India has a total road network of over 5.8 million km comprising national highways, state highways, expressways, and urban and rural roads. The total length of highways constructed during 2018-19 was 10,855 km, as against 9,829 km achieved in the previous year. Overall, road projects exceeding 52,000 km in length are in progress. The increasing level of activity in the sector will lead to a rise in demand for construction materials as well. In this context, the use of alternative materials can play a major role in reducing costs, improving performance and making construction more sustainable.
Need for alternative materials
Roads are typically constructed in distinct layers composed of materials such as asphalt, soil, stone aggregates, bitumen and cement.
However, natural resources that have been conventionally used for construction are depleting quickly. Consequently, the cost of extracting good quality natural material is increasing. The environmental costs associated with quarrying are also substantial. With rapid population growth and industrialisation, there has not only been an increase in the demand for traditional road construction materials but also in the quantity of waste generated.
With advances in technology, the use materials such as fly ash, demolition rubble, municipal and industrial waste, etc., offers economically viable and sustainable alternatives for road construction. This helps in recycling of materials which would otherwise have been disposed of as waste. Studies have shown that the performance of these materials is at par with conventional materials, and even better in some cases. Thus, the use of alternative materials for construction offers benefits to both the industry and the community.
Different materials being used in construction
The use of various alternative materials for construction of roads is being increasingly encouraged and promoted. In 2015, the Ministry of Road Transport and Highways (MoRTH) issued guidelines stating that new or alternative materials proven in India or abroad will be deemed to be accredited for adoption in the sector provided the developers/promoters furnish certified performance reports and establish a permanent base in India to show a long-term commitment towards innovative infrastructure development in the country.
The ministry has also implemented a value engineering programme to promote new technologies and materials in highway projects. The main aim of the programme is to use innovative technology, materials and equipment to reduce the cost of projects and make them more environment friendly. The MoRTH has also constituted a national panel of experts for approving proposals under the programme.
Some alternative materials whose use has gained traction in the industry are:
It is estimated that India generates around 15,000 tonnes of plastic every day, of which only 9,000 tonnes is recycled. The rest is burned or ends up in landfills causing environmental problems. An innovative solution to combat the increasing plastic waste is to use it for building roads. Both plastic and conventionally used bitumen are petroleum products that bond well when added to molten asphalt. This makes the road more durable, increases its life and also its ability to carry weight.
A 2009 study carried out by the Central Pollution Control Board confirmed that polymer-coated bitumen roads performed better despite their age as compared to most of the bitumen roads under similar conditions. The roads that used plastic did not develop any small cracks or potholes.
For construction of roads using plastic, the plastic waste is first shredded and then heated at 165 °C. The pieces are then added to bitumen mix which is heated at 160 °C. The plastic moulds with the bitumen resulting in a shiny tar surface. This final mix is used for road construction. A regular road requires 10 tonnes of bitumen for each km, while a plastic road requires 9 tonnes of bitumen and 1 tonne of waste plastic for coating. So, for every km, the plastic roads save 1 tonne of bitumen leading to cost savings of around Rs 50,000.
In 2015, the government made it mandatory for road developers to use waste plastic along with bituminous mixes for road construction within a 50 km radius of any city with a population of over 0.5 million, to overcome the growing problem of disposal of plastic waste.
Major cities such as Delhi, Mumbai, Chennai and Pune have actively started using shredded plastic waste in road construction. Other cities like Jamshedpur, Indore and Noida are also building plastic roads. Till 2018, over 100,000 km of roads had been built using plastic waste. National highway projects where plastic has been used include six-laning of the Hosur-Krishnagiri section of National Highway (NH)-7 and four-laning of NH-45 near Tindivanam and near Ulundurpet.
Geosynthetics are man-made polymers that are increasingly being used in the construction of roads and highways. They are of particular use in undertaking construction in difficult terrains such as marshy stretches and soft deposits. Geosynthetics include geotexiles, geogrids, geomembranes, geonets, geocomposites, geo-cell, geomats, paving fabric and paving grid.
They are generally used as separation, filtration, drainage, erosion control, reinforcement in pavement and impermeable barriers in waterlogged areas. The use of geosynthetics considerably improves the strength of weak soil strata. It also reduces the consumption of aggregates by 40 per cent in base and sub-base layers. The use of geosynthetics leads to cost savings, better performance of roads and a lower carbon footprint.
In July 2018, the MoRTH issued guidelines to further promote the use of geosynthetics in road construction. Under the guidelines, state governments have been advised to include various types of geosynthetics in their schedule of rates so that the estimated cost of the project including geosynthetics can be worked out.
Fly ash is a fine powder that is a by-product of coal combustion in thermal power plants (TPPs). Fly ash reacts with lime in the presence of moisture to form cementitious compounds. This is known as pozzolanic activity. The pozzolanic property of fly ash enables it to be used in concrete to partially replace cement.
More than 170 million tonnes of fly ash is generated in TPPs in the country. Its generation is expected to grow further as coal will continue to remain a major source of energy in the coming years. Most of the ash generated from the power plants is disposed of in the vicinity of the plant as waste material covering several hectares of valuable land. If not managed well, it can also create environmental challenges.
The use of fly ash in road projects for construction of embankments and stabilisation of the sub-grade and sub-base not only facilitates the disposal of fly ash but also provides significant benefits in terms of engineering and economic considerations. Currently, only 5 per cent of the fly ash generated is used in the road sector.
The Ministry of Environment, Forest and Climate Change has issued several notifications for fly ash utilisation, the key among which was issued in September 1999. Subsequently, this was amended through notifications in August 2003, November 2009 and January 2016. As per the guidelines, it is mandatory to use fly ash in the construction of roads and flyover embankments within a radius of 300 km from a TPP. Further, the cost of ash transportation for road construction projects within a radius of 100 km will be borne by the TPP itself while that between 100 km and 300 km will be shared equally between the road developer and the TPP. However, it has been observed that the major reason for low usage of fly ash in road construction activities is the reluctance on the part of the TPPs to bear the cost.
Another construction material that is slowly gaining traction is geopolymer concrete. It is an inorganic polymer composite formed by alkali activation of fly ash and furnace slag. It is an eco-friendly construction material and an alternative to portland cement.
Several new construction materials have emerged in the industry. However, their offtake by developers remains limited despite various guidelines in place for their promotion. Therefore, proactive steps including strong government intervention need to be taken to further increase their use in the road sector. w
(With inputs from a presentation by Sanjeev Kumar, Chief Engineer, MoRTH, at a recent India Infrastructure conference)