With conventional road building materials becoming scarce, and climate change a growing concern, the industry is looking for new, greener solutions.
Over the past decade, we’ve seen a dramatic increase in the use of recycled materials and eco-friendly by-products. Common materials include: reclaimed asphalt pavement (RAP), construction and demotion waste (C&D), crumb rubber from used tires, cement dust, recycled crushed glass, steel slag, rice husk, sawdust, old plastic bags, used engine and cooking oils. The list goes on.
But what are the implications of using these new materials? Are they beneficial, or even feasible? Here, we’ll consider the economic, technical, and environmental impact of such materials, and address the hurdles standing in the way of widespread use.
Above all else, roads need to be useable. While studies into the technical performance of recycled materials are ongoing, we’re already beginning to see numerous benefits.
Old tires are emerging as an early favourite. They can be used either as “dry track” aggregates, or as “wet tack” melts, which are added to asphalt. In both cases, tires are actually improving road quality. The same can be said of certain plastics and C&D waste. In addition to reducing our use of bitumen by around 10%, it appears these new materials are capable of improving the durability of our roads by some way.
It’ll come as no shock to learn that using recycled materials in construction is a boon for the environment. By cutting down on the use of virgin materials (either entirely, or in part), we’re able to conserve natural resources and reduce the overall energy consumption and carbon emissions associated with road building. In short, that makes for a cleaner and greener industry.
The use of recycled materials also diverts massive amounts of used materials away from landfill – thus helping to maintain the cleanliness of existing environments around the world.
Where infrastructure is concerned, money is always a factor. Unsurprising, then, that lifecycle costs form the basis for many recycling initiatives. Beyond the durability and longevity of materials, taxation is proving to be a major player here.
Denmark and the Netherlands serve as fine examples of how incentive and disincentive taxations on natural materials can help promote recycling. Landfill use also sees punitive taxation, further bolstering the case for using recycled materials.
In fact, the Netherlands has so successfully pioneered the use of recycled building materials, that supply is struggling to keep up with demand.
Hurdles and limitations
There are patently numerous benefits to the use of recycled materials, but that’s not to say it’s plain sailing (or driving, as the case may be).
In order to be suitable for use in pavement and road construction, recycled materials need to be processed in various ways. For example, waste products such as RAP and C&D require sorting – a process that demands man power, site space, management, and, in some cases, specialist equipment. This all comes with an economic and environmental cost.
With regard to manpower, the industry is currently suffering from a lack of experience. In order to be efficient, processing needs trained technicians and clear specifications. Both are on their way, but neither will be achieved overnight.
It’s also worth noting that, while technical performance indicators are promising, we still lack long-term data. Reliable information on field performance will be crucial to determining the feasibility of using recycled materials for road construction in the years to come.
Finally, as in any industry, there are certain contractors and departments that are proving somewhat resistant to change. In an already challenging environment, it’s inevitable that certain players will need more convincing. But with the evolution of reliable data, it’s expected that the arguments for will only become stronger with time.
A promising future
Hurdles, there may be. But overcoming difficulties is what infrastructure is all about. The scope for positive environmental, economic, and technical outcomes is such that we believe this to be an avenue well worth pursuing.
The barriers to long-term, widespread adoption are not insurmountable. In most cases, it is only a matter of time. The industry is learning more week on week. Comprehensive laboratory testing, field trials, and proper dissemination of information are all well underway. When compounded with a positive response from the world’s governments – spanning clear regulation and specifications – then the future of our highways looks a good deal cleaner, greener, and more sustainable than ever.