of seven years. When India is reeling under fuel crisis,
this single factor should lead to a decision that all future Expressway pavements should
be in concrete.
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(i) skid-resistance
In a bituminous surface, loss of skid-resistance can be overcome by providing a surface
treatment of suitable properties. In concrete pavements, the original texture can get
smoothened by traffic causing slipperiness. Restoring the texture can then be achieved
by grooving or acid etching. A carefully constructed concrete pavement can retain its
texture for many years.
(j)Imperviousness to water
Because of its dense mass, water can not penetrate through a cement concrete pavement.
If joints are well sealed, ingress of water through them can also be prevented. Concrete
pavements, therefore, enjoy imperviousness to water – a property highly valuable in
regions of heavily rainfall and flood-prone locations. The same cannot be said in respect
of bituminous surfaces. The voids in the mixture, cracks and potholes allow water to
penetrate into the lower layers and the subgrade.
(j) Reflectivity properties
Being light colored, concrete offers good reflectivity property so that night driving
becomes safer. On the other hand, bituminous surfaces are dark colored and do not
reflect the vehicle light or street light adequately.
(l) Conservation of nature’s resources
Road construction consumes nature’s resources in large quantities. Though India has
good reserves of stone, gravel, moorum and sand, yet there are regions where stone
materials are very scarce (e.g. Gangetic plains, Tripura, Mizoram etc.) even where stone
aggregates are available in abundance, reckless use of these materials should be avoided.
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Thus, when there is a choice, a pavement type which consumes the least quantity of
stone materials should get preference.
(m) Availability of binder
Bitumen and cement are the principal blinders for highway construction. Whereas
cement is a fully indigenous product, bitumen is derived from petroleum, much of which,
imported by India. Besides, Indian crude lack in bitumen content. The world wide Indian
crude is becoming more and more difficult as the reserves get depleted. On the other
hand, cement is produced from limestone of which the country has good deposits. The
cement industry in India has now modernized itself and there is a surplus of cement
production even at less than 80 per cent capacity utilization. This is a good opportunity
for introducing cement concrete roads in the country, and there can not be a better
beginning than the expressway system.
(n) Maintenance cost
It has been mentioned earlier that flexible pavements suffer deformations under traffic,
causing, rutting, cracking, raveling and potholing. Deterioration sets in the moment the
road is opened to traffic, necessitating constant maintenance effort. As the riding quality
becomes unbearable for the traffic and as the vehicle operating costs mount, it is timely
for an intervention with a surface renewal course. Perhaps at the end of 10 years, a
strengthening layer might also be needed. The routine maintenance like patch repairs and
surface renewal can cost up to Rs. 20,000 per km of two lane road. As against this,
virtually no maintenance is needed for a cement concrete pavement. The little attention
at joints costs as little as around Rs. 2000 per km. the implications of reduced
maintenance in terms of cost and reduced delay to traffic with a concrete road option are
not inconsiderable.
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(o) Initial cost
Flexible pavements can be constructed in stage. But this is an advantage which can be
availed of only on lower category road, and certainly not on expressways. On
expressways the full requirement of pavement needs to be provided at the start it self.
(p) Design precision
Though recent advances in pavement design have rendered the analysis of stresses and
strains in pavements very precise, the design of flexible pavement is still largely based
on empirical methods. The characterization of various materials in a flexible pavement
difficult. On the other hand, concrete is a material whose properties are well understood,
making it easy to analyse the stresses and strains accurately.
(q) Repairs of utilities
Many utility services like telephone cables, electricity cables, water pipes and sewers are
laid underneath the road pavement. Any repairs to or remodeling of these involves
cutting open the road pavement. This is easily done in a flexible pavement, but is
difficult in concrete roads. In expressway, a little bit of planning can easily get over this
problem, either by laying ducts to accommodate the utilities or by clustering the utilities
at one place across the road where a flexible width can be laid.
(r) Spillage of petroleum products
Concrete is unaffected by spillage of petroleum products, but bituminous surfaces are.
Thus, the dripping of oil from vehicles can cause disintegration of bituminous surfaces
easily.
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(s) Construction technology
To make good pavements for expressways, a high level of technology is a must.
Equipment needed for bituminous construction is by and large being manufactured in
India. It is a good coincidence that concrete paving equipment too is being manufactured
in India to meet the needs of concrete road construction; more modern concrete paving
equipment can also be introduced in the country. Production of high strength concrete is
a well-known process in India and there should be no difficulty to take up concreting
jobs for road construction.
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Chapter 5
Construction of cement concrete pavement
5.1Construction of Pavement slab
Various specifications for construction of cement concrete pavement are listed below.
1 Cement grouted layer
1 Rolled concrete layer
2 Cement concrete slab
1. Cement grouted layer
In cement grouted layer open graded aggregate mix with minimum size of aggregate as
18 to 25 mm is laid on the prepared subgrade and the aggregate are dry rolled. The loose
thickness is compacted to provide 80% of rolled thickness. The grout made of course
sand, cement, water is prepared. The proportion of cement to sand is taken as 1:1.5 to
1:2.5. To provide proper fluidity to grout, wetting agent is added to the mix. The grout is
applied on the surface and is allowed to seep through the aggregate matrix.
2. Rolled concrete layer:
In rolled concrete layer, lean mix concrete is used. Lean mix of aggregate, sand, cement
and water is prepared and laid on prepared subgrade and sub base course. The rolling is
done similar to WBM construction. The loose thickness of concrete is 20% more than
the compacted or finished thickness. Tandem roller is recommended. The rolling
operation is completed before the final setting of cement. Curing is done as per
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conventional method.
3. Cement concrete slab:
There are two modes of construction of cement concrete slab
I. Alternate bay method
II. Continuous bay method
Alternate bay construction method of construction means constructing bay or one slab in
alternation succession leaving the next or intermediate bay to follow up after a gap of one
week or so.
As shown in fig. in alternate bay construction the slabs constructed are in
sequence of x, y, z etc. leaving the gaps of bay x ’, y ‘ ,z ‘etc. This technique provides
additional working convenience for laying of slabs. The construction of joints is easier.
fig.1 Construction method of cement concrete road.
But it has many drawbacks as follows:
(1) Large number of transverse joint is to be provided. This increase the construction cost
and reduces the smooth riding quality of surface.
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(2) During rain, the surface water collected on the subgrade between the finished bays.
(3) The construction is spread over full width of road and traffic has to be completely
diverted.
In continuous bay method all the slab or bay are laid in sequence .i.e x’,y,z’,.
CONSTRUCTION STEPS FOR CEMENT CONCRETE PAVMENT SLAB
1. Preparation of sub grade and sub-base
The sub grade or sub base for laying of concrete slab should comply with the following
requirements; that no soft spots are present in the sub grade or sub base; that the
uniformly compacted sub grade or sub base extends at least 30cm on either side of the
width to be concreted; that the sub grade is properly drained; that the minimum modulus
of sub grade reaction obtained with a plate bearing test is 5.54 kg/cm2.
The sub grade is prepared and checked at least two days in advance of concreting. The
sub grade or sub base is kept in moist condition at the time when the cement concrete is
placed. If necessary, it should be saturated with water for 6 to 20 hours in advance of
placing concrete. Water proof paper may also be placed whenever the cement concrete is
laid directly over the soil sub grade. In such a case, the moistening of the sub grade prior
to placing of the concrete is not required.
2. Placing of forms
The steel or wooden forms are used for the purpose.
The steel forms are of M.S channel sections and their depth is equal to the thickness of
pavements. The section has a length of at lest 3 m except on curves less then 45.0 m
radius, where shorter section is used. When set to grade, the maximum deviation of top
surface of any section from a straight line is not exceeding by 3 mm.
Wooden frames are dressed on side; these have minimum base width of 10 cm pf slab
thickness of 20 cm and a minimum base width of 15 cm for slab over 20 cm thick. The
forms are jointed neatly and are set with exactness to the required grade and alignment.
Sufficient rigidity is obtained to support the form in such a position during the entire
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operation of compacting and finishing that they do not deviate more then 3mm from a
straight edge 3 m in length.
3. Batching of material and mixing
After determining proportions of ingredients for the field mix, the fine aggregate and
coarse aggregate are proportioned by weight in a weigh-batching plant and placed in to
the hopper along with the necessary quantity of cement. Cement is measured by the bag.
All batching of material is done on the basis of one or more whole bag of cement, the
weight of one bag is taken as 50 kg or the unit weight of cement is taken as 1440 kg/m3.
The mixing of cement concrete is done in batch mixer which will ensure a uniform
distribution of materials through out the mass, so the mix is uniform in color and is
homogenous.
The batch of cement, fine aggregate and coarse aggregate is lead together in to the
mixture. The water for mixing is introduced in to the drum within the first 15 second of
mixing. The mixing of each batch is commenced within one and half minute after all the
materials are placed in mixture.
4. Transportation and placing of concrete
The cement concrete is mixed in quantities required for immediate use and is deposited
in soil sub grade or sub base to required depth and width of the pavement section within
the frame work in continuous operation. Care is taken to see that no segregation of
materials results while the concrete is being transported from mixture to its placement.
The spread is done uniformly. A certain amount of re distribution is done with shovels.
Needle vibrator is employed in lieu of Roding splicing of the concrete.
5. Compaction and finishing
The surface of pavement is compacted either by means of a power driven finishing
machine or by a vibrating hand screed. For areas where the width of slab is very small as
at the corner of road junctions e.t.c.hand consolidation and finishing may be adopted:
(a) Concrete, as soon as placed, is struck off uniformly and screeded to the crown
and cross section of the pavement to conform the grade.
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(b) The tamper is placed on the side form and is drawn ahead in combination with a
series of lifts and drops to compact the concrete.
Floating and straight edging
The concrete is further compacted by means of the longitudinal float.
The longitudinal float is held in a position parallel to carriageway center line and passed
gradually from one side of pavement to the other. After the longitudinal floating is done
and excess water gets disappeared, the slab surface is tested for its grade and level with
the straight edge.
Belting, brooming and edging
Just before the concrete become hard, the surface is belted wit a two ply canvas belt. The
short strokes are applied transversely to the carriage way.
After belting, the pavement is given a broom finish with fiber broom brush. The broom is
pulled gently over the surface of the pavement transversely from edge to edge. Brooming
is done perpendicular to the centre line of pavement.
Before concrete develop initial set, the edge of the slab are carefully finished with an
edging tool.
6. curing of cement concrete
The entire pavement of the newly laid cement concrete is cured in accordance with the
following method:
Initial curing; the surface of the pavement is entirely covered with burlap, cotton or jute
mats. Prior or being placed, they are thoroughly saturated with water and are placed with
the wet side down to remain in intimate contact with the surface.
Final curing; the final curing is done with the any one of the following method:
Curing with wet soil exposed edges of the slab are banked with a soil free from stone is
placed. The soil is thoroughly kept saturated with water for 14 days.
Impervious membrane method; use of an impervious membrane which does not impart a
slippery surface to the pavement is used. Liquid is applied under pressure with a spray
29
nozzle to cover the entire surface with a uniform film. It hardens with 30 minutes after
the surface finishing.
When the concrete attains the required strength or after 28 days of curing the concrete
road is open to traffic.
(Source: 5)
5.2 Construction of joints
Design of joints
Need for joints
Concrete pavements are subjected to volumetric changes produced by temperature
variation, shrinkage during setting and changes in moistures content. If a long slab is
built, it is bound to crack can only be built if it is divided into mall slab by interposing
joints. These joints will then ensure that the stresses developed due to expansion,
contraction and warping of the slab are with in reasonable limits.
Types of joints:
Joints concrete slab are of four types
1. Expansion joints
2. Contraction joints
3. Warping joints
4. Construction joints
5. Longitudinal joints
Requirements of joints:
Before the detailed description of each type of joint is given, it is appropriate to outline
the general requirement of all types of joints. They are:
1. The joint must permit movement of the stabs without restraint.
2. The joints should not unduly weaken the slab structurally and the load should be
transferred from slab to anther effectively.
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3. The joints must be sealed to exclude water, grit and other external matter.
4. The riding quality of the pavement should not be impaired.
5. The construction of the joints must interfere as little at possible with lying of the
concrete.
1. Expansion joints:
Expansion joints, as the name itself signifies, are intended to provide space in the
pavement for expansion of the slabs. Expansion takes place when the temperature of the
slab rises above the value when it was laid. It is normally a transverse joint. Expansion
joints also relive stresses caused by contraction and warping. Expansion joints are
omitted altogether in modern practice
2. Contraction joints
When the temperature of concrete falls below the laying temperature the slab contracts.
If a long length of slab is laid, the contraction induces tensile stresses and the slab
cracks. If joints are provided at suitable intervals transversely, the appearance of cracks
at places other than the joints can be eliminated. Contraction joist also relieve warping
stresses to some extent.
3. Warping joints
Warping joints, also known as hinge joints, are joints which are intended to relieve
warping stresses. They permit hinge action but no appreciable separation of adjacent
slabs. Warping joints can be longitudinal or transverse. A major difference between the
warping joints and the expansion or contraction joints is that in the former appreciable
changes in the joints width are prevented.
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4. Construction joint
A construction joint becomes necessary when work has to be stopped at a point where
there would be otherwise no other joint. It is advisable to plan a day’s work such that the
work stops at a contraction or expansion joints. Such joints should be regular in shape,
by placing a cross-form in position. The reinforcement should be continued across the
joint. A groove in the joints with a sealing compound will arrest the entry of foreign
matter and desirable.
5. Longitudinal joints
When the pavement width is more than, say 5 m, it is necessary to provide a longitudinal
joint and construct the pavement in strips. These joints allow for warping and uneven
settlement of the sub grade. The very purpose of the longitudinal joints being warping
stresses and uneven settlements, it is very necessary to provided for some form of load
transferring device.
Spacing of joints:
The spacing of joints is governed by a number of factors such as (1) temperature
variation, (2) thickness of slab and (3) amount of reinforcement provided. The usual
practice in respect of reinforced cement concrete slabs is to space joints at 7.5-25 m and
to make every third or fourth joint an expansion joints. The remaining joints are made
contraction joints.
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Fig . 2 Expansion joint
Fig . 3 Tongue and groove Warping joint
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Fig . 4 Butt type longitudinal joint with tie bar
Fig . 5 Dummy contraction joint
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Chapter 6
Economics of concrete and flexible pavement
6.1 Comparison of initial cost
Various studies have been made in India comparing the initial cost of flexible and rigid
pavements. A fresh review is needed because the cost of material and the other input
undergone changes.
Material costs, particularly cost of stone aggregates, cement and bitumen affect the cost
of pavement. For the purpose of comparison, the cost of materials considered as given in
table 1. Since stone material costs very widely across the country four cases have been
considered. The rates of other material are as per current market values. Modern
equipment has been assumed, with approximate usage charges with suitable increase to
account for current costs. The computations of cost have yielded very useful formulae
which can readily give the cost of the two pavement types for expressways. These are
given in table 2. Table 3 gives a summary of the costs. Table 1 gives summery of
pavement thickness.
It is seen that:
(1) when stone material are costly, case 3 and case 4, rigid pavements are invariably
cheaper except for CBR of 7 in case 3. An economy of Rs 2 – 15lakhs per km is
possible, depending upon the soil conditions.
(2) When the soil condition are poor (CBR 2), rigid pavement emerges as the cheaper
alternative through out the country(except case 1)
(3) When the aggregate are cheap (case 1) and the soil condition are good (CBR 5 and
7), rigid pavements are costlier than flexible pavements.
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Table 1: Pavement thickness
Flexible pavement thickness in (mm)
Sub-base Macadam baseWet mix
Dense BituminousMacadam
AsphelticConcrete
Total
CBR:2 690 250 120 40 1100
CBR:5 410 250 120 40 820
CBR:7 330 250 120 40 740
Rigid Pavement Thickness (mm)
(For all CBR values) Sub base of Lean concrete Pavement in M-40 concrete
100 300
Table: 2 Cost of materials
Material Case1 Case2 Case3 Case4
Gravel (cost per cum) Rs 100 Rs 125 Rs 150 Rs 175
Sand (cost per cum) Rs 100 Rs 125 Rs 150 Rs 175
Stone aggregates 40 mm Rs 150 Rs 175 Rs 200 Rs 225
Stone aggregate 20 mm Rs 175 Rs 200 Rs 225 Rs 250
Stone aggregate 10 mm Rs 200 Rs 225 Rs 250 Rs 275
Stone dust 10 mm down Rs 100 Rs 125 Rs 150 Rs 175
Cement (Rs per bag) Rs 85
Bitumen (Rs per tonne ) Rs 3000
Steel (Rs per tonne) Rs 12000
Lime ( Rs per tonne) Rs 500
(source:3,4)
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Table: 3 Formulae for costs of expressway pavements
(Rs per km, 4 lanes )
Flexible Pavement
CBR:2 Cost = 6472 G + 379.4 S1 + 2686.6 S2 + 2095.8 S3 + 3819.2 S4 + 6472 S5
+ 265.4 B + 67.2 L + 16,53,540
CBR:5 Cost = 5740 G + 379.4 S1 + 2686.6 S2 + 2095.8 S3 + 3819.2 S4 + 5740 S5
+ 265.4 B + 67.2 L + 15,59,460
CBR:7 Cost = 3095.4 G + 379.4 S1 + 2686.6 S2 + 2095.8 S3 + 3819.2 S4 + 3095 S5
+ 265.4 B + 67.2 L + 15,32,580
Rigid pavement
All CBR values Cost = 2660 S1 + 1932 S2 + 460 S3 + 896 S4 + 1890 S5 + 39,774C +
1809ST + 5,08,219
Table: 4 Comparison of initial cost of flexible and rigid pavements for expressway
(Rs per km, 4 lanes)
Pavement type Aggregate
Cost:
Case1 Case2 Case3 Case4
CBR: 2
Flexible 5.1 5.7 6.2 6.8
Rigid 5.2 5.2 5.2 5.2
CBR: 5
Flexible 4.9 5.4 5.9 6.4
Rigid 5.2 5.2 5.2 5.2
CBR: 7
Flexible 4.3 4.7 5.1 5.4
Rigid 5.2 5.2 5.2 5.2
6.2 Life-cycle costs:
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Lifecycle costs of pavements are a better yardstick to judge the suitability of pavements
the initial cost alone. Flexible pavement needs periodic maintenance of much higher
order than concrete pavements. They also need some renewal course (at least 25 mm
thick aspheltic concrete) at every 10 th years. At the end of 20 years, which is the design
life of flexible pavement, a substantial overlay is needed this may be of order of 120mm
DBM and 40 mm AC . considering these additional costs, and discounting them to their
present value at a discount rate of 12 percent, the life cycle costs for period of 40 years
and at present value for the two pavements are given in table. The maintenance costs are
assumed as Rs 40,000 per Km for bituminous pavements and Rs 4000 per Km for
concrete pavements.
The conclusion from life cycle cost analysis is that concrete rods will able to bring about
considerable saving over the design period for all cost of aggregates and all soil
conditions
Added to the above savings are the savings in fuel, which are also of a very high order.
Table: 5 Comparison of life-cycle cost of flexible and rigid pavements for expressway
(Rs per km, 4 lanes)
Pavement type Aggregate
Cost:
Case1 Case2 Case3 Case4
CBR: 2
Flexible 5.8 6.4 6.9 7.9
Rigid 5.2 5.2 5.2 5.2
CBR: 5
Flexible 5.6 6.1 6.6 7.1
Rigid 5.2 5.2 5.2 5.2
CBR: 7
Flexible 5.0 5.4 5.8 6.2
Rigid 5.2 5.2 5.2 5.2
(source:3,4)
Chapter 738
Conclusion
Cement concrete have number of advantages over flexible pavement for adoption on
expressways. Adequately design and properly constructed concrete pavement have good
functional stability, long service life and very little maintenance needs. The special
requirement viz. structural mechanism of concrete, environmental mechanism of paving
concrete and rigidity of paving concrete needs to be adequately meet to realize the full
service potential of concrete pavement for expressways.
As regards cost, they compare very favorably with bituminous pavements even in initial
cost. When whole life-cycle costs are considered, their cost advantages is very attractive.
As an added benefit, they give fuel economy.
Hence, concrete pavements enjoy many advantages and can be a good specification for
India’s Expressway programme.
References
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(1) Kadiyali L. R. “Principles and practice of a highway engineering” Khanna Tech.
Publications, Delhi, 1989.
(2) “Road user cost study in India, final report,” central road research institute, New
Delhi 1982.
(3) “Modernisation of India’s road through cement concrete pavement,” cement
manufacturers’ association, New Delhi, 1988.
(4) Chakravarty, S.M.and Kadiyali, L.R., “Economics of concrete roads, Indian concrete
journal”, Bombay, 1989.
(5) “Highway engineering” by S.K.Khanna and C.E.G.Justo Nem chand Publication
2000.
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