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Sri Lanka’s economy is heavily oriented towards agriculture and trade, and the country’s transport system is mainly road-oriented. The national road network plays the pivotal role in transporting agricultural produce from rural to urban areas and in distribution of products islandwide. Moreover, efficient highways remain at the top of the infrastructure facilities expected by foreign investors. In this context, an efficient road network is an important requirement for Sri Lanka’s economic growth and social progress. Unfortunately, however, the Sri Lankan road network is not efficient enough "to deliver the goods", adversely affecting economic growth and social progress.

Acting as a roadblock to economic growth and social progress, the poor condition of Sri Lanka’s road network causes several problems such as traffic congestion, road accidents, regular maintenance of roads and vehicles, and wear and tear of vehicles. These problems lead to delays of work, mental and physical agony, waste of material and human resources, and degradation of health and environment.

One of the principal causes of this unfortunate situation is the road surface deterioration, which in turn is mainly due to the use of bitumen (i.e., tar) as the pavement (i.e., carriage-way) material of the roads, requiring regular road maintenance.

The emerging trend of concrete as the most suitable road construction material for Sri Lanka’s road modernisation programme, was highlighted in a presentation by Dr LR Kadiyali, a pioneer in India’s concrete roads, at the Annual Sessions 2004 of the Chamber of Construction Industry (CCI) recently. The following article is based on his presentation and a subsequent discussion with Eng Thilak Silva, Market Development Manager of Holcim (Lanka) Ltd.

Material selection for carriage-way (i.e., pavement) of roads

The carriage-way of a road should:

* Be strong and thick enough to withstand & transfer vehicle loads to the earth

* Provide a safe and comfortable riding surface

* Possess a hard, wearing surface and be durable

* Be economical

The main choices available for carriage-way (i.e., pavement) material are bitumen (i.e. tar) and concrete. In Sri Lanka, majority of the roads are bitumen roads. The main reasons for this choice had been lower initial cost and shortage of cement. The time has now for reconsideration of the choice of carriage-way material because:

* Bitumen is a byproduct of petroleum crude. The global scarcity and the rising prices of petroleum crude can affect the availability of bitumen.

* With the exposure to the tropical weather conditions, bitumen deteriorates, losing its strength. With time, bitumen roads become weaker while the forces they encounter are likely to become higher due to overloading.

* Although bitumen incurs a lower initial cost, it requires regular maintenance, which consumes resources and causes disturbance to traffic on already under-capacity (i.e., overcrowded) roads.

Why concrete is a better choice

When compared with the conventional choice for carriage-way of Sri Lanka’s roads (i.e., bitumen), concrete is emerging as a better alternative due to its superior performance in all respects:

* Durability

* Strength

* Riding quality

* Rider safety

* Environment friendliness

* Financial savings

Durability

A concrete road possesses a higher durability due to two reasons:

* In bitumen roads, the binder is bitumen; in concrete roads, the binder is the cement paste. In concrete roads, the bond between the binder and the aggregate (i.e., stone) is stronger.

* Under tropical weather conditions, bitumen tends to deteriorate, paving the way for potholes. This in turn makes the base course of the road permeable and allows water to seep into the sub-grade, causing the sub-grade to lose its load-bearing capacity. On the other hand, a concrete road with properly sealed joints acts as an impermeable layer, protecting the sub-grade from water. Moreover, concrete does not deteriorate under tropical weather conditions.

As a result, the maintenance requirement of a properly constructed concrete road is limited to the joint sealing once in 5-7 years. However, a bitumen road requires surface renewal once in 3-5 years and periodic overlaying once in 7-10 years.

Strength

Concrete is a material that develops its strength with time. Since its strength development is significant up to 28 days since being cast, the 28-day strength is used for the design. It is therefore a conservative value. Besides, concrete road design is based on fatigue load principles, enabling concrete roads to withstand overloading.

Riding quality

Unlike bitumen roads, which develop rutting of the surface, concrete roads maintain the initial riding quality for a long time.

Rider-safety

Concrete roads offer a better carriage-way surface during its design life of up to 30 to 40 years as opposed to the bitumen road surface which loses its surface quality in a few years after resurfacing. Concrete facilitates better roll of tyres. Both in dry and wet conditions, the concrete road surface maintains better skid resistance. However, the initial skid resistance of a concrete road wears down in several years’ time, requiring acid etching or regrooving. Concrete road surface is of lighter colour, increasing the reflectivity at night, enhancing the night visibility. Therefore, with concrete, the rider is safer both during day and night as well as in dry and wet weather.

Environment friendliness

The bitumen carriage-way requires a higher thickness in sub-base and sub-grade, leading to increased consumption of natural resources such as stone and gravel. For the same traffic loads, concrete requires smaller sub-base and sub-grade thicknesses.

On concrete roads, the interaction between the road surface and the tyres causes some noise. However, a modern development of concrete called "whisper concrete" has significantly reduced these noise levels.

Financial savings

Bitumen is a material based on petroleum crude, which is becoming expensive due to the rising demand and restricted supply, mainly due to the instability in the Middle-East. Concrete on the other hand requires cement, which is now available without any shortage unlike in the past.

For the same traffic loads, a bitumen road requires a higher thickness when compared with the corresponding concrete option. Thinner layers with the concrete option means less volume for excavation, less volumes for import to and export from the construction site. Thus, the concrete option reduces construction costs.

Regular maintenance required by bitumen roads incur several types of costs: material costs, plant and labour costs, costs due to regular disruption of traffic. Because of high durability, concrete roads save such costs.

Better riding quality offered by concrete roads reduces the wear and tear of vehicles. Moreover, research has revealed that concrete roads can reduce the fuel consumption of heavy trucks by 15%, which is an important saving in these times of rising fuel costs.

India’s success story

In India, concrete is emerging as the preferred option for highways and streets after the initial concrete road projects gaining the popularity among the Indian road-users. The concrete success stories include the 6-lane Mumbai-Pune expressway, the 4-lane Delhi-Mathura national highways, Indore bypass, city streets in Mumbai, airport taxiways and rural roads.

Summary

An efficient road network is an important requirement for Sri Lanka’s economic growth and social progress. Unfortunately, the efficiency of the road network is not satisfactory, a main reason being the choice of bitumen as the carriage-way (i.e., pavement) material. For Sri Lanka’s road modernisation programme, concrete is emerging as a better option due to its superior performance in all areas such as durability, strength, riding quality, rider-safety, environment-friendliness and financial savings.

Note:

Dr. L. R. Kadiyali possesses a BSc Eng Degree in Civil Engineering from the University of Bombay, a Postgraduate Diploma in Highway and Traffic Engineering from the University of Newcastle Upon Tyne, UK, and a Doctorate from the Regional College of Engineering, Warangal. He has served at the Ministry of Surface Transport, India, in various capacities from Highway Engineer to Chief Engineer, as Study Director for a World Bank funded project on Road User Costs, and as a Consultant to the Asian Development Bank. He has involved in design and implementation of several concrete roads in India. He has published two books and several technical papers. Convener of the Indian Roads Congress Committee on Rigid Pavements, Dr Kadiyali now heads his own consultancy firm in New Delhi.

Eng Thilak Silva (thilak.silva@holcim.com) possesses BSc Eng (Hons) from Moratuwa University and MEng in Construction Management from Moratuwa University in collaboration with Loughborough University of Technology in UK. He is a Chartered Engineer and serves as a Council Member of the Institution of Engineers Sri Lanka (IESL). He has served as Project Engineer at Mahaweli Engineering & Construction Agency, Design Engineer at Development Consultants (Pvt) Ltd, Chief Structural Engineer/Associate at Mihindu Keerthiratne Associates (Pvt) Ltd, Project Engineer (Structures) at Ministry of Defence Engineering Services, Sultanate of Oman, and Chief Engineer at China Geo-Engineering Corporation. Currently, he is Market Development Manager of Holcim (Lanka) Ltd.