Road Construction: A step towards green environment?

How could road construction provide a sustainable solution to use waste materials to our benefit?

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Various demographic and commercial changes in the metropolitan areas emphasize the need for better transportation facilities. As the human cardiovascular system transports blood and distributes nutrients to all parts of the body properly when there are no disruptions in the veins and arteries: a good transportation network is similarly necessary for economic and commercial development. The lack of access to remote areas of a country affects the country’s education, health and provision of social services adversely.

It is an undeniable fact that every construction process gives off two things: the product and the waste. Every day, a large amount of industrial and domestic waste is disposed off in landfills and oceans, creating damaging effects on the environment. The world is already fighting against environmental degradation problems like pollution, global warming and depletion of ozone layer. What if we could find a sustainable solution to use such waste materials to our benefit?

Recently, many research projects like ALT MAT, SAMARIS and POLMIT have been initiated in Europe to test the feasibility of alternative materials in road infrastructure. Traditionally, materials like crushed stones, cement, sand and gravel are used in the construction of roads. But now, certain waste materials such as asphalt pavement, plastic wastes, crushed glass, fly ash, bottom ash, steel slag and mine wastes are under test in the laboratories to check whether the proposed materials are environment-friendly and cost-effective. This can also minimize the use of non-renewable energy resources in road construction, which are expected to become extinct in the near future.

Various properties of these materials are analyzed such as their leaching behavior, hydrodynamic properties and their pH values. Fly ash and bottom ash are produced as a by-product of thermal power stations. The one which rises from the combustion towers is called fly ash and the one which settles down is called bottom ash. They are both toxic and they pose a serious threat to the atmosphere; therefore they are now being used as a filling material in roads and also as a lower-cost substitute for cement.

Fly Ash (Courtesy: daijiworld.com) 

Asphalt is a sticky viscous liquid produced as a by-product of refined crude oil. It is mixed with aggregates such as sand and gravel to produce a strong binding material for road surfacing and compaction. It is cheap, durable and recyclable. It also provides a smooth surface and helps save non-renewable energy sources. However, one disadvantage is that using asphalt as a pavement layer makes the surface prone to premature cracking.

Asphalt (Courtesy: gilsoniteco.com)

Different types of plastic are heated at 170°C and then mixed with hot aggregates such as bitumen. The mixture is then used for road construction. Los Angeles’ Abrasion test showed that plastic-made roads have a prolonged life and are safe from wear and tear for a long time. Soundness test showed that plastics also improve the quality and strength of the road. Since plastic is non-biodegradable, its disposal is a major problem.  The burning of these plastic waste materials produces toxic gases which are hazardous to our environment. Therefore, using plastic mixed with bitumen as an alternate material in road construction can reduce the problem of disposal of waste plastics. But toxins present in plastic tend to start leaching after some time.

The overall results of these European cooperative research programs came out to be positive to a good extent. But their employment is limited due to the perception of plastics as a “waste material”. Although there is an extensive scope of utilization of waste materials for the construction of roads, a better understanding of these materials is still needed to further encourage their usage on government level. Moreover, these alternative materials lack real field experience as people are not yet fully aware of their applications.

The usage of these materials also encourages recycling of materials and prevents waste productions which are otherwise disposed of in landfills. Appropriate legislation should be introduced to increase the tax on landfill and increase the usage of plastics for road constructions in both developed and developing countries.

 

References:

  1. Coni, F. Annunziata, “The employment of not traditional materials in road infrastructures”, Department of Land Engineering, University of Cagilari, Italy. http://people.unica.it/mauroconi/files/2011/10/coni82full.pdf
  2. http://www.transport-research.info/sites/default/files/project/documents/20040909_172706_52558_alt-mat.pdf
  3. http://samaris.zag.si/documents/sam_ge_de02a.pdf

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