19 May 2022
The Road More Traveled: An Asphalt Alternative for the Future?
Grab the snacks, fill the coffee thermos and make sure you’ve got your favorite music to while away the hours because we’re going on a road trip. From where to where? That’s an insignificant detail. Our goal is to drive every mile of paved road in the United States. Hopefully, the company and music are good, because even at an average speed of 65 miles per hour, driving for 12 hours per day, it’s going to take us a smidge over 14 years to complete the four million miles of US roadways that our nation’s CAD engineers and designers contribute to regularly. Buckle up, crank up the volume and let’s go!
Four million miles of two-lane paved roads. That’s a lot. And if you add in the additional mileage of multiple lanes, it doubles to around 8.3 million miles. According to the National Asphalt Paving Association, that’s 18 billion tons of blacktop, so let’s talk about asphalt. For civil engineers and state Department of Transport designers, there’s possibly an alternative material that is better for the health of the road crews, better for the environment, and better for budgets. We’ll be exploring that option here.
Annual estimates of asphalt-related aerosol emissions exceed those from motor vehicles.
Asphalt, also known as bitumen, is a sticky, black, highly viscous form of petroleum. In the US, 85 percent of asphalt is used for road surfaces and the balance is primarily shared amongst the roofing and waterproofing industries. The asphalt concrete mix used for paving roads is typically five percent asphalt cement and 95 percent aggregate, such as stone, sand and gravel.
When maintenance is performed on a road surface and damaged material is removed, that material can be reactivated and reused as a new pavement mix. According to the Federal Highway Administration and the National Asphalt Association, more than 99 percent of the asphalt that is removed each year during widening or resurfacing projects is reused as part of new pavement, roadbeds, shoulders and embankments. This makes asphalt an easily recyclable material with widespread applications such as parking lots, driveways, racetracks, airport grounds and runways, tennis courts, reservoir and pool linings, soundproofing, cable and pipe coatings, and newspaper ink production amongst others.
But what are the drawbacks?
In order to understand the need for an asphalt alternative, we’ll take a perfunctory look at the factors that have motivated engineers and environmentalists alike to seek other options.
Asphalt is a petroleum-based product that is mined from the earth. For road surfaces, rock, sand and gravel are also required, all of which are sourced from the earth. Drilling, mining, processing and transporting these materials is resource intensive.
Water flowing across road surfaces is exposed to contaminants in the asphalt itself, which then flow into municipal water systems, lakes, rivers, streams and the ocean, where they impact the environment.
Petroleum-based asphalt is a high-VOC compound. Volatile organic compounds release harmful gases into the atmosphere, not only from the road surfaces, but the production process also releases substantial VOC emissions.
Water exposed to contaminants in the asphalt flows into municipal water systems, lakes, rivers, streams and the ocean, exerting a negative impact on the environment.
In fact, in a recent scientific study of road — not vehicle — emissions, it was discovered that emissions were considerable at 60°C (140°F), a typical temperature for asphalt on a sunny day in Los Angeles. Even at lower temperatures, a moderate level of sunlight can increase harmful chemical emissions by as much as 300 percent. When heated to 140°C (284°F) — the temperature used for paving roads — the asphalt releases harmful organic compounds in especially large quantities. In each of the above scenarios, sufficient invisible aerosol particulate to cause lung damage was observed. In urban settings, annual estimates of asphalt-related aerosol emissions exceed those from motor vehicles.
Concrete roads are definitely a viable alternative, and while they’re highly durable and comparatively more environmentally friendly, they’re also significantly more expensive. Considering road safety, compared to concrete, asphalt provides slightly more traction in terms of snow and skidding, so concrete roads are best relegated to more moderate climates.
New Materials for New Miles
So, is there an entirely different option? A material that is sustainable, more environmentally friendly, more cost-effective, and suitable in all climates? There sure is. What is it? Look around you. It’s practically everywhere you look. It’s in your office, your car, your home. It’s in — well, technically, on — your morning to-go cup of coffee. Guessed it yet? If you guessed plastic, winner, winner, chicken dinner.
The concept is not new. It’s been around for almost twenty years in India, providing a reasonable length of time to study the initial results.
Outside New Delhi, countless vehicles speed over tons of plastic bags, bottle tops, and discarded polystyrene foam cups and food containers. It sounds gross, but it isn’t. This is not a journey across an ocean of litter. It’s a smooth, well-maintained road, the litter invisible to the naked eye — because it’s simply part of the road. An entire ton of plastic goes into every kilometer of road.
The system was developed by Rajagopalan Vasudevan, a chemistry professor at the Thiagarajar College of Engineering. It’s a simple process that requires very little in terms of high-tech equipment, which also makes it suitable for developing countries.
First, plastic waste is shredded and scattered onto an aggregate of crushed stone and sand before being heated to about 170°C (338°F) — at which point the plastics melt. The melted plastics coat the aggregate in a thin layer, which is then top coated with heated bitumen that solidifies the aggregate. Hey, presto! New road.
Many different types of plastics can be added to the mix. Plastic shopping bags, disposable cups, hard-to-recycle multi-layer films, and polyethylene and polypropylene foams have all found their way into India’s roads, and they don't have to be sorted or cleaned before shredding.
Apart from ensuring these plastics don’t end up in landfills, incinerators, or marine environments, it appears that the plastic creates more durable roads by slowing deterioration and minimizing potholes. The plastic content also seems to improve the flexibility of the surface. Ten years after installation, there were still no signs of potholes in Vasudevan’s early roads. He also calculated that using plastic waste (instead of incinerating it), saves three tons of carbon dioxide emissions for every kilometer of road, in addition to a savings of at least $670 per kilometer.
When asphalt roads heat up, sufficient invisible aerosol particulate to cause lung damage is emitted.
Plastic roads can withstand both heavy loads and heavy traffic, according to Vasudevan, who adds that they are also unaffected by rain or standing water.
With this data in hand, by 2015 the Indian government made it mandatory for plastic waste to be incorporated into roads near large cities. They’ve laid 2,500 kilometers of plastic roads in the country to date.
A study in the UK recognized that plastic roads cope better with expansion and contraction due to fluctuating temperatures, resulting in fewer potholes. And if a pothole does appear, filling it in with plastic waste destined for a landfill is a quick, inexpensive fix. As a result, the UK recently announced a £1.6 million budget for plastic road research.
Scotland’s first plastic road was laid in 2019. They’ve been laid in countries from Slovakia to Ghana to South Africa, and chemical giant, Dow, is using recycled plastics for projects in the US and Asia Pacific. Thus far, everywhere they’ve been installed, the estimate is that they have a three times longer lifespan than traditional asphalt or concrete roads. Considering that anything plastic — from Lego building blocks to single-use plastic utensils — can take anywhere from 400 to 1,000 years or more to break down, plastic roads sure seem to have a built-in longevity factor.
In the Netherlands, a plastic cycling path was installed in 2018 and, still in perfect condition, recorded its millionth user by 2020. This system uses no bitumen at all and consists almost entirely of recycled plastic — 25 kilograms per square meter — with a thin layer of mineral aggregate on the top surface. Carbon emissions are reduced by 52 percent compared to laying a conventional paved path.
Circular Solution to a Straight Problem
Earlier in this article, we mentioned the fact that asphalt roads are frequently recycled. Well, plastic roads are no different in that regard. Plastic roads are easily reused and repaved as their life cycle comes to an end. This creates a circular solution, which helps prevent the spread of plastic into the ecosystem. With plastic pollution currently one of the most pressing environmental issues globally, finding creative ways to reuse it is critical.
According to US and Canadian authorities, 100 percent plastic roads are perfectly sustainable options for low-traffic areas. They do not yet, however, consider that plastic roads meet the engineering requirements for widespread application in areas with a high-traffic load, although plastic roads with high traffic loads in other countries seem to be holding up just fine. Instead, for high-traffic roads, they concur that recycled plastic can be used as a binder in the asphalt mix, which reduces the amount of asphalt required. This mixed type of plastic road is currently the focus of most North American road construction projects.
Final Thoughts on Fantastic Plastic
Plastic roads are a great solution to the global plastic waste epidemic, reducing plastic pollution and contributing to carbon neutrality. What cannot be denied is the great potential of plastic roads to bring us closer to achieving sustainable development goals and protecting our environment and ecosystems for future generations.
Plastic roads are a great solution to the global plastic waste epidemic, reducing plastic pollution and contributing to carbon neutrality.
While plastic roads are relatively new, what is much older is the tedium and frustration that are part of the daily grind for CAD/BIM professionals using MicroStation®, Revit®, or AutoCAD®. Recognizing that it is the architects, engineers, and designers that are responsible for building our future, Axiom designs software to help you alleviate the above-mentioned tedium and frustration with an array of tools that’ll have you feeling like you’ve acquired a personal assistant.
If you want more time for me-time, or to get out of the office earlier, or more time to simply do what you do best — design — call 727-442-7774 to have a friendly Service Consultant help you determine which tool is best for your situation. Alternatively, MicroStation options are here, Revit help is here, and AutoCAD details are here.
See you out there — on the wide, open road!