Sustainable road construction: current practices and future concepts

The road sector produces the highest level of greenhouse gas, directly, through fossil energy used in mining, transportation, paving works... and indirectly through the emissions coming from vehicles. Indeed, the constant increase in the number of road vehicles – and therefore of the traffic – generates a substantial increase in pollution and noise disturbances. Besides, huge challenges await the road construction sector such as a cheaper and better production, construction and of course maintenance, all
Asphalt Paving, Compaction & Testing / November 23, 2015
screen print of The Fifth Element
The Fifth Element (released in 1997)
The road sector produces the highest level of greenhouse gas, directly, through fossil energy used in mining, transportation, paving works... and indirectly through the emissions coming from vehicles. Indeed, the constant increase in the number of road vehicles – and therefore of the traffic – generates a substantial increase in pollution and noise disturbances.

Besides, huge challenges await the road construction sector such as a cheaper and better production, construction and of course maintenance, all the more as raw materials are becoming scarce and the environmental laws are getting stricter regarding air pollution and noise disturbances. Like the rest of the sectors, the road construction sector needs to face the challenge of sustainability.

How can we define sustainability in the road construction sector?

Before getting to the heart of the matter, let’s define the global concept of sustainability. Sustainability is the ability to meet our needs without compromising the ability of next generations to meet theirs. This concept integrates the economic, societal and environmental aspects. Sustainability can be also defined as a way to use a resource so that the latter is not depleted or permanently damaged. The 13th of August 2015 was the Earth Overshoot Day, which means that humanity has already spent the Earth’s budget for the entire year, which proves that sustainability is hard to achieve.

One may wonder why we need sustainability. The reasons are quite obvious: the overall population is increasing (by 2050, the UN predict that the world population will reach 9.7 billion) and the amount of natural resources like crude oil, aggregates or iron core is finite. In this light, it seems like quite a challenge to reach sustainability in highway construction since the latter, by the nature of its activity, generates lots of energy and consumes a lot of fossil resources.

Like many other sectors, the road construction sector is subject to different types of rating systems, to assess their endeavours to reach sustainability.

The different Green Highway Rating Systems

What is a sustainable or green highway? It is a system of roads which limit their impact on the environment to a minimum through different sustainable practices. The goal is to maximize the lifetime of a highway while restricting its emissions. Amongst the different construction techniques, we find the use of recycled materials, the establishment of an ecosystem management, the implementation of energy reduction actions or stormwater retrieval systems (see next paragraph).

First and foremost, all projects involving roadway construction are subject to the mandatory Environmental Impact Assessment (EIA) procedure by the Ministry of Environment.

In Europe, European Road Assessment Programme (1200 EuroRAP) aims, through a constant assessment of road risks, to build a safer road system and to reduce the number of deaths on the road. In 2010, the Road Safety Foundation (UK charity) released the EuroRAP Star Rating results in the UK to demonstrate the efficiency of a well-thought-out road design and layout in the protection of road users. According to the results of the EuroRAP Star Rating of the trunk roads in England, half of the motorways are rated 4-star. This is an example of how sustainability can be implemented in a road construction context.

The USA are also very committed when it comes to implement “green” actions in the road sector. Indeed, most of the green road rating systems on the market have been initiated by the USA. Some have academic origins while others come from local departments of Transportation. Amongst those rating systems, we can find Greenroads (University of Washington), GreenLITES (New York State), I-LAST (State of Illinois), INVEST (Federal Highway Administration), STEED…The latter, which acronym means Sustainable Transportation Engineering and Environmental Design, has been initiated by H.W. Lochner which provides civil and structural engineering, environmental and construction services for transportation projects in the USA.

The principle of STEED rating system is built on 4 stages: Planning – Environmental – Design – As-built. Each stage of a project is evaluated, which allows to determine if goals are achieved and if not, analyze which stage needs to be improved. The goal is also to identify where sustainable practices can be implemented in the most efficient way to maximize the project sustainability.

But what do green roads look like? What are the main practices in terms of road sustainability?

Current practices in terms of sustainable highways

In Europe, 277.3 million tons of asphalt were produced in 2013 for the construction of roads (source: 5924 European Asphalt Pavement Association). Asphalt is produced at high temperatures (160 – 180°C). Per ton of asphalt, 275 MJoule is needed, which implies a consumption of 76 billion Mjoule in Europe. Therefore, asphalt production turns out to be one of the most energy consuming industry and as a consequence, generates huge quantities of CO2. How in this case, can we reach sustainability with asphalt?

Highway construction requires a lot of energy at different levels: for the production of asphalt and cement destined to pavements and excavating materials, for road maintenance, and by vehicles stuck in congestion due to poorly designed highways. To reduce the level of energy consumption, warm-mix asphalt (WMA) can be used to replace hot-mix asphalt (HMA). Besides the fact that WMA is produced at a lower temperature, it also induces great benefits such as an improvement of working conditions (less exposure to heat and fumes) and asphalt compaction, reduction of paving cost and longer hauling.

One of the options which would also allow to generate savings in energy and production costs is the use of “Bio-binders” as materials for sustainable asphalt pavements. Bio-binders – also known as biopolymer- come from natural resources and are fully bio degradable. They are rather cost effective and show good thermal stability.

Sustainability can also be reached through the use of recycled materials (like crushed concrete for instance), which entails a reduction in the consumption of energy needed to import new materials besides the obvious benefits of using recycled materials.

Among those recycled and renewable materials, we can find:

  •  Recycled Materials Components (RMCs), which are generated from industrial by-products, can reduce GHG emissions and be really cost-effective.
  • Reclaimed asphalt pavements (RAP)
  • Recycled concrete aggregate (RCA)
  • Coal Combustion Products (CCP’s), derived from coal burning in coal plants (fly ash, boiler slag...).
  • Environmentally Friendly Concrete (EFC), which minimizes the use of Portland cement (most common type of cement used over the world).
  • Microalgae: used by scientists to produce asphalt and therefore to create an alternative to petroleum. They are mixed with resins to improve their viscous properties.
  • New surface material: asphalt based material are being replaced by environmentally-friendly, organic resin-roads such as Eco-Pave.
  • Pozzolans, volcanic rocks from which cement was formerly produced before the arrival of Portland cement and which can be a substitute for cement

Apart from recycled materials, other sustainable practices exist such as the use of:

  • Local material
  • Long lasting pavement
  • Bioswales (landscape elements designed to clear surface runoff water from slit and pollution) in LID (Low Impact Development) stormwater management
  • Terminal blend asphalt rubber
  • Quiet pavements
  • Pavement design through perpetual pavements

Other practices include:

  • Recycling on-site debris
  • Training road construction workers to identify the potential environmental issues and therefore the best practices to adopt
  • Decreasing the fossil fuels energy consumption by non-road construction equipment
  • Using dust control measures
  •  Using highway design to realize energy savings especially through the mitigation of congestion (with traffic signals or by widening the shoulders in case of an emergency): lessening road congestion reduces the energy consumed and emissions released by vehicles.

These are the current practices in terms of road sustainability. Let’s have a look now at the future innovation and concepts in the road construction sector.

The future of road construction: innovation and new concepts

According to the current trends of road construction, how can we foresee the future of this sector?

Several approaches can be explored such as for instance the UAV’s – unmanned aerial vehicles. In spite of certain concerns, the usefulness of these “tools” is real : monitoring jobsites, inspecting structures, getting an aerial overview of road project…This allows the construction management team to review all the aspects of the construction process by getting accurate pictures of road conditions and therefore, to adopt appropriate actions.
Some solutions have already been tested such as:

  • Anti-icing roads (USA - 2013) which contains a de-icer on the surface (like SafeLane®)
  • Glow-in-the-dark roads markings (the Netherlands – 2013)
  • Dynamic paint (the Netherlands – 2013) which is a combination of symbols that appear on the road surface and warn drivers when the roadway is too cold, too hot or can be slippery. This contributes to improve drivers experience and minimize car accidents.
  • Solar energy roads (the Netherlands – 2014) : implementation of a 70-meter long bike path in Amsterdam that generates solar power (3000 kWh, the equivalent of the energy needed to power a small household for a year) thanks to glass-covered photovoltaic cells.

In a close future, other developments will have seen the light:

  • Interactive wind-powered lights (The Netherlands – 2018): only the presence of a car can turn on the light, which is powered by the wind.
  • Piezoelectric energy road (Israel– tested in 2008 but planned for 2020) : Energy is generated thanks to the vibrations of vehicles driving along the road

In the sector of road construction, many initiatives have been implemented to reduce the ecological footprint of roads and to promote sustainability not only from an environmental point of view but also from a societal one. In a few years, with the constant innovations in the sector, we might witness great changes in the highway landscape, and why not see flying roads?

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