The road sector produces the most greenhouse gases, directly, via fossil fuels used in mining, transport, paving work … and indirectly via emissions from vehicles. Indeed, the constant increase in the number of road vehicles – and therefore of traffic – generates a substantial increase in pollution and noise pollution.

In addition, huge challenges await the road construction industry as cheaper and better production, construction and of course maintenance, especially as raw materials become scarce and environmental laws become more and more. more stringent in terms of air pollution and noise pollution. Like the rest of the sectors, the road construction sector faces the challenge of sustainability.

How to define sustainability in the road construction sector?

Before getting to the heart of the matter, let’s define the overall concept of sustainability. Sustainability is the ability to meet our needs without compromising the ability of future generations to meet theirs. This concept integrates economic, societal and environmental aspects. Durability can also be defined as a way of using a resource so that it is not depleted or permanently damaged. August 13, 2015 was Earth Overshoot Day, which means humanity has already spent the Earth’s budget for the whole year, proving that sustainability is elusive.

It is questionable why we need sustainability. The reasons are quite obvious: the global population is increasing (by 2050, the UN predicts the world population will reach 9.7 billion) and the amount of natural resources like crude oil, aggregates or the iron core is limited. . From this perspective, achieving sustainability in the construction of motorways seems quite a challenge since the latter, by the nature of its activity, generates a lot 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 efforts to achieve sustainability.

The different rating systems for green highways

What is a sustainable or green highway? It is a road network that limits its impact on the environment to a minimum thanks to various sustainable practices. The objective is to maximize the life of a highway while limiting its emissions. Among the various construction techniques, we find the use of recycled materials, the implementation of ecosystem-based management, the implementation of energy reduction actions or even rainwater recovery systems (see paragraph following).

First, all projects involving road construction are subject to the mandatory environmental impact assessment (EIA) procedure by the Ministry of the Environment.

In Europe, the European Road Assessment Program (1200 EuroRAP) aims, through constant assessment of road risks, to build a safer road network and reduce the number of road fatalities. In 2010, the Road Safety Foundation (UK charity) published the results of the EuroRAP Star Rating in the UK to demonstrate the effectiveness of well-thought-out road design and development in protecting road users. road. According to the results of the EuroRAP Star Rating of national roads in England, half of the motorways are rated 4 stars. 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 implementing “green” actions in the road sector. Indeed, most of the green road rating systems on the market were initiated by the USA. Some have academic origins while others come from local departments of Transportation. Among these rating systems, we find Greenroads (University of Washington), GreenLITES (State of New York), I-LAST (State of Illinois), INVEST (Federal Highway Administration), STEED… The latter, whose acronym stands for Sustainable Transportation Engineering and Environmental Design, was initiated by HW Lochner which provides civil and structural engineering, environmental and construction services for transportation projects in the United States.

The principle of the STEED rating system is based on 4 stages: Planning – Environment – Design – As built. Each step of a project is evaluated, which makes it possible to determine whether the objectives are being achieved and if not, to analyze which step needs to be improved. The aim is also to identify where sustainable practices can be implemented in the most effective way to maximize the sustainability of the project.

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

Current sustainable highway practices

In Europe, 277.3 million tonnes of asphalt were produced in 2013 for road construction (source: 5924 European Association of Asphalt Pavements). Asphalt is produced at high temperature (160 – 180 ° C). Per ton of asphalt, 275 MJoule is needed, which implies a consumption of 76 billion Mjoule in Europe. Therefore, the production of asphalt turns out to be one of the most energy intensive industries and, as a result, generates huge amounts of CO2. How in this case to achieve sustainability with asphalt?

Motorway construction requires a lot of energy at different levels: for the production of asphalt and cement for pavements and excavation materials, for road maintenance, and for vehicles stuck in traffic jams due to poorly designed highways. To reduce the level of energy consumption, hot mix asphalt (WMA) can be used as a replacement for hot mix asphalt (HMA). Besides the fact that WMA is produced at a lower temperature, it also induces great advantages such as improved working conditions (less exposure to heat and fumes) and asphalt compaction, a reduced paving costs and longer transport.

One of the options that would also save energy and production costs is the use of “Bio-binders” as materials for sustainable asphalt pavements. Bio-binders – also called biopolymers – come from natural resources and are fully biodegradable. They are rather economical and have good thermal stability.

Sustainability can also be achieved through the use of recycled materials (like crushed concrete for example), resulting in a reduction in the energy consumption required to import new materials in addition to the obvious benefits of using recycled materials.

Among these recycled and renewable materials, we find:

  • Recycled Material Components (RMCs), which are generated from industrial by-products, can reduce GHG emissions and be truly profitable.
  • Reclaimed Asphalt Pavements (RAP)
  • Recycled concrete aggregate (RCA)
  • Coal combustion products (CCP), derived from the combustion of coal in coal-fired power stations (fly ash, boiler slag, etc.).
  • Environmentally friendly concrete (EFC), which minimizes the use of Portland cement (the type of cement most commonly used in the world).
  • Microalgae: used by scientists to produce asphalt and therefore create an alternative to petroleum. They are mixed with resins to improve their viscous properties.
  • New surface material: Asphalt-based materials are replaced by environmentally friendly organic resin roads such as Eco-Pave.
  • Pozzolans, volcanic rocks from which cement was once produced before the arrival of Portland cement and which can replace cement

In addition to recycled materials, other sustainable practices exist such as the use of:

  • Bioswales (landscape features designed to remove surface runoff from crevices and pollution) in LID (Low Impact Development) stormwater management
  • Asphalt rubber terminal mix
  • Pavement design through perpetual pavements

Other practices include:

  • Train road construction workers to identify potential environmental issues and therefore best practices to adopt
  • Decrease energy consumption of fossil fuels by off-road construction machinery
  • Use dust control measures
  • Use the design of highways to achieve energy savings, in particular by reducing congestion (with traffic lights or by widening shoulders in an emergency): reducing road congestion reduces the energy consumed and emissions from vehicles.

These are current road sustainability practices. Now let’s take a look at future innovations and concepts in the road construction industry.

The future of road construction: innovation and new concepts

Based on current trends in road construction, how can we predict the future of this industry?

Several approaches can be explored such as drones – unmanned aerial vehicles. Despite some concerns, the usefulness of these “tools” is real: monitoring of construction sites, inspection of structures, aerial view of a road project, etc. This allows the project management team to review all aspects of the construction process. construction by obtaining precise images of the state of the roads and, consequently, adopting appropriate actions.
Some solutions have already been tested such as:

  • Road anti-icing (USA – 2013) which contains a de-icer on the surface (like SafeLane®)
  • Phosphorescent road markings (Netherlands – 2013)
  • Dynamic paint (Netherlands – 2013) which is a combination of symbols that appear on the road surface and warn drivers when the road surface is too cold, too hot or can be slippery. This helps improve the driver experience and minimize car crashes.
  • Solar-powered roads (Netherlands – 2014): establishment of a 70-meter-long cycle path in Amsterdam that generates solar energy (3,000 kWh, the equivalent of the energy needed to power a small household for a year) thanks to photovoltaic cells under glass.

In the near future, other developments will have emerged:

  • Interactive wind lights (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 scheduled for 2020): Energy is generated by vibrations from vehicles traveling along the road

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

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