The Indian road sector has witnessed a major turnaround in activity during the past four to five years. The length of the projects awarded and constructed increased at a compound annual growth rate of over 45 per cent during the period 2013-14 to 2017-18. With growing road activity, the demand for construction materials too is bound to increase.
Traditionally, soil, stone aggregates, sand, bitumen, cement, etc., have been used for road construction. However, natural materials being exhaustible in nature, their quantity is likely to decline over time. Thus, countries are looking for alternative materials, and waste is one such option, especially since there has been concern regarding the increasing generation of waste through construction, industrial and household activities globally. Various options are being ex-plored to put the waste to productive use. Road construction has emerged as one such suitable option. The use of these waste materials is also aimed at reducing the consumption of scarce natural aggregates and recycling materials that would otherwise be disposed of as waste.
Like other countries, India too is experimenting with waste materials/by-products such as fly ash, municipal solid waste (MSW), plastic waste, demolition rubble, rubber, and slag for road construction. Among these waste materials, fly ash and plastic waste especially have generated a lot of interest.
The use of fly ash is being increasingly promoted in the road sector, where it is mostly used for the construction of roads, embankments and flyovers. It is also used by the cement industry as a pozzolanic material for manufacturing cement.
The country’s thermal power plants generate a vast quantity of fly ash annually, though a substantial portion of it remains unutilised. As of February 2019, NTPC Limited’s total fly ash availability stood at 542 tonnes. As per industry estimates, fly ash utilisation is in the range of 6-7 per cent in making fly ash-based building products and mine filling, and less than 5 per cent in the construction of roads.
The Ministry of Environment, Forest and Climate Change (MoEF&CC) 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 thermal power plant. Further, the cost of transportation of ash for road construction projects within a radius of 100 km will be borne by the thermal power plant itself while that between 100 km and 300 km will be shared equally between the road developer and the power plant. For a radius of 300 km or more, the thermal power plant will bear the entire transportation cost, as committed under the Pradhan Mantri Gram Sadak Yojana. Meanwhile, in order to ensure optimal utilisation of fly ash as an environmentally sustainable and economically viable product, the government has reduced the goods and services tax on fly ash and its products to 5 per cent.
From 2013-14 to 2017-18, the use of fly ash in the road sector grew from 2.2 million tonnes (mt) to 6.67 mt, a CAGR of around 32 per cent. In 2017-18, around 6.67 mt of fly ash was used for the construction of highways, roads and flyovers. This constituted 3.4 per cent of the total fly ash generated in the country.
NTPC is undertaking road projects at its plants to demonstrate the use of fly ash technology in road construction. The company has recently completed the construction of a fly ash-based geopolymer concrete road at its Dadri power station. It is also in the process of constructing similar roads, spanning a 1.2 km double-lane stretch, at Ramagundam and Farakka stations. In November 2018, NTPC invited bids for the construction of fly ash-based geopolymer concrete roads at all its plants.
Some road projects that have used fly ash:
- The Raichur Public Works Department, in collaboration with the Karnataka State and Central Road Research Institute, undertook the construction of a high-volume fly ash concrete road of 1 km length on an experimental basis, using a 50 per cent replacement level (that is, concrete with a minimum cement replacement level of 50 per cent by fly ash).
- One of the largest producers of cement, ACC Limited constructed roads using high-volume fly ash concrete with a 50 per cent replacement level in Greater Noida and Faridabad.
- A 100 metre stretch (pavement of 7 metres) at Fatehpur Beri, Mehrauli, was constructed with high-volume fly ash concrete utilising 50 per cent cement replacement level.
- During 2013-14, the overall utilisation of fly ash on road construction in Odisha was around 0.28 mt. Further, around 0.1 mt of fly ash was utilised in the National Highway-6 (Sohela- Sambalpur stretch) project.
- In April 2018, the National Highways Authority of India (NHAI) signed an MoU with the Department of Energy, Uttar Pradesh, for transportation of fly ash. Under the MoU, the ash will be transported by the respective power plants within a periphery of 300 km for construction of roads by NHAI.
The production of fly ash is estimated to reach 240 mt and 300 mt by 2020 and 2025 respectively. As per India Infrastructure Research, fly ash demand is projected to cross 150 mt by 2020 and reach 207 mt by 2023-24. The projection is based on growth in fly ash demand for the 10-year period from 2008-09 to 2017-18.
In the future, fly ash utilisation is expected to grow. This is likely to be realised on the back of the government’s increasing focus on using fly ash as one of the materials in the construction of roads and highways. With huge opportunities coming up in highway, flyover and rural road projects, the road sector has a large potential for fly ash utilisation.
Over the years, the use of fly ash in the construction of highways and roads has witnessed positive growth too. However, the offtake is still very low, as compared to other materials such as cement and bitumen. The main reason behind the low utilisation is the reluctance of thermal power plants to bear the transportation costs of ash to the road construction site and lack of knowledge with respect to fly ash usage. It is expected that the MoEF&CC guidelines to this effect will have a positive outcome, as this is necessary if fly ash uptake is to be increased.
According to a Council of Scientific and Industrial Research-Central Road Research Institute study, MSW contains 65-70 per cent of soil components which can be used in embankment construction after segregation from waste.
NHAI has used solid waste from Delhi’s Ghazipur landfill site for construction of the Delhi-Meerut Expressway. Recently, the Odisha government decided to take up a pilot project, and based on its success, waste from sanitary landfill sites will be utilised in road construction.
Of the municipal waste that India produces, plastic waste forms a significant portion. India produces about 15,000 tonnes of plastic waste daily, of which about 60 per cent (9,000 tonnes) is recycled. The remaining is either burnt, causing air pollution, or ends up in landfills or clogs drains. The large amount of plastic not being recycled can be used for road construction. Plastic has several properties which makes it a useful construction material. According to the World Economic Forum, roads constructed using waste plastic are durable in extreme weather conditions, cost-effective and pothole-resistant.
Once plastic waste is shredded, it is heated at 165 °C. Next, the shredded pieces are added to bitumen mix, which is also heated at 160 °C. The final mix is used for constructing roads.
The construction of a regular road requires 10 tonnes of bitumen per km, while a plastic road requires 9 tonnes of bitumen and 1 tonne of waste plastic for coating. This implies a saving of 1 tonne of bitumen (approximately Rs 50,000) per km. When plastic is used as a binder, the quantity of bitumen that is normally utilised for laying roads can be reduced by 6-8 per cent.
The Indian Roads Congress (IRC) released the standard, IRC: SP: 98: 2013, for the use of waste plastic in the construction of bitumen roads. The Plastic Waste Management Rules, 2016, recommend that urban local bodies encourage the use of plastic waste in construction of roads as per IRC guidelines. In case of non-availability of waste plastic, the road developer will have to seek approval from the Ministry of Road Transport and Highways for bitumen-only roads. So far, India has constructed about 100,000 km of roads in states such as Tamil Nadu, Himachal Pradesh, Madhya Pradesh, Kerala and Meghalaya using discarded plastic. The Tamil Nadu government banned the sale and use of “single use” plastic items in the state from January 1, 2019. The Chennai Municipal Corporation has collected 161.83 tonnes of banned plastic items in the city from January 1 to March 31, 2019. The seized plastic is planned to be used to lay roads. Manipur has also decided to use plastic waste in road construction. If the trial succeeds, it will be the second northeastern state after Meghalaya to do so.
Overall, the use of plastic remains limited in road construction. There are, however, significant interstate variations. In some states, such as Tamil Nadu, about 50 per cent of the roads are made using plastic. In Delhi, on the other hand, it has not moved beyond pilot demonstrations. This is both due to lack of acceptance by road developers as well as poor enforcement of rules by municipal authorities.
Undoubtedly, many new options are emerging as far as construction materials are concerned. However, more research as well as results of various pilot studies will need to be available for a final verdict on the new materials’ desirability and feasibility.