Concrete Block Pavements for Roads

    Brajendra Singh, Chief Consultant, Cement Manufacturers’ Association, New Delhi

    Road surfaces may be paved or unpaved. Paved roads have flexible, rigid or a combination of the two types of surfaces. Rigid pavements consist of several types. They could be made from concrete; they could be brick-paved or cobble stoned. They could also be sheer rock, as my personal experience has shown. Several years ago, I was the engineer-in-charge of carving out a road from the highly mountainous terrain of the Spiti Valley. Long stretches of the proposed road passed through sheer cliffs made out of solid rock. Cutting the alignment in such areas with individual hand-held, petrol motor powered drills, while suspended from ropes in mid-air, was an extremely instructive experience, but its details are not relevant to this article. What is relevant is that after the required width (normally 3 to 5 metres) had been scooped out of the virgin rock, we just did not have any material to lay on the road surface. So we let the cut remain as it were, the uneven but hard rock along its base acting as the road surface.

    Reverting back to the topic of this article, concrete roads can be constructed in a variety of ways –plain jointed concrete, fibre– reinforced concrete, 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. Relevant to this article. What is relevant is that after the required width (normally 3 to 5 metres) had been scooped out of the virgin rock, we just did not have any material to lay on the road surface. So we let the cut remain as it were, the uneven but hard rock along its base acting as the road surface. Reverting back to the topic of this article, concrete roads can be constructed in a variety of ways – plain jointed concrete, fibre– reinforced concrete, 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.

    The concept of block pavements for roads is not new Even 5000 years ago, brick pavements for highways were commonly used, as can be seen in the old ruins in the West Asian Region, which was earlier known as Mesopotamia. Evidence of such pavements using bricks laid in bitumen mortar, can still be seen in Babylon and surrounding areas, where as early as 3000 BC, the earliest use of bitumen 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, had a higher resistance to abrasion than the local stone variety commonly used in buildings near the site of excavations. It is abundantly clear from the properties of road and building materials used then, that due to 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 for improved strength and stability, is also evident from the construction techniques adopted then, as 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 developed to take the shape of modern block paving techniques, as it has in Europe, U.S.A. Australia and some other countries. The early city streets in European countries, particularly in Holland, were paved with cobble stones of about 100 to 150 mm 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 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 stone these wereabout 20 mm wide. In the 20thCentury, these joints were sealedin their lower portions with sand, the upper 40 mm of the joint beingfilled with limestone dust mixed with bitumen. Often the stones were laid in curves of about 1.5 mradius, the largest stones laid inthe center. 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 o rmaking it 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. 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 block of wood, 125 to 250 mm in length and 75 to 100 mm square in cross-section. Thesewere laid on end, with the grain running vertically, and bedded on 3 cm thick bituminous mixture. However, these proved to be slippery and noisy when wet so, because of their high absorptive characteristics, the technique was abandoned with the advent of modern pneumatic-tyred motor vehicles.

    In several European countries, vitrified 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 brickpavements 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 (fired at high temperatures) came into being, did these find a wider application. In areas, where hard stone metal needs to be carted from long distances while suitable type of clay is locally available (like in parts of Uttar Pradesh), good quality over-burnt 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 highlime content, moulded in steel forms under high pressure and fired at high temperatures, brick pavements gave a service life of even 30 years or more. The most extensive use of brick pavements appears to havebeen 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 date back to the end of 19th century. Their size initially was around 240 mm x 120 mmx 80 mm, nearly the size of a standard building brick. To start with, the cost of bricks and blocks were about the same, but with increasing mechanization and lower energy consumption, concrete blocks were 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, however, were better uniformity in concrete blocks compared to stone setts (thus doing away with the necessity of dressing the faces), higher strength, higher abrasive resistance and eventually, lower cost in comparison to paving bricks. In the first stage 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 to provide key-ins with adjoining units. Further alternations in shape and size were brought about to optimize performance under traffic and to permit convenient mechanical block laying at the same time.

    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 figures.

    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 196 0s 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 factorycontrolled quality.

    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.

    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 colored blocks can be easily delineated and hence pavement markings may not be necessary. At signalized intersections, where heavy vehicles have to frequently apply brakes to stop and again start, the tangential shear forces can be much more readily taken up by concrete block pavements as compared to the conventional bituminous pavements, which tend to deform under such high stresses. 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 cost, with least disruption to traffic during maintenance works.

    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 reinstated after making any changes in underground public utility services as may be required for repairs, changes or up gradation, and can be opened to heavy traffic directly after construction, without having to wait for curing or setting of pavement materials. Moreover, the maintenance costs 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 costs can be recovered through the increment in cost of houses/land. Block pavements also enhance the aesthetics of a residential area.

    Concrete paving blocks have been widely used in street side 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 colors 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 for providing surface drainage, as these areas are to be washed daily. At such places darker colors 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 s o common in petrol stations/service centres. Different companies tend to use a specific color 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 favorable 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 and the rest of 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. 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 experiences 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, practically unsusceptible to weathering deterioration and fuel/oil/ lubricant spillage. Moreover, it can save the country significant amounts of foreign exchange incurred on bituminous materials.

    For railways and airports also, immediate use can be made in railway on the aprons/taxiways at airport terminals besides internal/access roads in railway stations.

    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, colors and texture would be an architect’s delight as 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, particularly compared to when conventionally used bituminous materials are involved, and heating of bitumen as well as aggregates has be done at controlled temperatures. Furthermore, the technology can be suitably modified from the one being practised in the developed world, to make it reasonably labor-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 so 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.

    NBMCW September 2007

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