Concrete Block Pavements for Roads
Braje rajen ndra
Singh,
Chief
Consultant,
Cement
Manufacturers’
Association,
New
Delhi.
Roads are the lifelines for a nation. A good network of roads is vital for a developing country to become a developed one, since trou troubl blee-fr free ee
move movem ment ent
of
goo oods ds
and and
peo people ple
is
one one
of
the the
most most
impo import rtan antt
feat featur ures es
of
a
matur ature e
econ econom omy. y.
Road surfaces are of two types. Unpaved surfaces include earthen (reinforced or unreinforced), gravel and Water Bound Macadam (WBM). Paved surfaces can be flexible (various types of bitumen or tar), rigid (concrete, stone, brick etc.) or a combination of the two
types.
Rigid Rigid concrete concrete pavements pavements can be construct constructed ed in a variety variety of ways ways – plain plain jointed jointed concrete, concrete, fiber–reinfor fiber–reinforced ced concrete concrete,, roller roller compacted concrete, continuously reinforced concrete, pre-stressed concrete and concrete block paving. It is proposed to discuss the last-named i.e. concrete block paving, in this article, as the technique has certain unique advantages, advantages, which make it superior to the
others
especially
for
city
roads.
The concept of block pavements for roads is not new. Even 5000 years ago, brick pavements for highways were commonly used, as it can be seen in the old ruins in the West Asian Region, which was earlier known as Mesopotamia. Evidence of such pavements using clay bricks laid in coal tar mortar, can still be seen in Babylon and surrounding surrounding areas, where as early as 3000 BC, the earliest use of coal tar in road construction was recorded. The use of brick pavements for road construction, in the ancient Indus Valley civilization of our country, is also a proven fact. Nearer home, some recent excavations of old road works at Fatehpur Sikri near Agra have revealed that about 500 years back, hard stone blocks set with lime mortar were used for paving purposes at that time. In this context, it is interesting to note that the stone used there for purposes of paving roads was brought from outside the region and had a higher resistance to abrasion than the local stone variety commonly used in buildings near the site of excavations. It is thus abundantly abundantly clear from the properties of road building materials used then, that due importance was given to the wear and tear and damage caused by wheels of chariots, horses’ hooves and horse driven vehicles, to stone pavements. For paving purposes, higher quality stone was, therefore, imported from long distances. The importance attached to interlocking of stones and wedge action action for improved improved strengt strength h and stability, stability, is also also evident evident from the construct construction ion techniqu techniques es adopted adopted then, as revealed revealed by the excavations
at
Fatehpur
Sikri.
It is therefore not quite clear as to why in India, the ancient concept of block pavements has not been duly developed over the centuries to take the shape of modern block paving techniques, as it has in European nations, U.S.A., and some other countries. The early city streets in European countries, particularly in the Nitherland, were paved with cobble stones of about 100 to 150mm diameter which were taken from river beds, and laid on a layer of sand. Due to their rough and uneven surface characteristics, these were, in later years, replaced by stone setts (i.e. stones in the shape of squares or rectangles) generally made of granite, about 90 to 180 mm thick and laid 45° to the road axis in a stretcher or herringbone pattern. The joints in good quality stones were less than 10 mm wide, while in poor quality stones these were about 20 mm wide. Later on, in the 20th Century, such joints were sealed in their lower portions with sand, the upper 40 mm of the joint being filled with limestone dust mixed with bitumen. Due to the high cost of stone sett pavements, whenever the road surface started wearing out, recycling was resorted to by merely turning over the stone to expose a new face to traffic. Alternatively, the sett could initially be shaped in the shape of a cube, so that all six faces could be used in turn to carry traffic, which saved the cost of re-laying the pavement with fresh stones each time one side got worn out. In order to reduce the noise created by the steel or wooden wheels and horses’ hooves moving over stone sett pavements, the stone setts were replaced in some cases by blocks of wood, 125 to 250 mm in length and 75 to 100 mm square in cross-section. These were laid on end, with the grain running vertically, and bedded on a three cm thick bituminous mixture. However, these wooden blocks proved to be slippery and noisy when wet, because of their high absorptive characteristics. Hence, the technique was abandoned with the advent of modern pneumatic-tyred motor vehicles.
Separation of areas clearly marked by using colored blocks
In several European countries, vitrified (i.e. fired at high temperature) bricks have been used for the past two centuries on city streets, mainly for pedestrians, while stone sett pavements were used for carrying wheeled traffic. The durability of ordinary clay brick pavements in ancient times, like in Pre-aryan India, was of a low order and so they were not very popular. It was only after vitrified bricks came into being, did these find a wider application. In areas, where hard stone metal is scarce and therefore needs to be carted from long distances, while suitable type of clay is locally available (like in parts of Uttar Pradesh), good quality overburnt clay bricks have been widely used for paving purposes. Cost-wise, paving bricks were found, generally, to be more economical than stone setts. Usually the paving bricks used in Europe and in India were about 200 mm long, 100 mm wide and 80 mm deep. Brick pavements generally had a service life of less than 20 years; but in Hungary, where high quality bricks were made from clay with high lime content, moulded in steel forms under high pressure and fired at high temperature, brick pavements gave a service life of even 30 years or more. The most extensive use of brick pavements appears to have been in Holland. However, with high speed and high load intensity traffic, the brick pavements have gradually faded, giving way to the modern high strength concrete
block
pavements.
As an improvement on the use of stone setts the use of precast concrete blocks for paving purposes dates back to the end of 19th century. Their size initially was around 240 mm x 120 mm x 80 mm, nearly the size of a standard building brick. To start with, the cost of bricks and concrete blocks was about the same, but with increasing mechanization and lower energy consumption, concrete blocks were in due course of time, found to be more economical than bricks. In the middle of the last century, just after the Second World War, the acute shortage of bricks for building purposes gave a further fillip to the extensive use of concrete blocks for road paving purposes. The main advantages of the latter were better uniformity in concrete blocks compared to stone setts or bricks (there was no necessity of dressing the faces), higher strength, higher abrasive resistance and eventually, lower cost in comparison to both, stone setts and paving bricks. In the initial stages of evolution of using concrete blocks for roads, the same shape and dimensions as of paving bricks were adopted. Later, while still retaining the length, breadth and depth proportions of building bricks, the shape of concrete blocks was dentated (i.e. provided with tooth like projections on one sides and matching cuts on the other) to provide key-ins with adjoining units. Further alterations in shape and size were brought about, to optimize performance under traffic and to permit convenient mechanical block laying at the same time.
Typical cement concrete block pavement
During the latter half of the 20th Century, the growth of block paving has been fairly high in Europe, as indicated by the following representative Netherlands: Germany: Britain:
The The
figures: The
annual
annual annual
block
concrete use
of
paving
usage block
in
production block
paving
rose
manufacture
increased
over
seven
fold
increased 5
from four
times
2
times
from
to
14
from
2
to
1.3
0.25
mill ion to
8
sq. million
million
sq.
metres. tonnes. metres.
While earlier on, concrete block paving was already an accepted road building technique in Central and South America, and in South Africa, it was introduced in the 1960s in UK, Canada, USA, Australia, New Zealand and Japan. More recently, it is catching up in the Gulf
Region
and
other
parts
of
Asia.
The growing popularity of concrete block paving has resulted in a large number of various types of such paving systems being marketed, as well as world wide research on the subject. International conferences on this theme are also being held periodically. Concrete pavements for roads have several advantages over bitumen pavements, such as long life, negligible maintenance, user and environmental friendliness, usage of indigenous material and fuel saving. Over and above all these, concrete block pavements have additional advantages, such as no requirement of machinery for laying, they can be opened for traffic immediately, after laying,
they
provide
convenient
access
to
utilities
and
they
possess
factory- controll ed
qual ity.
Concrete paving block pavements have been thereby successfully used in India on city streets; residential streets and parking areas; markets, service stations and bus terminals. They have also been used for secondary roads in the northern parts of our country.
Cross-section of concrete block pavement for heavy traffic
Many city streets in major metropolitan cities of Europe, Australia, Central and South America, South Africa and Japan are now paved with concrete blocks. Such pavements are specially relevant on city streets in view of the ease with which access can be made to underground services like water pipes, cable ducts, telephone lines etc. Besides, block pavements can successfully carry heavy and slow moving traffic, at the same time keeping their maintenance economical, as also convenient. Pedestrian crossings with coloured blocks can be easily delineated and hence pavement markings will not be necessary. At signalized intersections, where heavy vehicles have to frequently apply brakes to stop and accelerate again to start, the tangential shear forces can be much more readily taken up by concrete block pavements as compared to the conventional bituminous pavements, which later tend to deform under the high stresses generated. A similar situation exists at roundabouts. In commercial/business and shopping centres, block pavements have been found successful due to their ability to carry heavy traffic at relatively low maintenance costs, with the least
disruption
to
traffic
during
maintenance
work.
In several developed countries, streets in and around residential areas and in housing complexes are increasingly being paved with concrete paving blocks, as these can be easily removed and reinstated after making any changes in underground public utility services as may be required for repairs, changes or upgradation, and roads can be opened for heavy traffic directly after construction, without having to wait for curing or setting of pavement materials. Moreover, the maintenance cost of such streets are low. Such block pavements are therefore known to enhance the property value of surrounding houses or building lots. Thus the slight increase in pavement construction cost by using concrete blocks, can be recovered through the increment in cost of houses/land. Block pavements also enhance the aesthetics of a residential area.
Pattern of precast block pavement
Concrete paving blocks have been widely used in streetside and other car parking areas, since their deterioration due to weathering is of a much lower order in comparison to conventional bituminous pavements and maintenance costs are also significantly lower. By using different colours and textures, the parking areas, access lanes and pedestrian crossings can be clearly and effectively demarcated
on
a
permanent
basis,
instead
of
repainting
of
lines
having
to
be
resorted
to,
every
year.
In market areas, concrete block pavements on approaches and in the market itself have been constructed in several countries to provide surface drainage, as these areas are to be washed daily. At such places darker colours of blocks are recommended so as not to be vulnerable to stains by market produce/foodstuff. These block pavements are designed to carry loaded trucks and have the
advantage
that
even
during
maintenance,
no
disruption
to
traffic
is
caused.
The use of block pavements in petrol stations/service centres has become popular in South Africa and Australia, besides Europe, since the concrete blocks, unlike conventional bituminous surfaces, remain unaffected by fuel/oil spillage so common in petrol stations/service centres. Different companies tend to use a specific colour identifiable with them, at all their stations/centres. Use of concrete block pavements has special relevance at bus stops, bus terminals and bus service depots. Firstly, the high stresses caused by buses and channelised slow moving traffic can be better withstood by concrete paving blocks in comparison to bituminous pavements; and secondly, frequent stopping and starting at bus stops, which causes rutting and shoving of bituminous pavements, does not cause any such problems in concrete block pavements. Also, the spillage of fuel and oil, associated with bus traffic and at bus terminals/ service centers do not pose any problem if concrete blocks are used instead of bituminous surfacings. These favourable aspects have made the concrete block pavements for bus depots/bus terminals and service centres very popular. When compared to the utilization of block paving technology in developed countries in Africa, Asia, Europe and USA, and even in less developed and developing countries of the World, it is to be admitted that our country is lagging far behind. In India, just a small beginning has been made in this direction although there appears to be an increasing awareness for the vast potential that this versatile technology holds for the country. With the rapidly developing economy of India, improved and modernized industrial activities are inevitable and endless possibilities exist in these for utilizing the block paving technology for roads sidewalks, parking lots etc.
Cement concrete blocks are proof against damage due to oil spills
In the transport sector, concrete block pavements have tremendous possibilities. In the roads sub-sector: city streets, particularly at signalized intersections, bus stops, terminals and service centres; side walks and cycle tracks; parking areas; roads in residential areas; market centers, commercial complexes and community centers, petrol stations etc. can be paved with concrete paving blocks in preference to conventional bituminous materials, thus overcoming several of the present-day problems with which all road users in India are familiar. Drawing on the experience of other countries, this technology can be utilized for lower maintenance cost, least disruption of traffic with the flexibility of easy alterations to modified designs, easy access to underground services, and practically immune to weathering deterioration and fuel/oil/ lubricant spillage. Moreover, it can save the country significant amounts of
foreign
exchange
incurred
on
bituminous
materials
which
come
almost
exclusively
from
imported
crude.
For railways and airports also, immediate use can be made on railway platforms and on the aprons/taxiways at airport terminals besides
internal/access
roads
in
railway
stations
and
airports.
For heavy duty paving, the concrete block technology can be adopted to advantage on roads in industrial areas, loading docks and ramps,
approaches
to
shipyards,
warehouses
and
godowns,
and
military
bases.
In the building sector, the concrete paving blocks in different shapes, sizes, colours and texture would be an architect’s delight, as it is
in
several
countries
abroad,
for
paving
of
driveways,
walkways,
parking
areas,
etc.
Of special importance in the Indian context is the aspect of quality control. Being pre-cast in a central plant, much more effective quality control can be exercised on paving blocks than what is possible for pavements laid at the site. This is particularly so compared to when conventionally used bituminous materials are involved, and heating of bitumen as well as aggregates is normally done at controlled temperature which often has practical difficulties. Furthermore, the technology can be suitably modified from the one
being
practised
in
the
developed
world,
to
make
it
reasonably
labour-intensive.
As the studies abroad indicate, the energy consumption is lower in case of concrete paving blocks in comparison to when road construction is done through the use of bituminous materials. Also, maintenance efforts and related maintenance costs are lower; aspects which are vitally important in the Indian context. Additionally, the foreign exchange component of costs in respect of concrete paving blocks will be significantly lower in comparison to paving with bituminous materials. This is because bitumen is obtained from crude oil, and Indian crudes, being non-asphaltic in nature, do not yield bitumen. All the bitumen we use, comes from imported crude oil.
References
•
IRC: SP: 63-2004 Guidelines for use of Interlocking Concrete Block Pavement
•
Specifications and Standards for Concrete Paving Blocks, Proceedings of the Third International Conference on Concrete Block Paving, Rome.
•
Cement and Concrete Association of New Zealand, Interlocking Concrete Block Road Pavements.
•
Cement Manufacturers’ Association, Handbook on Cement Concrete Roads.
•
Central Road Research Institute, A Note on the Old Road System at Fatehpur Sikri Unearthed during Recent Excavations.
•
Shackel, B., Design and Construction of Interlocking Concrete Block Pavements, Elsevier Science Publishers.
•
Lilley, A.A. and Walker, B.J., Concrete Block Paving for Heavily Trafficked Roads and Paved Areas, Cement and Concrete Association.
